Diagnosis and cure of the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardias during a single electrophysiologic test

BACKGROUND

We conducted this study to determine the feasibility of an abbreviated therapeutic approach to the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardia, in which the diagnosis is established and radiofrequency ablation carried out during a single electrophysiologic test.

METHODS

One hundred six consecutive patients were referred for the management of documented, symptomatic paroxysmal supraventricular tachycardias (66 patients) or the Wolff-Parkinson-White syndrome (40 patients). All agreed to undergo a diagnostic electrophysiologic test and catheter ablation with radiofrequency current. No patient had had such a test previously.

RESULTS

Among the 66 patients with paroxysmal supraventricular tachycardias, the mechanism was found to be atrioventricular nodal reentry in 46 (70 percent) (typical in 44 and atypical in 2), atrioventricular reciprocating tachycardia involving a concealed accessory pathway in 16 (24 percent), atrial tachycardia in 2 (3 percent), and noninducible paroxysmal supraventricular tachycardia in 2 (3 percent). A successful long-term outcome was achieved in 57 of 62 patients (92 percent) with paroxysmal supraventricular tachycardia in whom ablation was attempted and in 37 of 40 patients (93 percent) with the Wolff-Parkinson-White syndrome. The only complications were one instance of occlusion of the left circumflex coronary artery, leading to acute myocardial infarction, and one instance of complete atrioventricular block. The mean (+/- SD) duration of the electrophysiologic procedures was 114 +/- 55 minutes.

CONCLUSIONS

The diagnosis and cure of paroxysmal supraventricular tachycardia or the Wolff-Parkinson-White syndrome during a single electrophysiologic test are feasible and practical and have a favorable risk-benefit ratio. This abbreviated therapeutic approach may eliminate the need for serial electropharmacologic testing, long-term drug therapy, antitachycardia pacemakers, and surgical ablation.

Radiofrequency catheter ablation of accessory atrioventricular connections in 250 patients. Abbreviated therapeutic approach to Wolff-Parkinson-White syndrome

BACKGROUND

The purpose of this study was to report the results and complications of radiofrequency catheter ablation of accessory atrioventricular (AV) connections by using an abbreviated approach aimed at minimizing the duration of the procedure.

METHODS AND RESULTS

Two hundred fifty consecutive patients with the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardia involving a concealed accessory AV connection underwent catheter ablation with the use of radiofrequency current. In 179 of the 250 patients, catheter ablation was performed at the time of an initial electrophysiology test. Two hundred thirty-five patients had one accessory AV connection and 15 patients had two or more. One hundred eighty-three accessory AV connections were manifest and 84 were concealed. One hundred sixty-one were were located in the free wall of the left ventricle, 47 were in the right free wall, 44 were posteroseptal, 10 were anteroseptal, and five were intermediate test, and the ablation procedure was recorded for each patient, as was the total duration of fluoroscopy. A follow-up electrophysiology test was performed 2-3 months after the ablation procedure. Ninety-four percent of patients had all accessory AV connections successfully ablated and remained free of symptomatic tachycardia during a mean follow-up of 10 +/- 4 months. Two hundred nineteen patients (88%) had all accessory AV connections ablated during the initial attempt at catheter ablation. Mean duration of the entire procedure was 134 +/- 75 minutes. Procedure duration was longest in patients with multiple accessory AV connections, shortest in patients with intermediate septal accessory AV connections, and similar in all other locations. A nonfatal complication occurred in nine patients (4%).

CONCLUSIONS

The results of this study indicate that catheter ablation of accessory AV connections with radiofrequency current can be performed safely and expeditiously in a majority of patients and confirm in a large series the feasibility of catheter ablation at the time of an initial diagnostic electrophysiology test. This abbreviated therapeutic approach avoids the need for electropharmacological testing, long-term antiarrhythmic drug therapy, and surgical therapy in the majority of patients with the Wolff-Parkinson-White syndrome or with symptomatic tachycardias involving accessory AV connections.

Long-term results of catheter ablation of idiopathic right ventricular tachycardia

Ten consecutive patients with recurrent episodes of symptomatic, idiopathic, sustained monomorphic ventricular tachycardia (VT) originating in the right ventricle underwent an attempt at catheter ablation of the ventricular tachycardia. There were seven women and three men, with a mean age of 39 +/- 14 years (+/- SD). None of the patients had any evidence of structural heart disease. The VT had a left bundle branch block configuration and an inferior axis in each patient, and the mean cycle length was 313 +/- 75 msec. Based on the methods of induction of the VT and the response of the VT to verapamil, the VT mechanism was presumed to be reentry in six patients, triggered activity in three patients, and catecholamine-sensitive automaticity in one patient. Sites for ablation were guided by pace mapping, and an appropriate target site was identified in the right ventricular outflow tract in each patient. From one to three shocks of 100-360 J (mean total, 336 +/- 195 J) were delivered from a defibrillator between the tip of the ablation catheter (cathode) and a patch electrode on the anterior chest (anode). An electrophysiology test 7-9 days after ablation demonstrated that VT was still inducible in only one patient, who was treated with amiodarone. One other patient had a recurrence of VT 3 weeks after ablation and was treated with verapamil. Eight of 10 patients were not treated with antiarrhythmic medications and have had no episodes of symptomatic VT during 15-68 months of follow-up (mean follow-up, 33 +/- 18 months). There were no acute or long-term complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiation exposure during radiofrequency catheter ablation of accessory atrioventricular connections

BACKGROUND

Catheter ablation of accessory atrioventricular (AV) connections has been demonstrated to be effective in more than 85% of patients. One of the risks of this procedure is radiation exposure during the fluoroscopic imaging necessary to guide catheter manipulation. The objective of the present study was to measure the radiation received by patients and physicians during radiofrequency catheter ablation and to estimate the resultant somatic and genetic risks.

