Electrocardiogram

Question 1

Sinus rhythm

Answer 1

P before every QRS and QRS after every P

Question 2

Normal axis

Answer 2

Positive QRS in I an aVF (0 to 90 degrees)

Question 3

L axis deviation

Answer 3

Positive QRS in I and negative QRS in aVF. Up to -30 degrees is still a normal variant

Question 4

R axis deviation

Answer 4

Negative QRS in I and positive QRS in aVF. Up to 105 degrees is a normal variant.

Question 5

Normal intervals

Answer 5

Normal PR is 120-200 ms

Normal QRS is less than 120.

Question 6

AV block

Answer 6

PR interval greater than 200ms or P with no QRS after

Question 7

LBBB

Answer 7

QRS more than 120ms. No R wave in V1. Tall R waves in I, V5, V6.

Question 8

RBBB

Answer 8

QRS more than 120ms. RSR’ (rabbit ears), qR or R morphology with a wide R wave in V1

QRS with wide S wave in I, V5, V6

Question 9

Ischemia

Answer 9

New inverted T waves; poor R wave progression in precordial leads (the Vs).

ST segment changes (elevation or depression)

Question 10

Transmural infarct

Answer 10

Significant Q waves (more than 40 ms or more than one third of QRS amplitude); ST elevations with T wave inversions

Question 11

Long QT syndrome

Answer 11

QTc more than 440 ms. An underdiagnosed congenital disorder that predisposes to ventricular tachyarrhythmias

Question 12

Atrial enlargement

Answer 12

1) RA abnormality (P Pulmonale) - P wave amplitude in lead II is more than 2.5mm
2) LA abnormality (P mitrale) - P wave width in lead II is more than 120ms or terminal negative deflection in V1 is more than 1mm in amplitude and more than 40ms in duration. Notched P waves can frequently be seen in lead II.

Pulmonale causes Peaked P waves. Mitrale causes M-shaped P waves.

Question 13

LVH

Answer 13

1) Amplitude of S in V1 plus R in V5 or V6 is more than 35mm.

OR

2) Amplitude of R in aVL plus S in V3 is more than 28mm in men or 20mm in women.

Question 14

RVH

Answer 14

R axis deviation and an R wave in V1 is more than 7mm.

Question 15

Estimating HR

Answer 15

Count boxes between QRS complexes

300-150-100-75-60-50-43 (You start at 300. This is the line the first QRS is actually on. Then you count down from there)

Rhythm strip x 6

Question 16

College aged male “passed out” while playing basketball and had no prodromal symptoms or signs of seizure. Cardiac exam unremarkable. ECG shows a slurred upstroke of QRS. Next best steps?

Answer 16

This is WPW Syndrome

Advise against vigorous physical activity, treat arrhythmias with procainamide and refer for electrophysiology study