Background: Biventricular (BiV) pacing has been found to improve systolic function and exercise tolerance in patients with severe congestive heart failure and bundle branch block. The mechanisms behind this beneficial effect is still not sufficiently clarified.
Aim: To evaluate the regional myocardial perfusion (MP) during BiV pacing and after acute change of the pacing mode to conventional dual chamber (DDD) pacing, and single chamber atrial (AAI) pacing in patients with severe congestive heart failure and prolonged QRS width treated with chronic BiV pacing.
Methods and results: Fourteen patients (age 63+/-7 years, 13 male) were evaluated 13+/-7 months after implantation of a triple-chamber biventricular pacemaker. MP was quantified with 13N-labeled ammonia positron emission tomography during BiV pacing, DDD pacing, and AAI pacing. MP was assessed in the anterior, lateral, inferior, and septal regions, and the global mean MP was calculated. Clinical assessment was performed before pacemaker implantation and after at least 3 months of BiV pacing including a 6-min walk test (WT), New York Heart Association (NYHA) class functional score and echocardiography. Global mean MP (BiV: 0.65+/-0.20 vs. DDD: 0.65+/-0.21 vs. AAI: 0.65+/-0.18 mlg(-1)min(-1)) and MP in each of the four regions did not differ between the three pacing modes. The patients improved clinically during BiV pacing; 6 min WT increased (338+/-59 vs. 415+/-73 m, P<0.001), NYHA class score improved (class I/II/III/IV: 0/0/11/3 vs. 1/9/2/0, P<0.001), and left ventricular ejection fraction increased (21+/-5 vs. 29+/-8%, P=0.004).
Conclusion: No differences in regional MP are detectable after chronic BiV pacing when the pacing mode is changed acutely in patients with severe congestive heart failure and bundle branch block. This finding indicates, that the clinical improvement caused by BiV pacing is not associated with any increase in the MP and thereby oxygen demand.