A 37-year-old woman with non-Hodgkin lymphoma undergoing chemotherapy and no other significant medical history was incidentally noted to have an irregular heart rhythm on physical examination, and a 12-lead ECG was obtained. ECG (Figure 1) showed sinus rhythm with alternating pattern of right bundle-branch block (RBBB) and left bundle-branch block (LBBB). What is the mechanism of the alternating bundle-branch block pattern noted on the ECG? Figure 1. Twelve-lead ECG showing sinus rhythm with alternating right and left bundle-branch block pattern of ventricular conduction. 1. Alternating RBBB and LBBB premature ventricular contractions 2. Alternating phase 3 block in the bundle branches 3. Alternating phase 4 block in the bundle branches 4. Interpolated premature ventricular contractions with alternating bundle-branch morphologies Please turn the page to read the diagnosis. Irregular heart rhythm in this patient is the result of frequent atrial ectopic beats occurring in a bigeminal fashion. P waves are seen within the preceding T waves during ectopy, and the atrial coupling interval is constant (440 ms), which confirms that these are premature atrial …

中文翻译：

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交替束支座

偶然发现一名37岁患有非霍奇金淋巴瘤的妇女正在接受化疗且没有其他明显的病史，经身体检查发现其心律不规则，并获得了12导联的心电图。心电图（图1）显示窦性心律，右束支传导阻滞（RBBB）和左束支传导阻滞（LBBB）交替出现。ECG上记录的交替束支传导阻滞模式的机制是什么？图1.十二导联心电图显示窦性心律，心室传导的左右束支传导阻滞模式交替出现。1.改变RBBB和LBBB室性早搏2.改变束支中的3期阻滞3.改变束支中的4期阻滞4。内插性室性早搏伴束支分支形态改变请翻页阅读诊断。该患者的心律不规则是由于以双胎性方式频繁发生的心房异位搏动的结果。异位期间在先前的T波内可见P波，并且房颤耦合间隔是恒定的（440毫秒），这证实了这些都是早产的房性…