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Biomedical subjects

Bruce D Lindsay

Publications and source records attributed to Bruce D Lindsay.

17 recordsLinked to original sources
PubMed2006

Relation of T-wave alternans to regional left ventricular dysfunction and eccentric hypertrophy secondary to coronary heart disease.

Left ventricular (LV) hypertrophy and structural disease are associated with exaggerated repolarization dispersion and risk for cardiac arrest. We hypothesized that T-wave alternans (TWA) from the electrocardiogram, reflecting proarrhythmic repolarization dispersion, would increase with extent of eccentric LV hypertrophy and vary spatially with the distribution of myocardial scar. We studied 28 patients with coronary disease, systolic dysfunction, and nonsustained ventricular tachycardia. On echocardiography, 21 patients had wall motion abnormalities and 20 had LV hypertrophy (mass index > or =100 g/m(2)). TWA magnitude (voltage of alternation), which was computed spectrally during ventricular stimulation, varied linearly with LV mass index (p = 0.003). Spatially, positive TWA (magnitude > or =1.9 microV) in orthogonal electrocardiographic axes overlaid scar or wall motion abnormalities in corresponding echocardiographic segments (p <0.05 in x and y axes). After a follow-up of 35 +/- 13 months, positive TWA predicted the combined end point of death or sustained ventricular arrhythmias in all patients (p = 0.025), with a trend for those with echocardiographic LV hypertrophy (p = 0.058). In conclusion, in patients with systolic dysfunction due to coronary artery disease, TWA may indicate arrhythmic contributions from regional myocardial scar and eccentric LV hypertrophy.

Aged↗
PubMed2006

Radiofrequency ablation of atrioventricular nodal reentrant tachycardia using a novel magnetic guidance system compared with a conventional approach.

BACKGROUND: A novel magnetic guidance system has been developed that allows the operator to remotely navigate an electrophysiology mapping/ablation catheter to precise locations in the heart for treatment of tachyarrhythmias. To date, this new technology has not been directly compared with the conventional approach. OBJECTIVE: To compare the use of the magnetic guidance system to the conventional approach for ablation of atrioventricular nodal reentry tachycardia. METHODS: Between November 2002 and October 2004, 28 patients with atrioventricular nodal reentry tachycardia treated with the magnetic guidance system were retrospectively compared with 28 matched control patients. RESULTS: Patients treated using the magnetic guidance system had similar procedure durations and fluoroscopy times compared with the matched controls. The only statistically significant difference between the groups was a longer time between insertion of the ablation catheter and placement of the first radiofrequency lesion in the magnetic guidance system cohort (23.3 +/- 12.0 vs. 10.5 +/- 13.9, p=0.001), possibly due to the research protocol. However, there was a trend toward a shorter total time that radiofrequency energy was applied in the magnetic guidance system cohort (5.2 +/- 4.5 vs. 8.0 +/- 7.2, p=0.087). There were no major complications or recurrences after at least 3 months of follow-up among the patients treated with the magnetic guidance system. CONCLUSION: The magnetic guidance system appears to have similar, and possibly improved, clinical efficacy compared with conventional catheter navigation for the treatment of atrioventricular nodal reentrant tachycardia.

Adolescent↗
PubMed2006

Smokers are at markedly increased risk of appropriate defibrillator shocks in a primary prevention population.

BACKGROUND: Cigarette smoking is a known risk factor for sudden cardiac death (SCD). It is unknown whether smoking status affects implantable cardioverter-defibrillator (ICD) therapy. OBJECTIVE: The primary end point was appropriate ICD therapy according to smoking status. METHODS: A total of 105 consecutive patients who underwent ICD implantation for primary prevention of SCD were retrospectively analyzed. All patients had an abnormal response to programmed ventricular stimulation performed for nonsustained ventricular tachycardia in the setting of ischemic cardiomyopathy between January 1999 and December 2003. RESULTS: Among the 105 patients, 6 (37.5%) of 16 current smokers, 14 (25.9%) of 54 former smokers, and 2 (5.7%) of 35 of never smokers received an appropriate ICD therapy (P = .02). Kaplan-Meier analysis for survival free of appropriate ICD therapy comparing never smokers with both current smokers (P = .002) and former smokers (P = .01) demonstrated statistically significant differences by log rank over a mean follow-up of 21.8 +/- 13.7 months. Cox regression analysis found that current smoking was associated with an increased risk of appropriate therapy (hazard ratio 7.36; 95% confidence interval 1.42-38.10; P = .02) as was former smoking (hazard ratio 5.42; 95% confidence interval 1.20-24.47; P = .03). There was no difference in inappropriate therapy between groups (P = .12). CONCLUSIONS: Cigarette smoking is an independent predictor of appropriate ICD therapy in a primary prevention population. While outcomes differences among current smokers, former smokers, and never smokers are demonstrable, the effect of smoking cessation on ICD therapy requires further study.

Aged↗
PubMed2006

Use of magnetic navigation to facilitate transcatheter alcohol septal ablation for hypertrophic obstructive cardiomyopathy.

We describe a case of a 50-year-old male with hypertrophic obstructive cardiomyopathy (HOCM) who presented with syncope, progressively limiting dyspnea and chest discomfort. Coronary angiography showed an unusually extreme angle (approximately 130 degrees) to the origin of the major septal artery. After conventional guidewire cannulation failed, use of magnetic navigation with the Stereotaxis Niobe system permitted guidewire and balloon catheter cannulation of the septal artery to facilitate successful transcatheter alcohol septal ablation.

