No abstract

Systemic sclerosis (SSc) is a connective tissue disease characterized by vascular damage and interstizial fibrosis of many organs. Our interest was focused on the evaluation of cardiac autonomic function by measurements of heart rate variability (HRV) and microvascular damage detected by nailfold capillaroscopy (NC) in SSc patients. We examined 25 consecutive outpatients affected by systemic sclerosis and 25 healthy controls. Exclusion criteria were the presence of cardiac disease, hypertension, diabetes mellitus, or neurological diseases. All subjects underwent 24-h ambulatory ECG Holter recording and NC examination. Heart rate variability was evaluated in the time domain, using appropriate software, computing the time series of all normal-to-normal (NN) QRS intervals throughout the 24-h recording period. A semiquantitative rating scale was adopted to score the NC abnormalities, as well as a rating system for avascular areas and morphological NC patterns. In SSc patients, HRV analysis showed significantly lower values of SDNN (standard deviation of all NN intervals) (p=0.009), SDANN (standard deviation of the averages of NN intervals in all 5-min segments of the entire recording) (p=0.01), and pNN50 (the percentage of adjacent NN intervals that differed by more than 50 ms) (p=0.02), compared to the control group. These parameters in SSc patients significantly decreased with the worsening of semiquantitative capillaroscopy score. In conclusion, an abnormal autonomic nervous control of the heart might contribute to identify subclinical cardiac involvement in SSc patients. The coexistence of autonomic dysfunction with a more severe microvascular damage could be considered a potential prognostic tool in the identification of those patients particularly at risk for cardiac mortality.

The heart rate can be effectively used as a measure of the exercise intensity during long duration cycle-ergometer exercises: precisely controlling the heart rate (HR) becomes crucial especially for athletes or patients with cardiovascular/obesity problems. The aim of this letter is to experimentally show how the nonlocal and nonswitching nonlinear control that has been recently proposed in the literature for the HR regulation in treadmill exercises can be effectively applied to cycle-ergometer exercises at constant cycling speed. The structure of the involved nonlinear model for the HR dynamics in cycle-ergometer exercises is mathematically inspired by the structure of a recently identified and experimentally validated nonlinear model for the HR dynamics in treadmill exercises: the role played by the treadmill speed is played here by the work load while the zero speed case for the treadmill exercise is here translated into the cycling operation under zero work load. Experimental results not only validate the aforementioned nonlinear model but also demonstrate the effectiveness--in terms of precise HR regulation--of an approach which simply generalizes to the nonlinear framework the classical proportional-integral control design. The possibility of online modifying the HR reference on the basis of the heart rate variability (HRV) is also suggested and experimentally motivated.

The depolarization abnormalities, revealed by ECG-SA, probably reflect a longer extent of myocardial fibrosis in SLE patients with ECHO evidence of abnormal left ventricular filling. The simultaneous occurrence of ECHO and ECG-SA alterations could be a marker of subclinical myocardial involvement.

Myotonic dystrophy (MD) is associated with a wide spectrum of cardiac abnormalities, but only a few longitudinal studies have investigated the natural course of heart disease in MD. To assess whether neuromuscular involvement significantly predicts cardiac disorders in MD, 83 patients with various grades of disease severity were enrolled in a 13-year follow-up study (mean, 60.6 +/- 37.8 months) that included periodic physical and instrumental cardiac examinations (standard and Holter electrocardiography, echocardiography). During follow-up, muscular disease worsened clinically in 9 patients (11%) whose baseline severity grade changed accordingly; only 3 of them demonstrated parallel worsening of cardiac disturbance, however, compared with a large number of patients who showed additional cardiac abnormalities. These included further worsening of pre-existing pathologic features (19/83) and the appearance de novo of serious arrhythmias and/or conduction defects (23/83). Pacemaker implantation was necessary in 11 of 83 patients (13.2%) who had symptomatic bradyarrhythmias, bifascicular block, and P-R prolongation with a His-to-ventricle interval exceeding 55 ms, as documented by electrophysiologic study. Eight (9.6%) patients died: 2 from noncardiac and 1 from unknown causes, 1 from heart failure, and 4 from sudden death closely related to documented ventricular tachycardia. The incidence and seriousness of arrhythmic and conduction disturbances correlated with the severity of the muscular involvement. Nevertheless, cardiac and muscular disease did not show a linear progression. Cardiac involvement generally worsened more rapidly than did skeletal muscle disease.