ECG Review

A Question-Inducing SVT

By Ken Grauer, MD

Figure. 12-lead ECG obtained from a 57-year-old man.

Clinical Scenario: The 12-lead ECG shown in the Figure was obtained from a 57-year-old man. Review of this ECG should raise (induce) several questions in your mind. Which questions? Answer this even though you have not been provided with any clinical information about the patient.

Interpretation: The ventricular rhythm is irregularly irregular. A supraventricular etiology is confirmed by recognition that the QRS complex is narrow in all 12 leads. Despite the irregularity, this rhythm does not represent atrial fibrillation because organized atrial activity is present. Instead, the regular sawtooth pattern of atrial activity in the inferior leads identifies the rhythm as atrial flutter. The first unusual point about this tracing is the exceedingly large amplitude of the pointed flutter waves in lead V1. The second unusual point is the rate of flutter activity, which at 220/minute is clearly slower than the usual atrial range for flutter. This raises the first question, which is whether the patient might be taking any drug(s) that may act to slow the flutter rate (i.e., antiarrhythmic agents such as quinidine or amiodarone—or AV nodal blocking drugs such as verapamil or diltiazem). Although the most common ventricular response to atrial flutter is with 2:1 AV conduction, followed by 4:1 AV conduction—a variable ventricular response (as occurs here) also may be seen often.

The second question raised on interpreting this tracing is whether the patient has had an inferior infarction. Although QRS amplitude is markedly reduced in all six limb leads—small q waves do appear to be present in leads II, III, and aVF. Assessment for ST segment changes in these inferior leads is impeded by a relatively large amplitude of flutter activity, thus making it impossible to comment on the acuity of inferior changes.

A final question raised by interpreting this tracing relates to the meaning of ST segment changes in the lateral precordial leads. The very deep S wave in lead V2 strongly suggests left ventricular hypertrophy (LVH). We suspect ST changes in leads V4, V5, and V6 represent repolarization changes of LVH (i.e., "strain")—but simultaneous occurrence of flutter activity makes it difficult to verify this assumption.