Anthony D. Mercando

Long-Term efficacy of antitachycardia pacing for supraventricular and ventricular tachycardias

Over a 14-year period, 53 patients received implanted pacemakers to assist in the control of recurrent tachycardias. Indications were: prevention of tachycardia in 2 patients with supraventricular tachycardia (SVT), and 4 with ventricular tachycardia (VT); termination of tachycardia (15 SVT, 20 VT); and long-term periodic programmed electrical stimulation with potential for tachycardia termination (12 VT). Pacemakers for prevention of VT were implanted in 3 patients with prolonged QT interval syndromes and 1 in whom Holter monitoring showed a significant reduction in ectopic activity during pacing. Pacers were implanted for tachycardia termination only after patients underwent a rigorous protocol aimed at achieving 100 trials of the proposed modality. Patients with tachycardia also requiring antibradycardia pacemakers received pacemakers capable of noninvasive programmed stimulation for use during follow-up. There were no tachycardia recurrences among those patients in whom pacemakers were implanted for prevention. Pacers capable of outpatient programmed stimulation were useful, and it may be desirable to expand their use. The 15 patients with pacers designed for termination of SVT were followed for a mean of 68 months. Among these, actuarial continuation of pacing efficacy was 93% at 1 year, and 78% at 5 years. The 20 patients with pacers for termination of VT were followed for a mean of 37 months. Actuarial efficacy was 78% at 1 year, and 55% at 5 years. Sudden death occurred in 4 of these patients, none clearly pacer related. Pacemakers can play a major therapeutic role in some patients with recurrent tachycardias. The role of such pacemakers in patients with VT may be expanded with the advent of combined pacer-defibrillators.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical devices for treatment of arrhythmias

Electrical devices can be used for preventing and terminating tachycardia and for achieving hemodynamic improvement during a continuing tachycardia. Conventional approaches to tachycardia prevention include pacing at physiologic rates to prevent brady-cardia-related tachycardia or tachycardias associated with prolonged QT-interval syndromes. More exotic techniques, such as those involving stimulation during the refractory period, are undergoing investigation. Some tachycardias cannot be easily terminated or recur incessantly. Hemodynamics can be improved by pacing methods that result in a narrower QRS complex by coupled pacing and, in supraventricular tachycardias, by pacing rapidly enough to create atrioventricular block. Most clinical tachycardias are caused by reentry. Careful analysis of the timing of individual stimuli that successfully terminate tachycardias indicate that critical relations exist in the conduction velocity, refractoriness and physical properties and dimensions of the reentry circuit and the remaining myocardium. Elucidating these relations has permitted inferences into the mechanisms by which pacing terminates or accelerates tachycardias. A vast number of pacing patterns have evolved for use in tachycardia termination. None of these appear to be foolproof. There is widespread and justified concern about the risk of acceleration of tachycardia when antitachycardia pacing is used in the ventricle. Experience indicates that only a few patients are suitable for termination of ventricular tachycardia by pacing, but these carefully selected patients may do well. Both the results and the potential for widespread use may be better with pacing for termination of supraventricular tachycardia. Life-threatening tachycardias or fibrillation can be terminated by direct-current countershock. Although many technical problems remain, implantable cardioverter-defibrillators, possibly combined with antitachycardia pacemakers, will play an increasing role in the management or serious arrhythmias.

Prevalence of coronary artery disease, complex ventricular arrhythmias, and silent myocardial ischemia and incidence of new coronary events in older persons with chronic renal insufficiency and with normal renal function

In a prospective study of 98 persons > or = 65 years of age with chronic renal insufficiency (serum creatinine > 3.0 mg/dl) for > 1 year and 98 age- and sex-matched persons with normal renal function (serum creatinine < or = 1.2 mg/dl), new coronary events developed at 23-month follow-up in 69 persons (70%) with chronic renal insufficiency and at 48-month follow-up in 24 persons (24%) with normal renal function (p < 0.0001). Significant independent risk factors for new coronary events were age (risk ratio 1.1), prior coronary artery disease (risk ratio 3.5), complex ventricular arrhythmias diagnosed by 24-hour ambulatory electrocardiography (risk ratio 2.5), silent myocardial ischemia diagnosed by 24-hour ambulatory electrocardiography (risk ratio 1.9), and chronic renal insufficiency (risk ratio 3.4).

