New age- and sex-specific criteria for QT prolongation based on rate correction formulas that minimize bias at the upper normal limits.

BACKGROUND: Existing formulas for rate-corrected QT (QTc) commonly fail to properly adjust the upper normal limits which are more critical than the mean QTc for evaluation of prolonged QT. Age- and sex-related differences in QTc are also often overlooked. Our goal was to establish criteria for prolonged QTc using formulas that minimize QTc bias at the upper normal limits. METHODS AND RESULTS: Strict criteria were used in selecting a study group of 57,595 persons aged 5 to 89 years (54% women) and to exclude electrocardiograms (ECG) with possible disease-associated changes. Two QT rate adjustment formulas were identified which both minimized rate-dependency in the 98 th percentile limits: QTcmod, based on an electrophysiological model (QTcMod = QTx(120 + HR)/180)), and QTcLogLin, a power function of the RR interval with exponents 0.37 for men and 0.38 for women. QTc shortened in men during adolescence and QTcMod became 13 ms shorter than in women at age 20-29 years. The sex difference was maintained through adulthood although decreasing with age. The criteria established for prolonged QTc were: Age < 40 years, men 430 ms, women 440 ms; Age 40 to 69, men 440 ms, women 450 ms; Age ≥ 70 years, men 455 ms, and women 460 ms. CONCLUSIONS: Sex difference in QTc originates from shortened QT in adolescent males. Upper normal limits for QTc vary substantially by age and sex, and it is essential to use age- and sex-specific criteria for evaluation of QT prolongation.

Dofetilide-induced long QT and torsades de pointes.

Dofetilide, a new class III antiarrhythmic agent, has been approved as an antiarrhythmic agent for the treatment of atrial fibrillation and atrial flutter. Dofetilide selectively inhibits the rapid component of the delayed rectifier potassium current resulting in a prolongation of the effective refractory period. Like other drugs that affect potassium currents, the prolonged QT interval occurring in the patients treated with dofetilide can be complicated by torsades de pointes. We report four cases of dofetilide-induced QT prolongation and torsades de pointes. We discuss the risk factors for the development of dofetilide-induced long QT and torsades de pointes and review the current literature.

Pacemaker longevity: the world's longest-lasting VVI pacemaker.

OBJECTIVE: To describe VVI-pacemaker longevity by model type at our institution and report on a long-lasting model and the longest-lasting pacemaker to be described in the literature. BACKGROUND: Cardiac pacemakers are becoming increasingly common in the United States. Presently their batteries are expected to last up to 12 years. Pacemaker generator change is associated with increased cost to the health care system and is inconvenient for patients. METHODS: After identifying a group of very long-lasting CPI Microlith 605 VVI pulse generators, we reviewed records on all patients who had either Guidant or Medtronic pulse generator explantation at our institution over a 10-year period. Average longevities were calculated for all VVI pacemakers, four common VVI models, and the CPI Microlith 605. RESULTS: A total of 105 VVI-programmed pacemakers were identified. Their average longevity was 7.2 years. The two most common Medtronic VVI-programmed pacemakers explanted were the Thera (7.1 years) and Kappa (7.3 years). The two most common Guidant/CPI models were the Vigor (4.2 years) and Discovery (5.7 years). The CPI Microlith 605 (19.2 years) lasted more than 26 years in one patient before being explanted. CONCLUSION: At a time when pacemakers are being used more frequently, pacemaker longevity may decrease as a result of the use of dual-chamber pacing systems. In our study, the CPI Microlith 605 had an average longevity more than twice that of all other VVI pacemakers. We also report on a pulse generator that lasted 26.3 years.

Lightning-induced ventricular fibrillation.

We present a case of a previously healthy 17 year-old white male boy scout who collapsed after a lightning strike, and was found to be in ventricular fibrillation when emergency medical services arrived. The ventricular fibrillation was defibrillated into sinus rhythm after a single direct current (DC) countershock. However, the patient has remained in coma. Commotio cordis, sudden cardiac death from low-energy chest wall impact, is a phenomenon in which an exactly timed and located blow on the chest during the cardiac cycle results in ventricular fibrillation. Commotio cordis and electrical shock can both result in ventricular arrhythmias. We speculate that in this patient, ventricular fibrillation began immediately after the lightning, which probably struck at the peak of the T wave. (Cardiol J 2007; 14: 91-94).

The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study: approaches to control rate in atrial fibrillation.

