This is called syncope. Following investigations would be needed to identify the cause;
1) MRI with gadolinium contrast
2) Magnetic resonance angiography (MRA)
3) Tilt table test
4) Carotid sinus massage
5) Electroencephalography (EEG)
6) Stress cardiac test
7) Total creatine kinase (CK) and heart enzymes
8) Blood electrolytes and blood glucose.
These should be able to zero down the cause.
He should be evaluated for the following which are the commonest cause for sudden fall or syncope;
1) bradyarrhythmias; this is the sudden slowing of the heart. it is mainly due to sinus and atrial node dysfunctions. Sick sinus syndrome is a prototype of these arrhythmias and is a major cause for syncope. 24 hour Holter monitoring, echocardiography etc are the investigations done for it.
2) neurocardiogenic mechanisms; this is the fall of the blood pressure suddenly due to a sudden sympathetic failure (failure of the autonomic nervous system).
3) carotid hypersensitivity syndrome is an exaggerated response to carotid sinus stimulation. In some studies, almost 50% cognitively normal people who had experienced non-accidental fall were diagnosed with carotid hypersensitivity.
4) orthostatic hypotension is due to failure of the autonomic nervous system and related heart regulatory mechanisms.
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