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Pathophysiology - Cardiovascular > Basic Electrophysiology Principles and Arrhythmia Recognition > Flashcards

Basic Electrophysiology Principles and Arrhythmia Recognition Flashcards

1
Q

What are the five phases of the cardiac action potential?

A

Phase 0: Rapid depolarization - potential shifts from -90mV to positive (rapid inward sodium current)
Phase 1: Rapid repolarization (early) - via Ito1 channels
Phase 2: Plateau phase - equilibrium between L-type calcium channels and potassium channels
Phase 3: Final repolarization - restores to normal resting potential via potassium channels
Phase 4: Resting potential - stable at -90 mV

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2
Q

What is the characteristic of phase 4 in pacemaker cells? How does this play into phase 0?

A

There is a slow diastolic depolarization, and the resting potential is higher (-50 to -65 mV rather than -90 mV). This will eventually allow for Ca+2 channels to open at threshold and a slow phase 0 depolarization
-> slow propagation thru nodal regions

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3
Q

What are the locations of the three standard ECG leads?

A
  1. Left arm
  2. Right arm
  3. Left leg
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4
Q

What are the directions of leads 1, 2, and 3? What type of leads are they? Give the degree directions they correspond to as well.

A

Bipolar leads
Lead I: - right arm to + left arm: 0 degrees
Lead II: - right arm to + left leg: 60 degrees
Lead III: - left arm to + left leg: 120 degrees

All of the negative leads are in the arms

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5
Q

What are the unipolar leads and where do they point?

A

aVR: Point towards right arm: -150 degrees
aVL: Point towards left arm: -30 degrees
aVF: Point towards feet: 90 degrees

Negative is the center of the heart

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6
Q

Where are the precordial / chest leads placed?

A

V1: Right 4th intercostal space
V2: Left 4th intercostal space
V3: Between V2 and V4
V4: Midclavicular line, 5th intercostal space
V5: Between V4 and V6, anterior axillary line
V6: Midaxillary line, 5th intercostal space

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7
Q

What leads are considered the inferior leads?

A

II, III, and aVF

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8
Q

What leads are considered the septal leads?

A

V1 and V2: sense the depolarization of the septa moving towards them

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9
Q

What leads are considered lateral leads?

A

I, aVL, V5, and V6

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10
Q

What leads are considered anterior leads?

A

V3 and V4 (right over the heart)

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11
Q

How much time is a small block vs large block on ECG? How much distance is it (up vs down)?

A

Small block: 40 ms, large block = 5 small blocks = 200 ms

One small block is 1 mm

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12
Q

What is a normal P wave duration, and what leads should always be up or down?

A

80-200 msec

Upright in leads I and II
Inverted in aVR

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13
Q

What do the first and second halves of the P wave correspond to?

A

1st half - Right atrium
2nd half - Left atrium

Based on which depolarizes first

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14
Q

What is the length of a normal PR interval? What does it mean when it is prolonged?

A

120-200 msec

Prolonged = AV node dysfunction is present

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15
Q

What is the normal QRS duration? What does it mean if prolonged?

A

1-3 small boxes (<120 msec)

If prolonged, there is slowed conduction or bundle branch delay

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16
Q

How do you determine the mean electrical axis?

A

Look for the lead where the QRS sum is isoelectric (0), and the mean electrical axis is perpendicular to this, pointing towards the lead with the most positive net deflection

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17
Q

What is the normal mean electrical axis range, and which two leads help identify normal vs abnormal? How?

A

0 to 90 degrees, Leads I and aVF will do this.

Both positive = normal
Lead I positive, aVF negative = Left axis deviation
Lead I negative, aVF positive = Right axis deviation
Both negative = No man’s land

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18
Q

What is the normal heart rate range defined as, and how do you calculate it based on ECG?

A

60-100 beats per minute

For regular heart rates, divide 300 by number of large boxes between two R waves
For fast heart rates, divide 1500 by number of small boxes between two R waves
For irregular rates, count the number of R waves over 10 seconds, and multiply by 6

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19
Q

What is the soft upper limit of sinus tachycardia? Why?

A

About 160 beats per minute -> otherwise you have a tachyarrhythmia, hard to pump your heart via sinus rhythm that high.

Max = 220-age.

