[Auricular fibrillation and stroke in patients with sick sinus syndromeusing permanent pacemakers]. / Fibrilación auricular y accidente vascular encefálico en pacientes con enfermedad del nodo sinusal portadores de marcapasos definitivos.

INTRODUCTION AND OBJECTIVES: Since physiological pacing systems have become available, a debate has raged about the merits of atrial versus ventricular pacing in the sick sinus syndrome. The goal of this retrospective report was to study the long term incidence and the independent predictors for atrial fibrillation and stroke in 153 paced patients with sick sinus syndrome, adjusting for differences in baseline clinical variables with multivariate analysis. METHOD AND RESULTS: From 1980 to 1994, we implanted 32 dualchamber, 33 atrial, and 88 ventricular pacemakers to treat patients with sick sinus syndrome. After a maximum follow-up of 177 months (median 30 months for paroxismal atrial fibrillation, 45 months for chronic atrial fibrillation and 43,5 months for stroke) the actuarial incidence of paroximal atrial fibrillation was 7.8% at 1 year, 29% at 5 years and 42% at 10 years. The actuarial incidence of chronic atrial fibrillation was 1.3% at 1 year, 9.8% at 5 years and 22% at 10 years. Independent predictors for paroxismal AF from Cox's model was history of atrial tachyarrhythmias (p < 0.0001), chronic obstructive pulmonary disease (p = 0,006) and age (> 70 years-old) (p = 0.035). Only a history of atrial tachyarrhythmias before pacemaker implant was an independent predictor for chronic atrial fibrillation (p < 0.0001). The odd ratio for paroxismal atrial fibrillation in patients with previous atrial tachyarrhythmias and chronic atrial fibrillation were 6 (2.8-12) and 4 (1.6-9.7) (95% confiance limits). Actuarial incidence of stroke was 3% at 1 year, 10% at 5 years and 14% at 10 years. Independent predictors for stroke were history of peripheral vascular disease (p = 0.033) and hypertensive cardiomyopathy (p = 0.015). Development of paroxysmal and chronic atrial fibrillation during the follow-up were higher in patients with stroke (p < 0.001 and p < 0.05). CONCLUSIONS: Development of atrial fibrillation and stroke in paced patients with sick sinus syndrome are strongly determined by clinical variables. Preimplant paroxysmal atrial tachyarrhythmias is the most important predictor for atrial fibrillation in the follow-up.

[The automatic, beat-to-beat determination of the QT interval and analysis of its spontaneous variability under basal conditions]. / Determinación automática, latido a latido, del intervalo QT y análisis de su variabilidad espontánea en condiciones basales.

OBJECTIVES: An analysis is made of the automatic beat-by-beat measurement of QT and other intervals related to ventricular repolarization. The variability pattern of these intervals is investigated in normal subjects at rest, along with their relation to RR cycle variability. MATERIAL AND METHODS: The electrocardiographic signals (LII) from 11 normal subjects (mean age 31 +/- 10 years) were recorded over 5 min and processed by applying specific algorithms to determine beat-by-beat the RR, QT, RT, QTm and RTm intervals (Tm = peak of T wave). An analysis was made of the variability of these intervals in the time (standard deviation, variation coefficient, difference between maximum and minimum values) and frequency domains (spectral analysis applying the Fourier transform). RESULTS: The differences between the automatic measurements and those performed by two observers (n = 110) were respectively -1.3 +/- 6.4 and -3.7 +/- 6.5 ms for QT, - 1.0 +/- 1.4 and -1.0 +/- 2.3 ms for QTm, -0.3 +/- 1.4 and -0.2 +/- 1.8 ms for RTm, and 0.7 +/- 6.5 and -2.8 +/- 10.3 ms for RT. The QT and RT intervals exhibited greater variability (SD = 6 +/- 1 ms) than QTm and RTm (SD = 3 +/- 1 ms, p < 0.0001). These differences persisted on comparing the corresponding variation coefficients. The differences between the maximum and minimum measurements were 45 +/- 24 ms for QT and RT, the values being significantly less in the case of QTm (21 +/- 26 ms, p < 0.05) and RTm (20 +/- 27 ms, p < 0.05). In the frequency domain, the high- (HF) and low-frequency (LF) band energies were low in the series formed by the ventricular repolarization intervals, and the LF band normalized amplitude was significantly lower than in the RR series. There were no significant differences in the frequencies of the maximum values of the LF and HF bands of the RR series with respect to the QT series. The correlations between the RR intervals and the subsequent repolarization intervals obtained in each subject were not significant in 7 of the 11 subjects studied. CONCLUSIONS: The automatic beat-by-beat determination of the ventricular repolarization intervals is precise, particularly when considering the intervals defined by the T wave peak. Repolarization variability during the sinus rhythm at rest is small, and is not linearly related to modifications of the previous RR interval. Neurovegetative and humoral influences are postulated to explain QT variations. The neurovegetative and humoral influences that regulate cardiac cycle and ventricular repolarization variability at rest, are found to be quantitatively different.