Triggering of supraventricular premature beats. The impact of acute and chronic risk factors

Abstract

Supraventricular premature beat (SPB) is usually considered a benign heart rhythm disturbance. However, an isolated SPB can trigger episodes of atrial fibrillation [1,2], supraventricular tachycardia [3] and malignant ventricular tachyarrhythmia [4,5]. A high frequency of SPB has been linked to the increased risk of death or stroke [6,7]. Circadian, weekly and annual variations in the occurrence of ventricular tachyarrhythmias and triggering by emotional and physical stress have been well-described [8–14]. Until now, factors that could be involved in the triggering of supraventricular arrhythmias have not been rigorously investigated. Consecutive patients who underwent continuous 24-hour Holter monitoring between January and April 2001 in the Diagnostic Units of the Division of Cardiology, Department of Internal Medicine, University Hospital Split, Split, Croatia (n=501), were eligible for inclusion in the analysis. Patients who were unable to complete the diary, had atrial fibrillation, or their ECG recordings were inaccurate due to artifacts were excluded from the analysis (n=63). The study protocol conforms to the ethical guidelines of the 1975 Declaration of Helsinki and was approved by the Ethics Committee of the University Hospital Split. All participants gave their informed consent. The authors of this article have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [15]. The identification of SPB was based on 3 criteria: prematurity, morphology, and postcontraction pause. An SPBwas defined as a QRS of less than 0.12 seconds with a minimum shortening of 20% in the R-R interval. QRS complexes of duration of more than 0.12 seconds were considered SPB only if aberration was suspected. The postcontraction pause had to be noncompensatory. Differentiation from sinus arrhythmia was made according to the P-wave morphology, cyclic changes in preceding R-R intervals, or both. Activity compatible with level 4 or more according to a metabolic equivalents scale from 1 to 8 was considered as exposure to physical activity. Exposure to emotional upset was defined as an emotional state compatible with level 3 or more according to the Onset Anger Scale [8,10,16]. Meteorologic parameters (atmospheric temperature and pressure, relative airmoisture, wind speed and direction, rainfall and passages of coldorwarmatmospheric fronts)wereprovided for every 3 hours (at 1, 4, 7 and10AM, and1, 4, 7 and10PM). The frequencyof SPB in anhourwas expressed as a percentage of all episodes during recordingwhich reduced the distribution of absolute number of SPB during monitoring and made the data normally distributed. Linear regression analysis was used to investigate the direct impact of continuous meteorologic factors, repeated measures analysis of variance (ANOVA) to estimate whether the frequencies of SPB differed according to time of day, a two-way ANOVA to assess whether the circadian pattern of SPB occurrence depended on baseline characteristic and multi-way ANOVA was used to investigate the frequency of SPB according to physical, emotional and meteorologic stressors. A stepwise multiple regression analysis was used to simultaneously assess the independent predictive significance of both acute triggering and chronic (conventional) risk factors and medication. Baseline characteristics of the 438 participants are given in Table 1 and preliminary models for multivariate analysis according to age and gender are given in Table 2. Physical activity, followed by the periods of increasing relative air moisture (Fig. 1), showed the strongest association with the occurrence of SPB and both remained significant predictors in all participant subgroups (Tables 3 and 4). The occurrence of SPB was somewhat higher during blowing of southerly and westerly winds (Fig. 2), but after adjustment for other external triggering factors the significance of this difference disappeared (p=0.77). Atmospheric pressure was a predictor of SPB in men, while lower levels of relative air moisture and passage of