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20
Q

What is sinus bradycardia? Will the PR interval be longer than 0.20 sec?

A

<60 BPM.

No, ECG will be normal.

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21
Q

How long is a normal QT interval in men and women? What can you correct for? How?

A

Men < 450 ms
Women < 460 ms

Can correct for heart rate by dividing QT by the sqrt of the RR interval. Idea being, your QT interval will shorten with heartrate absolutely, but may still be long for that HR. Should be about half your RR interval.

22
Q

What are the common causes of prolonged QT?

A

Drugs (macrolides, Class IA and III antiarrhythmics, antipsychotics, TCAs, ondansetron)

Hypomagnesia, hypokalemia, hypocalcemia

Congenital long QT syndrome

Increased ICP

23
Q

What is the definition of first degree AV block?

A

Fixed and normally prolonged PR interval (>0.2 sec)

24
Q

What is the definition of Mobitz I, second degree AV block?

A

Also called Wenckebach

Gradually lengthening PR intervals, until QRS is dropped. Longest PR interval just before dropped beat, shortest after dropping a beat.

25
Q

What is the definition of Mobitz II? What will be the interval?

A

Another type of second degree AV block

PR intervals are fixed (does not get longer like Mobitz I), and will march through at a constant rate. A QRS beat will randomly be dropped.

Since the PR intervals are constant, if there is one dropped beat, the time between QRS complexes will be 2x normal RR, or 3x for two dropped beats.

26
Q

What is the overall definition of third degree AV block?

A

Complete absence of AV conduction -> NO supraventricular impulses conducted to ventricles.

Patient will have AV dissociation typically (a constant atrial and ventricular rate which are not linked)

Linked to syncope if it leads to ventricular standstill when self-terminating, or cause sudden cardiac death

27
Q

How does third degree AV block appear on ECG?

A

PR and QRS intervals are dissociated

Ventricular rate will be very slow because they are generated by a ventricular escape rhythm, and may appear irregular.

28
Q

What is the ECG definition for left atrial enlargement?

A

This is the criteria of 1s.

  1. P wave in V1 is -1.0 mm in depth for at least 1 small box
  2. P wave is notched (humped) in lead I with a duration of >120 msec.
29
Q

What is the ECG definition for right atrial enlargement?

A

P wave is tall and peaked, with a height of 2.5 mm or more in leads II, II, and aVF (all inferior leads).

30
Q

What is right atrial enlargement also called? What will these enlargements do to the P wave axis?

A

P pulmonale -> secondary to pulmonary disease.

P wave axis will be shifted to 75 degrees or greater depending on the degree of right atrial enlargement.

31
Q

What is the ECG definition for left ventricular hypertrophy?

A

The largest S wave of V1 or V2 (last part of LV depolarization) + largest R wave of V5 or V6 is > 35mm = LVH

32
Q

What is the ECG definition for left bundle branch block?

A

QRS duration of 120 msec or greater (3+ small boxes)
Presence of broad, monophasic R wave in leads I, V5, and V6
Displacement of ST segment and T wave opposite the major deflection of QRS complex (negative for the broad R wave leads)

33
Q

What is the ECG definition for right bundle branch block?

A
  1. QRS duration of 120 msec or greater (3+ small boxes)
  2. A secondary R’ wave in right precordial leads (V1/V2) after an initial R wave
    - > initial R wave caused by slight RV depolarization up until the right bundle branch
    - > secondary R wave caused by secondary depolarization from LV signal spreading to right ventricle
  3. A wide S wave in lateral leads (I, V5, V6)
    - > caused by a wide, delayed right ventricular depolarization
34
Q

What is used as the baseline for ST segment depression, and what are the three depression morphologies? Which ones are most convincing for ischemia?

A

Baseline = TP segment at normal rhythms, PR segment at higher heart rates (isoelectric)

  1. Upsloping
  2. Horizontal
  3. Downsloping

Horizontal and downsloping are most indicative of ischemia

35
Q

What correlates better with region of myocardial injury, ST segment depression or elevation?

A

ST segment elevation

  • > depression correlates more poorly
  • > i.e. 2+ concurrent leads indicates STEMI in that area
36
Q

What are the criteria for ST segment elevation in the limb and chest leads? Where should you start looking?

