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N A Mark Estes

Publications and source records attributed to N A Mark Estes.

67 records · Page 4Linked to original sources
PubMed2002

Ventricular pacing or dual-chamber pacing for sinus-node dysfunction.

BACKGROUND: Dual-chamber (atrioventricular) and single-chamber (ventricular) pacing are alternative treatment approaches for sinus-node dysfunction that causes clinically significant bradycardia. However, it is unknown which type of pacing results in the better outcome. METHODS: We randomly assigned a total of 2010 patients with sinus-node dysfunction to dual-chamber pacing (1014 patients) or ventricular pacing (996 patients) and followed them for a median of 33.1 months. The primary end point was death from any cause or nonfatal stroke. Secondary end points included the composite of death, stroke, or hospitalization for heart failure; atrial fibrillation; heart-failure score; the pacemaker syndrome; and the quality of life. RESULTS: The incidence of the primary end point did not differ significantly between the dual-chamber group (21.5 percent) and the ventricular-paced group (23.0 percent, P=0.48). In patients assigned to dual-chamber pacing, the risk of atrial fibrillation was lower (hazard ratio, 0.79; 95 percent confidence interval, 0.66 to 0.94; P=0.008), and heart-failure scores were better (P<0.001). The differences in the rates of hospitalization for heart failure and of death, stroke, or hospitalization for heart failure were not significant in unadjusted analyses but became marginally significant in adjusted analyses. Dual-chamber pacing resulted in a small but measurable increase in the quality of life, as compared with ventricular pacing. CONCLUSIONS: In sinus-node dysfunction, dual-chamber pacing does not improve stroke-free survival, as compared with ventricular pacing. However, dual-chamber pacing reduces the risk of atrial fibrillation, reduces signs and symptoms of heart failure, and slightly improves the quality of life. Overall, dual-chamber pacing offers significant improvement as compared with ventricular pacing.

Aged↗
PubMed2002

Clinical profile and spectrum of commotio cordis.

CONTEXT: Although blunt, nonpenetrating chest blows causing sudden cardiac death (commotio cordis) are often associated with competitive sports, dangers implicit in such blows can extend into many other life activities. OBJECTIVE: To describe the comprehensive spectrum of commotio cordis events. DESIGN AND SETTING: Analysis of confirmed cases from the general community assembled in the US Commotio Cordis Registry occurring up to September 1, 2001. MAIN OUTCOME MEASURE: Commotio cordis event. RESULTS: Of 128 confirmed cases, 122 (95%) were in males and the mean (SD) age was 13.6 (8.2) years (median, 14 years; range, 3 months to 45 years); only 28 (22%) cases were aged 18 years or older. Commotio cordis events occurred most commonly during organized sporting events (79 [62%]), such as baseball, but 49 (38%) occurred as part of daily routine and recreational activities. Fatal blows were inflicted with a wide range of velocities but often occurred inadvertently and under circumstances not usually associated with risk for sudden death in informal settings near the home or playground. Twenty-two (28%) participants were wearing commercially available chest barriers, including 7 in whom the projectile made direct contact with protective padding (baseball catchers and lacrosse/hockey goalies), and 2 in whom the projectile was a baseball specifically designed to reduce risk. Only 21 (16%) individuals survived their event, with particularly prompt cardiopulmonary resuscitation/defibrillation (most commonly reversing ventricular fibrillation) the only identifiable factor associated with a favorable outcome. CONCLUSIONS: The expanded spectrum of commotio cordis illustrates the potential dangers implicit in striking the chest, regardless of the intent or force of the blow. These findings also suggest that the safety of young athletes will be enhanced by developing more effective preventive strategies (such as chest wall barriers) to achieve protection from ventricular fibrillation following precordial blows.

Adolescent↗
PubMed2002

Effects of estrogen on cardiac electrophysiology in female mice.

