Cardio Flashcards
Normal refractory period of atria.
0.15 sec
P, QRS, T wave:
> represents the stage of depolarization of ventricles when ventricular muscle fibs begin to relax.
T wave. It occurs slightly before the end of ventricular contraction.
This muscle of the heart pulls the vanes of the valves inward toward the ventricles to prevent them bulging too far backward during ventricular contraction.
Papillary muscles and chordal tendineae
When the left ventricular pressure rises slightly above this pressure value, the ventricular pressures push the semilunar valves open during the period of ejection.
80mm Hg (and the R ventricular pressure slightly above 8 mm Hg
When at rest, how many liters of blood is pumped by the heart each minute?
4-6 L
Velocity of conduction of atrial and ventricular muscle
0.3 - 0.5 m/s
Specialized excitatory and conductive system of the heart that conducts impulse from atria to ventricle
AV bundle
The cause of slow conduction in AV bundle fibers
The slow conduction in the transitional, nodal, and penetrating A-V bundle fibers is caused mainly by diminished numbers of gap junc between successive cells in the conducting pathways, so that there is great resistance to conduction of excitatory ions from one conducting fiber to the next.
Effect of sympathetic stimulation to cardiac rhythm and conduction
1) increase sinus nodal discharge
2) increase level of excitability in all portions of the heart
3) increase force of conduction
What is/are the repolarization wave/s?
T wave
The rate of heartbeat can be determined easily from an ECG because the HR is the reciprocal of the time interval between 2 successive heartbeats. What is the normal interval bw 2 successive QRS complexes in the adult pErson?
About 0.83 second. This is a heart rate of 60/0.83 times per minute, or 72 beats per minute.
bipolar limb leads:
This illustrates the the two arms and the left leg form apices of a triangle surrounding the heart.
Einthoven’s triangle.
The two apices at the upper part of the triangle represent the points at which the two arms connect electrically with the fluids around the heart, and the lower apex is the point at which the left leg connects with the fluids.
Function of atria as primer pumps.
Normally, blood flows continually from the great veins into the atria.
80% of the blood flows directly thru the atria into the ventricles even without atrial contraction.
Atrial contraction causes additional 20% filling of the ventricles.
Therefore atria acts as primer pumps that increases the ventricular pumping effectiveness as much as 20%.
True or false. The semilunar valves are the valves which has chordae tendineae.
False. Semilunar valves are not supported by chordae tendineae. Only the AV valves are supported by this.
Te value of the End diastolic volume.
110-120 ml.
When large amt of blood flow into the ventricles during diastole, this becomes as great as 150-180 ml.
The amt of blood pumped by the heart each minute is determined almost entirely by the rate of blood flow into the heart from the veins, which is called ..
Venous return
Excess calcium ions causes the heart to go toward (spastic, flaccid) contraction.
Spastic. This is caused by a direct effect of calcium ions to initiate the cardiac contractile process.
Conversely, deficiency causes cardiac flaccidity.
Specialized excitatory and conductive system of the heart that conducts impulse to all parts of the ventricles
Left and right bundle branches of purkinje fibers
Cause of rapid transmission in ventricular purkinje system
The rapid transmission of action potentials by Purkinje fibers is believed to be caused by a very high level of permeability of the gap junctions at the intercalated discs between the successive cells that make up the Purkinje fibers.
Discharge rate of the ff
1) SA node
2) AV node
3) Purkinje fibers
SA node: 70-80 times per sec
AV node: 40-60 times per sec
Purkinje fibers: 15-40 times per sec
True or false: no potential is recorded in the ECG when the ventricular muscle is either completely polarized or completely depolarized.
True. Only when the muscle is partly polarized and partly depolarized does current flow from one part of the ventricles to another part, and therefore current also flows to the surface of the body to produce the ECG.
Note: Before stimulation, all the exteriors of the muscle cells had been positive and the interiors negative.
Note: in normal heart ventricles, current flows from negative to positive primarily in the direction from the base of the heart toward the apex during almost the entire cycle of depolarization
This law states that if the electrical potentials of any 2 of the 3 bipolar limb ECGic leads are known at any given instant, the third one can be determined mathematically by simply summing the first two.
Einthoven’s law.
At any given instant, the sum of the potentials in Leads I and III equals the potential in Lead II.
In what stage of nerve action potential where the membrane suddenly becomes very permeable to Nà ions, allowing tremendous numbers of (+) charged Nà ions to diffuse to the interior of the axon.
