Effect of av interval on the onset of mitral regurgitation in patients with cardiac resynchronization therapy

Abstract

Since short AV intervals can cause interruption of left atrial transport due to left ventricular contraction, it has been proposed that alignment of the end of the A wave and the onset of mitral regurgitation (MR) could be used as markers to optimize left heart AV in patients (Pts) with CRT pacemakers. Since MR takes place only when the LV pressure is higher than the left atrial pressure, it was hypothesized that AV interval may play a role in the time of crossing of atrial and ventricular pressures. The aim of this study was to evaluate the relationship between AV interval (and thus the timing of left atrial contraction) and the time of onset of mitral regurgitation (MRt) in Pts with CRT devices. Three Pts with CRT devices (two Medtronic InSync III and one InSync III Marquis) implanted for medically intractable heart failure were studied by Doppler echocardiography. All patients had documented left ventricular capture and were clinically responders to CRT. Mitral Doppler flow tracings were obtained from the apical view, ensuring adequate simultaneous recording of the A wave and MR flow. AV intervals were programmed between 100 and 240 ms in the atrial pacing-biventricular pacing mode to insure rate stability. MRt was measured from the biventricular pacing pulse to the onset of MR flow. Results As the AV interval was shortened, the MRt lengthened from 18-25 ms (at AV of 240 ms) to 123-165 ms (at AV of 100 ms). In addition, at AV intervals shorter than 200 ms the mitral flow A wave became narrower and of smaller amplitude, suggesting flow reduction, although the A wave frequently remained visible and with an apparently normal shape. Regression analysis of MRt vs. AV interval revealed a best fit with a polynomial equation, with R2 >0.99 (p<0.001) for the three Pts. Since MR occurs only when the LV pressure exceeds left atrial pressure, it was assumed that with gradually shorter AVs, progressively higher left atrial pressure is needed to overcome rising LV pressure.Complete atrial transport block (disappearance of A wave) occurred only at very short AVs. Conclusion 1. AV interval modulates the onset of MR in CRT patients, thus alignment of A-wave and MR may not be a reliable marker of AV optimization. 2. A visible mitral Doppler A wave does not necessarily mean physiological left atrial transport mechanism, since it may be associated with increased left atrial pressure.