INTRODUCTION: Understanding the molecular mechanisms that underlie gender- and hormonal-related differences in susceptibility to cardiac arrhythmias has been hampered by the lack of a suitable animal model. We examined the effect of hormonal status on the electrophysiologic (EP) properties of the mouse heart in an in vivo, closed chest model. METHODS AND RESULTS: Fifty-three female C57/J mice aged 10 to 12 weeks were studied. Thirty-six mice underwent bilateral ovariectomies; 18 received estrogen (OVX+E) and 18 received placebo (OVX). Seventeen female mice underwent only sham surgery. All animals underwent in vivo EP studies. Select EP parameters were measured after quinidine treatment. Data were analyzed by a blinded observer. Compared with the intact female mice, the PR and AH intervals were significantly shorter in the OVX mice, and these parameters normalized with estrogen replacement (PR = 45.9+/-4.5 msec in the intact mice, 42.1+/-4.3 msec in the OVX group, and 46.9+/-3.5 msec in the OVX+E group, P < 0.005; AH = 36.5+/-4.9 msec in the intact mice, 34.4+/-4.7 msec in the OVX group, and 38.8+/-2.7 msec in the OVX+E group, P = 0.03). The right ventricular effective refractory period was significantly shorter in the OVX mice versus the intact mice, and this also normalized with estrogen replacement. Hormonal status did not significantly affect any other EP variable, including QT interval. CONCLUSION: In female mice, estrogen prolongs AV nodal conduction and the right ventricular effective refractory period. Taken together, these data suggest that hormonal status affects aspects of cardiac EP function. Future application of this mouse model will be helpful in determining the molecular pathways that mediate hormonal differences in cardiac EP.

Analysis of Variance↗
PubMed2002

Inducible ventricular flutter and fibrillation predict for arrhythmia occurrence in coronary artery disease patients presenting with syncope of unknown origin.

INTRODUCTION: Ventricular fibrillation and ventricular flutter (cycle length < or = 230 msec) induced at electrophysiologic studies are thought to be nonspecific findings in patients presenting with syncope of unknown origin. However, there are limited data on the prognosis of these patients in long-term follow-up. METHODS AND RESULTS: We followed 274 consecutive patients with coronary artery disease presenting with syncope or presyncope who underwent electrophysiologic studies from January 1992 to June 1999 and assessed the risk of subsequent arrhythmias stratified by the electrophysiologic result at the time of their presentation with syncope. Ventricular fibrillation was induced in 23 patients (8%); ventricular flutter in 24 (9%), sustained ventricular tachycardia in 41 (15%); and nonsustained ventricular tachycardia 42 (15%). In 37 +/- 25 months of follow-up, there have been ventricular arrhythmias in 34 patients, including 3 (13%) of 23 who had induced ventricular fibrillation, and 7 (30%) of 24 with induced ventricular flutter, compared to 13 (32%) of 41 with sustained ventricular tachycardia, 7 (17%) of 42 with nonsustained ventricular tachycardia, and only 4 (3%) of 144 noninducible patients (P < 0.001 for induced ventricular fibrillation and ventricular flutter vs noninducible patients). The inducibility of ventricular fibrillation and ventricular flutter were independent risk factors for arrhythmia occurrence in follow-up. CONCLUSION: Ventricular fibrillation and ventricular flutter induced at electrophysiologic studies have prognostic significance for arrhythmia occurrence in patients presenting with syncope. These induced arrhythmias may not be as nonspecific as previously thought and treatment should be considered for these patients.

Aged↗
PubMed2002

Advances in implantable cardioverter defibrillators.

Implantable cardioverter defibrillators (ICDs) have become an important therapeutic modality for patients who have had a cardiac arrest or are at risk for life-threatening ventricular arrhythmias. Clinical trials have confirmed the role of the ICD for patients with sustained ventricular arrhythmias and have expanded the indications to include patients with coronary artery disease, left ventricular dysfunction, nonsustained ventricular tachycardia, and inducible ventricular tachycardia. Numerous technologic advances in ICDs have resulted in decreased size, greater ease of placement, and increased functionality. Important advancements have been made in the effectiveness of arrhythmia classification and electrogram storage. Dual-chamber ICDs have become increasingly sophisticated with rate-adaptive sensors. Biventricular pacing is being combined with ICD function in patients with heart failure, systolic dysfunction, and QRS widening. Future advances in devices will likely lead to improved arrhythmia classification, more advanced automated features, and additional features including more sophisticated sensors and biventricular pacing systems.

Arrhythmias, Cardiac↗
PubMed2002

Cardiac arrhythmias in the athlete: the evolving role of electrophysiology.

