A Computational Study of the Electrophysiological Substrate in Patients Suffering From Atrial Fibrillation.

In the context of cardiac electrophysiology, we propose a novel computational approach to highlight and explain the long-debated mechanisms behind atrial fibrillation (AF) and to reliably numerically predict its induction and sustainment. A key role is played, in this respect, by a new way of setting a parametrization of electrophysiological mathematical models based on conduction velocities; these latter are estimated from high-density mapping data, which provide a detailed characterization of patients' electrophysiological substrate during sinus rhythm. We integrate numerically approximated conduction velocities into a mathematical model consisting of a coupled system of partial and ordinary differential equations, formed by the monodomain equation and the Courtemanche-Ramirez-Nattel model. Our new model parametrization is then adopted to predict the formation and self-sustainment of localized reentries characterizing atrial fibrillation, by numerically simulating the onset of ectopic beats from the pulmonary veins. We investigate the paroxysmal and the persistent form of AF starting from electro-anatomical maps of two patients. The model's response to stimulation shows how substrate characteristics play a key role in inducing and sustaining these arrhythmias. Localized reentries are less frequent and less stable in case of paroxysmal AF, while they tend to anchor themselves in areas affected by severe slow conduction in case of persistent AF.

High intensity, interval exercise improves quality of life of patients with chronic heart failure: a randomized controlled trial.

BACKGROUND: The aim of this study was to evaluate the effect of high intensity, interval exercise on quality of life (QoL) and depression status, in chronic heart failure (CHF) patients. METHODS: A randomized controlled trial (phase III). Of the 100 consecutive CHF patients (NYHA classes II-IV, ejection fraction ≤ 50%) that were randomly allocated to exercise intervention (n = 50, high-intensity intermittent endurance training 30 s at 100% of max workload, 30 s at rest, for 45 min/day-by-12 weeks) or no exercise advice (n = 50), 72 (exercise group, n = 33, 63 ± 9 years, 88% men, 70% ischemic CHF and control group, n = 39, 56 ± 11 years, 82% men, 70% ischemic CHF) completed the study. QoL was assessed using the validated and translated Minnesota Living with Heart Failure questionnaire. Depressive symptomatology was evaluated using the validated and translated Zung Depression Rating Scale (ZDRS). Maximal oxygen uptake (VO(2max)) and carbon dioxide production (VCO(2max)) were also measured breath-by-breath. RESULTS: Data analysis demonstrated that in the intervention group MLHFQ score was reduced by 66% (P = 0.003); 6-min-walk distance increased by 13% (P < 0.05), VO(2max) level increased by 31% (P = 0.001), VCO(2max) level increased by 28% (P = 0.001) and peak power output increased by 25% (P = 0.001), as compared with the control group. CONCLUSION: High intensity, systematic aerobic training, could be strongly encouraged in CHF patients, since it improves QoL, by favorably modifying their fitness level.

Gender variation of exercise-induced anti-arrhythmic protection: the Ikaria Study.

BACKGROUND: Regular physical activity (PA) has shown substantial cardiac benefits. We sought to investigate whether habitual PA is associated with changes of the electrical action potential duration, as it is represented by the QT duration on a rest ECG, in a population based sample of middle-aged and elderly individuals of Ikaria island. METHODS: In a cross-sectional survey 1071 inhabitants of Ikaria Island (65 ± 13 years, 47% males) were enrolled. PA was estimated by means of IPAQ classifying the participants into low, moderate and vigorous group. QT duration was measured from a surface electrocardiogram; while using Bazett's formula the heart-rate-corrected QT (QTc) was calculated. RESULTS: Among participants, 85% reported at least moderate PA levels. Women in the 'vigorous' and 'moderate' PA level compared to those in the 'low' PA level had significantly shorter QTc (408 ± 2 ms vs. 411 ± 1 ms vs. 419 ± 2 ms, P = 0.001, respectively). In contrast, no significant difference in QTc according to PA levels was observed in men (P = 0.053). Linear regression analysis revealed that PA level was significantly associated with shorter QTc in women after adjustment for established confounders; while no such association was evident in men. Furthermore, compared to the 'low' PA group, women in the 'vigorous' PA group were 5.5-times less likely to have QTc interval above 450 ms (P = 0.031). CONCLUSION: Increased PA is associated with shorter QTc interval only in middle-aged and elderly women of Ikaria Island irrespectively of participant's habits or medical conditions, illustrating gender differences in the cardioprotective effect of habitual exercise.