Alcohols↗
PubMed2005

T-wave alternans phase following ventricular extrasystoles predicts arrhythmia-free survival.

OBJECTIVE: The purpose of this study was to assess the value of T-wave alternans (TWA) following ventricular extrasystoles in predicting arrhythmia-free survival. BACKGROUND: Stratifying risk for sudden death in patients with coronary disease and moderate left ventricular (LV) dysfunction remains a challenge. We hypothesized that, in such patients, a discontinuity in beat-to-beat T-wave alternation (TWA phase reversal) following single ventricular extrasystoles reflects transiently exaggerated repolarization dispersion, and predicts spontaneous ventricular arrhythmias. METHODS: We studied 59 patients with ischemic LV dysfunction (mean LV ejection fraction 38.7 +/- 5.3%) and nonsustained ventricular tachycardia undergoing programmed stimulation. TWA was computed spectrally from the ECG during ventricular pacing, and TWA phase reversal was reflected by a discontinuity in T-wave oscillation after single ventricular extrasystoles. RESULTS: Patients induced into ventricular arrhythmias (n = 36) had greater TWA magnitude (V(alt): 6.60 +/- 6.46 microV vs 2.61 +/- 1.97 microV; P = .001) and more frequent TWA phase reversal (62.1% vs 44.4%; P = .02) than those who were not (n = 23). During a mean follow-up of 36 +/- 12 months, positive TWA (V(alt) > or =1.9 microV) and TWA phase reversal both (P < .05) predicted events (all-cause mortality, ventricular tachycardia, ventricular fibrillation). Univariate predictors of arrhythmia-free survival were TWA phase reversal (P < .005), positive TWA (P < .05), age (P = .008), and LV mass index (P = .043). On multivariate analysis, only TWA phase reversal and age predicted events; if TWA phase was excluded, only positive TWA and age predicted events. CONCLUSION: Phase reversal in TWA following ventricular extrasystoles predicts spontaneous ventricular arrhythmias and all-cause mortality in patients with moderate ischemic LV dysfunction and was a better predictor than positive TWA or programmed ventricular stimulation.

Aged↗
PubMed2005

Implantable cardioverter-defibrillator therapy improves long-term survival in patients with unexplained syncope, cardiomyopathy, and a negative electrophysiologic study.

OBJECTIVES: The purpose of this study was to evaluate the long-term outcomes of patients with unexplained syncope, ischemic or nonischemic cardiomyopathy, and a negative electrophysiologic study (EPS). BACKGROUND: EPS is frequently performed to evaluate syncope in patients with left ventricular dysfunction. Limited long-term data evaluating all-cause mortality in patients with no inducible arrhythmia or examining the potential benefits from implantable cardioverter-defibrillator (ICD) therapy are available. METHODS: We evaluated 102 consecutive patients with unexplained syncope, cardiomyopathy, and a negative EPS from September 1996 to December 2000. A blinded matched case-control analysis utilized 51 of these patients (19 treated with an ICD and 32 matched controls treated with conventional therapy). We compared primary endpoint of death and documented cardiac arrest of patients treated with ICD therapy to matched controls. RESULTS: Baseline characteristics were similar between groups. There were 14 primary events among the study population during a follow-up period of 44.3 +/- 20 months: 2 in the ICD group and 12 in the conventional therapy group. The hazard ratio for the risk of event in the ICD group compared with the conventional therapy group was 0.18 (95% confidence interval, 0.04-0.85; P = .04). Other comorbid conditions, including age, sex, ischemic etiology of heart failure, ejection fraction, and antiarrhythmic use, did not predict outcome. Appropriate ICD shocks occurred in 26% of patients at 2 years. CONCLUSIONS: This study suggests that empiric ICD therapy improves long-term outcomes in patients with unexplained syncope, ischemic or nonischemic cardiomyopathy, and negative EPS.

Aged↗
PubMed2003

Magnetic guidance system for cardiac electrophysiology: a prospective trial of safety and efficacy in humans.

OBJECTIVES: We evaluated in humans the safety and efficacy of a novel magnetic guidance system (MGS) for electrophysiological mapping, pacing, and ablation. BACKGROUND: Catheter ablation of atrial fibrillation and other complex arrhythmias requires precise catheter manipulation and stabilization. We have shown in animals that the MGS can precisely manipulate a mapping catheter within the heart with an external magnetic field rather than manual catheter control. METHODS: Thirty-one adults referred for diagnostic electrophysiology studies were enrolled in a prospective trial of the MGS. The magnetic catheter was navigated to preselected sites in the right atrium (RA) and right ventricle (RV) in the first 20 patients. Electrograms were recorded at each target site, and pacing thresholds were measured. In a subset of five patients, RA and RV electrograms and stimulation thresholds were recorded with both a standard ablation catheter and the magnetic catheter. Eleven additional patients were recruited for supraventricular tachycardia (SVT) mapping, and seven of these underwent ablation. RESULTS: Navigation was successful in 200 of 202 predetermined right-sided navigation targets and 13 of 13 targets in the left atria. Pacing thresholds and electrogram amplitudes in the RA and RV were not significantly different between the standard and magnetic catheters. The SVT mapping with the magnetic catheter was successful in 13 patients, including 4 with left-sided accessory pathways. The MGS was used for successful ablation of SVT in seven of seven patients. There were no procedural complications. CONCLUSIONS: These results demonstrate that the MGS can be used for intracardiac mapping, pacing, and ablation safely and effectively.

Adult↗