Biventricular pacing for heart failure alters electro-mechanical coupling of both ventricles

Aim: The exact mechanisms whereby biventricular pacing enables cardiac resynchronisation are not completely understood. This study looked at the effect of biventricular pacing on interventricular asynchrony in patients submitted to biventricular pacing. Methods: A prospective series of 13 consecutive patients were selected from those referred for biventricular pacing. Criteria used included heart failure and QRS factors, as well as echocardiographic evidence of both intraventricular and interventricular asynchrony. Midterm follow-up of clinical and echocardiographic parameters are presented. Results: All patients' clinical conditions improved significantly. Expectedly, diastolic filling parameters, ejection fraction and mitral regurgitation also improved significantly. The difference in the timing of left and right ventricular ejections of 65 ms at the baseline was corrected to 3 to 5 ms during six-month follow-ups after biventricular pacing. This effect was achieved by significant shortening of the left ventricular pre-ejection interval by 29 to 39 ms (p < 0.01) and by significant prolonging of the right ventricular pre-ejection interval by 18 to 30 ms (p < 0.01). Conclusion: Complete interventricular mechanical resynchronisation due to biventricular pacing occurred not only by the expected advancement in left ventricular ejection, but also by a delay in right ventricular ejection. The specific significance of correcting interventricular asynchrony with regard to the benefit and selection of patients for resynchronisation therapy remains to be fully established.