Arrhythmia management has undergone a revolution in the past decade. The diagnosis and treatment of arrhythmias in the athlete can be complicated by the need to compete and exercise. Some arrhythmias may be benign and asymptomatic, but others may be life threatening. Sinus bradyarrhythmias are common and even expected in athletes; these are rarely a cause for concern. Heart block is unusual and merits a thorough work-up. Atrial fibrillation may be more common in the athlete, and supraventricular tachycardias other than atrial fibrillation warrant consideration of radiofrequency ablation for cure. Ventricular arrhythmias in the athlete generally occur in the setting of structural heart disease that is genetically determined (hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, anomalous coronary arteries), or acquired (coronary artery disease, myocarditis, idiopathic dilated cardiomyopathies). In these conditions the arrhythmia is life threatening. Ventricular arrhythmias that occur in the athlete without structural heart disease are not thought to be life threatening. Athletes with structural heart disease and those with exertional syncope merit a complete evaluation.

Arrhythmia, Sinus↗
PubMed2002

Reduced risk of sudden death from chest wall blows (commotio cordis) with safety baseballs.

OBJECTIVES: In an experimental model of sudden death from baseball chest wall impact (commotio cordis), we sought to determine if sudden death by baseball impact could be reduced with safety baseballs. BACKGROUND: Sudden cardiac death can occur after chest wall impact with a baseball (commotio cordis). Whether softer-than-standard (safety) baseballs reduce the risk of sudden death is unresolved from the available human data. In a juvenile swine model, ventricular fibrillation (VF) has been shown to be induced reproducibly by precordial impact with a 30-mph baseball 10 to 30 ms before the T-wave peak, and this likelihood was reduced with the softest safety baseballs (T-balls). To further test whether safety baseballs would reduce the risk of sudden death at velocities more relevant to youth sports competition, we used our swine model of commotio cordis to test baseballs propelled at the 40-mph velocity commonly attained in that sport. METHODS: Forty animals received up to 3 chest wall impacts at 40 mph during the vulnerable period of repolarization for VF with 1 of 3 different safety baseballs of varying hardness, and also by a standard baseball. RESULTS: Safety baseballs propelled at 40 mph significantly reduced the risk for VF. The softest safety baseballs triggered VF in only 11% of impacts, compared with 19% and 22% with safety baseballs of intermediate hardness, and 69% with standard baseballs. CONCLUSION: In this experimental model of low-energy chest wall impact, safety baseballs reduced (but did not abolish) the risk of sudden cardiac death. More universal use of these safety baseballs may decrease the risk of sudden death on the playing field for young athletes.

Animals↗
PubMed2002

Adverse cardiovascular events temporally associated with ma huang, an herbal source of ephedrine.

OBJECTIVE: To evaluate possible cardiovascular toxic effects associated with use of dietary supplements containing ma huang, an herbal source of ephedrine. METHODS: We reviewed the comprehensive database Adverse Reaction Monitoring System of the Food and Drug Administration, which included clinical records, investigative reports, and autopsy reports related to ma huang use. The main outcome measurements were stroke, myocardial infarction, and sudden death. RESULTS: From 1995 to 1997, 926 cases of possible ma huang toxicity were reported to the Food and Drug Administration. In 37 patients (23 women and 14 men with a mean +/- SD age of 43 +/- 13 years), use of ma huang was temporally related to stroke (in 16), myocardial infarction (in 10), or sudden death (in 11). Autopsies performed in 7 of the 11 patients who experienced sudden death showed a normal heart in 1, coronary atherosclerosis in 3, and cardiomyopathies in 3. In 36 of the 37 patients, use of ma huang was reported to be within the manufacturers' dosing guidelines. CONCLUSIONS: Analysis of the 37 patients indicates the following findings: (1) ma huang use is temporally related to stroke, myocardial infarction, and sudden death; (2) underlying heart or vascular disease is not a prerequisite for ma huang-related adverse events; and (3) the cardiovascular toxic effects associated with ma huang were not limited to massive doses. Although the pathogenesis of the cardiac toxic effects of ma huang remains incompletely defined, available observational and circumstantial evidence indicates that use of the substance may be associated with serious medical complications.

Adult↗