Graciela Aurora Ruiz

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 fre‐quency 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 base line and Hi 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 re gression analysis encompassing age, HUT outcome, gender, and number of syncope episodes was per formed. In young patients, the LF and HF areas and the L/H ratio changed significantly between baseline and Rl. The L/H ratio increases from baseline to Rl. 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 ail HRV parameters analyzed, whereas the tilt test outcome correlates poorly with HF normalized units and LF normalized units during Rl, and the L/H ratio changes between baseline and Rl. 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 pa tients’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.

Insulin sensitivity in young women with vasovagal syncope.

BACKGROUND Insulin, in addition to its known metabolic effects, has sympatho-excitatory and vasodilatory actions on muscular blood vessels. The goal of this study was to evaluate insulin sensitivity in young women with vasovagal syncope and positive tilt test results (HUT+) and to compare it with that in patients with negative tilt test results (HUT-) and in control subjects without a history of syncope. METHODS Different indices of insulin sensitivity were obtained by an oral glucose tolerance test (OGTT) in 13 young women with syncope and HUT+ (age 26.8 +/- 9.1 years, body mass index 20.4 +/- 2.1), 8 patients with HUT- (age 26 +/- 5.6 years, body mass index 21.9 +/- 2.4), and 13 control subjects without syncope and HUT- (age 28.9 +/- 8.8 years, body mass index 23.1 +/- 1.7). The following parameters were assessed: fasting glucose and insulin levels (G(0), I(0)); G(0)/I(0) ratio; G(0) x I(0); areas under the curve for glucose and insulin; homeostatic model assessment (HOMA); quantitative insulin sensitivity check index (QUICKI); and composite whole-body insulin sensitivity index (ISI). RESULTS G(0) and I(0) values were significantly lower in patients with HUT+ than in control subjects (G(0) 4.9 vs 81.9, P <.05, I(0) 4.7 vs 9.1, P <.005). All the fasting values-based indices (ie, HOMA 0.9 vs 1.9, P <.005) and the ISI (12.8 vs 7.1, P =.01) differed significantly in both groups. None of the parameters showed significant differences between patients with HUT- and control subjects. Sixty-one percent of patients with HUT+ had a vasovagal reaction during OGTT. CONCLUSIONS Young women with vasovagal syncope and HUT+ have a greater insulin sensitivity. They have a propensity to reproduce symptoms during the OGTT. This hypersensitivity could be one of the predisposing factors for vasovagal episodes.

Role of nitric oxide in young patients with vasovagal syncope

AIMS Nitric oxide (NO) formed in the vascular endothelium produces, among other effects, a strong vasodilation. In order to evaluate the possible role of NO in hypotension induced by head-up tilt test (HUT), we measured plasma levels of its metabolites, nitrites and nitrates (NOx), during the test. METHODS AND RESULTS Twelve patients with vasovagal syncope and positive HUT [HUT(+)] (mean age: 23+/-5 years) and 13 healthy volunteers with negative HUT (controls) (mean age: 24+/-5 years) were included. Venous blood samples were obtained during the baseline stage for biochemical measurements. Plasma values of NOx were obtained under baseline conditions (T0), at the end of the HUT (T1), and 15 min after the end of the HUT (T2). The baseline biochemical values as well as haemodynamic parameters were similar in HUT(+) patients and controls. NOx plasma values (in micromol/L) were as follows [HUT(+) vs. controls]: T0: 5.7+/-1.6 vs. 8.8+/-4.7 (P=0.05), T1: 6.1+/-3.2 vs. 8.5+/-3.6 (P=NS), and T2: 6.1+/-3 vs. 10.2+/-8.9 (P=NS). The NOx levels were directly correlated with the insulin levels (Spearmans R=0.53, P=0.008). CONCLUSION Baseline plasma levels of NOx were significantly lower in HUT(+) patients than in controls. However, since the expected increase in NOx values during HUT-induced syncope was not observed, the possible role of NO in vasovagal hypotension is uncertain.

Symptomatic, Inspiration-Induced Atrioventricular Block: Treated with Pacemaker Implant: SYMPTOMATIC, INSPIRATION-INDUCED ATRIOVENTRICULAR BLOCK

The respiratory sinus arrhythmia is the most common cardiac arrhythmia. It consists of phasic variations of sinus cycle length produced by an autonomic reflex, and is characterized by increased heart rate during inspiration and decline in expiration. This phenomenon is due to a reduction of the parasympathetic tone during inspiration, causing a rise in the heart rate, while during expiration the opposite phenomenon occurs. This arrhythmia is more frequent in young adults, although it can also be seen in any age group.

Cardiovagal Reflex Blood Pressure Set Point Determination by Time Domain Analysis

The baroreflex is not only an important marker of cardiac risk, but also can serve as a monitor of improvements in baroreflex sensitivity and consequences of drug treatments, physical training, etc. Sensitivity is not the only parameter of baroreflex function, but another very important is the set point. This allows to know the value of blood pressure that baroreflex tries to stabilize. A method to obtain the Blood Pressure Set Point corresponding to vagal baroreflex curve, based on the analysis of blood pressure and heart pulse interval variability is presented. The Eurobavar, which is a heterogeneous dataset, extracted from subjects with different reflex response is used to test the method. Systolic Blood Pressure (SBP) and interval time between beats (RR) series are constructed using records from that Dataset. From both series baroreflex sequences are extracted using traditional Sequence Method. Instead of computing the average of the slopes obtained from all arterial pressure points, we segment the pressure space in non-overlapping windows of 10 mm of Hg wide averaging the gain values corresponding to pressure values within each window (data binning). The Blood Pressure corresponding to the maximum of histograms curves, constructed from SBP of the baroreflex sequences, is used to contrast the result obtained with other method. Results were 119 ± 17,7mmHg for method 1 and 118 ± 21,9 mmHg for method 2. In conclusion, with only rearranging the data, an important parameter, such as Set Point of the baroreflex, can be achieved.

885 The bradycardia-hypotension reaction during head-up tilt test: clinical and hemodynamic characteristics related to blood pressure and heart rate behavior during the early stage of the test

There was no correlation between delayed increase of aldosterone and NTG provocation during HUT. The delayed increase of aldosterone observed in 22% of all patients was related to syncope recurrence during follow-up, but not to the phase of tilt in which syncope occurred. Conclusions: 1. The delayed increase of aldosterone concentration during HUT-induced syncope is a risk factor of syncope recurrence during follow-up. 2. The delayed increase of aldosterone could be the marker of disturbed activation of RAA system predisposing the patients to vasovagal syncope.