What is the cause of syncope?

- Syncope is relatively common in patients with cardiomyopathy who have implanted defibrillators. A proper identification of the cause allows optimization of therapy.
- Systematic analysis of pacemaker ECGs should include evaluation of atrial activity; a frequently omitted task.
- In a patient with long-standing atrial fibrillation and an implanted defibrillator, the presence of sinus P waves following syncope points to ICD shock being the most likely cause.
- If the ICD shock occurs more than 7-8 s into a non-perfusing rhythm, the patient may lose consciousness prior to the ICD discharge and therefore be unaware of the ICD shock.