Cardinal symptoms are cardiac (tachycardia, widened QRS complex) and neurological disturbances.

The COMPANION trial demonstrated that CRT improved survival in individuals with NYHA class III or IV heart failure with a widened QRS complex on an electrocardiogram.

It is contraindicated in patients who are on long-term benzodiazepines, those who have ingested a substance that lowers the seizure threshold, or in patients who have tachycardia, widened QRS complex on ECG, anticholinergic signs, or a history of seizures.

Electrocardiographic changes are characterized by slowed conduction, including prolonged P-R interval, widened QRS complex, shortened Q-T interval, shortened or absent S-T segments, and possibly abrupt sloping and early peaking of the proximal limb of T waves.