Echocardiographic optimization of the atrioventricular and interventricular intervals during cardiac resynchronization
An optimized atrioventricular (AV) interval can maximize the benefits of cardiac resynchronization therapy (CRT). If programmed poorly, it may curtail beneficial effects of CRT. AV optimization will not convert non-responder to responder, but may convert under-responder to improved status. There are many echocardiographic techniques for AV optimization but there is no universally accepted gold standard. The optimal AV delay varies with time, necessitating periodic re-evaluation. As the optimal
... on. As the optimal AV delay may lengthen on exercise, a rate-adaptive AV delay should not be routinely programmed. Intraand interatrial conduction delays may require AV junctional ablation when AV optimization is impossible in patients with a poor clinical response. Fusion with the spontaneous QRS complex may be acceptable on a trial basis to seek a better clinical response or with a short PR interval. Routine VV optimization is presently controversial but programming may prove beneficial in some patients with a suboptimal CRT response where no cause is found. It may partially compensate for less than optimal left ventricular (LV) lead position and may correct for heterogeneous ventricular activation including a prolonged LV latency interval and slow conduction (scarring) near the LV pacing site. VV timing is generally programmed using the aortic velocity-time integral, and long-term variations of the optimal value necessitate periodic re-evaluation. Programming the atrioventricular interval Although optimization of the left-sided atrioventricular (AV) interval is important, the benefits of acute and long-term cardiac resynchronization therapy (CRT) to heart failure (HF) patients depends mostly on reliable resynchronization [with the proper choice of left ventricular (LV) pacing site] and less on AV optimization itself. 1,2 Programming of the leftsided AV interval should not be ignored because appropriate AV interval timing can maximize the benefit of CRT, but if programmed poorly, it has the potential to curtail the beneficial effects. AV optimization will not convert a non-responder to a responder, but it may convert an under-responder to improved status. The optimal AV delay in CRT patients exhibits great variability from patient to patient. 1,3 Consequently, empirical programming of the AV interval is suboptimal in many patients and is generally not recommended. The optimal atrioventricular relationship Optimized AV synchrony is achieved by an AV delay that provides the best left atrial contribution to LV filling, the maximum stroke volume, shortening of the isovolumic contraction phase, and the longest diastolic filling time ( Figure 1) . The shortest AV delay should not compromise the transmitral Doppler A wave and the end of atrial contraction should coincide with onset of rise in LV pressure. In addition, it should eliminate diastolic mitral regurgitation in patients with a long PR interval. 4,5 The optimal AV delay setting results in maximal stroke volume and cardiac output by virtue of complete late-diastolic filling by atrial contraction and the maximum LV diastolic filling time. Prolonged atrioventricular conduction and too long atrioventricular delay Prolonged AV conduction is not uncommon in HF patients. In this situation, atrial contraction occurs too early in diastole and results in ineffective or decreased atrial contribution to cardiac output (Figure 1) . Atrial depolarization begins too early, causing superimposition of atrial contraction on the early diastolic LV-filling phase. On the transmitral Doppler signal, a relatively early A wave fuses with a relatively late E wave resulting in shortening of the LV diastolic filling time. A prolonged PR/AV interval induces diastolic mitral regurgitation. Following atrial contraction, the mitral valve remains open because LV contraction is delayed and LV * Corresponding author. 5806 Mariner's Watch Drive, Tampa, FL 33615, USA. Fax: þ1 813 891 1908.