Depolarization stage
Regulation of arterial blood pressure by baroreceptor system. What happens if there is high arterial pressure? Low arterial pressure?
High arterial pressure: baroreceptors sends impulse to medulla to inhibit vasomotor system. Decrease or lack of impulse causes the decrease pumping of heart and dilation of blood vessels allowing increased blood flow. These effects decreases the arterial pressure.
Low arterial pressure: baroreceptors relaxes the stretch receptors causing vasoconstriction and increased pumping of heart. Thus increases the arterial pressure.
Cardiac muscle is a syncytium of many heart muscle cells in which the cardiac cells are interconnected that when one of these cells becomes excited, the AP spreads to all of them.
The atria are separated from the ventricles by fibrous tissue that surrounds the AV valvular openings between the atria and ventricles. Normally, potentials are not conducted from the atrial syncytium into the ventricular syncytium directly through this fibrous tissue. Instead, they are conducted only by way of a specialized conductive system called..
Pressure changes in the atria: the A, c, v waves
> caused by atrial contractions
A wave
The value of the stroke volume output which occurs during systole.
The ejection fraction of 60%, thus the stroke volume output is 70ml.
Difference of semilunar valves from AV valves
1) requires higher pressure to be closed.
2) because of smaller openings, the velocity of blood ejection is greater
3) due to rapid closure and rapid ejection, edges of aortic and pulmonary valves are subjected to much greater mechanical abrasion
Right or left heart:
>pulmonary circulation
>systemic circulation
Right heart: pulmonary circulation, deoxygenated blood
Left heart: systemic or peripheral circulation, oxygenated blood
It is a cardiac event that occurs form the beginning of one heartbeat to the beginning of the next.
Cardiac cycle. It is initiated by a spontaneous generation of action potential in the sinus node. This node is located at the superior lateral wall of right atrium near the opening of SVC. The AP travels from here rapidly thru both atria and then thru AV bundle into the ventricles.
Frank-starling mechanism means..
The greater the heart muscle is stretched during filling, the greater is the force of contraction and the greater the quantity of blood pumped into the aorta. Or stated another way, Within physiologic limits, heart pumps all the blood that returns to it by the way of the veins.
True or false: heat increases the permeability of the cardiac muscle membrane to ions that control the heart rate.
True. Resulting in acceleration of the self-excitation process.
Explanation behind the One-way conduction thru the AV bundle.
The inability of AP in AV bundle to travel from ventricles to the atria, allowing only forward conduction from atria to ventricles.
Furthermore, the AV fibrous tissue acts as an insulator to prevent passage of the cardiac impulse between atrial and ventricular muscle thru an other route.
ECG wave that is caused by electrical potentials generated when the atria depolarize befor atrial contraction begins.
P wave
It is the time between the beginning of the P wave and the beginning of the QRS complex and is the interval between the beginning of electrical excitation of the atria and the beginning of excitation of the ventricles.
P-Q interval. (Often this interval is called the P-R interval because the Q wave is likely to be absent.)
What are the 3 different electrocardiographic leads?
1) bipolar limb leads
2) chest leads (precordial leads)
3) augmented unipolar limb leads
The pressure in capillaries is about how many mm Hg greater inside than outside?
20 mm Hg
Three major types of cardiac muscle
Atrial muscle
Ventricular muscle
Excitatory or conductive muscle (purkinjie fibers)
Period of relaxation.
Period of contraction.
Diastole: period of relaxation, during which the heart fills with blood followed by …
Systole: period of contraction
The atria are separated from the ventricles by fibrous tissue that surrounds the AV valvular openings between the atria and ventricles. Normally, potentials are not conducted from the atrial syncytium into the ventricular syncytium directly through this fibrous tissue. Instead, they are conducted only by way of a specialized conductive system called..
AV bundle
The value of the end systolic volume which is the remaining volume in each ventricles after systole.
40-50 ml.
Web the heart contracts strongly, the volume can be decreased to as little s 10-20 ml.
Pressure changes in the atria: the A, c, v waves
> occurs when the ventricles begin to contract
C wave
The first heart sound is characterized by
Low pitch and long lasting. It is caused by closure of AV valves.
The pumping effectiveness of the heart is controlled by what nerves?
Sympathetic nerves and parasympathetic (vagus) nerves.
Specialized excitatory and conductive system of the heart that generates the normal rhythmical impulse of the heart.
