CLINICAL COMPARISON OF ACUTE SINGLE TO DUAL-CHAMBER PACING IN CHRONOTROPICALLY INCOMPETENT PATIENTS WITH LEFT-VENTRICULAR DYSFUNCTION

Dual chamber, rate responsive (DDDR) pacing is felt to be superior to ventricular, rate responsive (VVIR) pacing since it more closely mimic s the normal electrical and hemodynamic activity of the heart. This re asoning has been used to justify the higher initial costs and increase d complexity of dual chamber systems. This study was designed to deter mine if objective criteria could be identified during acute testing to justify implanting a dual chamber instead of a single chamber,system in patients with left ventricular dysfunction. Eight patients with DDD R pacemakers (implanted for chronotropic incompetence) and left ventri cular dysfunction underwent exercise radionuclide angiography and grad ed exercise treadmill testing. Each patient performed the tests in the single (VVIR) and dual (DDDR) chamber modes in a randomized, blinded fashion. We found that objective parameters such as ejection fraction (31% +/- 13% vs 31% +/- 10%), exercise tolerance (6.1 +/- 2.7 min vs 6 .3 +/- 2.9 min), oxygen consumption (VO2) (941 +/- 286 mL/min vs 994 /- 314 mL/min) carbon dioxide production (VCO2) (995 +/- 332 mL/min vs 1054 +/- 356 mL/min), and maximum attainable workload (43 +/- 24 W vs 46 +/- 22 W) did not differ between the single and dual chamber pacin g modes. These findings suggest that in the acute setting, the additio nal cost and complexity of dual chamber, rate responsive pacing cannot be justified by objective improvements in exercise tolerance in patie nts with underlying left ventricular dysfunction.