Arrhythmias in the Normal Human Heart

This chapter is concerned with arrhythmias occurring in the normal heart particularly in response to stress. Various aspects are considered including the incidence of arrhythmia in people with apparently normal hearts as determined by electrocardiographic (ECG) recordings at rest, during 24-h ambulatory monitoring and during exercise; evidence that emotion may induce arrhythmia in normal people; the relationship of the sympathetic and parasympathetic nervous system; and prognostic importance and clinical implications. Problems arise in view of the inevitable difficulties of defining the “normal”. Research interest has been largely directed towards the abnormal heart and there is a relative paucity of information on the “normal”. Some reliance therefore has to be placed on control groups which in a number of instances are lacking in detail. There is a wide variation in the literature in the degree to which normality has been established, ranging from angiographic evidence in a few, through non-invasive studies in some to merely the absence of symptoms in the majority. The asymptomatic subjects tend to span a wide age range and it is inevitable that a proportion with significant cardiac disease will have been included. This may be important in view of the fact that the number exhibiting arrhythmia is relatively small.