Week 1 Flashcards
What are the phases of a cardiac action potential?
- Phase 0: Rapid Na+ influx through open fast Na+ channels
- Phase 1: Transient K+ channels open and K+ efflux returns TMP to 0mV
- Phase 2: Influx of Ca2+ through L-type Ca2+ channels is electrically balanced by K+ efflux through delayed rectifier K+ channels
- Phase 3: Ca2+ channels close but delayed rectifier K+ channels remain open and return TMP to -90mV
- Na+, Ca2+ channels closed, open K+ rectifier channels keep TMP stable at -90 mV
What is electro-mechanical coupling?
Electrical events cause mechanical events and their
inter-relationship in the heart is important for function
What do we measure with ECG?
Electrical signal. It’s relationship to mechanical and
functional properties of the heart is what makes it a valuable component of the cardiac exam
What does an electrocardiogram do?
Captures the electrical activity produced by the heart’s contraction cycle.
What forms the basis for an electrocardiogram?
The detection of current electrical impulses generated from the flow of charged particles along this pathway that are detectable
on the surface of the skin
Where are the electrodes of an ECG in reference to the body?
The negative is on the right arm and the positive electrode is usually on the left leg
ECG leads capture signal going from where to where?
From the negative terminal to the positive terminal
What end of the ECG captures/receives the signal?
The positive terminal
What do ECG bipolar leads utilize?
A negative and positive electrode and record the electrical activity between them.
What do ECG unipolar leads utilize?
Utilize a single positive recording electrode and a combination of the other electrodes to serve as a composite negative electrode
Where do the bipolar leads go?
Limb: Right arm, left arm, left leg
Where do the unipolar leads go?
- Precordial (Chest)
* Unipolar (Augmented)
Where do the precordial (Chest) leads go?
- V1: 4th IC space to the right of the sternum (Septal)
- V2: Forth IC space to the left of the sternum (Septal)
- V3: between V2 and V4 (Anterior wall)
- V4: midclavicular line, 5th IC space (Anterior Wall)
- V5: anterior axillary line @ level of V4 (Lateral Wall)
- V6: midaxillary line @ level of V4 (Lateral Wall)
Primarily on the left side
Why are augmented leads termed as unipolar leads?
Because there is a single positive electrode that is referenced against a combination of the other limb electrodes.
What portion of the heart does augmented lead: aVF(augmented vector foot) look at?
The inferior portion of the heart
What portion of the heart does augmented lead: aVL(augmented vector lateral/left arm) look at?
The lateral wall of the heart
What portion of the heart does augmented lead: aVR(augmented vector right arm) look at?
It looks at the heart backwards, so its signal is flipped.
Called the orphan lead
What is the most basic ECG?
The 3 lead ECG. It uses 3 electrodes. (RA, LA and LL)
The 3 lead ECG is able to obtain a signal for the ____ leads
The 3 lead ECG is able to obtain a signal for the bipolar limb leads
What is the 3 lead ECG used for?
Basic monitoring and Research
purposes
Where are the lead placements for the 5 lead ECG?
RA, RL, LA, LL and Chest
What is displayed on the monitor of the 5 lead ECG?
The bipolar leads (I, II and III) AND a single chest/precordial lead
- (depending on position of the brown chest lead (positions V1–6)
In what setting is the 5 lead ECG commonly used?
In Acute Care
What are the characteristics of the 12 lead ECG?
• 10 electrodes. • Electrodes on all 4 limbs - (RA, LL, LA, RL) • Electrodes on precordium - (V1–V6) • Monitors 12 leads - (V1–V6), (I, II, III) and (aVR, aVF, aVL)
What does a 12 lead ECG allow?
Allows interpretation of specific areas of the heart
What is a 12 lead ECG used for?
Diagnostics, stress testing
What is the location and coronary artery of a V1, V2 lead?
Location: Anterior
Coronary artery: LAD
What is the location and coronary artery of a V3, V4 lead?
Location: Apical- septal
Coronary artery: LAD
What is the location and coronary artery of a II, III, and avF lead?
Location: Interior
Coronary artery: PDA( 80% RCA, 20% LCx)
What is the location and coronary artery of a I, V5, V6, and avL lead?
Location: lateral
Coronary artery: LCx
What do the thin lines on an ECG paper mean?
1 mm intervals or 0.04 sec
What do the thick lines on an ECG paper mean?
5 mm intervals or .2sec
What do the 1 thick lined box (5 boxes) on an ECG paper mean?
.20 sec or 5mm
What do the 5 thick lined box (25 boxes) on an ECG paper mean?
