RESULTS OF PERMANENT DUAL-CHAMBER PACING IN SYMPTOMATIC NONOBSTRUCTIVE HYPERTROPHIC CARDIOMYOPATHY

Because dual-chamber (DDD) pacing has been shown to be of benefit rega rding symptoms, rest and pacing hemodynamics, and exercise duration in patients with obstructive hypertrophic cardiomyopathy (HC), the effec t of DDD pacing was assessed in patients with nonobstructive HC who we re significantly symptomatic despite medical management. Echocardiogra phy, treadmill exercise testing, thallium-201 scintigraphy, radionucli de angiography, and invasive measurement of rest and semi-erect bicycl e exercise hemodynamics were performed in 12 patients before and appro ximately 4 months after permanent DDD pacing. One patient died 3 month s after pacemaker implantation, because of worsening diastolic heart f ailure. Of the remaining 11 patients, 10 improved regarding symptoms, and treadmill exercise duration was longer during DDD pacing than duri ng the baseline study in sinus rhythm (6.8 +/- 2.8 to 8.5 +/- 2.8 minu tes; p <0.01), with a significant increase in the peak double product achieved (28.9 +/- 6.1 to 31.0 +/- 6.8 x 10(3); p <0.05). However, the re were significant reductions in cardiac (3.7 +/- 0.9 to 3.1 +/-0.5 m l/min/m2; p <0.01) and stroke volume (47.4 +/- 11.4 to 38.7 +/- 6.5 ml /beat/m2; p <0.01) indexes, and a trend toward reduction in submaximal stroke volume index during DDD pacing as compared with the baseline s tudy in sinus rhythm (44.7 +/- 13.5 to 40.9 +/- 10.9 ml/beat/m2; p = 0 .097). No change in peak heart rate, cardiac or stroke volume index, m ean blood pressure, or pulmonary artery or pulmonary capillary wedge p ressure occurred with peak exercise during DDD pacing as compared with the initial exercise study in sinus rhythm. Furthermore, repeat exerc ise thallium-201 scintigraphy during DDD pacing in 9 patients showed n o consistent change due to pacing. Of 10 patients >1 year after pacema ker implantation, cardiac medications have been reinitiated in 6, and DDD pacing was discontinued in 1, because of persistent or worsening s ymptoms. Thus, although DDD pacing in patients with nonobstructive HC was associated with improvement in symptoms and effort tolerance, ther e was absence of objective evidence of hemodynamic benefit, and a comm on need for reinitiation of medical therapy. Currently, chronic DDD pa cing cannot be recommended for routine use in the management of patien ts with nonobstructive HC who are symptomatic despite medical manageme nt.