beta-carotene and Arrhythmias--Cardiac

Brugada syndrome (BrS), caused by ion channel abnormalities, is characterized by ST segment elevation and negative T waves in the right precordial electrocardiographic (ECG) leads recorded over the right ventricular outflow tract (RVOT). BrS is sensitive to body temperature and can lead to T-wave alternans (TWA), ventricular tachycardia, and sudden death. Recent studies in an isolated canine RVOT model of BrS demonstrated that reversal of the transmural gradient of repolarization caused the ECG characteristics and that major intraepicardial and transmural dispersion of action potentials (APs) initiated phase 2 reentry, premature ventricular activations, and tachyarrhythmias. Hypothermia enhanced the heterogeneity of the AP and promoted the origination of phase 2 reentry in the epicardium of the RVOT, but the prolonged AP duration frequently blocked reentry. Hyperthermia abbreviated the AP and facilitated the maintenance of reentry and tachyarrhythmias. Bradycardia promoted alternans in the phase 2 dome of the AP within the epicardium of the RVOT, resulting in TWA. The above phenomena were localized in the epicardium of the RVOT. Blockade of the transient outward current, I(to), reduced AP heterogeneity and prevented arrhythmias in the BrS model. In addition, epicardial activation delay led to fragmented QRS, a risk marker of prognosis in BrS. Body surface mapping in patients with BrS supported these experimental findings. In conclusion, the AP heterogeneity within the epicardium of the RVOT contributes to the ECG characteristics, temperature sensitivity, TWA, and arrhythmias in BrS, and body surface mapping and fragmented QRS can be effective predictors of risk in patients with BrS.

Topics: Animals; Arrhythmias, Cardiac; beta Carotene; Body Temperature; Brugada Syndrome; Calcium Channels; Electrocardiography; Electrophysiologic Techniques, Cardiac; Heart Conduction System; Heart Ventricles; Humans; Risk Assessment; Sodium Channels

Several factors are known to limit cardiac transplantation, such as number of donors, quality of cardiac graft preservation, and ischemia-reperfusion injury. Some mechanisms of reperfusion injury are now recognized; they include oxygen free radical (OFR), white blood cells activation, changes in calcium influx, alteration of microvascular blood flow, and sympathetic activation. The goal of this study was to assess the effects of two types of cardioplegia with long-term storage, either static or continuous perfusion, in 30 isolated sheep hearts as a model for heart transplantation. We examined myocardial function, histology, ischemic damage, and markers of oxidative stress. Two types of cardioplegia and storage conditions using a Langendorff reperfusion were studied in a combined approach: crystalloid (CP) [groups I and III] or cold oxygenated autologous blood (BC) [groups II and IV], immediate storage during 8h in profound hypothermia (groups I and II), or reperfused with crystalloid (group III), or blood cardioplegia (group IV). All perfusate samples were drawn from the coronary sinus. Lactate levels increased progressively in groups I, II, and IV, but not in group III, as no significant elevation was shown [90 min: 13.6+/-1.7 versus 5.2+/-1.0 mmol/L (P<0.01)]. Arrhythmias were more frequent when using BC (n=5) than CP (n=0). For plasma thiobarbituric acid-reactive substances (TBARS) levels a significant difference was found between group III and the other groups since 15 to 90 min (P<0.05). Vitamin E concentration decreased significantly from 5 min for groups II and IV, 15 min for group I, and 30 min for group III, with a significant difference between groups II and IV (P<0.05) but not between groups I and III. CP followed by a reperfusion with the same solution showed a significantly lower ischemic injury and OFR production, less frequent ventricular arrhythmias while stable hemodynamic parameters carried on. However, this protocol did not act on the early postoperative contractile function.

Topics: Animals; Arrhythmias, Cardiac; beta Carotene; Blood Transfusion, Autologous; Cryopreservation; Glutathione Peroxidase; Graft Survival; Heart Arrest, Induced; Heart Transplantation; Lactic Acid; Lipid Peroxidation; Myocardial Contraction; Myocardium; Organ Preservation; Oxidative Stress; Potassium Compounds; Reperfusion Injury; Sheep; Superoxide Dismutase; Thiobarbituric Acid Reactive Substances; Ventricular Pressure; Vitamin A; Vitamin E

Of 138 patients with suspected acute myocardial infarction (AMI), 29 were excluded. Remaining 109 patients and 182 healthy controls of similar age and sex and same population were studied in detail for demographic variables, clinical and biochemical data for comparison. Mean age, sex, body weight, body mass index and blood pressures were comparable in the two groups whereas blood lipids, blood glucose and cardiac enzymes were raised in AMI patients compared to controls. Mean levels of vitamin C, E, A and beta-carotene were significantly less in AMI patients than controls whereas the lipid peroxides were significantly higher in AMI patients. The reduction in vitamin C and beta-carotene was more marked than decrease in other vitamins. With in AMI patients, those 28 patients who had cardiac arrhythmias showed greater decrease in vitamins compared to rest of the patients. Within both groups, smokers and diabetes patients had greater reduction in vitamin C and beta-carotene than other patients and subjects without confounding factors. Smokers also had higher lipid peroxides level than non-smokers. The inverse relation between AMI and low plasma vitamin levels remained significant after exclusion of patients with smoking and diabetes. These findings suggest that vitamin deficiency may be a risk factor of AMI and these patients may benefit by administration of these antioxidant vitamins for primary and secondary prevention of coronary artery disease.

Topics: Antioxidants; Arrhythmias, Cardiac; Ascorbic Acid; beta Carotene; Carotenoids; Case-Control Studies; Female; Humans; Lipid Peroxides; Male; Middle Aged; Myocardial Infarction; Oxidative Stress; Prospective Studies; Vitamin A; Vitamin E; Vitamins