A 69-year-old woman awakens with chest pain. She has had intermittent episodes of chest pain for the past few days, but this is the first to occur during sleep. At presentation, the patient describes the pain as 4 out of 10 on the pain scale, with radiation into the left neck. Associated symptoms include shortness of breath and palpitations. She says her heart “just doesn’t feel right.” 

Medical/surgical history is notable for a dilated cardiomyopathy, mitral regurgitation with a mitral valve replacement performed 10 years ago, hyperlipidemia, and diabetes mellitus. The woman also has stable normocytic anemia and chronic renal insufficiency, and she is on chronic anticoagulation for a mechanical heart valve. Social history demonstrates no evidence of tobacco or alcohol abuse.

Her medications include furosemide, potassium chloride as needed, losartan, gemfibrozil, digoxin, and warfarin. She has no allergies.

Vital statistics include a height of 5’1”; weight, 104 lb; blood pressure, 164/90 mm Hg; pulse, 160 beats/min; respiratory rate, 20 breaths/min; and O₂ saturation, 97% on room air. The patient is uncomfortable but in no acute distress, lying on an exam bed with the head raised 30°. Jugular venous distention is present to the angle of the jaw. The cardiac rate is rapid and irregular, no murmur or rub is heard, and there is a rapid, crisp mechanical valve click.

Examination of the chest reveals a well-healed median sternotomy scar. There are decreased breath sounds bilaterally at the bases, with no crackles or wheezes. There is no peripheral edema. Peripheral pulses are present and equal bilaterally, and the neurologic exam is normal without focal findings.

The automated printout of the ECG records the following: a ventricular rate of 163 beats/min; PR interval, 128 ms; QRS duration, 130 ms; QT/QTc interval, 286/470 ms; R axis, 131°; and T axis, 19°. Given the history, physical exam, and other available information, what is your interpretation of this ECG? Is there anything in the automated measurements that may be misleading?

ANSWER

The ECG shows a supraventricular tachycardia at a rate of 163 beats/min, a right bundle branch block (RBBB), and right-axis deviation. The automated printout showing a PR interval of 128 ms is misleading. The rhythm is regular, but at a rate of 163 beats/min, P waves are not clearly discernible. The differential diagnosis includes sinoatrial node reentry, intra-atrial reentry, automatic atrial tachycardia, atrioventricular nodal reentrant tachycardia (AVNRT), and atrioventricular reentrant tachycardias due to accessory pathways (eg, Wolff-Parkinson-White syndrome).

Supraventricular arrhythmia refers to a diverse group of abnormal rhythms occurring at a rate of 150 to 250 beats/min. The QRS duration is normal unless a bundle branch block is present (note that this patient has an RBBB). If P waves are identifiable, their morphology usually varies from a sinus P wave and may occur before, during, or after the QRS complex.  

Without clear identification of P waves, the more generic supraventricular tachycardia, rather than something more definitive, is an accurate diagnosis. Further workup revealed AVNRT. This patient did not have ischemia, and her chest pain did not return following termination of her tachycardia.