This morning, a 90-year-old man experienced progressive shortness of breath, fatigue, and lethargy after waking. He was in his usual state of health last night and had an uneventful night’s sleep.

Following the onset of symptoms this morning, he checked his pulse and thought it was approximately 40 beats/min. He called his son, who confirmed a pulse of 38 beats/min, and the son transported the patient to the emergency department (ED).

According to the patient and his son, this has never happened before, despite a medical history that includes coronary artery disease, hypertension, hyperlipidemia, and congestive heart failure. The patient denies chest pain, paroxysmal nocturnal dyspnea, syncope, or near-syncope.

His medication list includes aspirin, atenolol, enalapril, furosemide, and atorvastatin. He is allergic to ciprofloxacin and sulfa. He has a remote history of tobacco use and does not consume alcohol. 

Upon his arrival in the ED, the patient’s pulse drops further to 30 beats/min, and he becomes lethargic and hypotensive, with a blood pressure of 80/56 mm Hg.  He becomes increasingly difficult to arouse but does not lose consciousness. 

The cardiac exam is remarkable for bradycardia with a grade III/VI systolic murmur, jugular venous distention of 7 cm H₂O, and 2+ radial pulses with diminished dorsalis pedis pulses. The skin is warm and well perfused, and mucous membranes are pink and moist. There are no signs of cyanosis. 

A stat ECG is ordered and reveals the following: a ventricular rate of 28 beats/min; PR interval, 280 ms; QRS duration, 134 ms; QT/QTc interval, 716/827 ms; P axis, 143°; R axis, 101°; and T axis, 61°. What is your interpretation of this ECG?

ANSWER

This ECG reveals profound sinus bradycardia with second-degree atrioventricular (AV) block (Mobitz II) with a 3:1 AV conduction pattern, and a right bundle branch block (RBBB).

Bradycardia occurs at rates of less than 60 beats/min. The bradycardia seen here is sinus, as there is a P wave with a consistent interval associated with each QRS complex.

Second-degree AV block (Mobitz II) is distinguished by the sudden loss of conduction from the atria to the ventricles without prior or subsequent lengthening of the PR interval. This may occur in patterns. In this ECG, the pattern is 3:1 (three P waves for each QRS complex). Note that in this ECG, one of the P waves is hidden within the T wave. This can be discerned by “marching” the P waves with ECG calipers. 

The ECG also shows a RBBB pattern exemplified by a widened QRS duration of 134 ms and an R-S-R’ complex in leads V₁ through V₃.

The patient underwent emergent placement of a temporary pacing lead, followed by implantation of a dual-chamber permanent pacemaker system for symptomatic bradycardia.