HEART-BLOCK

The treatment of minor grades of heart-block is directed towards elimination of the cause. Little can be done by drugs to improve the conductivity of a damaged a-v bundle. Many cases are due to excessive dosage with digitalis, potentiated it may be by potassium loss induced by diuretics, and improvement occurs when these are withheld and potassium chloride (a g./day) is given. Others are due to an intercurrent streptococcal throat infection, and subside as this clears up. Many occur in cases of active rheumatic carditis, and for them the treatment is that for rheumatic carditis. A few cases are due to reflex inhibition of the bundle through vagal stimulation, in whom atropine in full doses of i to 2 mg. intravenously may help. In the minority of cases of syphilitic origin, potassium iodide may be of benefit, but actual gummata of the bundle are very rare. Partial or complete heart-block occurs as a relatively infrequent sequel to acute myocardial infarction, and is generally transient. Recently treatment of this type with corticosteroids has been widely advocated, but the self-limiting course in untreated cases renders assessment of the value of the treatment difficult. In the large group of cases due to ischasmia from arterial degeneration, we have no specific drug of proved value. Simple prolongation of the a-v conduction time, or the occurrence of dropped beats are of no moment as regards the mechanical efficiency of the heart. Patients with long-standing 2 : i heart-block may experience no limitation of effort, and demand no special treatment. It is to be emphasized that digitalis is contra-indicated in partial heart-block, as the drug may depress the bundle further and aggravate the condition.
Established complete heart-block is likewise not amenable to drug therapy. It is usually due to scarring of the bundle, which is irreparable. The manage¬ment of such a case, however, is important: the patient should be warned to live within his reserve, and cautioned as to the risks of strenuous exertion, such as running upstairs, lifting heavy articles, etc. Undue exertion can in such patients lead to syncope since the heart cannot accelerate and increase its output to meet the demands for increased blood flow to the tissues, and the cerebral circulation suffers accordingly.
High-grade heart-block in an unstable state is manifested clinically by recurrent classical Adams-Stokes attacks : these can sometimes be prevented by isoprenaline or, more effectively, by electronic pacemakers.