![]() ![]() ![]() Treatment is directed at the cause of the conduction defect, which can include myocardial infarction (MI) or ischemia, heart failure, pulmonary embolism, or valvular disease.Īn acute RBBB is often associated with an anterior-wall MI. This type of BBB can be acute or chronic. You'll see RBBB more often than left bundle-branch block (LBBB) in patients without structural heart defects RBBB also often occurs, without any apparent cause, in apparently normal hearts. But because the right bundle branch is blocked, the impulse then must cross the interventricular septum to activate the right ventricle after a short delay.Ī blocked right bundle branch is the most common defect in ventricular conduction. In RBBB (see Trouble on the right), the interventricular septum is activated normally, and the impulse travels rapidly down the left bundle branch to activate the left ventricle. Now let's look at how to distinguish specific types of BBBs. For a summary, see Recognizing ventricular conduction problems. This makes bedside determination of BBBs easier because you don't always need a 12-lead ECG. The primary leads used to assess BBB are V 1 and V 6, and most times the diagnosis can be accurately made using only lead V 1. That is, if most of the QRS is positive, the T wave will be negative, and vice versa. Abnormal repolarization produces T-wave deflection in the opposite direction of the main QRS deflection. Because depolarization is abnormal in BBBs, so is repolarization. The QRS shape isn't normal because the signal travels a different, abnormal path through the ventricles. The right ventricle is then depolarized late as the signal sneaks through a back path while the left ventricle depolarizes. If the right bundle branch is blocked, the signal travels normally down the left bundle branch and depolarizes the left ventricle. This is because the ventricles aren't depolarized simultaneously. Normally, the QRS duration is between 0.06 and 0.10 second, but in a BBB, it will be 0.12 second or greater. All BBBs share some common characteristics: The ECG will be your main clue to the electrical problem. Most patients with BBBs are asymptomatic unless they have other cardiac problems. This article describes how to recognize left and right bundle-branch blocks (BBBs), hemiblocks, and incomplete BBBs. When part of the heart's bundle-branch electrical conduction system is blocked, you'll see changes on several parts of the ECG tracing. Heart Beats: Understanding bundle-branch blocks ![]()
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