![]() Regarding pacemakers for bradycardia, some studies have reported on the optimization of AV delay. Therefore, studies have been conducted to explore optimum AV delay for cardiac resynchronization therapy (CRT). ![]() AV synchronization is very important for maintaining adequate SV, particularly in patients with heart failure. It has been reported that echocardiography is useful for optimizing AV delay settings in patients with pacemakers. Although the intrinsic rhythm allows for physiological ventricular contraction, excessive delays in AV conduction time (PR interval) may lead to diastolic mitral regurgitation or adversely affect left ventricular (LV) function. In patients with functioning atria (without atrial fibrillation), ventricular contraction with appropriate timing after atrial contraction is an important factor to ensure adequate stroke volume (SV). Synchronization between the atria and ventricles is also important for cardiac function. Therefore, some studies have suggested that intrinsic AV conduction should be preserved to prioritize physiological ventricular contractions as much as possible. However, ventricular contraction during right ventricular (RV) pacing might be less efficient than physiological ventricular contraction during intrinsic AV conduction because of dyssynchrony caused by RV pacing. Sick sinus syndrome and advanced atrioventricular (AV) block are often treated with a pacemaker. RV pacing should be avoided in patients with high E/Eʹ ratio under intrinsic AV conduction or RV pacing. Mean baseline E/E′ ratio in patients who developed HF (HF group) during RV pacing was higher than in patients without HF (non = HF group 17.9 ± 8 versus 11.5 ± 2, P = 0.018) Even within HF group patients without a high baseline E/E′ ratio, it increased with RV pacing (22.2 ± 6 versus 11.6 ± 2 P 15 during intrinsic AV conduction or RV pacing. During follow-up, seven patients developed HF. Therefore, pacemakers were set to the DDD to deliver RV pacing. SV was greater with RV pacing with optimal AV delay of 160 ms than with intrinsic AV conduction rhythm in all patients. At baseline, mean intrinsic PQ interval was 250 ± 40 ms. Echocardiographic evaluation was performed for 6-month follow-up period. Stroke volume (SV) was measured to determine the optimal AV delay with the intrinsic AV conduction rhythm and the DDD pacing delivering RV pacing. This study aimed to compare a pacing mode-preserving, intrinsic AV conduction with the DDD mode delivering RV pacing in terms of echocardiographic parameters in patients with first-degree AV block and to investigate whether RV pacing induces heart failure (HF). However, there is no clear cutoff AV interval to determine whether intrinsic AV conduction should be preserved or RV pacing should be delivered. To avoid right ventricular (RV) pacing, preserving intrinsic AV conduction as much as possible is recommended. Some patients with pacemakers present with first-degree atrioventricular (AV) block.
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