= 1 second
What do the tick marks on rhythm strip on an ECG paper mean?
3 secs
10 mm on an ECG paper is equal to ___
1 mV
What does the P wave on an ECG represent?
Atrial Depolarization
What are the normal ranges for a P wave on an ECG?
- Duration: < 0.12s OR 3 small boxes)
* Amplitude: < 2.5mm OR 2.5 small boxes)
What does the P-R interval on an ECG represent?
The propagation of the cardiac
action potential from the atria through the AV node into the ventricles.
What are the normal ranges for a P-R interval on an ECG?
- Duration: 0.12- 0.2s OR 3-5 small boxes
* Will shorten during exercise as heart rate increases
What does the QRS complex on an ECG represent?
Ventricular Depolarization
What are the normal ranges for a QRS complex on an ECG?
- Duration: 0.06- 0.10s OR 1.5-2.5 small boxes,
* Some healthy patients may have wider QRS (0.10-0.12s), but the absolute cut off is 0.12s
What is the amplitude for a QRS complex on an ECG?
• >0.5 mV in at least one standard lead (5 small
boxes)
• >1.0 mV in at least one precordial lead (10 small boxes)
• Upper limit 2.5 – 3.0 mV (25 small boxes)
What does the S-T segment on an ECG represent?
The interval between ventricular depolarization and repolarization.
What are the normal ranges for a S-T segment on an ECG?
• A discrete ST segment distinct from the T wave is usually absent.
• Often at higher heart rates (exercise) the ST-T segment is a smooth, continuous line
beginning at the J-point (end of QRS), slowly rising to the peak of the T-wave
What does the T wave on an ECG represent?
Ventricular repolarization
What are the normal ranges for a T wave on an ECG?
• It’s deflection should be the same direction as the largest component of the QRS wave complex (usually the R wave
- Ie, if the R wave is positive the T wave should be positive.
- Ex; in lead aVR it is normal for the T wave to be negative, since the QRS is also negative
What does the R-R Interval on an ECG represent?
- The duration between subsequent “heart beats”.
* This is duration is used to calculate heart rate.
What are the normal ranges for the R-R Interval on an ECG?
• Should be regular and consistent,
- Especially at rest.
• Will shorten during exercise as heart rate increases.
What does the Q-T Interval on an ECG represent?
- It represents the time taken for ventricular depolarization and repolarization.
- Shortens during faster heart rates, lengthens during slower heart rates
What are the normal ranges for the Q-T Interval on an ECG?
• Duration:
- Men 0.4- 0.44s OR 10-11 small boxes
- Women: 0.44- 0.46s OR 11-11.5 small boxes.
Why is the corrected QT (QTc) interval more often used?
Since the duration of QT varies inversely with the heart rate, the raw QT interval is often not used
How is the corrected QT (QTc) calculated?
QTc = measured QT interval
divided by
square root of R-R interval
What is the normal value for the corrected QT (QTc)?
< 0.44 sec
What does the J point on an ECG represent?
• The initiation of ventricular
repolarization
• Junction between the termination of the QRS complex and the beginning of the ST segment
What are the normal ranges for the J point on an ECG?
Should be in line with the isoelectric line
What is the R wave progression?
Small R waves begin in V1/V2 and progress in size to V4/V5.
• The R in V6 is usually smaller than R in V5.
What occurs at leads V3 or V4?
The transition from S>R to R>S
Where do s-waves begin when in reverse?
In reverse, the s-waves begin in V6 or V5 and progress in size to V2.
• The S in V1 is usually smaller than the S V2.
What is the QRS axis?
The direction of the mean QRS vector in the frontal plane
Normally all QRS segments are positive, except for ___
aVR
What are the characteristics of the Left Axis Deviation LAD of the QRS axis?
- QRS is positive (dominant R wave) in leads I and aVL
* QRS is negative (dominant S wave) in leads II and aVF
What are the characteristics of the Right Axis Deviation LAD of the QRS axis?
- QRS is negative (dominant R wave) in leads I and aVL
* QRS is positive (dominant S wave) in leads II or III and aVF
What are the components of the systematic analysis of an ECG?
• Rate
- Is the rate fast or slow
• Rhythm
- Regular or irregular
• Are a P wave and QRS complex with each cycle
• Do the P waves look alike
• Is there a P wave preceding every QRS
• Is the PR interval within normal limits
• Is the QRS duration within normal limits
• Does the rhythm come from the SA Node, AV node, or the ventricles
• Does the atrial rate = ventricular rate
What should the atrial rate to ventricular rate of an ECG be?
