Rosh Internal Medicine Boost Practice Exam

What is identified as the underlying rhythm on the ECG for this patient?

1. Narrow-complex supraventricular tachycardia

2. Ventricular fibrillation

3. Atrial flutter

4. Wide-complex tachycardia

The correct answer is: Narrow-complex supraventricular tachycardia

In this context, identifying narrow-complex supraventricular tachycardia (SVT) as the underlying rhythm on the ECG is supported by characteristics typically observed in such a rhythm. Narrow-complex SVT is characterized by a rapid heart rate (usually over 100 beats per minute) with QRS complexes that are narrow (typically less than 0.12 seconds). The presence of a regular rhythm, the absence of any ventricular dissociation, and a consistent narrow QRS complex suggest that the rhythm originates above the ventricles, commonly from the atria or the atrioventricular node. Conditions such as atrial fibrillation or atrial flutter can present with narrow complexes but may lack the regularity seen in typical SUVT, which often has a consistent, fast rate. In contrast to other options, wide-complex tachycardia would present with QRS complexes that are wider than 0.12 seconds, indicative of a different arrhythmogenic source, often from the ventricles. Ventricular fibrillation would not have discernible complexes and would appear chaotic. Atrial flutter can present with a rapid rhythm, but it generally shows a characteristic "sawtooth" pattern (F-waves) on the ECG