Why do I have a slow heart rate?
The magic of a full physical examination
Vol.18, No.03, March 2010

J.G., a 44-year-old man with history of hypertension and asthma, is referred for assessment of ongoing slow heart rate. Two years ago, his slow heart rate of about 40 beats per minute (bpm) was noted on a pre-operative assessment. At the time, ECG showed junctional bradycardia. Then, he saw an internist and a cardiologist and had an echocardiogram that was reported to be normal with grade 1 LV function except for enlarged left atrium at 50 mm. He also underwent a stress test and exercised for 10 minutes on the Bruce protocol. He showed no symptoms or ST changes, but only achieved 75% of predicted heart rate. He underwent an uneventful cholecystectomy.

He remains asymptomatic and lives a sedentary life. He denies symptoms of palpitations, dizziness, chest pain or tightness. He has no symptoms of orthopnea, paroxysmal dyspnea or ankle swelling. He denies feeling fatigued and his energy level is reasonable. He has no history of any involvement in athletic activities. Functional inquiry is remarkable for occasional numbness of the left hand at night.

He is on perindopril 4 mg/day, hydrochlorothiazide 25 mg/day, flovent twice a day and ventolin as required. He smokes a pack a day and has done so for 20 years and drinks socially. Family history is negative for premature coronary artery disease or history of “slow heart rate.”

Physical exam is essentially unremarkable for a man of J.G.’s age with blood pressure of 154/80 mm Hg, with a regular but slow heart rate of 40 bpm. Head, neck examination is unremarkable and JVP is not elevated. Chest is resonant, symmetrical with fair air entry. Heart sounds are normal without any added sounds or murmurs. There is no pedal edema. Tinel’s sign is weakly positive at left wrist. Neurological exam is non-focal and deep tendon reflexes are symmetrical but diminished, while the upper arms and calves are atrophic but there’s no weakness. There is mild flexion contracture at both elbows, more prominent at right.

A thyroid stimulating hormone, serum calcium, electrolytes and creatine kinase were normal. An ECG shows junctional bradycardia with rate of 36 bpm, possibly U or retrograde P waves, left axis deviation with left anterior fascicular block and RSR’ complex in V1.

ANSWER
Emery-Dreifuss humeroperoneal muscular dystrophy

The atrophy of upper arm and calf muscles intrigued me. I googled the term, “junctional bradycardia AND myopathy” and got 1,610 entries in 0.13 seconds with most entries of Emery-Dreifuss humeroperoneal muscular dystrophy (EDMD). A review of the patient’s clinical features — atrophy of humeral and peroneal muscles, hyporeflexia, flexion contractures and the cardiac arrhythmia (junctional bardycardia) — showed that all were consistent with a diagnosis of EDMD.

EDMD is an inherited condition affecting skeletal and cardiac muscles that is often X-linked but autosomal dominant and recessive inheritance has been described. The symptoms of X-linked and autosomal dominant forms are similar but symptoms occur later in life in the autosomal variant. New mutations account for 10% of cases. Symptoms vary depending upon the severity. The creatine kinase may be normal or slightly elevated.

Heart disease associated with EDMD can be unpredictable and may be life threatening. It may present with cardiac conduction defects, heart muscle degeneration, and unusual tissues (abnormal fatty and fibrous tissues) growing into the heart. Conduction defects can manifest as heart rhythm disturbances known as arrhythmias or heart block. Arrhythmias and heart block can lead to fainting or even sudden death. Not all patients with EDMD develop heart involvement, which shows no correlation with the level of skeletal involvement. Heart involvement oftenbecomes apparent in the second to third decade of life, but in rare cases a heart problem may be the first observed symptom of EDMD. Early recognition of heart involvement is of utmost importance as placement of a pacemaker/defibrillator may be lifesaving.

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Mr. J.G.’s ECG results
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