Should be 1:1
What does it mean when the rhythm of an ECG comes from the AV Node or above (SA, AV, atria, nodal tracts)?
The QRS is narrow
What does it mean when the rhythm of an ECG comes from below the AV node?
Wide QRS
What does it mean when the rhythm of an ECG has no p wave but normal QRS?
AV node
What is normal heart rate at rest?
60- 100 bpm
What is tachycardia?
HR above normal
What is bradycardia?
HR below normal
How is the rhythm of an ECG analyzed?
Whether or not it is regular looking at the distance from each R interval to the other
How are P wave and QRS complex with each cycle analyzed?
Is there a P wave preceding each QRS complex?
How is the P wave analyzed?
- Do the P waves look alike?
- Are the distances similar?
- Do we see multiple P waves?
How do we analyze the PR interval?
Is it within normal limits of 0.12- 0.2
How do we determine if the QRS duration is within normal limits?
The cutoff is 0.12 secs/ 3 small boxes
When can we assume that the rhythm of the ECG is sinus?
If we see a normal looking P wave prior to a narrow QRS
When can we assume that the rhythm of the ECG is supraventricular?
It indicates that somewhere above the ventricles is controlling the HR. The QRS will be narrow, without a P wave
When can we assume that the rhythm of the ECG is ventricular?
When the rhythm/impulse generated is below the atria., Below AV node (ventricles). The QRS will be wide
How do we calculate HR?
Using the ECG paper, after the 1st QRS complex, divide 60/.2, then add (0.2) for every other thick line you hit. (60/.4), (60/0.6)……
What happens if the QRS doesn’t fall on a thick line?
Use the distance between the two intervals the QRS lies between. Subtract the little number from the big number,, then divide it by 5, because there are 5 thin boxes that equals 3 bpm
What method is used when the R to R interval is invariable?
- Count number of QRS complexes in a six second interval and multiply by 10
- 30 thick lined boxes
What is a regular rhythm in an ECG?
- 1 P wave per QRS complex
* RR interval constant
What is a regularly irregular rhythm in an ECG?
• RR interval variable but with a pattern.
• Normal and ectopic beats grouped together and
repeating over and over.
What is a irregularly irregular rhythm in an ECG?
RR interval and ectopy variable with no pattern, totally irregular
Why do children have a faster HR?
Because their heart doesn’t fully develop until 12
What does sinus bradycardia look like?
R to R interval is consistent, everything looks good. However the rate is 60 bpm
What does sinus tachycardia look like?
Normal P wave, followed by a normal QRS, R to R interval is consistent, but the rate is faster than 100 bpm
What does sinus arrythmia look like?
Normal sinus signals, morphology, normal P wave,, everything else is normal, but the R to R interval isvery variable
What is an ectopic pacemakers/foci?
Abnormal pacemaker sites located outside of the
SA node that display automaticity.
How is the activity of an ectopic pacemaker normally suppressed?
Via overdrive suppression. by
the higher rate of the SA node.
Where can an ectopic foci occur?
Within the atria or ventricles.
What is the most common type of rhythm caused by an ectopic foci?
Supraventricular Tachycardia (SVT)
What are the characteristics of an atrial flutter?
- Regular atrial activity with a saw-tooth apperances
- Ventricular rate usually 60-100bpm
- Conduction ratio usually between 2:1 and 4:1
- Not frequently encountered in clinic
An atrial flutter and fibrillation is technically a ____ rhythm
Supraventricular rhythm
What is an atrial fibrillation?
Atrial activity is poorly defined; may see course or fine undulations or no atrial activity at all.
What causes an atrial fibrillation?
Multiple ectopic pacemakers in the atria
What are the characteristics of an atrial fibrillation?
• Ventricular response is irregularly irregular
- Ventricular response can be rapid, moderate or slow
• Adequate Control (HR <110bpm)
• Inadequate Rate Control (HR >110 bpm), need medication modification
What are the differences between an atrial fibrillation and atrial flutter?
• The p wave in Aflutter has a distinct saw tooth morphology
• Afib p waves will be variable, heart to detect or not demonstrated at all
• The rhythm of Aflutter is usually fairly regular, limited R-R variability
• The rhythm of Afib is usually very irregular, high R-R variability, with isoelectric
line variability
• Aflutter usually has a fixed or consistent conduction block pattern
• Ie, 4 saw tooth p waves then a QRS = 4:1 block
• Afib p waves are often not discernable and follow no consistent pattern
What does a patient with an aflutter feel?