Sinus node or Sinoatrial (SA) node
Explanation behind the self-excitation of sinus nodal fibers.
High Nà concentration due to an already open moderate number of Nà channels in which the positive Nà ions normally tend to leak to the inside.
Why does sinus node rather that AV node or Purkinje fibers control the heart’s rhythmicity?
the discharge rate of the sinus node is considerably faster than the natural self-excitatory discharge rate of either the A-V node or the Purkinje fibers. Sinus node discharges again before either the A-V node or the Purkinje fibers can reach their own thresh- olds for self-excitation. Therefore, the new impulse from the sinus node discharges both the A-V node and the Purkinje fibers before self-excitation can occur in either of these.
ECG wave that is caused by potentials generated when the ventricles depolarizes before contraction, that is, as the depolarization wave spreads thru the ventricles.
QRS wave
What is the normal time of PQ interval?
The normal P-Q interval is about 0.16 second.
Bipolar limb leads:
In recording of this limb lead, the negative terminal of the ECG is connected to the right arm and the positive terminal to the left arm.
Lead I
Heart pumps how many liter of blood per minute?
5 L of blood/minute
Type of cardiac muscle which contract the same way as skeletal muscles except that the duration is longer
Atrial and ventricular muscle
P, QRS, T wave:
> caused by spread of depolarization thru the atria.
P wave. This is followed by atrial contraction which causes slight rise in atrial pressure curve immediately after P wave
Pressure changes in the atria: the A, c, v waves
> occurs toward the end of ventricular contraction
V wave
The second heart sound is characterized by
Heard with a rapid snap when the the semilunar valves close at the end of systole for a short period.
Heart valves that prevents back flow of the blood from the ventricles to the atria during systole.
AV valves
What causes the long action potential and the plateau in cardiac muscle?
1) AP is caused by opening of 2 types of channels:
>the same fast Nà channels as those in sk.m
>slow Ca channels, which are also called Ca-Nà channels ( slower to open and, remain open for several tenths of a second) During this time, a large quantity of both Ca and Na ions flows through these channels to the interior of the cardiac muscle fiber, and this maintains a prolonged period of depolarization, causing the plateau in the AP.
2) Immediately after the onset of the AP, the permeability of the cardiac muscle membrane for K ions decreases about fivefold
Vagal fibers are distributed mainly in (atria, ventricle).
Atria
Specialized excitatory and conductive system of the heart that conducts impulse from the SA node to AV node.
Internodal pathways
Threshold voltage of sinus nodal fiber for action potential to start.
-40 mV
A delayed pickup of heartbeat or a Syncope accompanied with complete heart block.
Stoke-Adams syndrome
ECG wave that is caused by potential generate a the ventricles recover from the state of depolarization. This process normally occurs in ventricular muscle 0.25 to 0.35 second after depolarization.
T wave
It is the time during the contraction of the ventricle that lasts almost from the beginning of the Q wave (or R wave, if the Q wave is absent) to the end of the T wave.
Q-T interval
Bipolar limb leads:
In recording of this limb lead, the negative terminal of the ECG is connected to the right arm and the positive terminal to the left leg.
Lead II
Other function of SER aside from lipid synthesis.
Glycolysis and detoxification
Type of cardiac muscle which contracts feebly because it contains few contractile fibers
Excitatory and conductive muscle
P, QRS, T wave:
> appears as a result of electrical depolarization of the ventricles
QRS wave. This initiates contraction of the ventricles and causes ventricular pressure to begin rising. Begins slightly before the onset of ventricular systole.
Amt of the energy that the heart converts to work during each heartbeat while pumping blood into the arteries.
Stroke work output
Heart valves that prevents back flow of the blood from the aorta and pulmonary arteries into the ventricles during diastole.
Semilunar valves
Vagal stimulation in the heart (increase, decrease) the heart rate?
Decrease. Strong sympathetic stimulation increases the heart rate.
Specialized excitatory and conductive system of the heart where delayed impulse form atria occurs before passing into ventricles.
AV node
The atrial conductive system is organized so that the cardiac impulse does not travel from the atria into the ventricles too rapidly; this delay allows time for the atria to empty their blood into the ventricles before ventricular contraction begins
The AV node is located in the posterior wall of right atrium immediately behind the tricuspid valve
Effect of parasympathetic stimulation to heart
Stimulation of the parasympathetic nerves to the heart (the vagi) causes the hormone acetylcholine to be released at the vagal endings wc greatly increases the permeability of the fiber membranes to K ions. Which causes the ff:
1) decreases the rate of rhythm of the sinus node
2) decreases the excitability of the A-V junctional fibers between the atrial musculature and the A-V node, thereby slowing transmission of the cardiac impulse into the ventricles.
