Isoprenaline increases the slopes of restitution trajectory in the conscious rabbit with ischemic heart failure.

Roughly speaking, restitution is the dependence of recovery time of cardiac electrical activity on heart rate. Increased restitution slope is theorized to be predictive of sudden death after heart injury such as from coronary artery occlusion (ischemia). Adrenaline analogs are known to increase restitution slope in normal hearts, but their effects in failing hearts are unknown.

Pharmacologic modulation of parasympathetic activity in heart failure.

In the congestive heart failure state, autonomic dysregulation involves an increase in sympathetic tone and decrease in parasympathetic tone and is associated with increased mortality. It is possible that augmentation of the parasympathetic nervous system (PNS) with pharmacologic therapy may lead to improved symptoms and/or clinical outcomes. There are several new and established pharmacologic interventions that have been studied for their effect on the PNS, including antagonists of the renin-angiotensin system, beta-adrenergic antagonists, digoxin, and vasodilators.

Angiotensin II and CRF receptors in the central nucleus of the amygdala mediate hemodynamic response variability to cocaine in conscious rats.

Stress or cocaine evokes either a large increase in systemic vascular resistance (SVR) or a smaller increase in SVR accompanied by an increase in cardiac output (designated vascular and mixed responders, respectively) in Sprague-Dawley rats. We hypothesized that the central nucleus of the amygdala (CeA) mediates this variability. Conscious, freely-moving rats, instrumented for measurement of arterial pressure and cardiac output and for drug delivery into the CeA, were given cocaine (5 mg/kg, iv, 4-6 times) and characterized as vascular (n=15) or mixed responders (n=10).

Increased ventricular premature contraction frequency during rem sleep in patients with coronary artery disease and obstructive sleep apnea.

Background: Patients with obstructive sleep apnea are reported to have a peak of sudden cardiac death at night, in contrast to patients without apnea whose peak is in the morning. We hypothesized that ventricular premature contraction (VPC) frequency would correlate with measures of apnea and sympathetic activity.

Methods: Electrocardiograms from a sleep study of 125 patients with coronary artery disease were evaluated.

Demonstration of circadian rhythm in heart rate turbulence using novel application of correlator functions.

Background: Demonstration of a circadian rhythm in two parameters of heart rate turbulence--turbulence onset (TO) and turbulence slope (TS)--has been difficult.

Objective: The aim of this study was to devise a new method for detecting circadian rhythm in noisy data and to apply it to selected Holter recordings from two postmyocardial infarction databases: Cardiac Arrhythmia Suppression Trial (CAST, n = 684) and Innovative Stratification of Arrhythmic Risk (ISAR, n = 327).

Methods: For each patient, TS and TO were calculated for each hour with >4 ventricular premature contractions (VPCs).

Heart rate turbulence slope reduction in imminent ventricular tachyarrhythmia and its implications.

Introduction: The aim of this study was to see whether heart rate turbulence (HRT) parameters change preceding imminent ventricular tachyarrhythmias (VT/VF).

Methods And Results: The Spontaneous Ventricular Tachyarrhythmia Database (Medtronic Version 1.0) consisting of 83 paired (control and pre-VT/VF) sets of 1,000 RR intervals recorded by the Medtronic Jewel Plus ICD was used.

QRS duration and late mortality in unselected post-infarction patients of the revascularization era.

Aims: To assess the association of prolonged QRS duration and late mortality in unselected post-infarction patients of the revascularization era.

Methods And Results: A total of 1455 survivors of acute myocardial infarction (MI) in sinus rhythm and under 76 years of age were enrolled. Ninety eight percent of the patients received reperfusion/revascularization therapy (90% percutaneous coronary intervention).

Turbulence dynamics: an independent predictor of late mortality after acute myocardial infarction.

Introduction: The prognostic value of heart rate turbulence for predicting mortality after acute myocardial infarction is well established. This study investigates a new measure of heart rate turbulence, termed turbulence dynamics, which quantifies the relationship between turbulence slope and underlying heart rate (HR(VPC)).

Methods: Six hundred eight patients participating in the European Myocardial Infarction Amiodarone Trial had > or =25 ventricular premature complexes/24 h.

Heart rate turbulence: a 5-year review.

April 2004 marks the fifth anniversary of the first heart rate turbulence (HRT) publication, which demonstrated the usefulness of HRT in predicting cardiac death in postmyocardial infarction patients. Since then, HRT has been shown to predict prognosis of patients with dilated cardiomyopathy and of patients with heart failure of mixed etiology. HRT also has been shown to be predictive even in the current lower-mortality era of acute revascularization therapy for myocardial infarction.

Reduced prognostic power of ventricular late potentials in post-infarction patients of the reperfusion era.

Aims: To test the prognostic value of ventricular late potentials (LPs) in a large cohort of post-infarction patients in the modern reperfusion era.

Methods And Results: 1800 consecutive survivors of acute myocardial infarction in sinus rhythm and under 76 years of age were enrolled. Many (99%) of the patients received reperfusion/revascularization therapy (91% percutaneous coronary intervention) and up-to-date pharmacological treatment (99% aspirin, 93% beta-blockers, 90% ACE-inhibitors, and 85% statins).

Heart rate turbulence: a new predictor for risk of sudden cardiac death.

Initial acceleration and a subsequent deceleration of sinus rhythm following a ventricular ectopic beat with a compensatory pause has been termed heart rate turbulence (HRT). The changes in sinus rhythm are thought to be mediated by a baroreflex response to the lower stroke volume of the ectopic beat. HRT is vagally mediated and abolished by atropine, whereas beta-blockers have no effect.

Low-order chaos in sympathetic nerve activity and scaling of heartbeat intervals.

The mechanism of 1/f scaling of heartbeat intervals remains unknown. We recorded heartbeat intervals, sympathetic nerve activity, and blood pressure in conscious rats with normal or high blood pressure. Using nonlinear analyses, we demonstrate that the dynamics of this system of three variables is low-order chaos, and that sympathetic nerve activity leads to heartbeat interval and blood pressure changes.

Effects of ventricular premature stimulus coupling interval on blood pressure and heart rate turbulence.

Background: Heart rate turbulence (HRT) is a promising noninvasive risk stratifier for mortality after myocardial infarction. On the basis of a study of ventricular premature complex coupling interval and sympathetic nerve burst amplitude, we hypothesized that measures of HRT would increase with increased prematurity of the coupling interval.

Methods And Results: Twenty-eight patients undergoing programmed electrical stimulation were studied (12 with prior myocardial infarction, aged 60+/-18 years).

Mathematical analysis of dynamics of cardiac memory and accommodation: theory and experiment.

Decreasing the slope of the dynamic, but not conventional, restitution curves is antifibrillatory. Cardiac memory/accommodation underlies the difference. We measured diastolic interval (DI) and action potential duration (APD) in epicardial, endocardial, and Purkinje tissue from eight dogs.