There are lots of cardiac causes of syncope, and they account for 10 - 30% of syncopal episodes. Cardiac causes include: arrhythmias, cardiac failure, ventricular dysfunction (eg. hypertrophic obstructive cardiomyopathy HOCM) and valvular heart disease.
The most common cardiac causes of syncope, and the arrhythmia should be treated.
Bradycardias - Mobitz II and complete AV block are most likely to cause syncope.
Tachycardias - Narrow and Broad
Sick sinus syndrome - the sinoatrial node is damaged,because of either abnormal automaticity or sinoatrial conduction abnormalities.Syncope is due to long pauses caused by sinus arrest or sinoatrial block and a failure of escape mechanism. It is a completely different pathogenesis to carotid sinus syndrome. It is more likely to happen in people >65 years old, with ischaemic heart disease risk factors. ECGs can show many things, including sinus bradycardia.
Arrhythmia related syncope can be diagnosed on ECG in the presence of:
Sinus bradycardia rate under 40 bpm
Mobitz II second degree block or above
Alternating right and left bundle branch block
Ventricular tachycardia or rapid supraventricular tachycardia
This will be diagnosed as normal.
The ECG needs careful scrutiny.
Aortic stenosis needs excluding. What better summary than the one from The Calgary Guide here.