First-degree AV block is slowed conduction without any missed beats. This is the type more likely to be seen as an adverse effect of psychotropic medications. In second-degree AV block, some atrial impulses do not reach the ventricle. Third-degree AV block is complete dissociation of atrial and ventricular impulses. First-degree block has good prognosis. Second-degree block can convert into a third-degree block, which has the potential to be fatal.

The prognosis of bundle branch block depends on the associated cardiac condition.

AV block can be physiologic due to increased vagal tone as occurs with sleep and increased athletic activity. Most common pathologic causes for both AV block and bundle branch blocks are conditions that cause structural or ischemic heart disease. AV block can also be caused by medications (e.g., calcium channel blockers, beta blockers, antiarrhythmics).

Tricyclic antidepressants (TCAs) are associated with both AV block and bundle branch block. The AV block is usually first but can be second degree. Any conduction delay is usually with drug overdose. It is rare at therapeutic doses but there is a small increase in risk in those with preexisting heart disease [1]. Since TCAs also prolong QTc and cause orthostatic hypotension, overall cardiovascular risk is increased. Conduction abnormalities are reversible on stopping the TCA.

Lithium has an effect on the sinus node and myocardium [2]. There are case reports of first-degree AV block even at therapeutic doses, though it is much more common with toxicity. Rare cases of complete heart block have been reported. The effect can occur at any stage of treatment. Arrhythmia from lithium appears to be reversible on cessation of medication or correction of toxicity.

The principal arrhythmic effect of antipsychotics is the QTc prolongation.

Beta-blockers (e.g., propranolol) cause an expected decrease in resting heart rate. The small doses used for anxiety do not generally cause symptomatic bradycardia, especially in healthy people with no cardiac disease.