Also known as third-degree AV block, complete heart block is a condition where there is dissociation between the electrical activity of the atria and ventricles. As a result, the two chambers contract independently with the ventricle in its own rhythm. The ventricular escape rhythm is typically bradycardic, with heart rates usually less than 40 beats/min. This may result in a low cardiac output state with symptoms such as angina or pre-syncope.
The mainstay of treatment for complete heart block is pacing the ventricle. Depending on the acuity of the situation, transcutaneous, transvenous endocardial, or an epicardial pacemaker would be appropriate. Intravenous drugs may be used with caution as a temporizing measure while instituting pacing therapy. Atropine can be used for a very slow idioventricular escape rhythm or block from the AV node. Also, catecholamines (ex: isoproterenol) can be used transiently to increase heart rate.
According to ACE8B question 32: “Most commonly, patients with significant AV nodal dysfunction (including third-degree AV block and Mobitz type-II second-degree block) are paced with mode DDD following cardiac surgery.” The VOO mode is not recommended if the patient has an underlying ventricular rhythm as VOO increases the risk of V-fib due to R-on-T.
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