Feel like the heart is fluttering, maybe skipping a beat here or there, HR will generally be faster, not as severe as an afib
Patients with an Afib is at a high risk for ____
Patients with an Afib is at a high risk for blood clots, because the atria is quivering, the blood is turbulent, but is not being properly ejected
When will an AV node block present?
When the P-R > 0.2 sec
What is a 1st degree AV node block?
PR>0.20 sec. Might have a slower HR, fairly benign
What is a 2nd degree AV node block?
- Type I (Mobitz I or Wenckeback): increasing PR interval until a QRS complex is dropped. It is usually benign.
- Type 2 (Mobitz II): QRS dropped without any progressive increase in PR interval (i.e., PR interval is constant but still >0.20 sec).
What is a 3rd degree AV node block?
- Aka: “Complete Heart Block
- 3rd degree AV Block: atria and ventricles are electrically dissociated.
- P waves and QRS complexes will occur independent of each other.
- As always, use the QRS complexes to determine heart rate.
What method is used when calculating the HR of a 2nd degree AV node block?
The second method to calculate HR: count the number of QRS complexes for the 6 sec strip, then multiply it by 10
What does a patient with an AV node block feel?
They feel that their heart skips a beat
What is a 3 to 1 block?
When you have 3 normal QRS complex in a row, then a missing one. Can be used for any
What may change a type 2 2nd degreeAV node block?
Exercise, conduction blocks, and as demand increases on the myocardium
Why might a patient with an AV node be symptomatic?
Due to the loss of cardiac output. A “dropped” or “lost” QRS indicates the ventricles did not depolarize, which means they don’t contract to push blood into the systemic circulation for that time period
What is observed in a Premature Atrial Contraction (PAC)?
The amplitude of the R wavs is usually a lot smaller, there will be a normal QRS, but then out of the blue, there will be a random bit of ectopy caused by a random ectopic foci. Usually benign
What causes a Premature Atrial Contraction (PAC)?
A small random ectopic foci which is caused by irritants to the myocardium, or stress.
What happens if a Premature Atrial Contraction (PAC) falls on the relative refractory period?
A more concerning rhythm can be set off, called ventricular fibrillation
When is the relative refractory period?
After the QRS and before the down slope of the T wave
What is observed in a Premature ventricular Contraction (PVC)?
A wide funky looking QRS, which happens spontaneously
What causes a Premature ventricular Contraction (PVC)?
Caffeine, or anything that will cause the heart to be irritable
What is the cutoff for a Premature ventricular Contraction (PVC)?
6 PVCs/min, anymore is a cause for concern
What should be done if a person has more than 6 PVCs/ min?
It will affect cardiac output, so check BP, stop exercise and further assess
What are the things to always look for when assessing a PVC?
Always look for the size of the QRS and the morphology, if the PVC is from the same area of the heart, the shape of the wave will be consistent. If the shapes are different, it means the PVCs are originating from different parts of the heart
What are PVCs that all look the same called?
Monomorphic
What are PVCs that all look different called?
Polymorphic
What is a bigeminy PVC?
A PVC that occurs every other beat
Why is a bigeminy PVC concerning?
Because if the PVC happens prior to the heart filling sufficiently, that ventricle is not ejecting sufficient amounts of blood. So the more we have,, the more concerned we are that we are not getting an effective cardiac output, hence there is no tissue perfusion
What is a trigeminy PVC?
A PVC that occurs every 3 beats
What is a quadrigeminy PVC?
A PVC that occurs every 4th beat
Why is a trigeminy less concerning than a bigeminy, and a quadrigeminy less concerning than a trigeminy?
Because there are less or them per minute
What is a couplet PVC??
2 PVCs in a row
What are the implications of a PVC, especially a couplet?
Blood won’t be pumped out properly, hence tissues like the brain and such could get damaged, or can lead to a heart attack
What is Ventricular Tachycardia?
When the ventricles are pumping quickly, which may not allow them to fill sufficiently. (4 or more PVCs in a row)
What is Non- Sustained Ventricular Tachycardia?
Ventricular tachycardia that lasts less than 30 secs in duration. Patients often go into breif bout of it
What do you do when you see a patient with a Non- Sustained Ventricular Tachycardia?
Stop exercise, assess the patient, and make sure they are stable
What is Sustained Ventricular Tachycardia?
Anything that doesn’t revert back into normal rhythm after about 30 secs
What is a pulseless electrical activity?
When we see an electrical rhythm whose rate is beating out of control and may not be filing
What is ventricular fibrillation?
When the ventricles demonstrate a worm like pattern, they are not pumping effectively, hence not moving any blood
What is Torsades de pointes?
