“临床病例解析”房室传导阻滞

A 55-year-old man comes to his physician for a follow-up visit随诊, after being hospitalized 2 weeks earlier for an inferior wall myocardial infarction (MI)下壁心梗. The patient has a history of coronary artery disease. His ECG is shown in Figure 3.

01.What pathology does the ECG in Figure 3 depict?

Second-degree atrioventricular (AV) block type I二度Ⅰ型房室传导阻滞, also known as Mobitz type I block or Wenckebach block文氏阻滞. Progressive lengthening of the PR interval from one beat to the next is seen until finally a beat is dropped (a P wave is not followed by a QRS complex), as seen in Figure 3.PR间期逐渐延长，直到P波下传受阻，脱漏一个QRS波群。

02.What is the pathophysiology of this condition?

Second-degree AV block type I occurs secondary to impaired conduction传导功能受损at the level of the AV node房室结, such that atrial impulses fail to reach the ventricles. Given the location of the patient’s prior MI, it is possible that it may have compromised the conductive ability of his AV node. An MI involving the right coronary artery may disrupt blood supply to the sinoatrial (SA) node窦房结and atrioventricular (AV) node. (Note that the AV node artery is typically a branch off the dominant coronary artery, which most commonly is the RCA; however, occasionally it can branch from the L circumflex.) By contrast, involvement of the left anterior descending coronary artery causes infarction of the His-Purkinje system.

①本病例是下壁心梗患者，左、右冠状动脉病变均可导致下壁心肌梗死，但罪犯血管多为右冠状动脉，回旋支次支，前降支最少。

②传导系统供血：窦房结的血液60%由右冠状动脉供给，40%由左旋支供给；房室结的血液90%由右冠状动脉供给，10%由左旋支供给；右束支及左前分支由前降支供血，左后分支由左旋支和右冠状动脉双重供血。

③综上所述：房室传导阻滞是急性下壁心肌梗死的常见并发症。

03.How is this condition classifed?

一度房室传导阻滞：指从心房到心室的电激动传导速度减慢，心电图表现为PR间期延长超过0.20s，但是每个心房激动都能传导至心室。

二度房室传导阻滞：又分为I型（文氏或称莫氏I型）和II型（莫氏II型）。

二度I型房室传导阻滞是最常见的二度房室传导阻滞类型，是指从心房到心室的传导时间逐渐延长，直到有一个心房的激动不能传递到心室。

二度II型房室传导阻滞是指心房的激动突然阻滞不能下传至心室，心电图表现为QRS波群有间期性脱漏。

三度房室传导阻滞：又称完全性房室传导阻滞，是指全部的心房激动都不能传导至心室，特征为心房与心室的活动各自独立、互不相干；且心房率快于心室率。

04.What is the treatment for this condition?

Often, no treatment is necessary in asymptomatic patients with a second-degree Mobitz type I block. In symptomatic patients, atropine阿托品 or isoproterenol 异丙肾上腺素may be used, or a pacemaker起搏器 may be required. In contrast, patients with type II or type III heart block are often treated with pacemakers.

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