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Radiofrequency (RF) catheter ablation is an accepted treatment for supraventricular tachycardia. However, the determinants of success, difficulty, or risk of complication associated wit ablation have not been defined. This study evaluated patient age and location of the accessory or extranodal pathway as determinants of these procedural variables. Patients were stratified by age, with those aged 2 to 12 years classified as children, those aged 13 to 19 years as adolescents, and those [greater than to equal]20 years as adults. Locations were defined as right, septal, or left free wall accessory pathways, or extranodal slow pathways associated with atrioventricular node reentrant tachycardia. A total of 443 RF ablation procedures performed in 413 patients were evaluated. All procedures were performed in the same laboratory by the same group of physicians. Success rates for ablation of supraventricular tachycardia did not differ among the 3 age groups, ranging from 93% to 9S%. Procedural aspects, including total procedure time, fluoroscopy time, and number of applications of RF energy also did not differ by age group. However, analysis of outcome and procedural complexity with respect to pathway location demonstrated that ablation of right free wall and septal accessory pathways was significantly more difficult than left free wall or slow pathway (success rates of 85% and 88% vs 97% and 98%, respectively, p = 0.01 and 0.02), irrespective of age. Additionally, right free wall pathways required significantly greater procedure time (mean = 5.1 hours), fluoroscopy time (mean = 78 minutes), and RF applications (median = 16) than ablations performed at other sites. In experienced centers, young age does not represent an independent risk factor for the failure or complexity of RF ablation procedures. However, accessory path. way location may be a critical variable affecting performance of these procedures, regardless of age. (Am J Cardiol 1994;74:786.-789)

Serial testing of antiarrhythmic drugs by programmed electrical stimulation can be costly in time, expense and risk. The purpose of this study was to evaluate the results of serial electropharmacologic tests for similarities that might obviate the need for protracted drug testing, Serial electropharmacologic testing was performed in 283 patients with coronary artery disease and clinical sustained ventricular tachycardia (VT) or fibrillation (VF). Drug tests were defined as concordant if sustained VT or VF could be consistently induced, or failed to be consistently induced during all such trials in a given patient. The following drugs were included for testing; procainamide, quinidine and disopyramide (class IA); phenytoin, mexiletine and tocainide (class IB); and flecainide and encainide (class IC). All patients were serially tested with [greater than or equal to]2 (mean and median, 3) antiarrhythmic agents regardless of results from drug-free testing or initial acute drug testing. Overall, the results of serial drug trials directed by programmed stimulation were concordant in more than two thirds of patients. Concordance was comparably high whether patients were serially tested with drugs within the same antiarrhythmic class, or with drugs from differing classes, and was not related to patients' clinical or electrophysiologic characteristics. Protracted serial electropharmacologlc testing does not appear necessary for predicting successful or unsuccessful antiarrhythmic drug therapy in survivors of clinical VT or VF. Single drug testing can identify most patients whose arrhythmia will or will not respond to medications.

Forty-nine patients with coronary artery disease and documented clinical sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) were studied twice in the drug-free state and twice during treatment with an identical antiarrhythmic medication at therapeutic plasma concentrations using an identical programmed electrical stimulation protocol. Tested drugs included procainamide, quinidine, disopyramide and phenytoin. During their 2 paired tests, 11 patients had nearly identical therapeutic plasma concentrations of antiarrhythmic agents (group I) and 38 patients had therapeutic plasma concentrations, but with more variation in drug levels between otherwise identical paired drug tests (group II). Overall, 71% of patients had inducible sustained VT or VF during drug testing. induced ventricular arrhythmias were not reproducible in 45% of group I patients, despite restudy at nearly identical therapeutic plasma concentrations of an identical antiarrhythmic agent. induced arrhythmias were also not reproducible in 16% of group II patients. This variability could not be attributed to the electrophysiologic characteristics of the patients studied. Drug trials directed by programmed stimulation should be cautiously interpreted because time-associated changes can mimic a change attributed to a beneficial or deleterious drug effect. (Am J Cardiol 1990;66:725-730), Ventricular tachycardia (VT) refers to a very rapid heart rate and ventricular fibrillation (VF) describes a tremulous, ineffective heart beat. They are often considered together as tachyarrhythmias, which are irregular, rapid heart rhythms. Studies have revealed daily variations in ventricular tachyarrhythmias, induced during programmed intracardiac electrophysiologic stimulation (PIES). In fact, clinically significant variations in induced tachyarrhythmias have been reported in up to 27 percent of patients with VT or VF when they undergo repeated electrophysiologic testing. This indicates that studies designed to evaluate the effects of drugs on VT and VF must be interpreted with caution. To determine the day-to-day reproducibility of antiarrhythmic drug testing, 49 patients with coronary artery disease, VT or VF were treated with the same antiarrhythmic drugs, using identical PIES protocols. Of the patients tested, 11 patients had identical blood concentrations of the test drug (group 1), while 38 showed variability in blood levels of the drug during identical, paired drug tests (group 2). VT or VF occurred in 71 percent of the patients during drug testing. In 45 percent of the group 1 patients, and in 16 percent of group 2, the induced arrhythmias were not reproducible. These results indicate that drug trials using programmed stimulation should be interpreted with caution, since day-to-day variations could be misinterpreted as resulting from the drug treatment. (Consumer Summary produced by Reliance Medical Information, Inc.)

