A 75-year-old man presents to your office with complaints of shortness of breath. He states he has had “the flu” for the past week, but it doesn’t seem to be getting any better. His shortness of breath has persisted without change, and he is concerned he may be developing pneumonia. He denies having a productive cough, fevers, chills, or night sweats.

Medical history is remarkable for GERD, hyperlipidemia, hypertension, and complete heart block with implantation of a dual-chamber permanent pacemaker in 2010. He has had several surgeries, including a right inguinal hernia repair and an appendectomy.

Family history is positive for breast cancer, colon cancer, and stroke. There is no family history of cardiac or pulmonary disease. Social history reveals a retired accountant who lives at home with his wife. He has an occasional brandy in the evening and has never smoked. His current medications include metoprolol, rosu­\vastatin, and omeprazole. He has no known drug allergies.

The review of systems is unremarkable, with the exception of the shortness of breath. The patient is concerned, however, that since his pacemaker was interrogated one week ago, he hasn’t “felt the same.”

Physical examination reveals a blood pressure of 130/70 mm Hg; pulse, 70 beats/min; respiratory rate, 16 breaths/min^-1; temperature, 36.6°C; and O₂ saturation, 97% on room air.  The patient’s weight is 105 kg. 

The cardiovascular exam reveals a regular rate of 70 beats/min, and a grade II/VI early systolic murmur best heard at the left upper sternal border and without radiation. There are no rubs, gallops, or bruits. The pulmonary exam reveals scattered crackles in the right lower chest, which clear with coughing. There are no rhonchi or bronchial breath sounds. All other exams yield normal results.

The patient provides a copy of an interrogation report from one year ago, which states his pacemaker is programmed DDDR at a rate of 60 beats/min, with an upper tracking and sensing rate of 130 beats/min, a paced AV delay of 150 ms, and a sensed AV delay of 120 ms. Given the patient’s concern about his most recent interrogation, you call an experienced practitioner to determine whether the patient’s device is functioning appropriately. 

While waiting, you obtain an ECG, which reveals the following: a ventricular rate of 70 beats/min; PR interval, not measurable; QRS duration, 200 ms; QT/QTc interval, 500/540 ms; no P axis; R axis, –83°; and T axis, 71°. What is your interpretation, and is there any concern regarding his pacemaker function?

ANSWER
This ECG is remarkable for ventricular pacing at a rate of 70 beats/min, with an underlying sinus rhythm at the same rate as the pacemaker but dissociated from ventricular pacing. Ventricular pacing is evidenced by the presence of a pacing spike before each QRS complex, and the fact that each QRS complex in all leads is wide (200 ms) and does not demonstrate variability within an ECG lead. The T waves are similar in each lead as well. A left-axis deviation of –83° is attributable to pacing from the right ventricle.

What is interesting to note is that P waves are visible and are at a rate very close to that of the ventricular paced beats; however, they show no association with the pacing spike or the QRS complexes. This is most evident in lead V₁ and the rhythm strip of lead I, which shows the P waves marching through the QRS and T-wave complexes without being associated with any ventricular conduction. This is an unusual situation in which the sinus rate and the paced ventricular rate are very similar. 

Interrogation of the pacemaker generator revealed that the programming had been inadvertently changed from DDDR at a rate of 60 beats/min to VVI at a rate of 70 beats/min. After the device was reprogrammed to its original settings, the patient’s symptoms resolved.