8. Drug effects
Digoxin, amiodarone, and verapamil (a calcium antago¬nist) may rarely cause complete heart block.
9. Iatrogenic
Therapeutic AV node ablation, inadvertent damage during procedures, postoperative or traumatic causes, and occa¬sionally therapeutic irradiation of the chest may cause complete heart block.
bundle branch. This type of block often progresses insidiously to complete heart block with Stokes-Adams attacks. This diagnosis is made from the ECG when at least two regular and consecutive atrial impulses are conducted with the same PR interval before the dropped beat and the P to P intervals are equal. Permanent pacing is usually required.
C. Diagnosis
Findings of heart block on the ECG are diagnostic (see the chapter Electrocardiography). Figure 2 shows complete absence of AV conduction manifested by P waves and QRS complexes that are entirely independent. There are more P waves than QRS complexes, and the ventricles beat regularly. This is indicated by regularly occurring QRS complexes. The ventricular rate (heartbeat) is less than 40 beats per minute, but with congenital heart block it may be as high as 50 beats per minute or more. Plenty of P waves are visible and the P to P intervals are equal and constant.

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