What is/are the depolarization wave/s?
P and QRS wave
What is the start time of Q-T interval?
About 0.35 second
Bipolar limb leads:
In recording of this limb lead, the negative terminal of the ECG is connected to the left arm and the positive terminal to the left arm.
Lead III
A movement of an entire cell in relation to its surroundings, such as movement of WBC thru tissues.
Ameboid movement
Most common occluded vessels in the heart in a myocardial infarction. (3)
- Anterior interventricular branch
- Right coronary artery
- Circumflex branch
What artery supplies both the SA (50% of the time) and AV bode (90%).
Right coronary artery. Sometimes branches from left circumflex artery
Why is it plateau is desirable in the spread if the impulses in cardiac purkinje fibers?
Because plateau creates a refractoryr period during purkinje fiber discharge that protects the heart against excessively rapid arrhythmias.
Difference between calcium and sodium channel mechanism.
Calcium channels operate more slowly. In cells where calcium channels are prominent, there is a plateau in AP and recovery of the membrane potential is delayed
True or false: AP generated by the SA node is self-generating.
True, no stimulus is necessary because there is a spontaneous depolarization. The slow upsweep is the result of leakiness of the Cm to Nà, which seeps into the cell, resulting to spontaneous AP.
AP in an atrial muscle cell has plateau which represents the influence of the slow Ca channels and a prolongation of the time of depolarization. This helps to protect against a too rapid heart rate. That is, it allows enough time for the atrialmuscle to contract completely and empty the atria.
AP in ventricular muscle cells have an even more prolonged plateau. The influence of Ca is especially important in muscle cells, since Ca ions activate the interaction between actin and myosin that is necessary for muscular contraction.
Norepinephrine released by sympathetic fibers acts with what adrenergic receptors on cardiac muscle cells.
Beta-1 receptors which leads to increased cardiac contractility, increased firing rate of SA node and increased conduction potential
Parasympathetic fibers releases what hormone that decreased cardiac pumping by innervating the SA and AV nodes and the atria.
Acetylcholine. Thus decreases conduction velocity, decreases contractility of the atria (not ventricles) and increase membrane permeability of the SA node to K.
True or false: heart can pump quite well without pumping action of the atria.
True. The “suction” generated by ventricular diastole is the main driving force for ventricular filling. The atrial contraction function becomes more important with vigorous exercise, during which the extra kick to ventricular filling may be particularly helpful.
Stimulation of these Adrenergic receptors will increase the sympathetic nerve effects.
Alpha-1, beta-1 and beta-2 receptors
Stimulation of this Adrenergic receptor will inhibit release of norepinephrine and will decrease the sympathetic nerve effects.
Alpha-2 receptor
Effect of calcium channel blockers
Delay influx of calcium into cell, thud decreases myocardial contractility and maybe useful in decreasing oxygen consumption in angina. My also be useful as vasodilators in treating hypertension and in increasing coronary blood flow.
Action of beta-1 blockers
Beta-1 blockers decrease hHR, decrease cardiac contractility and decrease conduction time through the AV node because of the corresponding locations of beta- 1 receptors in the heart.
These drugs are therefore useful in treating hypertension, through decreased cardiac output (by decreasing HR and stroke volume).
As beta-1 receptors on kidney granular cells (of the juxta- glomerular apparatus) normally cause renin release when stimulated, beta-1 blockers also reduce blood pressure through inhibition of renin release.
This adrenergic receptor when stimulated, releases renin in juxta-glomerular apparatus in kidney.
beta-1 receptors on kidney granular cells thus beta-1 blockers also reduce blood pressure through inhibition of renin release.
Stimulation of this adrenergic receptor is important in maintaining broncho and vasodilation.
Beta-2 receptor. In treating cardiac disease, it is often desirable to use a beta-blocker that specifically exhibits beta-I, but not beta-2 antagonism (especially patients with COPD and asthma)
In a very general way, cardiac depolarization spreads from upper right to lower left (in reference to the body as a whole), considering the tilt of the heart.
