To editor:

Recently, a device-based algorithm (DVA) that adjusts atrioventricular delay (AVD) based on intra-cardiac electrocardiogram has been clinically available. Ikeda and colleagues demonstrated that a long-term repeated adjustment of AVD using DVA improved survival in patients with cardiac resynchronization therapy (CRT) [1]. Several concerns should improve the implication of their findings.

The authors investigated the prognostic impact of DVA, which optimized AVD, as compared with those without DVA [1]. However, the impact of DVA would vary depending on the baseline PR interval. Were PR intervals different between those with and without DVA?

The inclusion criteria might be unclear. Some CRT devices are implanted as up-grade from the pacemaker or intra-cardiac defibrillator and others are implanted for those with systolic heart failure dependent on ventricular pacing (i.e., blocked heart failure) [2]. The impact of AVD might be different between those with preserved atrioventricular conduction and those dependent on pacing. Were these patients excluded from this study?

The PR interval would trend as a progression of primary disease, particularly non-ischemic cardiomyopathy [3]. Atrioventricular conduction would worsen as up-titration of beta-blocker following CRT device implantation. Thus, the clinical implication of periodical and automatic optimization of AVD would trend with age. Did the authors measure the trend in PR interval with age?

One of the optimal indexes to adjust AVD is the distance between E wave and A wave in the echocardiographic trans-mitral flow [4]. In addition to left ventricular end-systolic volume and ejection fraction, a trend in the distance between both waves would be helpful to assess how AVD was appropriately adjusted during the observational period.