Although sudden cardiac deaths and ischemic cardiac events clearly occur in a circadian pattern, such a pattern has not been shown for primary arrhythmic events. Because primary arrhythmic events are thought to play an important role in sudden cardiac death, a large series of ventricular stimulation studies was analyzed to determine whether circadian variation in ventricular electrical instability exists. If such a circadian variation could be shown, it could have implications for the conduct and interpretation of electrophysiologic testing and the etiology of circadian variation in sudden cardiac death. Results of 2 drug-free ventricular stimulation studies performed 4 to 28 hours apart in each of 162 patients with coronary artery disease were analyzed. Rate and duration of induced arrhythmia, number of extrastimuli required to induce arrhythmia and changes in these factors between the 2 tests in each patient were analyzed. Comparisons were made by half-day, by hour and in a temporally continuous manner to eliminate errors associated with any single method. No significant circadian variation was found in any electrophysiologic measure of ventricular electrical instability despite adequate statistical power. These findings show that the time of day during which ventricular stimulation tests are peformed does not affect test results, and therefore does not need to be controlled during electrophysiologic studies. if these findings are parallel to those in ambulatory patients with coronary artery disease, then circadian changes in ventricular electrical instability may not play as important a role in the circadian pattern of sudden cardiac death as had been previously thought. (Am J Cardiol 1990;65: 1351-1357), Sudden cardiac death and episodes of myocardial ischemia, the insufficient supply of blood to the heart, occur in a circadian or 24-hour pattern. Arrhythmias or abnormal heart rhythms, particularly those arising within the ventricle, play an important role in the development of sudden cardiac death. However, it is not clear whether the development of ventricular arrhythmias also follows a circadian pattern. The existence of a circadian variation would be an important consideration when assessing the electrical activity of the heart and determining the causes of circadian variation in sudden cardiac death. Various measures of the electrical instability of the ventricles were assessed over a 24-hour interval to determine whether a circadian variation existed. The study involved 162 patients with coronary artery disease, a heart disorder involving the major blood vessels supplying the heart. The rate, duration, and conditions for development of arrhythmias were assessed each hour, each half-day, and continuously over time. The findings revealed that there was no circadian variation in any factor used to measure the electrical instability of the ventricles. Thus, ventricular electrical instability does not appear to play a major role in the circadian pattern of sudden cardiac death. (Consumer Summary produced by Reliance Medical Information, Inc.)

Six patients presented with wide-complex tachycardias with QRS morphologies similar to those seen on their electrocardiograms that showed normal sinus rhythms. During normal sinus rhythm, each patient had an underlying intraventricular conduction abnormality or bundle branch block. Despite the similarity of the QRS complexes to those seen during sinus rhythm, the tachycardias subsequently proved to be ventricular in origin in each patient. It is important not to misdiagnose these disorders as supraventricular tachycardia as an erroneous diagnosis may result in inappropriate management. (Halperin BD, Kron J, Cutler JE, et al: Misdiagnosing ventricular tachycardia in patients with underlying conduction disease and similar sinus and tachycardia morphologies. West J Med 1990 Jun; 152:677-682), A tachycardia showing wide QRS complexes on electrocardiograms (ECGS) can be ventricular or supraventricular in origin. The misdiagnosis and mistreatment of ventricular tachycardia as supraventricular tachycardia, or vice versa, can [...]

Since the initial case report in 19151 and the formal characterization of the Wolff-Parkinson-White syndrome in 1930,(2) an extensive body of literature concerning the significance and treatment of the disorder [...]

Radiofrequency catheter ablation is very effective in eliminating conduction over accessory pathways in patients with Wolff-Parkinson-White syndrome. However, accessory pathway conduction recurs in approximately 5 to 9 percent of patients [...]