Leads I, II, III, aVR, aVL, and aVF look at the heart along the vertical (frontal) plane, whereas leads VI-V6 look at the heart along the horizontal (transverse) plane.
Normally, depolarization spreads toward the positive ECG electrodes, except for ______ (what lead)?
AVR. Therefore, there tends to be a positive (upward) polarity of the P and QRS waves throughout most ECG leads, except for AVR.
In progressing from leads V1 through V6, the overall QRS tends to become progressively more positive, in keeping with the positions of these electrodes in relation to the direction ofelectrical discharge. The net QRS direction in V1 commonly is (down, up)?
Down. since the ventricular electrical activity moves left, away from V1.
The downward deflection of the Q wave in the QRS complex occurs because septal depolarization proceeds from left to right, arising from connections from the left bundle branch.
Ventricular depolarization spreads from the subendocardial surface of the heart to the subepicardial surface.
Systole (SYS) occurs between the first (S1) and second (S2) heart sounds. Heart sounds normally result from valve closure. Valve opening is not normally heard. Which heart sound reflects closure of the atrioventricular (tricuspid and mitral) valves during systole? Which heart sound reflects closure of the semilunar (pulmonary and aortic) valves during diastole?
First heart sound reflects closure of the AV (tricuspid and mitral) valves during systole.
Second heart sound reflects closure of the semilunar (pulmonary and aortic) valves during diastole.
This represents rapid passive ventricular filling, occurring when the ventricles begin to expand during diastole.
S3.
The S3 and S4 heart sounds normally are not heard through the stethoscope, although the S3 may heard in normal children and young adults. S3 is heard pathologically in older adults with ventricular failure as a “ventricular gallop,” sounding like “Ken-tuc-ky,” the three syllables representing S1,S2 and S3 respectively.
This represents rapid active ventricular filling, which occurs when the atria contract and empty in the latter part of ventricular diastole.
S4. It may be heard in various cardiac diseases as an “atrial gallop,” sounding like “Ten-nes-see,” reflecting S4, S1, and S2 in sequence
True or false: aortic valve opens before mitral valve closes, and closes before the mitral valve opens.
True. Because of the high pressure in the aorta. Thus the aortic valve is open for a shorter time than is the mitral valve.
THere are atrial “a,” “c,” and “v” pressure waves. Which wave relects a rise in atrial pressure during late diastolic atrial contraction.
A wave.
Which wave occurs after closure of the A-V valves during systole?
C wave
Which wave arises from atrial filling during systole?
V wave
Most of the filling of the ventricles occurs during the first third of 1. (systole,diastole) , and most of the emptying of the ventricles occurs during the first third of 2. (systole, diastole).
- Diastole
2. Systole
True or false: The aortic valve normally closes slightly before the pulmonary valve (as one might expect, given the large back pressure of the aorta).
True. This difference in closure times is most pronounced during inspiration, where the (-) pressure during inspiration increases the inflow to the R side of the heart and decreases inflow from the lungs to the L atrium and ventricle). The resultant increased volume within the R ventricle and decreased volume of the L ventricle result in a more prolonged R ventricular contraction and, hence, a delay in the closure of the pulmonary valve during inspiration.
It is the increase in tension in ventricular cardiac muscle fibers when the ventricle expands in diastole.
Preload. This passive increase in tension is the result of the increasing volume of the ventricles during diastole.
It is the increase in tension in tIle ventricular cardiac muscle fibers when they actively contract against the expanded ventricular volume to expel the blood through the aortic valve.
Afterload.
Is it isometric or isotonic contraction during preload?
Isometric contraction against the increasing volume during diastole.
Is it isometric or isotonic contraction during afterload?
Isotonic contraction which forces the blood out of the ventricles during systole
True or false. Increasing the preload of the after load increases the energy demand of the heart.
True. This may be more clearly understood through the Laplace equation which states that (T=Pr)
Increased blood pressure = increases after load and cardiac stroke volume
Increased blood volume = increases preload and cardiac stroke volume
What ECGic lead is this? One electrode placed on the anterior surface of the chest directly over the heart which is connected to the positive terminal of ECG, and the negative electrode, called the indifferent electrode, is connected thru equal electrical resistances to the R arm, L arm and L leg all at the same time.
Chest leads or precordial leads. Usually six standard chest leads are recorded, one at a time, from the anterior chest wall, the chest electrode being placed sequentially at the six points. The different recordings are known as leads V1, V2, V3, V4, V5, and V6.