A pulseless electrical activity that often happens when there is a PVC that falls somewhere from a elongated Q-T interval
What is a Aystole (Flat line)?
When the patient is electrically dead in the heart
What are ventricular pacemakers used for?
Patients that have abnormal rhythms, specifically type 2 second degree AV node blocks or complete heart blocks, and in patients with a significant A-fib
What do we see on a ventricular pacemaker?
We see spikes followed by a ventricular beat
What is the general rule of thumb when it comes to the ischemic changes seen in an ECG?
When we start having reduced blood flow to the myocardium, it affects its ability to conduct an action potential and will also drastically begin to change the membrane potential, or inhibit the ability for the myocardium to move electrons, specifically potassium and sodium across the barrier that requires ATP. This will eventually lead to the membrane rupturing and result in troponin and other enzymes in the blood
What is a T- wave inversion?
It is a sign of ischemia whose changes is significant only when seen in buddy leads. It is the 1st sign we see of ischemia
What does a T wave inversion progress to, in the presence of ischemia?
ST segment changes, specifically ST depression. Due to the membrane potential being altered, which may eventually progress to ST elevation.
What is ST elevation?
When the membrane potential has been completely disrupted and we probably have some infarction or cell death
How do we confirm ischemic changes/ heart attack?
If the heart dies, it releases bio- markers, troponin creating kinase lactate dehygrenase, because we are not able to pump ions across the membrane, because we lost blood flow, energy, which will lead to the loss of the NaK pump, which causes the cell to rupture
What is an NSTEMI?
When there is no ST elevation, but there was an heart attack because we have positive bio markers
What is a STEMI?
A heart attack that is accompanied by ST elevation
What can the comment “demand ischemia” and elevated troponin mean on a patient’s chart?
It can be due to poor cardiac output and does not represent an MI. The patient may be at risk for additional ischemia related to activity, so proceed cautiously
What is the criteria for ST depression for ischemia?
Greater than 1mm at the J point
In what direction should the T wave be?
In the same direction of the greatest QRS
What is the most common cause of ST segment
elevation?
Myocardial ischemia and
infarction
What are the threshold values for ST segment elevation?
STEMI are Jpoint elevation of >2 mm in leads V2 and V3 or >1 mm in all other leads.
ST elevation greater than ____ is concerning
ST elevation greater than one box is concerning
In what patient presentation do we see pathologic Q waves?
In people with healed scarred tissue after the tissue has died from a heart attack
What is a pathologic Q wave?
A really deep Q wave and an almost absence of the normal QRS
What happens in a bundle branch block in ischemia?
Due to some sort of change in the conductive system in the bundle branches, there is some sort of delay in the conductive system. They look like wind peaked QRS waves that are usually a little wider on the left ones and on the right ones, we see twin peaks
What are the non- ischemic causes of ST depression?
• RVH (right precordial leads) or LVH (left precordial leads, I, aVL)
• Digoxin effect on ECG
• Hypokalemia
• Mitral valve prolapse (some cases)
• CNS disease
• Secondary ST segment changes with conduction abnormalities (e.g., RBBB,
LBBB, WPW, etc)
What are the non- ischemic causes of ST elevation?
- LVH (left precordial leads, I, aVL)
- Conduction abnormalities (such as LBB, WPW and non-specific intracardiac conduction delay)
- Early repolarization pattern
- Aneurysm/old myocardial infarction
- Pericarditis/myocarditis
- Brugada pattern
- Takotsubo (apical ballooning) syndrome
- Hyperkalemia
- Hypercalcema
What are the types of ST depression?
- Normal
- Upsloping
- Horizontal
- Downsloping
When does the common changes in the ST segment?
During exercise
What is a normal ST segment?
When it returns to the isoelectric line
What are the types of ischemic ST depression?
Horizontal or downsloping
When do we see upsloping ST depression?
It is fairly normal during exercise
What is a common cause of a diffuse ST elevation?
Pericarditis
What is pericarditis?
Inflammation of the cardiac sac and tissues which causes compression of the myocardium
What are the characteristics of pericarditis and ST elevation?
- Concave upwards ST elevation in most leads except aVR
- No reciprocal ST segment depression (except maybe aVR)
- T waves are usually low amplitude, and heart rate is usually increased.
- May see PR segment depression, a manifestation of atrial injury due to compression
What are hyperkalemia?
An elevated potassium level
What are the non ischemic T wave changes?
Changes that occur as a result of hyperkalemia which affects the membrane potential especially during repolarization, which will be identified with a peaked T wave, which will be much greater than the amplitude of the QRS
