Heart rate variability and apnea during sleep in Down's syndrome

Autonomic system dysfunction has been reported to occur frequently in patients with Down's syndrome (DS) and is constituted mainly by an imbalance between the sympathetic and vagal systems. The analysis of heart rate variability (HRV) during sleep is a quantitative reliable method for studying such a mechanism, but it has not yet been extensively and adequately applied in DS. In this study, HRV during sleep was evaluated in seven DS patients and in six normal controls, by also controlling for the presence of sleep apnea or arousal. The main results were an increased sympathetic function (low-frequency component of HRV) and a decreased vagal activity (high-frequency component of HRV) in DS with respect to normal controls, during apnea-free periods. Moreover, the presence of apnea, in DS, induced a further significant increase in low-frequency and very low-frequency components of HRV during sleep Stage 2. This study provides additional evidence of a brainstem dysfunctioning in DS, responsible for the abnormal imbalance between the sympathetic and vagal systems and confirms the brainstem involvement already suggested in the literature in order to explain brainstem-auditory evoked potential abnormalities and central sleep apnea in these patients.     

The acute cardiovascular actions of intravenous thyrotrophin releasing hormone (TRH) in man are mediated by non-catecholaminergic mechanisms

1. Intravenous bolus doses of thyrotrophin releasing hormone (TRH, 50–1000 μg) caused statistically significant, non-dose dependent and transient rises in blood pressure, heart rate and plasma catecholamines in healthy young males.
2. Mean peak incremental rises in systolic blood pressure (mean ± s.e. mean) following 50, 200 and 500 μg TRH were 14.3 ± 2.9 mmHg, 15.7 ± 3.2 mmHg and 17.1 ± 3.9 mmHg respectively (all P < 0.05 vs placebo). Mean incremental rises in heart rate for the three doses of TRH were 8.2 ± 2.2 beats min⁻¹, 7.1 ± 1.8 beats min⁻¹, and 1O.7 ± 2.9 beats min⁻¹ respectively (all P < 0.05 vs placebo).
3. Following the 50 μg and 1000 μg doses of TRH, plasma noradrenaline and adrenaline rose significantly (P < 0.05) between 4 and 8 min. Mean ± s.e. mean incremental plasma noradrenaline rise following 50, 200 and 1000 μg TRH were 0.4 ± O.13 nmol 1⁻¹, 0.37 ± 0.21 nmol 1⁻¹ and 0.41 ± 0.18 nmol 1⁻¹ respectively. Mean ± s.e. mean incremental rise in adrenaline for the 50, 200 and 1000 μg dose were 0.13 ± 0.04 nmol 1⁻¹, 0.08 ± 0.03 nmol 1⁻¹, and 0.11 ± 0.05 nmol l⁻¹ respectively.
4. Following administration of the ganglion blocking drug pentolinium (5 mg) the incremental systolic blood pressure and heart rate rises following 500 μg TRH alone 16.6 ± 2.8 mmHg and 1O.4 ± 3.1 beats min⁻¹ respectively.
5. The rises in plasma noradrenaline and adrenaline following TRH were attenuated by prior ganglion blockade.
6. α-adrenoceptor blockade with thymoxamine (0.3 mg kg⁻¹ bolus + 0.3 mg kg⁻¹ h⁻¹ infusion), singly and combined with intravenous propranolol (10 mg i.v. over 10 min), did not alter the pressor or tachycardic effects of 500 μg TRH.
7. In conclusion, although plasma noradrenaline rises following i.v. TRH, suggesting activation of the sympathetic nervous system, this effect is not responsible for the pressor response to TRH, which appears to be due to either a direct vasoconstrictive effect on the peripheral resistance vessels or a direct inotropic/chronotropic effect on the heart.

