### Learning objectives The aim of cardiac resynchronisation therapy (CRT) is to improve cardiac function by delivering more physiological cardiac activation to patients with conduction system disease. The most widely investigated method for delivering CRT is biventricular pacing (BiV-CRT). Multiple randomised control trials (RCTs) have found BiV-CRT improves outcomes when it is delivered to patients with heart failure, reduced ejection fraction (EF) and prolonged QRS duration.1–3 The majority of patients included in RCTs assessing BiV-CRT had left bundle branch block (LBBB), were in sinus rhythm, New York Heart Assocation (NYHA) class II or greater and had an EF ≤35%. BiV-CRT is also used as an alternative to right ventricular (RV) pacing in patients who have ventricular impairment and require a high percentage of ventricular pacing.4 Understanding the mechanism through which BiV-CRT delivers its beneficial effects is useful when considering patient selection. ### Improving ventricular electrical dyssynchrony When a patient develops LBBB, this prolongs left ventricular (LV) activation time and produces a non-physiological LV activation pattern. These changes result in less efficient contraction and reduced cardiac output.5 BiV pacing aims to deliver more effective ventricular activation by pacing the left and right ventricles. Ventricular activation occurs via cell-to-cell conduction with activation wavefronts originating from the two pacing sites. The activation time during BiV pacing is typically longer than occurs during activation via the intact conduction system and is relatively constant regardless of intrinsic activation.6 The potential for BiV pacing to deliver improvements in ventricular activation time is dependent on the presenting (intrinsic) conduction delay. A …

中文翻译：

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心脏再同步治疗的进展：适应症和治疗选择的回顾

### 学习目标 心脏再同步治疗 (CRT) 的目的是通过为患有传导系统疾病的患者提供更多的生理性心脏激活来改善心脏功能。研究最广泛的 CRT 方法是双心室起搏 (BiV-CRT)。多项随机对照试验 (RCT) 发现，当 BiV-CRT 应用于心力衰竭、射血分数 (EF) 降低和 QRS 持续时间延长的患者时，可改善预后。1-3 评估 BiV-CRT 的 RCT 中纳入的大多数患者左束支传导阻滞 (LBBB)，窦性心律，纽约心脏协会 (NYHA) II 级或以上，且 EF ≤ 35%。BiV-CRT 还可用作心室功能不全且需要高比例心室起搏的患者的右心室 (RV) 起搏的替代方案。4 了解 BiV-CRT 发挥有益作用的机制在考虑患者选择时非常有用。### 改善心室电不同步 当患者出现 LBBB 时，左心室 (LV) 激活时间会延长，并产生非生理性 LV 激活模式。这些变化导致收缩效率降低并减少心输出量。5 BiV 起搏旨在通过对左心室和右心室起搏来提供更有效的心室激活。心室激活通过细胞间传导发生，激活波前源自两个起搏部位。BiV 起搏期间的激活时间通常比通过完整传导系统激活期间的激活时间长，并且无论内在激活如何，都相对恒定。6 BiV 起搏改善心室激活时间的潜力取决于呈现的（内在）传导延迟。A …