Decrease in mortality by propranolol in patients with heart disease and complex ventricular arrhythmias is more an anti-ischemic than an antiarrhythmic effect

Abstract We reported in a prospective, randomized study of 245 patients (mean age 81 years) with heart disease, complex ventricular arrhythmias, and a left ventricular ejection fraction of ≥40% that, compared with no antiarrhythmic drug, propranolol caused a 47% significant decrease in sudden cardiac death, a 37% significant decrease in total cardiac death, and a 20% insignificant decrease in total death. 1 Follow-up 24-hour ambulatory electrocardiograms were obtained in 112 of 123 patients (91%) treated with propranolol and in 109 of 122 patients (89%) treated with no antiarrhythmic drug. This article presents data correlating the reduction in mortality by propranolol with reduction in complex ventricular arrhythmias and in abolition of myocardial ischemia.

Automatic methods for detection of tachyarrhythmias by antitachycardia devices

Electrical devices play an increasingly important role in the control of tachyarrhythmias. Antitachycardia pacing and automatic defibrillation have been severely limited by the poor specificity of tachycardia discrimination in commercially available devices. Although absolute heart rate has been the principal means of automatic diagnosis, several new detection algorithms and methods are being investigated. Multiple electrode timing comparison, signal processing and pattern recognition are employed in these newer techniques. Although each offers some improvement over present technology, none is capable of identifying all arrhythmias. The methods employing comparison of atrial and ventricular rates, without additional criteria, are unable to detect ventricular tachycardia in the presence of 1:1 retrograde conduction. Electrographic analysis techniques require very stable electrodes and may not tolerate normal morphologic variations. A combination of two or more approaches may ultimately be required. All techniques will require that certain critical variables be programmable to allow for individualization in each clinical situation. Soft-ware-controllable devices and those capable of sensing from both the atria and the ventricles will provide the sophistication necessary for the implementation of complex tachycardia detection algorithms. This report reviews automatic tachycardia detection techniques in current use and under investigation.

Prevalence of and association between silent myocardial ischemia and new coronary events in older men and women with and without cardiovascular disease.

OBJECTIVES: To investigate the prevalence of silent ischemia (SI) in older men and women detected by 24‐hour ambulatory electrocardiograms (AECGs) and the association between SI and new coronary events.

Prognostic value of the changes in the mode of ventricular tachycardia induction during therapy with amiodarone or amiodarone and a class 1A antiarrhythmic agent

The prognostic value of 3 previously reported programmed stimulation efficacy criteria was studied in 70 patients taking amiodarone for sustained ventricular tachycardia (VT). At baseline all patients had VT inducible by programmed stimulation. After amiodarone loading (935 +/- 271 mg/day for 16 +/- 7 days), efficacy of amiodarone was determined by 3 programmed stimulation criteria (criterion I = VT not inducible or 15 beats or less; criterion II = VT not inducible or harder to induce; criterion III = VT not easier to induce). Amiodarone was effective in 12, 25 and 49 of 70 patients by criteria I, II and III, respectively. There were 16 recurrences or cardiac arrest during the follow-up period (19 +/- 19 months). Actuarial arrhythmia-free survival rates at 1 and 2 years were: 90% and 90% in patients with efficacy by criterion I and 78% and 78% in patients with inefficacy, respectively; 84% and 84% in patients with efficacy by criterion II and 78% and 78% in patients with inefficacy, respectively; and 80% and 80% in patients with efficacy by criterion III and 79% and 79% in patients with inefficacy, respectively (difference not significant for all). From the results of follow-up at 2 years, sensitivities of criteria I, II and III were 92%, 75% and 33%, respectively. Specificities were 17%, 26% and 70%, respectively, and predictive accuracies were 43%, 43% and 67%, respectively. Thus, patients with efficacy by criterion I appear to have a better prognosis when compared with patients with inefficacy. However, many patients with inefficacy by criterion I had a good outcome (nonspecificity).(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of silent myocardial ischemia detected by 24-hour ambulatory electrocardiography, and its association with new coronary events at 40-month follow-up in elderly diabetic and nondiabetic patients with coronary artery disease

