To the Editor

Abstract

I found the article “Prospective comparison of echocardiographic atrioventricular delay optimization methods for cardiac resynchronization therapy” by Kerlan et al 1 Kerlan J.E. Sawhney N.S. Waggoner A.D. Chawla M.K. Garhwal S. Osborn J.L. Faddis M.N. Prospective comparison of echocardiographic atrioventricular delay optimization methods for cardiac resynchronization therapy. Heart Rhythm. 2006; 3: 148-154 Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar in the February 2006 issue of Heart Rhythm to be timely, challenging, and controversial. In light of the latter, I have several concerns I would like to share. 1Two established methods of AV delay optimization were compared: aortic velocity time integral (VTI), which can be applied to most stimulation modes, and the Ritter method, 2 Ritter P. Dib J.C. Lelievre T. et al. Quick determination of the optimal AV delay at rest in patients paced in DDD mode for complete AV block. Eur J CPE. 1994; 4 (abstr): A163 Google Scholar which is intended only for patients with complete AV block and DDD pacemakers. With cardiac resynchronization therapy (CRT), left ventricular (LV) contraction starts shortly after the biventricular pacing (BiVP) pulse, whereas in AV block with DDD, LV contraction is delayed by approximately 80 ms after the right ventricular pacing pulse. 3 Chirife R. Ortega D. Barja L. Pacing-induced inter-ventricular conduction time expected values and its effect on left heart atrioventricular interval. Pacing Clin Electrophysiol. 1993; 16: 1150 Crossref Scopus (16) Google Scholar Consequently, application of Ritter’s formula to CRT patients may not be appropriate. 2Only the VDD + LV mode was tested in the study, not the AV sequential mode. This is an important shortcoming, as atrial pacing may be required because of use of β-blockers and/or antiarrhythmic drugs. Atrial pacing extends the interatrial delay by approximately 55 ms 4 Chirife R. Tentori M.C. Mazzetti H. Dasso D. Automatic beat-to-beat left heart AV normalization is it possible?. Pacing Clin Electrophysiol. 2003; 26: 2103-2110 Crossref PubMed Scopus (9) Google Scholar ; as a result, an optimal AV calculated for atrial sensing (AS)-biventricular pacing may not be optimal for atrial pacing (AP)-biventricular pacing. If the AV is too short, left atrial (LA) and LV contraction may overlap, causing pacemaker syndrome. 5 Chirife R. Helguera M. Elizalde G. et al. Pacemaker syndrome during biventricular multisite DDD pacing in a patient with dilated cardiomyopathy. Europace. 2000; D223 Google Scholar 3The authors found that some AVs <60 ms were better than control. If we assume an average P-sense offset of 30 ms, the effective AV will be 90 ms. For example, if the interatrial electromechanical delay (from the onset of the right atrial P wave to the onset of the mitral Doppler A wave) is 120 ms, LA transport will start 30 ms after the biventricular pacing pulse. This may cause pacemaker syndrome due to overlap of LA and LV contractions. 4Figure 2, part B is missing. If the photograph shown is Figure 2A, then publication of Figure 2B should be of interest. 5There was no correlation between optimized AV intervals by the two methods, even though both increased aortic VTI in most patients. Do the authors have an explanation for this? 6Improving aortic VTI may not the only objective of AV optimization in patients with heart failure. Backward manifestations (increased LA pressure and reversal of pulmonary vein flow) that occur with LA/LV contraction overlap also play a role and cannot be ignored. In addition, if no change in VTI is observed after AV changes, some other method of optimization is needed to prevent the deleterious consequences of backward manifestations. Possibly an adaptation of Ritter’s method would work for CRT.