     

Low protein alimentation normalizes renal haemodynamic response to acute protein ingestion in type 1 diabetic children

The effect of an acute protein load (2 g kg-1 bodyweight [BW]) was studied in nine type 1 diabetic children. Patients were maintained on two different dietary regimens. In study one, patients were on a high protein diet providing from 2.7 to 1.8 g of protein/kg of BW per day. In study two, patients were reevaluated after three weeks of a diet providing from 1.0 to 1.2 g kg-1 of BW per day of protein. In study one (High Protein Diet), we failed to observe any rise in GFR and RPF following the protein meal (137 +/- 21 basal vs. 110 +/- 14 and 472 +/- 93 basal vs. 494 +/- 93 ml/1.73 m2 of SA min-1 at 60 min. This is in contrast with results from seven age matched controls consuming a free diet, which showed a significant rise in both GFR and RPF. In study two (low protein diet), basal GFR was significantly reduced. However after the protein load, both GFR (92 +/- 11 vs. 126 +/- 18 ml/1.73 m2 of SA min-1) and RPF (467 +/- 83 vs. 705 +/- 102 ml/1.73 m2 min-1) rose significantly (P less than 0.05 vs. basal). The data indicate that: 1. short term protein restriction reduces significantly GFR in type 1 diabetic children; 2. diabetic children maintained on an high protein intake show an altered haemodynamic response to protein ingestion; 3. a normal response to protein ingestion can be restored by short term dietary protein restriction.     

High Energy Transcatheter Cardioversion for Chronic, Poorly Tolerated Atrial Fibrillation

Between August 1991 and May 1993, 14 patients affected by chronic, poorly tolerated atrial fibrillation (AF) were submitted to high energy transcatheter Cardioversion. Mean duration of AF was 27.4 ± 45.1 months. In nine patients (56%), AF lasted for > 1 year. All patients had underlying heart disease, with a mean LVEF of 45.2%± 11.8% and a NYHA Class ≥ II. Previously, a mean of 2.9 ± 1.3 patients failed external electrical Cardioversion, with and without antiarrhythmics, have been attempted. Transcatheter conversion was performed by pulling the His-bundle catheter back in the right atrial cavity until no His bundle activity was recorded on distal poles, and then delivering the shock between a proximal electrode (cathode) and a back plate (anode). In all patients, transcatheter conversion restored sinus rhythm. Transient complete atrioventricular (AV) block was observed in four patients (28%), and treated by prophylactic temporary pacing. At 1 year, seven patients (50%) were still in sinus rhythm. In this series, only younger age could be related to AF recurrence (46.1 ± 10.8 vs 63.4 ± 6.8 years, P ≤ 0.004), even if prophylaxis with amiodarone showed a positive trend versus sinus rhythm maintenance (71 % vs 14%, P = NS). In conclusion, high energy transcatheter Cardioversion is a safe and effective method of restoring sinus rhythm in patients with chronic, poorly tolerated AF. In these patients, high energy transcatheter Cardioversion could be considered as an alternative to AV node ablation techniques, avoiding pacemaker implant and embolic risk. Larger studies are needed to determine better patient selection and delineate drug strategy after the procedure.     

Mapping and Ablation of a Perisinusal Atrial Tachycardia with Noncontact Mapping

Perisinusal atrial tachycardia may represent a challenging situation due to unsustained burst characterizing the arrhythmia, sensitivity to bumping, and potential complications including sinus node ablation. This case describes the use of a noncontact mapping system to map and ablates this arrhythmia. Benefit of this technology is described. (PACE 2013; 36:e11–e14)     

Human immunodeficiency virus infection among heterosexuals in the northeastern part of Italy

A cross-sectional, seroprevalence study was conducted between1984 and 1991 to investigate prevalence and risk factors forhuman immunodeficiency virus (HIV) infection in heterosexualsin the northeastern part of Italy. Two hundred and eighty-twoheterosexuals self-referring for HIV testing (109 men and 173women), without history of intravenous drug use or of otherrisk factors for HIV infection, constituted the study group.The overall seroprevalence was 17% (95% confidence interval(Cl): 13–22%), similar in men (18%) and in women (17%),and it tended to increase over time. Age was directly associatedwith HIV antibody seropositivity in men, and inversely relatedin women. Fifteen men and 63 women were steady partners of anHIV-positive person. Among them, 33% of men and 27% of womenwere infected with HIV (odds ratio (OR)=2.8, 95% Cl: 0.7–11.4in men; OR=3.5, 95% Cl: 1.4–8.6 in women). Men with promiscuousoccasional partners had a nearly 3-fold higher risk of infection(95% Cl: 0.8–12.7). Among women, a significantly increasedrisk emerged among those who reported intravenous drug usersamong their occasional partners (OR=5.7). Sixty per cent ofmales and 76% of females never used a condom with occasionalpartners and 70% of males and 72% of females never used onewith steady partners.