ACSM-EP Electrocardiography — Questions and Answers
Question 1: A resting 12-lead ECG shows a regular rhythm with a PR interval of 0.26 seconds and every P wave followed by a QRS. What is the interpretation?
- Normal sinus rhythm
- First-degree AV block (Correct answer)
- Mobitz type II second-degree AV block
- Complete (third-degree) AV block
Correct answer: First-degree AV block
A consistently prolonged PR interval above 0.20 s with every P conducted is first-degree AV block.
The normal PR interval is 0.12-0.20 seconds (3-5 small boxes). A constant PR above 0.20 s with 1:1 conduction defines first-degree AV block, which is usually benign and may be seen in trained athletes. Mobitz II shows intermittently dropped QRS complexes with a constant PR, and third-degree block shows complete AV dissociation with no relation between P waves and QRS. Clients with first-degree block can generally exercise, but new or worsening block should be referred.
Question 2: During an exercise test, which ST segment change is the standard ECG criterion for a positive (ischemic) response?
- Upsloping ST depression of 0.5 mm at the J point
- Horizontal or downsloping ST depression of 1 mm or more, 60-80 ms after the J point (Correct answer)
- ST elevation in lead aVR of 0.5 mm
- T wave flattening in lead V1
Correct answer: Horizontal or downsloping ST depression of 1 mm or more, 60-80 ms after the J point
Horizontal or downsloping ST depression of at least 1 mm (0.1 mV) measured 60-80 ms after the J point indicates ischemia.
The accepted criterion for a positive exercise ECG is horizontal or downsloping ST depression of 0.1 mV (1 mm) or more measured 60-80 ms after the J point in at least 3 consecutive beats. Upsloping depression is common at high heart rates and is typically a normal finding unless it remains depressed at 80 ms. Isolated T wave flattening is nonspecific. ST elevation in non-Q-wave leads (excluding aVR) is also a termination criterion.
Question 3: On a 6-second rhythm strip with a regular rhythm, the R-R interval spans 4 large boxes. What is the heart rate?
- 60 bpm
- 100 bpm
- 75 bpm (Correct answer)
- 150 bpm
Correct answer: 75 bpm
Heart rate = 300 divided by the number of large boxes between R waves = 300/4 = 75 bpm.
For regular rhythms, divide 300 by the number of large boxes (0.2 s each) between consecutive R waves: 300/4 = 75 bpm. Alternatively, 1,500 divided by the number of small boxes (20) gives the same 75 bpm. A 60 bpm rate would need 5 large boxes, 100 bpm needs 3, and 150 bpm needs 2. For irregular rhythms, count QRS complexes in a 6-second strip and multiply by 10.
Question 4: During an exercise test, which rhythm finding requires immediate termination of the test?
- Occasional isolated PVCs
- Sustained ventricular tachycardia (Correct answer)
- Sinus tachycardia at 85% of age-predicted maximum
- Occasional premature atrial contractions
Correct answer: Sustained ventricular tachycardia
Sustained ventricular tachycardia is an absolute indication to stop exercise because it can degenerate to ventricular fibrillation.
ACSM lists sustained VT as an absolute indication for terminating an exercise test. Isolated PVCs and PACs are common and generally benign unless they increase markedly, become frequent couplets or triplets, or are accompanied by symptoms. Sinus tachycardia at 85% of predicted maximum is an expected response. Other termination criteria include drop in systolic BP of more than 10 mmHg despite increasing workload, angina, and ST changes concerning for ischemia.
Question 5: A client has ST elevation in leads II, III, and aVF on a resting ECG. Which myocardial wall is affected?
- Anterior wall
- Lateral wall
- Septal wall
- Inferior wall (Correct answer)
Correct answer: Inferior wall
Leads II, III, and aVF view the inferior wall of the left ventricle, usually supplied by the right coronary artery.
Leads II, III and aVF are the inferior leads, representing the inferior wall, which is typically perfused by the right coronary artery. Leads V1-V4 reflect the septal and anterior walls (LAD), and leads I, aVL, V5 and V6 reflect the lateral wall (circumflex). Resting ST elevation with symptoms suggests acute MI and requires emergency referral, not exercise. Knowing lead groupings helps interpret location of ischemia during stress testing.
Question 6: Which rhythm is characterized by an irregularly irregular ventricular response and no distinct P waves?
- Atrial fibrillation (Correct answer)
- Atrial flutter with 4:1 conduction
- Sinus arrhythmia
- Mobitz type I second-degree AV block
Correct answer: Atrial fibrillation
Atrial fibrillation produces chaotic atrial activity, so P waves are absent and R-R intervals are irregularly irregular.
In atrial fibrillation the atria fibrillate at 350-600 per minute, so there are no discrete P waves and the ventricular response is irregularly irregular. Atrial flutter shows sawtooth flutter waves and, with fixed conduction, a regular rhythm. Sinus arrhythmia and Mobitz I (Wenckebach) both have P waves; Wenckebach shows progressive PR lengthening before a dropped beat. AF raises stroke risk and exercise heart rates can be high, so clients need medical clearance and RPE-based monitoring.