In leads V1 and V2, the QRS recordings of the normal heart are mainly negative because the chest electrode in these leads is nearer to the base of the heart than to the apex, and the base of the heart is the direction of electronegativity during most of the ventricular depolarization process.
Conversely, the QRS complexes in leads V4, V5, and V6 are mainly positive because the chest electrode in these leads is nearer the heart apex, which is the direction of electropositivity during most of depolarization.
What ECGic lead system is this? two of the limbs are connected through electrical resistances to the negative terminal of the ECG, and the third limb is connected to the positive terminal. When the positive terminal is on the right arm, the lead is known as the aVR lead; when on the left arm, the aVL lead; and when on the left leg, the aVF lead.
Augmented unipolar limb lead
When a vector is exactly horizontal and directed toward the person’s left side, the vector is said to extend in the direction of 0 degrees. In a normal heart, what is the average direction of the vector during spread of the depolarization wave through the ventricles, called the mean QRS vector?
+59 degrees
Because the septum and endocardial areas of the ventricular muscle depolarize first, it seems logical that these areas should repolarize first as well. However, this is not the usual case because the septum and other endocardial areas have a longer period of contraction than most of the external surfaces of the heart. Therefore, the greatest portion of ventricular muscle mass to repolarize first is the entire outer surface of the ventricles, especially near the apex of the heart. The endocardial areas, conversely, normally repolarize last.
Because the outer apical surfaces of the ventricles repolarize before the inner surfaces, the positive end of the overall ventricular vector during repolarization is toward the apex of the heart. As a result, the normal T wave in all three bipolar limb leads is positive, which is also the polarity of most of the normal QRS complex.
True or false: vector is greatest when about half the heart is in the polarized state and about half is depolarized.
True
Depolarization of the atria begins where?
Sinus node and spreads in all direction over the atria.
True or false: Spread of depolarization through the atrial muscle is much faster than in the ventricles
False. Slower because the atria have no Purkinje system for fast conduction of the depolarization signal. Because of this, the area in the atria that also becomes repolarized first is the sinus nodal region, the area that had originally become depolarized first.
Change in the position of the heart in the chest.
If the heart itself is angulated to the left, the mean electrical axis of the heart also shifts to the left. When does such shift occurs?
(1) at the end of deep expiration,
(2) when a person lies down, because the abdominal contents press upward against the diaphragm, and
(3) quite frequently in stocky, fat people whose diaphragms normally press upward against the heart all the time.
angulation of the heart to the right causes the mean electrical axis of the ventricles to shift to the right. When does such shift occurs?
(1) at the end of deep inspiration,
(2) when a person stands up, and
(3) normally in tall, lanky people whose hearts hang downward.
Hypertrophy of One Ventricle.
When one ventricle greatly hypertrophies, the axis of the heart shifts toward the hypertrophied ventricle for two reasons. What are those?
First, a far greater quantity of muscle exists on the hypertrophied side of the heart than on the other side, and this allows excess generation of electrical potential on that side.
Second, more time is required for the depolarization wave to travel through the hypertrophied ventricle than through the normal ventricle.
when the sum of the voltages of all the QRS complexes of the three standard leads is greater than 4 millivolts, the patient is considered to have a high-voltage electrocardiogram.
Most often, what is the cause of high-voltage QRS complexes?
most often is increased muscle mass of the heart, which ordinarily results from hypertrophy of the muscle in response to excessive load on one part of the heart or the other.
What are the causes of the decreased voltage of ECG?
The most common causes is a series of old myocardial infractions with resultant diminished muscle mass. Another is the fluid in pericardium.
What are the effects of hypertrophy and Purkinje system block in terms of the voltage and QRS?
Hypertrophy causes increased voltage and prolonged QRS.
Purkinje system block causes decreased voltage and prolonged QRS as well.
The normal QRS complex lasts 0.06 to 0.08 second, whereas in hypertrophy or dilatation of the left or right ventricle, the QRS may be prolonged to..
0.09 to 0.12 second.
The normal QRS complex lasts 0.06 to 0.08 second. If complete block of one of the bundle branches occur, the duration of the QRS complex usually is increased to..
0.14 or greater.
Many different cardiac abnormalities often cause part of the heart to remain partially or totally depolarized all the time. When this occurs, current flows between the pathologically depolarized and the normally polarized areas even between heartbeats. This is called a current of injury.
the injured part of the heart is negative, because this is the part that is depolarized and emits negative charges into the surrounding fluids, whereas the remainder of the heart is neutral or positive polarity.
