Unit 1 Flashcards
Intrinsic regulation
The heart beats all by itself.
Frank Starling’s mechanism of the heart
The greater the heart muscle is stretched during filling, the greater the force of contraction and the greater the quantity of blood pumped into the aorta
Length tension relationship
Cardiac muscle sarcomeres are naturally short and resist stretch more than skeletal muscle. The increase in length increases the number of functional cross bridges between actin and myosin, therefore greater force of contraction
The longer the sarcomere, the weaker it is. Therefore the cardiac muscle is strong
Right arterial stretch ______ (increases/decreases) heart rate by ________%
Increases
10-20%
Skipped heart beat causes next beat to be harder because
The myosin are overlapped
Mechanisms that work to match the venous return
Frank Starling’s mechanism and Right Atrial Stretch
Frank Starling’s Law
CO=VR
Cardiac output = venous return
If one drops, so does the othereventually.
Innervation of the heart via the autonomic nervous system. Tells the heart to speed up or slow down
Extrinsic regulation.
Increases heart rate
Increases force of contraction
Sympathetic
Decreases heart rate
Weakly decreases force of contraction
Parasympathetic
Sympathetic chain
Series of ganglia on each side of spine from the spine to the chain from the chain to the heart (?) Review this
Ability for parasympathetic to directly impact the heart rate is _____ (weaker/stronger) than the sympathetic
Weaker
Vagus nerve is cranial nerve
X
Maximum sympathetic stimulation:
Approx 24 L/min
Normal sympathetic stimulation
Approx 14 L/min
Other influences on heart function (3)
Potassium (Hyperkalemia, or too much K, slows heart rate, abnormal rhythms and potentially death)
Calcium ions (Too much is hypercalcemia causes spastic contractions)
Temperature (fever causes an increase in heart rate. The warmer you are, the faster your heart rate)
Natural pacemaker
Fastest heart rate of all cardiac tissue
Sinus node (SA node)
Conduction system
Specialized cardiac muscle cells
Location of the SA node
Superior posterolateral RA
Why does the SA node self-excitation and inherent rhythmicity?
It has a sodium leak, and it has a higher RMP (resting membrane potential)
SA node connects to the _____ muscle and ________ fibers
Atrial muscle and intermodal fibers
Fibers receives action potential from SA node
Connects to the AV node
Internodal fibers
Node that delays action potential (slow velocity through node, low # gap juncions to allow time for the atria to relax)
Located posterior RA
AV node
Purkinje System
Fibers lead from the AV node, through the AV bundle (Bundle of His), through the left and right bundle branches, then throughout the ventricular muscle.
Purkinje system has a very _____ (fast/slow) conduction velocity
Fast
Heart rate vs conduction velocity
All of heart has the same heart rate
Conduction velocity is the propagation, how long it takes from point A to point B is different. They start at the same time, but some take longer
Speed for conduction to go from SA node to AV node
moderately fast
Conduction rate from AV node to bundle
Slow
Conduction speed from bundle to ventricular muscle
Very fast
If SA node no longer works, what takes over as the pacemaker? Why?
What takes over after that?
AV node. It has the 2nd fastest firing rate. The heart rate would be slower.
After that would be Purkinje System
QRS Wave
Ventricular depolarization
T wave
Ventricular depolarization
P wave
Atrial depolarization
Developer of the ECG
Will EM Einthoven
Difference between ECG and action potential depends on
Where electrodes are placed, among other things
To record voltage change, need 2 electrodes. Explain the 2.
One is the reference (negative) electrode
One is the recording (positive) electrode
For Action Potential AND ECG
A signal is detected by the recording device (oscilloscope) when there is an electrical difference
Action potential electrodes are placed:
ECG Electrodes are placed:
Deep to the axons
Epidermis
Recording where RMP records a negative value, and records a positive value during AP
Action Potential recording
Recording where depolarizations and depolarizations are deflections from zero (isoelectric) lines
ECG recording
Recordings that are Monophysite
Action Potentials
Recordings that are biphasic
ECG
Recordings that only show amplitude of voltage changes as recorded at a point in a cell
Monophasic
Recordings of both amplitude and direction of waves of voltage changes through heart muscle. This is a ____.
Biphasic
Vest or
Time between the beginning of the P wave to the beginning of the Q wave. 0.16 sec
P-R interval
Interval from 1 R wave to the next R wave
R-R interval
Time it takes from Q wave to end of T wave
Q-T interval
Time it takes from end of S to beginning of T wave
ST Segment
Very important segment to look at, as it is a presensitive indicator of cardiac eschimia
ST Segment
Reduction of blood flow, usually pathologically
Eschemia/hypoxia with eschemia
Deviations of the ECG (PQRST)
Isoelectric line
Vector rules for depolarization
A wave of depolarization moving towards a positive electrode records a positive deflection.
Moving away from a positive electrode records a negative deflection
Vector rules for repolarization
A wave or repolarization moving towards a positive electrode records a negative deflection
Moving away from a positive electrode records a positive deflection
What happens if a wave of depolarization/repolarization was moving at right angles to both electrodes?
Deflection would be 0
What would happen if a wave of depolarization was moving at an oblique angle to the electrodes?
Deflection would be positive, but not as large
How many electrodes are typically used in an ECG? How many leads?
