Frequency-domain analysis of heart rate variability during positive and negative head-up tilt test: importance of age.

The study of autonomic behavior during a head-up tilt test (HUT) has been deemed important to understand the loss of consciousness mechanism. Though HRV in patients with HUT(+) and HUT(-) has been compared, few trials emphasized the importance of age. HRV in frequency domain was analyzed based on 5-minute samples in the supine position, and between 5 and 10 minutes during early tilt test (R1) in 102 patients with one or more episodes of syncope (mean age 44.3 +/- 20.8, range 15-85 years, 55 women). Two subgroups were selected afterwards: (1) young patients between 15 and 35 years of age (41 patients) and (2) elderly patients aged 60 or more (36 patients). The following parameters were taken into account: the sum of low (LF) and high frequency (HF) (LF and HF in absolute values and in normalized units), the LF/HF ratio (L/H ratio), and the percentage of change between baseline and R1 values. The HRV behavior in young and elderly patients with positive and negative HUT was established. We then analyzed the correlation between HRV and age and HUT outcome. A multiple regression analysis encompassing age, HUT outcome, gender, and number of syncope episodes was performed. In young patients, the LF and HF areas and the L/H ratio changed significantly between baseline and R1. The L/H ratio increases from baseline to R1. Conversely, these differences were not significant in the elderly. No differences between HUT(+) and HUT(-) within the same age group were observed. Age related significantly to practically all HRV parameters analyzed, whereas the tilt test outcome correlates poorly with HF normalized units and LF normalized units during R1, and the L/H ratio changes between baseline and R1. By means of a multivariate analysis, only age shows a significant correlation with the HRV values. Despite an all age triggering of vasovagal syncope during HUT, the young and elderly patients' autonomic behavior differs. The young considerably increase their sympathovagal balance during HUT, whereas the elderly have a mitigated autonomic response. No significant differences were observed during the first minutes of the test between those with a HUT(+) and those with a HUT(-) within the same age group. Age, and not the HUT response, is the major determinant of the autonomic behavior during early HUT.

Tolerance to lower body negative pressure exposure: comparison between patients with neurocardiogenic syncope and controls.

Lower body negative pressure exposure (LBNPE) produces hemodynamic modifications similar to those produced by head-up tilt test (HUT). Patients with vasovagal syncope are more susceptible to HUT than healthy persons. The supine position during LBNPE would facilitate the simultaneous performance of complementary methods. The aim of this study was to compare tolerance to LBNPE between a group of patients with vasovagal syncope and a group of healthy volunteers. Eleven patients with vasovagal syncope and positive HUT and 13 healthy volunteers without prior history of syncope and negative HUT were included. The following protocol was used: -10 mmHg, 1 minute; -20 mmHg, 1 minute; -30 mmHg, 3 minutes, and -40, -50, -60, and -70 mmHg, 5 minutes for each stage. Tolerance was expressed as: maximum tolerated negative pressure (Max NP), maximum tolerated time (Max T), and sigma P x T, where P = pressure and T = time. Syncope or presyncope during the test was considered positive LBNPE. LBNPE was positive at -50 or -60 mmHg in 8 of 11 patients (73%). One healthy volunteer had presyncope after 5 minutes at -70 mmHg. Tolerance, as expressed by any of the three parameters, was significantly higher for the healthy volunteers (Max NP: -59.1 +/- 7.9 vs -70, P < 0.01; Max T: 19.1 +/- 4.2 vs 24.4 +/- 0.3, P < 0.01; sigma P x T: 836.3 +/- 269.5 vs 1214.6 +/- 18, P < 0.01). We conclude that patients with neurocardiogenic syncope have a significantly lower tolerance to LBNPE than subjects with no previous history of syncope.

Active vs passive rhythms as an explanation of bigeminal rhythm with similar P waves.

We describe the criteria for differential diagnosis between 3:2 sinoatrial block from atrial bigeminy due to an ectopic focus in the sinus or parasinus zone. In the 3:2 sinoatrial block the RR interval of the basic rhythm is similar to the short R-R interval of the paired rhythm. In atrial bigeminy, the R-R interval of the basic rhythm is similar to the long R-R interval of the paired rhythm.

Recasting the approach to the treatment of potentially malignant ventricular arrhythmias after the CAST study.

The best therapeutic approach to the therapy of potentially malignant ventricular arrhythmias is still unknown, particularly in view of the increased mortality with flecainide and encainide shown in the CAST study. Various ongoing studies, particularly with amiodarone, will show whether better results can be obtained with other agents. Flecainide and encainide do, however, have a restricted place when other agents cannot be used. Low-dose amiodarone with low-dose flecainide may be worth trying.