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Biomedical subjects

Anthony Tang

Publications and source records attributed to Anthony Tang.

8 recordsLinked to original sources
PubMed2007

Right ventricular apical pacing: a necessary evil?

PURPOSE OF REVIEW: Clinical trial evidence suggests that traditional right ventricular apical pacing may be harmful. This review summarizes the existing evidence and outlines the major avenues of ongoing research in this field. RECENT FINDINGS: Despite theoretical advantages of dual-chamber pacing, large randomized trials found only a small advantage over single-chamber ventricular pacing. Subsequent analysis of one of these trials suggested that this was due to the tendency for dual-chamber pacemakers to produce frequent, unnecessary right ventricular pacing. This hypothesis is supported by a prospective study among defibrillator recipients, showing that dual-chamber pacing results in a very high frequency of ventricular pacing and worse clinical outcomes, compared with backup ventricular pacing. These observations have led to a renewed interest in single-chamber atrial pacing for sinus node dysfunction, the development of new dual-chamber pacemaker algorithms designed to minimize right ventricular pacing, and the search for better ways to pace the ventricles in patients who require ventricular pacing. SUMMARY: Conventional right ventricular apical pacing should be avoided whenever possible. In patients who require ventricular pacing, ongoing research will determine if selected-site pacing or multisite pacing improves clinical outcomes compared with traditional right ventricular apical pacing.

Arrhythmias, Cardiac↗
PubMed2006

Improving SVT discrimination in single-chamber ICDs: a new electrogram morphology-based algorithm.

INTRODUCTION: Wide-spread adoption of ICD therapy has focused efforts on improving the quality of life for patients by reducing "inappropriate" shock therapies. To this end, distinguishing supraventricular tachycardia from ventricular tachycardia remains a major challenge for ICDs. More sophisticated discrimination algorithms based on ventricular electrogram morphology have been made practicable by the increased computational ability of modern ICDs. METHODS AND RESULTS: We report results from a large prospective study (1,122 pts) of a new ventricular electrogram morphology tachycardia discrimination algorithm (Wavelet Dynamic Discrimination, Medtronic, Minneapolis, MN, USA) operating at minimal algorithm setting (RV coil-can electrogram, match threshold of 70%). This is a nonrandomized cohort study of ICD patients using the morphology discrimination of the Wavelet algorithm to distinguish SVT and VT/VF. The Wavelet criterion was required ON in all patients and all other supraventricular tachycardia discriminators were required to be OFF. Spontaneous episodes (N = 2,235) eligible for ICD therapy were adjudicated for detection algorithm performance. The generalized estimating equations method was used to remove bias introduced when an individual patient contributes multiple episodes. Inappropriate therapies for supraventricular tachycardia were reduced by 78% (90% CI: 72.8-82.9%) for episodes within the range of rates where Wavelet was programmed to discriminate. Sensitivity for sustained ventricular tachycardia was 98.6% (90% CI: 97-99.3%) without the use of high-rate time out. CONCLUSIONS: Results from this prospective study of the Wavelet electrogram morphology discrimination algorithm operating as the sole discriminator in the ON mode demonstrate that inappropriate therapy for supraventricular tachycardia in a single-chamber ICD can be dramatically reduced compared to rate detection alone.

Algorithms↗
PubMed2006

Reasons for escalating pacemaker implants.

Surveys of pacing practice have shown a steady increase in pacemaker implantation rates in the past 15 years, despite no major changes in United States guidelines for permanent pacing. There are no data to explain why this is occurring. In this study, records were extracted from the National Hospital Discharge Survey to investigate this. There were 3 major findings. First, age-adjusted implantation rates increased progressively over the study period from 370 per million in 1990 to 612 per million in 2002. Second, it was found that the escalating implantation rate is attributable to increasing implantation for isolated sinus node dysfunction (SND). Implantation for SND increased significantly over the study period (by 102%), whereas implantation for all other indications did not. The increasing implantation for SND is due primarily to the increasing prevalence of SND, with a lesser increase in implantation rate relative to prevalence rate. The third major finding of this study is that there has been a progressive relative and absolute increase in the dual-chamber implantation rate. In 2002, 82.8% of all initial pacemaker implantations were dual-chamber devices. Furthermore, the National Hospital Discharge Survey data indicate that the major randomized pacing trials seem to have had no impact on pacing practice in the United States. In conclusion, age-adjusted implantation rates increased progressively over the study period. This escalating implantation rate is primarily attributable to increasing implantation for SND.