A

Limb leads - 1mm above baseline (1 box)
Chest / Precordial leads - 2mm above baseline (2 boxes)

Look 0.08 seconds to the right of J point (2 boxes)

37
Q

What would ST elevation in leads V1 through V5 indicate?

A

Anterior wall infarction

-> LAD STEMI

38
Q

What would ST elevation in leads II, III, and aVF indicate?

A

Inferior / right wall infarction

-> RCA STEMI

39
Q

What would ST elevation in leads II, III, aVF, and V4-V6 indicate? What other leads would be depressed to indicate posterior wall infarction?

A

RCA STEMI, with Inferior, Posterior and Lateral involvement, especially in a right-sided heart

V1 / V2 leads may be depressed in this context to show infarction (otherwise this usually means ischemia)

40
Q

What is the definition of a supraventricular tachycardia? What two arrhythmias are classically associated with this term?

A

Supraventricular -> Origin of the rapid ventricular rate is above the ventricle

Tachycardia -> Ventricular rate is above 100 bpm

Classically AVRT and AVNRT

41
Q

What causes AVNRT?

A

AVNRT - AV nodal re-entrant tachycardia
-> caused by a premature contraction which does not transduce through the normal, rapid-conducting, long-refractory period alpha pathway. It is transmitted through the slow-conducting, short-refractory period beta pathway, which can then loop around and reactive that alpha pathway and start a re-entry loop.

Basically, it is anterograde and retrograde conduction through the two pathways in the AV node, making a circuit initiating ventricular tachycardia

42
Q

What causes AVRT?

A

Atrioventricular re-entrant tachycardia
-> caused by an ectopic retrograde transmission somewhere in the cardiac skeleton which allows a circular loop to form in electricle conduction

43
Q

How does AVNRT appear on ECG?

A
  1. Narrow complex tachycardia ~150 pm (no bundle block to make it wide)
  2. No visible P waves before QRS to initiate depolarization
  3. P waves may be visible as retrograde (inverted) following the QRS complex (best seen in lead II)
44
Q

What is the definition between atrial fibrillation and atrial flutter?

A

Atrial fibrillation - due to ectopic foci originating from around pulmonary veins (left atrium) -> more disordered

Atrial flutter - due to a macrocircuit in the right atrium -> more ordered

45
Q

How is atrial fibrillation detected on ECG?

A
  1. Irregularly irregular rhythm
  2. No P waves -> coarse or fine undulating fibrillatory waves
  3. Variable ventricular rate -> time between QRS intervals varies must count them over 10 seconds and multiply by 6
46
Q

How is atrial flutter diagnosed via ECG?

A
  1. Narrow QRS tachycardia - usually around 150 bpm. May be slower if on medications to slow AV node conduction
  2. Regular atrial activity at about 300 bpm
  3. Flutter waves “saw tooth” seen in leads II, III, and aVF
47
Q

What is multifocal atrial tachycardia? What condition is associated with it? ECG characteristics?

A

Multiple ectopic foci in atrial cavities leading to discrete P waves with at least 3 different morphologies, ALL of which are transmitted to the ventricles

Associated with underlying pulmonary disease (COPD, asthma)

48
Q

What are the ECG characteristics of multifocal atrial tachycardia?

A
  1. At least 3 different P wave forms in the same lead, with no dominant atrial pacemaker
  2. Atrial rate > 100 bmp.
  3. PR and RR intervals will vary, but P waves are more obvious than in atrial fibrillation and are ALL transmitted to the ventricles
49
Q

What are the ECG characteristics of ventricular tachycardia, and its two types?

A
  1. Regular rhythm
  2. Broad QRS complexes originating from distortion of myocardial tissue -> previous MI, dilated cardiomyopathy, fibrosis

Two types:

  1. Unifocal -> all QRS will be uniform in shape
  2. Multifocal -> multiple QRS morphologies can be present
50
Q

What are the ECG characteristics of ventricular fibrillation?

A

Chaotic irregular deflections of varying amplitude
No identifiable wave forms of any kind, rate 150 to 500 waves per minute

Amplitude decreases with duration, coarse -> fine

51
Q

Where will ST elevations be for a lateral STEMI? What might produce this?

A

Leads I, V5, V6, and aVL

May be produced by occlusion of left circumflex artery

Pathophysiology - Cardiovascular (24 decks)

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