A 25-year-old man with myotonic muscular dystrophy type 1 presented to the emergency department complaining of palpitations and chest discomfort. A regular wide QRS complex tachycardia with right bundle-branch block (RBBB) morphology (Figure 1) was recorded on electrocardiogram (ECG), being treated with direct electrical cardioversion. An echocardiogram revealed normal biventricular cardiac systolic function. He did not take medications. The patient was referred to our Arrhythmia Unit for an electrophysiological study. Baseline ECG is shown in Figure 2. During the electrophysiological study, infrahisian conduction delay (His-Purkinje disease) was manifested by an HV interval of 75 ms. Programmed electrical stimulation reproducibly induced 2 forms of regular wide QRS complex tachycardia (Figure 3); the first (Figure 3A) showing RBBB morphology (the clinical tachycardia), and the second (Figure 3B) showing left bundle-branch block morphology. What is the most likely mechanism for clinical and induced tachycardia? How should the patient be managed?

Figure 1. Twelve-lead electrocardiogram of the clinical wide QRS complex tachycardia.

Figure 2. Baseline 12-lead electrocardiogram.

Figure 3. Twelve-lead of the 2 types of induced tachycardia.A, Right bundle-branch morphology regular wide tachycardia. B, Left bundle-branch morphology regular wide tachycardia.

Please turn the page to read the diagnosis.

Figure 1 shows a regular wide monomorphic tachycardia with RBBB morphology, QRS width of 220 ms, right superior QRS axis, early precordial QRS morphology transition in V2, and heart rate of 250 beats per minute (same induced tachycardia showed in Figure 3A presented a heart rate of 200 beats per minute). Baseline ECG (Figure 2) exhibits normal sinus rhythm at 80 beats per minute with a first-degree atrioventricular block (PR interval of 230 ms) and RBBB with a QRS width of 130 ms. Substantial differences in QRS morphology, QRS width, and frontal plane axis were evident between baseline ECG and clinical tachycardia. The second induced tachycardia (Figure 3B) presented left bundle-branch block morphology, QRS width of 220 ms, leftward frontal plane axis, and heart rate of 222 beats per minute.

The history of myotonic dystrophy type 1 and the finding of severe His-Purkinje disease were highly suspicious of bundle branch reentrant ventricular tachycardia (BBR-VT). Myotonic muscular dystrophy type 1, or Steinert disease, is an autosomal dominant inherited neuromuscular disease caused by a mutation in the 3′ untranslated region of the myotonic dystrophy protein kinase gene on chromosome 19. Although respiratory failure is the leading cause of death in myotonic dystrophy type 1, heart disease is the cause of death in approximately one-third of cases, with sudden arrhythmic death occurring in 10%.¹ This disease, for reasons that are not completely clear yet, has a particular predilection for the His Purkinje system, with interstitial fibrosis, fatty infiltration, and vacuolar degeneration. Although left ventricular systolic dysfunction can be observed in patients with myotonic dystrophy type 1, it occurs less frequently and at later stages than conduction disturbances.

The electrophysiological study (Figure 4) confirmed the diagnosis of clockwise BBR-VT for both the clinical and RBBB morphology–induced tachycardia, and counterclockwise BBR-VT for the left bundle-branch block morphology non–clinically induced tachycardia.² The clinically documented BBR-VT represents the much more infrequent type of BBR-VT (also called atypical BBR-VT). By contrary, the non–clinically induced type of BBR-VT with left bundle-branch block morphology (counterclockwise BBR-VT) is the most commonly seen type of BBR-VT (also called typical BBR-VT) in clinical practice. BBR-VT is usually seen in the setting of underlying bundle-branch block, so tachycardia resembles the baseline ECG. The existence of conduction disease in both main branches of the His-Purkinje system, at a similar extent, can explain the differences seen for the QRS morphology in the present case. Of note, the induction of clockwise BBR-VT and counterclockwise BBR-VT in the same patient is a very rare phenomenon.

Figure 4. Twelve-lead electrocardiogram and intracardiac electrograms during both types of induced BBR-VT.A, Atypical or clockwise type. B, Typical or counterclockwise type. A schematic diagram explaining the mechanism for the tachycardia is at the bottom of each panel. For the atypical type, retrograde conduction occurs via the right bundle branch and anterograde conduction occurs via the left bundle branch. For the typical type, retrograde conduction occurs via the left bundle branch and anterograde conduction occurs via the right bundle branch. His deflection preceding each ventricular activation with longer HV interval during tachycardia than during sinus rhythm is evident. A indicates atrial electrogram; H, His bundle electrogram; HV, His to ventricular interval; LB, left bundle branch; and RB, right bundle branch.

Ablation of a bundle branch precludes the induction of BBR-VT and is currently considered as the treatment of choice. After ablation of the bundle branch, many patients require permanent pacing owing to either secondary atrioventricular block or severe His-Purkinje system disease especially for patients with left ventricular systolic dysfunction. In our patient, a rapid intramyocardial ventricular tachycardia was induced as well with programmed electrical stimulation. Extensive areas of fibrosis were detected on a cardiac magnetic resonance study. A dual-chamber cardiac defibrillator was implanted, and catheter ablation of the right bundle branch was performed. After 3 years of follow-up, no arrhythmic episodes have been recorded.