Abstract Patients with diabetes mellitus have a higher prevalence and incidence of coronary artery disease (CAD) than nondiabetic patients. The prevalence of silent myocardial ischemia was found to be increased in diabetic patients by some investigators,1,2 but not by others.3,4 We report the results from a prospective study determining the prevalence of silent myocardial ischemia and the incidence of new coronary events associated with silent ischemia in diabetic and nondiabetic patients with CAD.

Combination of disopyramide and mexiletine for better tolerance and additive effects for treatment of ventricular arrhythmias

The efficacy and tolerance of disopyramide and mexiletine used alone and in combination were studied in 21 patients with frequent (greater than or equal to 30/h) ventricular premature complexes. Ambulatory electrocardiographic monitoring was performed at baseline and during therapy with disopyramide alone, mexiletine alone and a combination of disopyramide and mexiletine. During single drug therapy, the dose of disopyramide was 602 +/- 152 mg/day and that of mexiletine was 738 +/- 144 mg/day. During combination therapy with smaller doses of disopyramide (524 +/- 134 mg/day) and mexiletine (652 +/- 146 mg/day), no patient had side effects. At baseline before therapy, the mean number of ventricular premature complexes per hour, was 608 +/- 757, of couplets per hour was 22.4 +/- 45.8 and of episodes of nonsustained ventricular tachycardia/24 h was 219.7 +/- 758.2. The mean number of ventricular premature complexes per hour was reduced to 156 +/- 217 with disopyramide alone, 188 +/- 298 with mexiletine alone and 76 +/- 144 with combination therapy (p less than 0.05 for combination therapy versus disopyramide or mexiletine alone; p = NS for disopyramide versus mexiletine). Individually, an effective regimen (greater than 83% reduction in ventricular premature complexes and abolition of nonsustained ventricular tachycardia) was found in 5 (24%) of 21 patients during therapy with disopyramide alone, in 3 (14%) receiving mexiletine alone and in 13 (62%) receiving combination therapy (p less than 0.05 for combination therapy versus disopyramide or mexiletine; p = NS for disopyramide versus mexiletine). Thus, the antiarrhythmic effects of disopyramide and mexiletine are additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility of electrophysiologic testing during antiarrhythmic therapy for ventricular arrhythmias secondary to coronary artery disease

Although electrophysiologic studies are often used to assess antiarrhythmic drug efficacy in patients with ventricular tachycardia (VT), the reproducibility of these studies during therapy has not been definitively established. Confirmation studies were performed during drug therapy in 64 patients (51 men, mean age 63 years) with sustained ventricular arrhythmias induced during initial study to assess the reproducibility of drug effect. All patients had coronary artery disease. The stimulation protocol used included the serial introduction of up to 3 premature ventricular stimuli during sinus rhythm and with ventricular pacing at 2 pacing rates. Rapid ventricular pacing techniques were also used. Antiarrhythmic drug efficacy was confirmed in 77% of patients. Sustained VT was induced at repeat electrophysiologic study in 19% of patients during antiarrhythmic therapy that was previously thought to be effective. In summary, electrophysiologic study results during antiarrhythmic therapy exhibit significant day-to-day variability. Sustained VT can be induced during antiarrhythmic therapy that was previously defined as effective by programmed stimulation in a substantial number of patients.