It is the zero reference potential for analyzing current of injury
The J point
An abnormal sinus rhythm defined in an adult person as faster than 100 beats per minute.
Tachycardia
An abnormal sinus rhythm defined in an adult person as fewer than 60 beats per minute.
Bradycardia
It is an instrument that records by the height of successive spikes the duration of the interval between the successive QRS complexes in the ECG.
Cardiotachometer
ECG showed that the HR increased and decreased no more than 5% during quiet respiration, then during deep respiration, the HR increased and decreased with each respiratory cycle by as much as 30%. It is a result of an alteration of strength of sympathetic and parasympathetic nerve signals to the sinus node.
Sinus arrhythmia
What abnormal condition shows sudden cessation of P waves, with resultant standstill of the atria? However, the ventricles pick up a new rhythm, the impulse usually originating spontaneously in the (A-V) node, so that the rate of the ventricular QRS-T complex is slowed but not otherwise altered.
Sinoatrial block
AV bundle is also known as…
Bundle of His
What is the normal lapse time between the beginning of P wave and beginning of QRS complex?
0.16 sec
What incomplete AV heart block shows prolonged PR interval (>0.20s) and is defined as a delay of conduction from atria to ventricles but not actual blockage of conduction?
First degree block.
What incomplete AV heart block shows prolonged PR interval (>0.25 to 0.45s) because the conduction thru AV bundle is slow? ECG shows P wave but no QRS-T complex wave (“dropped beats”).
Second degree heart block
What condition shows that ventricles spontaneously establish its own signal originating from AV node or bundle? The P waves become dissociated from the QRS-T wave.
There is no relation between rhythm of P waves and that of QRS-T complex because ventricles have “escaped” from control by atria and they’re beating at their own natural rate.
Complete AV block (third degree block)
Each time A-V conduction ceases, the ventricles often do not start their own beating until after a delay of 5 to 30 s. This results from the phenomenon called OVERDRIVE SUPPRESSION. This means that ventricular excitability is at first in a suppressed state because the ventricles have been driven by the atria at a rate greater than their natural rate of rhythm.
However, after a few seconds, some part of the Purkinje system beyond the block, usually in the distal part of the A-V node beyond the blocked point in the node, or in the A-V bundle, begins discharging rhythmically at a rate of 15 to 40 times per minute and acting as the pacemaker of the ventricles. This is called VENTRICULAR ESCAPE (Stokes-Adams syndrome).
Brain cannot remain active for more than how many seconds without blood supply?
4-7 sec
It is a contraction of the heart before the time that normal contraction would have been expected. This condition is also called extrasystole, premature beat, or ectopic beat.
Premature contraction.
A-V block can also block impulse conduction in the peripheral ventricular Purkinje system. This results from partial intraventricular block every other heartbeat. This ECG also shows tachycardia.
Incomplete intraventricular block - electrical alterans
Condition that shows P wave occurred too soon.
PR interval shortened (indicating ectopic origin is in atria near AV node).
Interval between this premature co traction and the next succeeding contraction is slightly prolonged.
Premature atrial contraction
When the heart contracts ahead of schedule, the ventricles will not have filled with blood normally, and the stroke volume output during that contraction is depressed or almost absent. Therefore, the pulse wave passing to the peripheral arteries after a premature contraction may be so weak that it cannot be felt in the radial artery.
Note
Premature contraction that ECG shows a missing P wave, instead the P wave is superimposed onto QRS-T complex
AV nodal or AV bundle premature contraction
Premature contraction wherein ECG shows prolonged QRS complex and has high voltage. T wave has electrical potential polarity opposite to that of QRS complex
Premature ventricular contractions (alternating with normal contractions)
PVC’s QRS complex has high voltage. Why?
1) Normally, impulse passes both ventricles simultaneously; while in PVC one entire side or end of ventricles is depolarizes ahead of the other.
2) normally, depolarization waves of 2 sides of the heart partially neutralize each other; while in PVC impulse travels in one direction so that there is no neutralization effect
A condition that is rapid rhythmical discharge of impulses spread in all directions throughout the heart.
HR becomes rapid in paroxysms, with the paroxysms beginning suddenly and lasting for few sec, min, hrs or longer and usually ends as suddenly as it begins.