None.

https://www.ahajournals.org/journal/circ

一名25岁患有1型强直性肌营养不良症的男子因出现心pit和胸部不适而出现在急诊科。在右心电图（ECG）上记录了具有右束支传导阻滞（RBBB）形态（图1）的常规宽QRS复杂性心动过速，接受直接电复律治疗。超声心动图显示正常的双心室心脏收缩功能。他没有吃药。该患者被转介到我们的心律不齐科进行电生理研究。基线心电图如图2所示。在电生理研究中，以75毫秒的HV间隔表现出次传导延迟（His-Purkinje病）。程序性电刺激可重现2种形式的常规宽QRS复杂性心动过速（图3）；第一个（图3A）显示RBBB形态（临床心动过速），第二个（图3B）显示左束支传导阻滞形态。临床和诱发性心动过速的最可能机制是什么？应该如何管理患者？

图1. 临床广泛的QRS复杂性心动过速的十二导联心电图。

图2. 基线12导联心电图。

图3. 两种类型的诱发性心动过速的十二导联。A，右束支形态正常的宽心动过速。B，左束支形态正常的宽心动过速。

请翻页阅读诊断。

图1显示了规则的宽单形心动过速，具有RBBB形态，QRS宽度为220 ms，右QRS上轴，V2早期心前区QRS形态转变以及每分钟250次心跳（图3A中显示的相同诱发性心动过速表现为心脏每分钟200次跳动）。基线心电图（图2）以每分钟80次搏动表现出正常的窦性心律，并伴有一级房室传导阻滞（PR间隔为230 ms）和RBBB，QRS宽度为130 ms。在基线心电图和临床心动过速之间，QRS形态，QRS宽度和额平面轴存在明显差异。第二次诱发的心动过速（图3B）表现为左束支传导阻滞形态，QRS宽度为220 ms，额叶面轴向左，心律为每分钟222次。

1型强直性肌营养不良的病史和严重的His-Purkinje病的发现高度怀疑束支折返性室性心动过速（BBR-VT）。1型强直性肌营养不良症或Steinert病是一种常染色体显性遗传性神经肌肉疾病，由19号染色体上的强直性肌营养不良蛋白激酶基因3'非翻译区的突变引起。尽管呼吸衰竭是导致强直性肌营养不良死亡的主要原因1型心脏病是大约三分之一病例的死亡原因，而心律失常性猝死的发生率为10％。^1个由于尚不完全清楚的原因，该疾病特别适合His Purkinje系统，包括间质纤维化，脂肪浸润和液泡变性。尽管在1型强直性肌营养不良患者中可以观察到左心室收缩功能障碍，但与传导障碍相比，它的发生频率更低，发生的时间更晚。

电生理研究（图4）证实了临床和RBBB形态学诱发的心动过速均为顺时针BBR-VT的诊断，非临床诱发的左束支传导阻滞形态为逆时针BBR-VT的诊断。²临床证明的BBR-VT代表了很少见的BBR-VT类型（也称为非典型BBR-VT）。相反，在临床实践中，非临床诱发型的BBR-VT具有左束支传导阻滞形态（逆时针BBR-VT）是最常见的BBR-VT类型（也称为典型BBR-VT）。BBR-VT通常见于潜在的束支传导阻滞，因此心动过速类似于基线心电图。在相似的程度上，His-Purkinje系统的两个主要分支中都存在传导性疾病，可以解释本例中QRS形态的差异。值得注意的是，在同一患者中诱发顺时针BBR-VT和逆时针BBR-VT是非常罕见的现象。

图4. 两种类型的BBR-VT期间的十二导联心电图和心内电图。A，非典型或顺时针类型。乙，典型或逆时针类型。解释心动过速的机制的示意图位于每个面板的底部。对于非典型类型，逆行传导通过右束支发生，而顺行传导通过左束支发生。对于典型类型，逆行传导通过左束支发生，而顺行传导通过右束支发生。在心动过速期间比在窦性心律期间更长的HV间隔使他在每次心室激活之前发生偏转。A表示心电图；H，他的束电描记图；HV，His至心室间隔；LB，左束支；和RB，右束支。

束支的消融排除了BBR-VT的诱导，目前被认为是治疗选择。消融束支后，由于继发性房室传导阻滞或严重的His-Purkinje系统疾病，许多患者需要永久起搏，特别是对于左心收缩功能不全的患者。在我们的患者中，通过程序性电刺激也诱发了快速的心肌内室性心动过速。在心脏磁共振研究中检测到广泛的纤维化区域。植入双腔心脏除颤器，并进行右束支的导管消融术。经过3年的随访，未发现心律失常发作。

没有。

https://www.ahajournals.org/journal/circ