Pacemaker Implantation for Sinus Node Dysfunction in a Young Patient With Duchenne Muscular Dystrophy

Abstract

A 25-year-old patient was admitted to our institution for palpitations and dyspnea. His medical history was pertinent for Duchenne muscular dystrophy (DMD), tracheotomy for full mechanical ventilation, and vertebral arthrodesis for scoliosis. The diagnosis of DMD was made with genetic analysis, which disclosed duplication in the exon 44–49. The patient’s mother was a carrier without any cardiac symptoms. The patient took perindopril and bisoprolol for subclinical cardiomyopathy. No history of atrial fibrillation (AF), hypertension, or congestive heart failure was experienced by the patient. On admission, body temperature was 37°C; blood pressure, 110/80 mm Hg; and heart rate, 66 beats per minute. No syncope, stroke, or clinical peripheral embolism was present. Biological results were normal, with negative troponin T value (<0.04 μg/L) and normal brain natriuretic peptide value (61 pg/mL). Electrocardiography (ECG) revealed AF (Figure 1). Anticoagulation therapy (heparin) was begun and the bisoprolol was pursued. Echocardiography revealed normal valves, normal left ventricular (LV) ejection fraction (60%) with indexed LV end-diastolic diameter (26 mm/m²), and normal kinetic wall motion. The LV myocardium disclosed normal thickness (end-diastolic interventricular septal thickness, 7 mm; end-diastolic posterior wall thickness, 7.5 mm) without noncompaction. Holter ECG was performed and disclosed a sinus node dysfunction (SND) with 3 sinus pauses (Figure 2). Because the patient continued to be symptomatic, pacemaker implantation was performed. β-Blocker therapy was pursued, and heparin was changed to oral anticoagulation. The patient was discharged home 3 days later without any complication and profited from pacemaker implantation. Electrocardiographic findings: atrial fibrillation. Holter electrocardiographic findings: sinus node dysfunction. DMD is an X-linked recessive disorder that affects 1 of 3500 male births.1 This disease is caused by the absence of dystrophin.1 Dystrophin is a protein located on the inner side of the skeletal and the cardiac muscle cells. This protein has a major structural role in muscle, as it links the internal cytoskeleton to the extracellular matrix. The lack of dystrophin leads to progressive fiber damage and membrane leakage. The consequence is a progressive muscle wasting and weakness of variable distribution and severity. Clinical manifestations in DMD are visible at the age of 5 to 6 years and are characterized by progressive loss of strength (muscles of the pelvic and shoulder girdles). By the age of 12, most patients are confined to wheelchairs. Cardiac involvement is present in about 90% of the patients, and 20% of patients die of cardiac complications.1 Heart involvement is due to the progressive replacement of cardiomyocytes and Purkinje system by connective tissue or fat.1 Atrophy and scaring of the posterobasal region and the lateral wall of the left ventricle have been reported.1 Also, AF has been reported in the literature in DMD patients. In muscular dystrophy, SND may be present in young patients. Pathophysiology of SND includes electrical remodelling with conduction abnormalities because of fibrosis in the atria and significant conduction delay across the crista terminalis.2 Arrhythmias are attributed to progressive fibrosis of the cardiac conduction system and impairment in the cardiac autonomous nervous system.1 The most frequent cardiac abnormality in DMD is sinus tachycardia. Atrial premature beats are frequent in DMD. The cardiac autonomic nervous system is also affected in DMD, particularly the parasympathetic system.3 Heart rate variability is often reduced; this phenomenon can be explained by structural and functional abnormalities of the sinoatrial node and by impaired mechanoreceptor- or baroreceptor-mediated reflexes.1 Medical management of DMD patients with heart involvement relies on angiotensin-converting enzyme (ACE) inhibitors and β-blockers. It has been reported that the combination of β-blockers and ACE inhibitors can delay LV dysfunction onset and can improve LV systolic function in DMD patients. In this case report, these drugs were pursued and a pacemaker was implanted because of the SND. Permanent pacemaker implantation is indicated (class I) for SND with documented symptomatic bradycardia, including frequent sinus pauses that produce symptoms (level of evidence: C).4 However, in DMD, because of the poor prognosis and the thoracic anatomic particularities (chest deformation), the decision of pacemaker implantation is problematic and requires careful discussion about risks and benefits.