Transmural temporospatial left ventricular activation during pacing from different sites: potential implications for optimal pacing.

AIMS: Previous studies showed that right ventricular (RV) endocardial pacing can be deleterious even in individuals with initially normal left ventricular (LV) function. The mechanism(s) by which RV endocardial pacing may cause LV dysfunction is unknown. This study compares the temporospatial LV transmyocardial activation profiles during sinus rhythm with normal His/Purkinje conduction vs. currently utilized and proposed cardiac pacing sites.

METHODS AND RESULTS: Mongrel dogs were instrumented with transmural electrodes that tracked transmyocardial activation sequences at five sites in the LV. Pacing/recording catheters were positioned in the RV apex and on the RV and LV sides of the ventricular septum. An epicardial pacing electrode was also sewn to the mid-lateral LV epicardium. Electrograms were recorded during sinus rhythm and pacing from the RV endocardium, LV septum, LV epicardium and during biventricular pacing. Compared to normal sinus/His/Purkinje rhythm (NSR), RV endocardial pacing significantly (P < 0.05) prolonged transmural activation (NSR endocardium 6.1 +/- 1 ms vs. RV endocardium 23.0 +/- 2.6 ms). The highly ordered temporospatial pattern of transmural activation during sinus rhythm was replaced with dispersion and intermingling of endo-, mid-, and epicardial activation. LV epicardial and biventricular pacing did not correct these abnormalities. Only LV septal pacing achieved the transmural and transseptal activation sequences similar to sinus rhythm.

CONCLUSION: Clinically utilized pacing modalities, including biventricular pacing, cause abnormal transmyocardial activation. LV septal pacing results in transmyocardial activation patterns that closely resemble those seen in sinus rhythm.