A detailed history is very useful in the evaluation of many cardiac disorders, more so in the assessment of syncope. In some of the causes for syncope, only diagnostic clue will be from the history. Associated symptoms like nausea, sweating, pallor, abdominal discomfort and yawning are usually considered features of neurally mediated syncope . Evaluation of syncope can be difficult as one previous study has shown that the cause remained unknown in 97 of the 204 patients . The situation might be better now because we have better diagnostic modalities including implantable loop recorders which are quite useful in elucidating an arrhythmic cause when the episodes are not very frequent. Identifying the cause is very important as demonstrated by the 14% overall mortality at one year . Same study documented 24% sudden death with a cardiovascular cause compared to 4% for non cardiovascular cause and 3% for syncope of unknown origin.
Several types of syncope can be identified based on the history. In a typical vasovagal syncope, it is precipitated by an event like sudden fear, severe pain, strong emotion or medical instrumentation. A syncope which occurs during or soon after micturition, defecation, coughing or swallowing can be called situational syncope . Carotid sinus syncope could be induced by a tight collar. When the syncope follows the introduction of a new drug which can cause postural fall in blood pressure, it can be called drug induced syncope. Exertional syncope is seen in severe aortic stenosis while the syncope in hypertrophic obstructive cardiomyopathy is usually during rest after exertion or post exertional syncope.
While evaluating the history of syncope, precipitating and predisposing factors should be documented. Duration of loss of consciousness in case of witnessed syncope and any features seen in the recovery phase should be noted. Total number of episodes and interval between episodes in case of recurrent syncope is written down. Whether syncope occurred in a warm or crowded place and was it preceded by prolonged standing or over tiring are important historical aspects. Other features sought are whether it was precipitated by turning the neck and the position in which it occurred – standing, sitting or supine. Duration of prodromal symptoms and type of prodromal symptoms are noted. Occasionally syncope may be associated with convulsion even without being a seizure disorder (convulsive syncope). Post prandial syncope is defined as syncope during or within one hour of a meal.
Duration of prodromal symptoms are generally longer for vasovagal syncope than syncope of cardiac origin . In a study comparing the clinical history in neurocardiogenic syncope, syncope due to ventricular tachycardia and atrioventricular block, it was shown that histories of those with ventricular tachycardia and atrioventricular block are similar . Duration of prodromal symptoms of 5 seconds or less was noted in those with syncope due to atrioventricular block or ventricular tachycardia.