Significance of a Q wave in lead I in the newborn

Similarities between ischemic preconditioning and 17beta-estradiol mediated cardiomyocyte KATP channel activation leading to cardioprotective and antiarrhythmic effects during ischemia/reperfusion in the intact rabbit heart

The aims of our present work were to assess whether treatment with either ischemic preconditioning (IPC) or 17beta-estradiol or both combined produce proarrhythmic or antiarrhythmic effects, and whether opening of the sarcolemmal or mitochondrial KATP channels is relatable to this effect; to assess biochemically the effects of IPC and/or 17beta-estradiol on oxidant stress and antioxidant defenses in the myocardium; to examine the effects of nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) pretreatment in rabbits treated with either IPC or 17beta-estradiol (because 17beta-estradiol evoked NO release has been implicated in KATP activation and IPC); and examine the effects of ischemic preconditioning and 17beta-estradiol on myocardial energy metabolism during ischemia and reperfusion in a well-standardized model of reperfusion arrhythmias in anesthetized adult male New Zealand White rabbits (n = 124) subjected to 30 minutes occlusion of the left coronary artery followed by 120 minutes of reperfusion. Pretreatment with either 17beta-estradiol (10 microg/kg, i.v.) or one cycle of ischemic preconditioning prior to the period of coronary occlusion offers significant infarct size reduction (18.6 +/- 2.2% and 19.4 +/- 1.9%, respectively versus 40.1 +/- 3.9% in saline control and 39.2 +/- 3.2% in vehicle control groups; P < 0.01) and antiarrhythmic effects. Both 17beta-estradiol and ischemic preconditioning treatment significantly attenuated the incidence of life-threatening arrhythmias like sustained VT (13% and 13%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001) and other arrhythmias (25% and 25%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001), and were quite effective in increasing the number of animals that survived without developing any arrhythmia during ischemia and reperfusion. 5-hydroxydecanoate(5-HD; 5 mg/kg, i.v.) alone offered no cardioprotective and antiarrhythmic activities. Pretreatment with 5-HD but not HMR 1883 (3 mg/kg, i.v.) abolished the beneficial effects of 17beta-estradiol and ischemia preconditioning on reperfusion-induced arrhythmias and cardioprotection suggesting that such effects have been achieved via the selective activation of cardiomyocyte mitochondrial KATP channels rather than sarcolemmal KATP channels. The reduced reperfusion arrhythmic incidence and durations induced by estrogen was not significantly altered by ICI 182 720 (2.5 mg/kg, i.v.). The lack of effect of ICI 182 720 on antiarrhythmic and infarct-limiting effects of 17beta-estradiol and ischemic preconditioning suggest that these favorable effects are rapid, direct, and non-genomic effects. This study demonstrates similarities between 17beta-estradiol and ischemic preconditioning of the rabbit myocardium in terms of cardioprotection, antiarrhythmic, and metabolic activities. Ischemic preconditioning and 17beta-estradiol appear to share a final common effector; the mitochondrial KATP channel.

Acute myocardial infarction in the neonatal period

We describe two neonates presenting with myocardial infarction, due to two different aetiologies of this extremely rare but potentially treatable condition, and discuss the management. One neonate had myocardial infarction complicating enteroviral myocarditis and recovered completely. The second had fatal myocardial infarction due to thrombosis of the left coronary artery. Although rare, the attending paediatrician should have a high index of suspicion when evaluating a neonate with acute onset of collapse. Electrocardiographic changes are diagnostic, but further echocardiographic assessment and prompt management at a tertiary cardiac centre are advised.

Differential effects of sarcolemmal and mitochondrial K(ATP) channels activated by 17 beta-estradiol on reperfusion arrhythmias and infarct sizes in canine hearts

We have demonstrated the effects of estrogen on modulation of ATP-sensitive K(+) channels; however, the subcellular location of these channels is unknown. The purpose of the present study was to investigate the role of the sarcolemmal and mitochondrial ATP-sensitive K(+) channels in a canine model of myocardial infarction after stimulation with 17 beta-estradiol. Anesthetized dogs were subjected to 60 min of the left anterior descending coronary artery occlusion followed by 3 h of reperfusion. Infarct size was markedly reduced in estradiol-treated dogs compared with controls (14 +/- 6 versus 42 +/- 6%, P < 0.0001), indicating the effective dose of estradiol administrated. Pretreatment with the mitochondrial ATP-sensitive K(+) channel antagonist 5-hydroxydecanoate completely abolished estradiol-induced cardioprotection. The sarcolemmal ATP-sensitive K(+) channel antagonist 1-15-12-(5-chloro-o-anisamido)ethyl-methoxyphenyl)sulfonyl-3-methylthiourea (HMR 1098) did not significantly attenuate estradiol-induced infarct size limitation. In addition, estradiol administration significantly reduced the incidence and duration of reperfusion-induced ventricular tachycardia and ventricular fibrillation. Although 5-hydroxydecanoate alone caused no significant effect on the incidence of reperfusion arrhythmias in the presence or absence of estradiol, the administration of HMR 1098 abolished estrogen-induced improvement of reperfusion arrhythmias. Pretreatment with the estrogen-receptor antagonist faslodex (ICI 182,780) did not alter estrogen-induced infarct-limiting and antiarrhythmic effects. These results demonstrate that estrogen is cardioprotective against infarct sizes and fatal reperfusion arrhythmias by different ATP-sensitive K(+) channels for an estrogen receptor-independent mechanism. The infarct size-limiting and antiarrhythmic effects of estrogen were abolished by 5-hydroxydecanoate and HMR 1098, suggesting that the effects may result from activation of the mitochondrial and sarcolemmal ATP-sensitive K(+) channels, respectively.