OBJECTIVERight ventricular apical pacing may induce cardiac desynchronize and deteriorate left ventricular systolic performance. We hypothesized that right ventricular outflow tract (RVOT) pacing could produce better mechanical synchrony and left ventricular contraction.

METHODSWe enrolled nine patients without structural heart disease who underwent electrophysiological studies. The pacing sites (right apex, low septum, free wall and septum of RVOT of the right ventricle) were defined with fluoroscopy and ECG. The atrioventricular sequential pacing was applied every 5 minutes in a random order at a rate of 120 bpm. Tissue Doppler imaging was carried out with GE VIVID 7 for off-line analysis at each pacing site. The global systolic contraction amplitude (GSCA) was calculated as the average shortening amplitude of all 16 segments of left ventricle.

RESULTSThe GSCA during pacing was 5.76 mm +/- 0.66 mm at free wall of RVOT and 5.66 mm +/- 1.00 mm at septum of RVOT, respectively. The GSCA at both sites was significantly higher than that at apical pacing 4.82 mm +/- 0.94 mm (P < 0.05) or low septum pacing 4.82 mm +/- 1.06 mm (P < 0.05). Moreover, segmental displacement analysis showed that the longitudinal displacement of lateral, posterior, and inferior walls significantly decreased at apical pacing compared with RVOT pacing, although no difference could be demonstrated in anterior and septum walls. Accordingly, the curve of the myocardial displacement at apical or low septum pacing was M-shaped, and had a negative wave at the end of the diastole in lateral, posterior, and inferior walls. The tissue velocity during isovolumic contraction period was also higher than systolic tissue velocity in these walls. The phenomenon could seldom be seen at RVOT pacing.

CONCLUSIONRVOT pacing in patients without structural heart disease is associated with more favorable immediate myocardial contraction and mechanical synchrony compared with right apical pacing or low septum pacing.