10 electrodes
12 leads
Difference between lead and electrode
Electrode is the actual wire attached to the body
Lead is the pathway
12 leads:
3 standard bipolar limb leads
3 augmented unipolar limb leads
6 precordial chest leads
Each lead assigns one electrode as the positive electrode and 1 or more as the negative ones
Standard bipolar limb leads
One positive and one negative on each one
Lead 1: Negative electrode on the right wrist/chest. Positive on the left wrist/chest. Wave moves horizontal and towards the left.
Lead 2: Use same negative electrode as lead 1 on right wrist. Positive electrode on left ankle
Lead 3: Use same positive electrode as lead 2 on left ankle, and same negative electrode as lead 1 on left wrist.
Standard bipolar limb leads, AKA:
Einthoven’s Triangle
Einthoven’s Law
In regards to the amplitude of the R wave:
Lead II= Lead I + Lead III
This is true for any accurate ECG
Augmented unipolar limb leads:
3 electrodes
Each lead has 1 positive and 2 negatives
aVR (Right wrist): Positive electrode on right wrist. Negative electrodes are left wrist and left ankle. Line goes towards middle of left wrist and left angle
AVL (left wrist): Positive on left wrist. Negative electrodes are right wrist and left ankle. Line goes towards right rest and left ankle
AVF (Left ankle) Positive on left ankle. Negative on right and left wrists. Line goes straight up
Precordial (chest) leads:
V1: 4th intercostal space to the Rt of the sternum V2: 4th ICS to the left of the sternum V3: Between V2 and V4 V4: 5th ICS, left mid-clavicular line V5- 5th ICS, L anterior axillary line V6- 5th ICS, left mid-axillary line
Why use only 1 ankle instead of both for the ECG?
Use left bc it is in the path of the heart.
They do use an electrode on the right, but as the grounding
The trick to interpreting ECGs is to know:
Which vectors (directions) each lead is sensitive to, and from that figure out what the heart is doing electronically.
The ECG _______ the electrical activity that is happening at a particular time
Averages
Normal mean P wave vector represents:
The depolarization activity of the atria
Atrial T wave is normally obscured by:
The QRS complex
Repolarization usually follows :
the same direction that depolarization goes
The pattern of ventricular repolarization begins:
From the apex toward the base of the heart
This explains why the T wave is positive (lead II)
Common theories for the cause of the U wave (very small sometimes seen wave) include:
Delayed repolarization of purkinje fibers
Prolonged repolarization of mid-myocardial M-cells
After-potentials resulting from mechanical forces in the ventricular wall
The repolarization of the papillary muscle
Different stages of ventricular depolarization ins QR and S vectors
Septal activation (A)- Q wave Apical activation (B)- R peak (most significant) Left ventricular activation (C) - R wave return Late left ventricular activation (D)- S wave
Vector analysis used to determine the vector of depolarization through the heart
Hexaxial reference system
What does the hexaxial reference system concentrate on?
The mean QRS vector for the analysis
Precise way of vector analysis requires
Requires the use of any 2 of the 6 limb leads
Steps of the precise way for vector analysis
The direction and magnitude of the QRS vector is plotted from two of the 6 limb leads
Right angles are drawn from the points of the vectors
Where they intersect is the AXIS OF VENTRICULAR DEPOLARIZATION.
This angled is measured with a protractor
Normal vector axis determination
0-90 degrees
Vector axis determination, left axis deviation
QRS axis of 0 to -90 degrees
Right axis deviation of QRS vector axis
QRS axis of 90-180 degrees
Extreme axis of QRS vector axis determination
-90 to -180 degrees
Easy way for vector anazlysis: QRS can be estimated by:
Comparing the size of the QRS complexes of all 6 limb leads
In the easy method of vector analysis, the lead with the larges deviation from the isoelectric line can be used to:
Estimate the QRS vector in the heart.
Significance of an axis deviation for left axis
Short stock build, obesity
LV hypertrophy (hypertension- systemic, aortic valve stenosis, aortic valve regurgitation (something going from where is is to where it shouldn’t be))
Left bundle branch block (causes cardiac cycle to go slower)
Significance of a right axis deviation
Tall, long-waist, lean build
RV hypertrophy (pulmonary valve stenosis/regurgitation, interventricular septal defect., tetralogy of Fallot)
R bundle branch black
Tetralogy of Fallot
4 problems
1- Interventricular septal defect
2- over-riding aorta
3- pulmonary stenosis
4- RV hypertrophy.
QRS voltages should be a sum of
I II and III = 2-4 mV
Individual normal BRS voltages
.5-2 mV
Increased QRS voltage is typically due to
Hypertrophy
Decreased QRS voltage could indicate
Damages heart muscle
Normal time frame of QRS
.04-.11 sec
Prolonged QRS would be due to
Bundle branch block or hypertrophy
Acute damaged heart muscle, like during an MI, does not:
Repolarization normal and therefore becomes a source of current.
They cannot generate enough ATP to generate action potentials.
Heart muscle is injured, and there is some sort of current interference
Current of Injury
Resting heart rate faster than 110bpm
Tachycardia
Causes of tachycardia
Fever
Certain toxins
SNS activity
Resting heart rate slower than 60 bpm
Bradycardia
Potential causes of bradycardia
Athletes (typically endurance athletes)
Vagus nerve is over-stimulated.
