EXERCISE TESTING IN THE STUDY OF ARRHYTHM IAS

Exercise testing may be used to assess symptoms occurring on effort, t o search for and evaluate arrhythmias or conduction defects, antiarrhy thmic drugs, pacemakers or implantable cardioverter defibrillators. In terpretation of exercise testing is difficult because of the complexit y of the factors in play. Exercise itself induces changes in myocardia l metabolism and the autonomic nervous system, the nature and importan ce of which are influenced by the underlying cardiac disease and the p resence of cardiac failure or myocardial ischaemia. This is particular ly true when studying the behaviour of arrhythmias on effort, which de pends on many parameters, in that they may appear or disappear during exercise, irrespective of their relationship to autonomic nervous syst em activation. The main problem lies in the interpretation of changes in the heart rate before the onset of an arrhythmia. The sinus rhythm is both a passive indicator of the vago-sympathetic equilibrium and on e of the determining factor of the arrhythmia (relationship to the rat e), but it is, itself, dependent on the presence of myocardial dysfunc tion, a source of arrhythmias, and its changes then become difficult t o interpret. These reasons explain why exercise testing is certainly a valuable tool in assessing arrhythmias but the poor reproducibility, especially in the evaluation of ventricular arrhythmias, advises prude nce in the interpretation of results.