The effect of right ventricular pacing on myocardial oxidative metabolism and efficiency: relation with left ventricular dyssynchrony.

PURPOSE: Right ventricular (RV) apical pacing induces dyssynchrony by a left bundle branch block type electrical activation sequence in the heart and may impair left ventricular (LV) function. Whether these functional changes are accompanied by changes in myocardial perfusion, oxidative metabolism and efficiency, and the relation with the induction of LV dyssynchrony are unknown. Our study was designed to investigate the acute effects of RV pacing on these parameters.

METHODS

Ten patients with normal LV ejection fraction and VVI/DDD pacemaker were studied during AAI pacing/sinus rhythm without RV pacing (pacing-OFF) and with RV pacing (pacing-ON) at the same heart rate. Dynamic [15O]water and [11C]acetate positron emission tomography was used to measure perfusion and oxidative metabolism (kmono) of the LV. An echocardiographic examination was used to assess LV stroke volume (SV) and LV dyssynchrony. Myocardial efficiency of forward work was calculated as systolic blood pressure × cardiac output/LV mass/kmono.

RESULTS

RV pacing decreased SV in all subjects (mean decrease 13%, from 76 ± 7 to 66 ± 7 ml, p = 0.004), but global perfusion and kmono were unchanged. The efficiency tended to be lower with pacing-ON (70 ± 20 vs 81 ± 21 mmHg l/g, p = 0.066). In patients with dyssynchrony during pacing (n = 6) efficiency decreased by 23% (from 78 ± 25 to 60 ± 14 mmHg l/g, p = 0.02), but in patients without dyssynchrony no change in efficiency was detected. Accordingly, heterogeneity in myocardial perfusion and oxidative metabolism was detected during pacing in patients with dyssynchrony but not in those without dyssynchrony.

CONCLUSION

RV pacing resulted in a significant decrease in SV. However, deleterious effects on LV oxidative metabolism and efficiency were observed only in patients with dyssynchrony during RV pacing.