ECG Review-Regular Tachycardia in a 42-Year-Old Man

Clinical Scenario: The ECG shown in the Figure was obtained from a 42-year-old man complaining of atypical chest discomfort intermittently over the past few weeks. The patient was previously healthy. He was symptomatic at the time this tracing was recorded. What entities should be considered in your differential diagnosis? Is there evidence of atrial activity in the Figure?

Interpretation: There is a regular supraventricular tachycardia (SVT) at a rate of just under 150 beats/minute. Practically speaking, the differential diagnosis of a regular SVT at this rate consists of three entities: sinus tachycardia, atrial flutter, and paroxysmal supraventricular tachycardia (PSVT). Definitive diagnosis is unfortunately not possible from this single tracing. The rhythm could be sinus tachycardia, with an upright P wave concealed within the T wave seen in lead II. Atrial flutter always should be considered in the differential diagnosis of a regular SVT at a ventricular rate that is close to 150/minute, but the absence of any semblance of flutter activity in all 12 leads on this tracing makes this possibility less likely. Consequently, the most probable diagnosis is PSVT, which we strongly suspect because of the suggestion of subtle retrograde (negative) atrial activity that appears to be notching the terminal portion of the QRS complex in each of the inferior leads and which produces a terminal positive deflection (simulating an r’) in lead V1.