More than 25 years ago, dual-chamber pacing was promoted as a specific treatment remedy and panacea for hypertrophic cardiomyopathy (HC), in the absence of conduction system disease. Considerable enthusiasm for this new management strategy was generated based on claims that pacing reliably obliterated the left ventricular (LV) outflow gradient and mitral regurgitation and, thereby, eliminated heart failure–related symptoms (e.g., exertional dyspnea), thinned the LV wall to virtual normality, prevented development of LV hypertrophy, and by inference represented a long-term resolution for the overall disease process. The attractiveness of this treatment strategy for HC was enhanced by the perception at that time that pacing was also otherwise benign, both acutely and chronically, without the risks of surgical myectomy and provided a relatively simple answer to clinical decision making surrounding LV outflow obstruction.
Although dual-chamber pacing for HC was pursued by a number of institutions and investigators during much of the decade of the 1990s, this intense interest seemed to expire rather abruptly in the United States with the publication of 2 randomized crossover trials and a widely publicized ethical debate, and somewhat later in Europe after yet another pacing trial. Together, these latter data made a compelling case that improvement in symptoms with dual-chamber pacing was explained largely by a placebo effect unrelated to any direct impact of the pacemaker on the underlying disease process (with the possible exception in selected elderly patients). Furthermore, reduction in outflow tract gradient (and mitral regurgitation) ultimately proved to be unpredictable and only modest. Interest in a treatment alternative to surgical myectomy soon turned away from pacing to yet another new therapeutic approach, that is, percutaneous alcohol septal ablation.
Nevertheless, in the course of about 10 years, literally hundreds of patients (including many children and young adults) with obstructive HC had pacemakers implanted with little consideration given to the potential deleterious consequences of pacing for extended periods of time (>10 to 20 years) in patients with a genetic disease characterized by substantial increases in LV hypertrophy and mass, microvascular ischemia, and diastolic dysfunction. Aside from this pacing experiment in HC, the only situation in which long-term pacing has been used in young patients is congenital complete heart block, which is unassociated with LV hypertrophy and the pathophysiologic features of HC.
The present editorial revisits an overlooked and largely forgotten episode in the annals of modern cardiology and raises the provocative question: Can long-term right ventricular pacing itself potentially alter the natural history of HC adversely? Relevant to this discussion is the following report of the first patient with HC in whom a pacemaker was implanted (as a young adult), as part of the experimental investigative program designed and promoted by the National Institutes of Health in the early 1990s.
Case Report
This 51-year-old woman with a history of HC in her father and brother was diagnosed with this disease by echocardiography at age 21 years (1982), after recognition of a precordial murmur. There was a relatively brief history of exertional dyspnea, and cardiac catheterization reportedly disclosed an LV outflow tract gradient of 70 mm Hg at rest; mitral regurgitation was absent. Left ventricular end-diastolic pressure was 20 mm Hg; pulmonary arterial pressure was 36/18 mm Hg.
A dual-chamber pacemaker was implanted (as a nonconventional measure) to reduce LV outflow tract obstruction. Except for some initial transient improvement in symptoms, this patient continued to be functionally limited throughout her life. Her disability worsened 6 years ago, particularly in the last 18 months, and she is now in New York Heart Association functional class III to IV, unable to walk 1 block on level ground or 1 flight of stairs without stopping because of dyspnea and chest discomfort. There has been no evidence that long-term pacing reduced LV wall thickness. A variety of drugs have been administered throughout, including β blockers, verapamil, sotalol, amiodarone, prednisone, disopyramide, and currently dabigatran.
At the age of 41 years, the atrioventricular node was ablated after only 1 episode of atrial fibrillation (AF) and rapid ventricular response (converted with intravenous diltiazem). Subsequently, multiple episodes of drug refractory AF and/or flutter occurred with increasing frequency. The patient has now undergone 5 AF radiofrequency ablations and 9 electrical DC cardioversions but nevertheless continues to experience paroxysmal AF, during which her symptoms exacerbate. Arteriography excluded significant coronary arterial narrowing.
Echocardiographic findings included hypertrophy in 2 noncontiguous areas of the distal LV: posterior ventricular septum (21 mm) and anterior free wall (19 mm), consistent with the nonobstructive form of HC. Systolic anterior motion of the mitral valve was absent, and outflow tract velocity was within normal limits (2.6 m/s at rest). The LV chamber was nondilated (end-diastolic dimension of 42 mm), and the left atrium was enlarged (57 mm). Ejection fraction was within normal limits (65%), and mitral regurgitation was mild. Tricuspid regurgitation was marked, and the estimated systolic pulmonary arterial systolic pressure was 50 mm Hg. There was evidence of diastolic dysfunction: deceleration of E-F was 342 m/s (normal <220 m/s); tissue Doppler imaging velocities were reduced: e′ for septum of 5 cm/s and 12.7 cm/s for lateral wall. Pulmonary wedge pressure was 25 mmHg. Interrogation of the pacemaker revealed a recent 7-beat run of nonsustained ventricular tachycardia at 170/min.
The only remaining treatment option for this patient was heart transplantation, for which she is currently listed and awaiting.
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