OBJECTIVES: We sought to evaluate approaches used to control rate, the effectiveness of rate control, and switches from one drug class to another in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study. BACKGROUND: The AFFIRM study showed that atrial fibrillation (AF) can be treated effectively with rate control and anticoagulation, but drug efficacy to control rate remains uncertain. METHODS: Patients (n = 2,027) randomized to rate control in the AFFIRM study were given rate-controlling drugs by their treating physicians. Standardized rate-control efficacy criteria developed a priori included resting heart rate and 6-min walk tests and/or ambulatory electrocardiographic results. RESULTS: Average follow-up was 3.5 +/- 1.3 years. Initial treatment included a beta-adrenergic blocker (beta-blocker) alone in 24%, a calcium channel blocker alone in 17%, digoxin alone in 16%, a beta-blocker and digoxin in 14%, or a calcium channel blocker and digoxin in 14% of patients. Overall rate control was achieved in 70% of patients given beta-blockers as the first drug (with or without digoxin), 54% with calcium channel blockers (with or without digoxin), and 58% with digoxin alone. Adequate overall rate control was achieved in 58% of patients with the first drug or combination. Multivariate analysis revealed an association between first drug class and several clinical variables. There were more changes to beta-blockers than to the other two-drug classes (p < 0.0001). CONCLUSIONS: Rate control in AF is possible in the majority of patients with AF. Beta-blockers were the most effective drugs. To achieve the goal of adequate rate control in all patients, frequent medication changes and drug combinations were needed.

Lower observed versus expected (based on U.S. age and gender specific rates) survival in patients treated for near-fatal ventricular arrhythmias.

Implantable cardioverter defibrillators (ICDs) have improved survival for patients with ventricular fibrillation (VF) or sustained vertricular tachycardia (VT). However, the survival of these patients compared to the general population has not been assessed. Observed survival rates for patients randomized to either antiarrhythmic drug therapy (mainly amiodarone) arm or ICD arm were compared to expected rates, calculated using age and sex-specific survival rates derived from the 1989-1991 US population life tables and applied to the age and sex distribution of patients in each arm. Consistent with the results of the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial, patients randomized to receive ICDs experienced significantly higher survival than those in the drug arm; however, both groups experienced significantly lower survival than expected using age and gender matched U.S. survival rates. Within arms, the difference between the observed and expected rates increased over 3 years of follow-up from 7.7% to 15.3% for the ICD arm, and from 14.6% to 26.4% for the drug arm. These results quantify the improvements in survival that can be expected for VF or VT patients using drug or ICD therapies and underscore the need for continued research into methods for further improving the overall level of health of these patients.

Driving and arrhythmias: implications of new data.

Patients with ventricular arrhythmias are often restricted from driving by their physicians for several months. These recommendations are based more on convention than evidence, due to the paucity of data previously available on the safety of driving in these patients. Over the past few years, however, more data have become available that suggests that it is safe to drive within three months of their ventricular tachyarrhythmia. In this paper, we look at this more recent data and make the suggestion that patients with well maintained cardiac function, no recurrent ventricular arrhythmias (i.e. electrical storm) and no persistent medical condition predisposing them to ventricular arrhythmias should be allowed to resume driving soon after their ventricular tachyarrhythmia.

Cost-effectiveness of the implantable cardioverter-defibrillator versus antiarrhythmic drugs in survivors of serious ventricular tachyarrhythmias: results of the Antiarrhythmics Versus Implantable Defibrillators (AVID) economic analysis substudy.

BACKGROUND: The implantable cardioverter-defibrillator (ICD) is an effective but expensive device. We used prospectively collected data from a large randomized clinical trial of secondary prevention of life-threatening ventricular arrhythmias to determine the cost-effectiveness of the ICD compared with antiarrhythmic drug (AAD) therapy, largely with amiodarone. METHODS AND RESULTS: Charges for initial and repeat hospitalizations, emergency room, and day surgery stays and the costs of antiarrhythmic drugs were collected on 1008 patients. Detailed records of all other medical encounters and expenses were collected on a subgroup of 237 patients. Regression models were then created to attribute these expenses to the rest of the patients. Charges were converted to 1997 costs using standard methods. Costs and life years were discounted at 3% per year. Three-year survival data from the Antiarrhythmics Versus Implantable Defibrillators trail were used to calculate the base-case cost-effectiveness (C/E) ratio. Six-year, twenty-year, and lifetime C/E ratios were also estimated. At 3 years, total costs were $71 421 for a patient taking AADs and $85 522 for a patient using an ICD, and the ICD provided a 0.21-year survival benefit over AAD treatment. The base-case C/E ratio was thus $66 677 per year of life saved by the ICD compared with AAD therapy (95% CI, $30 761 to $154 768). Six- and 20-year C/E ratios remained stable between $68 000 and $80 000 per year of life saved. CONCLUSIONS: The ICD is moderately cost-effective for secondary prevention of life-threatening ventricular arrhythmias, as judged from prospectively collected data in a randomized clinical trial.