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A passing out / fainting episode is called syncope. Sometimes it is difficult to diagnose as the initial screening investigative protocol may be negative. Thus a repeat investigations at three to six months may be detected by the same work up. Following are the commonest cause for the fainiting or syncope;
1) bradyarrhythmias; this is 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 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 autonomic nervous system and related heart regulatory mechanisms.
These are the more frequent causes of syncope but there can be other like hormonal issues like excessive insulin production (Insulinoma, which decreases the blood sugar suddenly). Following investigations need to be pursued or repeated in her case;
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; done immediately after the fainting episode and would tell about the abnormal brain or heart activity which caused the fainting.
8) Following also may be done after the fainting episode; blood electrolytes and blood glucose.
These should be able to zero down the cause.
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