ECG Challenge

Young Man Thinks He is 
Having a Heart Attack

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The 24-year-old male graduate student whom you saw one month ago for palpitations (see July 2013 ECG Challenge) returns without an appointment, stating that his heart is “flip-flopping” just as it has in the past. The problem started abruptly about 45 minutes ago, and he is afraid he might be having a heart attack. A quick check of his pulse reveals a rate of 80 beats/min. At his previous visit, an ECG showed sinus rhythm with sinus arrhythmia and a blocked premature atrial contraction (PAC). A rhythm strip documented that his palpitations coincided with blocked PACs. You recall that he reported having two episodes of tachycardia in the past, while “pulling all-nighters” for finals as an undergraduate. Today, he denies shortness of breath, nausea, vomiting, chest pain, and symptoms of near-syncope or syncope, but says his heart is “flopping around” in his chest and he can feel his heart beat in his throat. He has no prior cardiac or pulmonary history and has not recently been ill. Medical history, medication list, allergies, family history, and review of systems are unchanged since his last visit: Medical history is remarkable only for fractures of the right ankle and the left clavicle. He takes no medications and has no drug allergies. Family history is significant for stroke (paternal grandfather), diabetes (maternal grandmother), and hypertension (father). The patient consumes alcohol socially, primarily on weekends, and does not binge drink. He smokes marijuana during snowboard season, but denies use at other times of the year. A 12-point review of systems is positive only for athlete’s foot and psoriasis on both upper extremities. The physical exam reveals an anxious but otherwise healthy, athletic-appearing male. Vital signs include a blood pressure of 140/88 mm Hg; pulse, 80 beats/min; respiratory rate, 20 breaths/min-1; and O2 saturation, 99% on room air. His height is 70” and his weight, 161 lb. His lungs are clear, there is no jugular venous distention, and cardiac auscultation reveals no murmurs, gallops, or rubs. The abdominal exam is normal without organomegaly, and peripheral pulses are regular and strong bilaterally. His neurologic exam yields normal results. As you examine the ECG, you note the following: a ventricular rate of 80 beats/min; PR interval, unmeasurable; QRS duration, 92 ms; QT/QTc interval, 388/444 ms; P axis, 265°; R axis, 72°; and T axis, 66°. What is your interpretation of this ECG?


 

ANSWER
The correct interpretation of this patient’s ECG is atrial flutter with variable atrioventricular block. Atrial flutter is a macro re-entrant supraventricular arrhythmia arising in the right atrium and usually (but not always!) identified by saw-tooth–appearing flutter waves.

The atrial rate in atrial flutter typically ranges from 200 to 350 beats/min. The QRS appearance will be narrow and similar to that of sinus rhythm, because conduction occurs normally down the atrioventricular node unless there is aberrant conduction.

The ventricular rate is dependent on the ability of the node to control rapid conduction. In this case, there appear to be three flutter waves for each QRS complex (3:1 flutter). If the ventricular rate is 80 beats/min, the rate in the atrium is approximately 240 beats/min. A regular ventricular rate of 150 beats/min should make you suspicious for atrial flutter (2:1 flutter).

The variable atrioventricular block on this ECG is evidenced by the presence of two, rather than three, flutter waves per QRS complex (seen after the fourth, fifth, and 10th QRS complexes on the rhythm strip). This case illustrates that flutter may be present with a ventricular rate of less than 100 beats/min.

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