Paroxysmal tachycardia.
Can be stopped by eliciting vagal reflex.
Paroxysmal tachycardia that show inverted P wave before QRS complex and P waves are partially superimposed into normal T wave
Atrial paroxysmal tachycardia
Paroxysmal tachycardia that show series of ventricular premature beats occurring one after another without any normal beats interspersed.
Ventricular paroxysmal tachycardia.
It is a serious condition for 2 reasons: (1) it does not occur unless considerable ischemic damage us present in ventricles and (2) it freq initiates ventricular fibrillation
Most serious of all cardiac arrhythmias which, if not stopped within 1 to 3 min, is almost invariably fatal.
Ventricular fibrillation
If the originally stimulated muscle fibers are still in a refractory state, the impulse then dies out because refractory muscle cannot transmit a second impulse. But there are three different conditions that can cause this impulse to continue to travel around the circle, that is, to cause “re-entry” of the impulse into muscle that has already been excited. This is called a “CIRCUS MOVEMENT.” What are those 3 conditions?
1) if pathway around the circle is too long (which typically occurs in dilated hearts)
2) if the length of the pathway remains constant but the velocity of conduction becomes decreased (freq results from blockage of purkinje system, ischemia of muscles or high blood K levels)
3) if the refractory period of the muscle might become greatly shortened (commonly occurs in response to drugs such as epinephrine, or after repetitive electrical stimulation)
One can readily see when a vicious circle has been initiated:
More and more impulses are formed; these cause more and more patches of refractory muscle, and the refractory patches cause more and more division of the impulses.
Therefore, any time a single area of cardiac muscle comes out of refractoriness, an impulse is close at hand to re-enter the area.
In ventricular fibrillation, what does the ECG shows?
ECG is bizarre and ordinarily shows no tendency toward a regular rhythm of any type.
Thus no repetitive ECGic pattern can be ascribed to ventricular fibrillation.
It is a technique for pumping the heart without opening the chest consists of intermittent thrusts of pressure on the chest wall along with artificial respiration. This, plus defibrillation, is called…
Cardiopulmonary resuscitation, or CPR.
Lack of blood flow to the brain for more than 5 to 8 minutes usually causes permanent mental impairment or even destruction of brain tissue.
Remember that except for the conducting pathway through the A-V bundle, the atrial muscle mass is separated from the ventricular muscle mass by fibrous tissue. Therefore, ventricular fibrillation often occurs without atrial fibrillation. Likewise, fibrillation often occurs in the atria without ventricular fibrillation.
The mechanism of atrial fibrillation is identical to that of ventricular fibrillation, except that the process occurs only in the atrial muscle mass instead of the ventricular mass. A frequent cause of atrial fibrillation is atrial enlargement resulting from heart valve lesions that prevent the atria from emptying adequately into the ventricles, or from ventricular failure with excess damming of blood in the atria.
In atrial fibrillation, what does the ECG shows?
one can see either no P waves from the atria or only a fine, high-frequency, very low voltage wavy record.
Conversely, the QRS-T complexes are normal unless there is some pathology of the ventricles, but their timing is irregular.
In the same manner that ventricular fibrillation can be converted back to a normal rhythm by electroshock, so too can atrial fibrillation be converted by electroshock. The procedure is essentially the same as for ventricular fibrillation conversion—passage of a single strong electric shock through the heart, which throws the entire heart into refractoriness for a few seconds
The procedure is essentially the same as for ventricular fibrillation conversion—passage of a single strong electric shock through the heart, which throws the entire heart into refractoriness for a few seconds
It is another condition caused by a circus movement in the atria. It is different from atrial fibrillation, in that the electrical signal travels as a single large wave always in one direction around and around the atrial muscle mass
Atrial flutter.
In atrial flutter, what does the ECG shows?
The P waves are strong because of contraction of semicoordinate masses of muscle. However, QRS-T complex follows an atrial P wave only once for every two to three beats of the atria, giving a 2:1 or 3:1 rhythm.
It results from cessation of all electrical control signals in the heart. That is, no spontaneous rhythm remains. It is especially likely to occur during deep anesthesia, when many patients develop severe hypoxia because of inadequate respiration.
Cardiac arrest
Characteristics of aortic stenosis
SAD
Syncope
Angina
Dyspnea
Beck’s triad (cardiac tamponade)
3 Ds
Distant heart sound
Distended jugular vein
Decreased arterial pressure
