Twenty-four-hour ambulatory ECG monitoring was performed using a three-channel DMS-cassette-tape recorder and carefully analyzed using the Del-Mar Avionics StrataScan System (Del Mar Avionics, Irvine, California, USA) by a trained observer blind to the study in order to assess the presence of ventricular arrhythmia and atrioventricular conduction disturbances. Variables assessed in the 24h ambulatory ECG were: i) isolated premature supraventricular contractions ii) nonsustained supraventricular tachycardia defined as a sequence of three of more supraventricular ectopic beats, iii) isolated premature ventricular contractions, and iv) ventricular tachycardia episodes (defined as: heart rate >100 bpm, QRS duration >120 ms, three or more consecutive ventricular complexes, and atrial-ventricular dissociation).