Age Factors↗
PubMed2005

Comparison of induced and spontaneous atrial tachyarrhythmias in patients with a history of spontaneous atrial tachyarrhythmias.

INTRODUCTION: This retrospective study investigated whether induced episodes could be used to predict the morphology of future spontaneous atrial episodes. METHODS: Eighty-two patients (64 +/- 12 years; 77% male; CAD in 60%; left ventricular ejection fraction 45 +/- 16%) with a history of atrial tachycardia or atrial fibrillation (AT/AF) were implanted with a dual-chamber implantable cardioverter defibrillator (ICD) and followed for 6 months. A total of 224 episodes of induced and spontaneous AT/AF were classified into type I, II, and III according to the method of Israel et al. and then compared based on average cycle length (CL) and atrial amplitude. Episodes were also grouped as "pace-terminable" or "nonpace-terminable" based on the CL definition of Gillis et al. RESULTS: The analysis of 121 induced episodes (from 80 patients) and 103 spontaneous episodes (from 43 patients) showed that within each arrhythmia type, there were no significant differences in CL or mean amplitude between induced and spontaneous episodes. Additional analysis of patients that had both induced and spontaneous episodes (n = 41) showed 78% had at least one spontaneous episode that matched the induced episode. Fifty-seven percent of spontaneous episodes were considered to be pace-terminable based on CL. CONCLUSIONS: Our data suggest that there is no significant difference between induced and spontaneous episodes of AT/AF of the same type. The majority of patients had at least one spontaneous episode of the same type as the induced episode, showing that induced atrial arrhythmias may be useful in predicting the morphology of future spontaneous episodes and in identifying patients potentially benefiting from atrial antitachycardia pacing.

Adult↗
PubMed2005

Implanted cardioverter defibrillators for the prevention of sudden death.

Implantable cardioverter defibrillators (ICDs) are effective in preventing sudden death from ventricular arrhythmias. Recent clinical trials have demonstrated reductions in all-cause mortality in ICD-treated patients, especially those with severe left ventricular dysfunction. However, selecting appropriate patients for ICD implantation, especially for the primary prophylaxis of all-cause death, is a challenge. Patients with recent myocardial infarction (less than 40 days) or those that have just undergone coronary artery bypass graft surgery do not benefit from ICD implantation. On average, annual death rates are reduced by 1.5% to 3.0%, but the risk of death in an individual patient is hard to quantify. Poor left ventricular function is the best predictor of both mortality risk and ICD benefit. Other risk predictors need to be identified.

Death, Sudden, Cardiac↗
PubMed2004

Use of implantable cardioverter defibrillators after out-of-hospital cardiac arrest: a prospective follow-up study.

BACKGROUND: Survivors of out-of-hospital cardiac arrest are at high risk of recurrent arrests, many of which could be prevented with implantable cardioverter defibrillators (ICDs). We sought to determine the ICD insertion rate among survivors of out-of-hospital cardiac arrest and to determine factors associated with ICD implantation. METHODS: The Ontario Prehospital Advanced Life Support (OPALS) study is a prospective, multiphase, before-after study assessing the effectiveness of prehospital interventions for people experiencing cardiac arrest, trauma or respiratory arrest in 19 Ontario communities. We linked OPALS data describing survivors of cardiac arrest with data from all defibrillator implantation centres in Ontario. RESULTS: From January 1997 to April 2002, 454 patients in the OPALS study survived to hospital discharge after experiencing an out-of-hospital cardiac arrest. The mean age was 65 (standard deviation 14) years, 122 (26.9%) were women, 398 (87.7%) had a witnessed arrest, 372 (81.9%) had an initial rhythm of ventricular tachycardia or ventricular fibrillation (VT/VF), and 76 (16.7%) had asystole or another arrhythmia. The median cerebral performance category at discharge (range 1-5, 1 = normal) was 1. Only 58 (12.8%) of the 454 patients received an ICD. Patients with an initial rhythm of VT/VF were more likely than those with an initial rhythm of asystole or another rhythm to undergo device insertion (adjusted odds ratio [OR] 9.63, 95% confidence interval [CI] 1.31-71.50). Similarly, patients with a normal cerebral performance score were more likely than those with abnormal scores to undergo ICD insertion (adjusted OR 12.52, 95% CI 1.74-92.12). INTERPRETATION: A minority of patients who survived cardiac arrest underwent ICD insertion. It is unclear whether this low usage rate reflects referral bias, selection bias by electrophysiologists, supply constraint or patient preference.

Age Distribution↗