METHODS AND RESULTS

Radiation exposure to patients and physicians was measured during attempts at radiofrequency catheter ablation of accessory AV connections in 31 consecutive patients. Radiation exposure was measured using thermoluminescent sensors placed on the patient and on the physician. Somatic and genetic risks were estimated based on the radiation levels recorded using these sensors. The durations of fluoroscopy and of the catheter ablation procedure were recorded for each patient. Catheter ablation was successful in 28 of 31 patients (90%). Mean +/- SD duration of fluoroscopy was 44 +/- 40 minutes. The largest patient radiation dose was measured over the ninth vertebral body posteriorly (median, 7.26 rem [roentgen equivalents man]; range, 0.31-135.7 rem). Median radiation dose to the thyroid was 0.46 rem (range, 0.06-7.26 rem), and median radiation dose to the posterior iliac crest was 2.43 rem (range, 0.01-8.3 rem). The greatest radiation dose to the operator was recorded at the left hand (99 mrem). Mean radiation dose to the operator's eyes was 28 mrem.

CONCLUSIONS

Radiofrequency catheter ablation of accessory AV connections may result in significant radiation exposure to the patient and to the physician. Each hour of fluoroscopic imaging is associated with a lifetime risk of developing a fatal malignancy of 0.1% and a risk of a genetic defect of 20 per 1 million births. Although these risks must be recognized, they are relatively small compared with the risks associated with alternate approaches to management, including no therapy, antiarrhythmic drug therapy, and surgery.

Electrogram criteria for identification of appropriate target sites for radiofrequency catheter ablation of accessory atrioventricular connections

BACKGROUND

Catheter ablation of accessory atrioventricular (AV) connections using radiofrequency current has been demonstrated to be effective in the majority of patients with the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardia involving a concealed accessory AV connection. However, electrogram criteria have not been established to guide attempts at radiofrequency catheter ablation.

METHODS AND RESULTS

The characteristics of local electrograms recorded at successful and unsuccessful sites of radiofrequency catheter ablation were determined in 132 patients. Electrograms recorded at a total of 438 sites were analyzed: 338 recorded during ablation of 90 manifest accessory AV connections and 100 recorded during ablation of 44 concealed accessory AV connections. During ablation of manifest accessory AV connections, the independent predictors of outcome were electrogram stability (p less than 0.001), the interval between activation of the ventricular electrogram and onset of the QRS complex (p less than 0.001), and the presence of an accessory AV connection potential (p less than 0.001). Radiofrequency energy delivery at sites demonstrating stable electrograms, a probable or possible accessory AV connection potential, and activation of the local ventrical electrogram before the onset of the QRS complex had a 57% probability of success compared with a 3% probability of success at sites without these features. During ablation of concealed accessory AV connections, the independent predictors of outcome were electrogram stability (p = 0.02), the presence of an accessory AV connection potential (p = 0.05), and the presence of retrograde continuous electrical activity (p = 0.04). Sites demonstrating a stable local electrogram, an accessory AV connection potential, and retrograde continuous electrical activity had an 82% probability of success compared with only a 5% probability of success at sites demonstrating none of these features.

CONCLUSIONS

The local electrogram parameters of greatest importance in predicting the success or failure of radiofrequency catheter ablation of accessory AV connections are electrogram stability, the presence of an accessory AV connection potential, and the timing of ventricular activation relative to the QRS complex (for manifest accessory AV connections) or retrograde continuous electrical activity (for concealed accessory AV connections). Awareness of these variables during attempts at radiofrequency catheter ablation of accessory AV connections may minimize the number of unnecessary applications of radiofrequency energy.

Radiofrequency catheter ablation of the atrioventricular junction from the left ventricle

BACKGROUND

The purpose of this study was to describe a new technique for catheter ablation of the atrioventricular junction using radiofrequency energy delivered in the left ventricle.

METHODS AND RESULTS

Catheter ablation of the atrioventricular (AV) junction using a catheter positioned across the tricuspid annulus was unsuccessful in eight patients with a mean +/- SD age of 51 +/- 19 years who had AV nodal reentry tachycardia (three patients), orthodromic tachycardia using a concealed midseptal accessory pathway, atrial tachycardia, atrial flutter (two patients), or atrial fibrillation. Before attempts at catheter ablation of the AV junction, each patient had been refractory to pharmacological therapy, and four had failed attempts at either catheter modification of the AV node using radiofrequency energy or surgical and catheter ablation of the accessory pathway. Conventional right-sided catheter ablation of the AV junction using radiofrequency energy in six patients and both radiofrequency energy and direct current shocks in two patients was ineffective. The mean amplitude of the His bundle potential recorded at the tricuspid annulus at the sites of unsuccessful AV junction ablation was 0.1 +/- 0.08 mV, with a maximum His amplitude of 0.03-0.28 mV. A 7F deflectable-tip quadripolar electrode catheter with a 4-mm distal electrode was positioned against the upper left ventricular septum using a retrograde aortic approach from the femoral artery. Third-degree AV block was induced in each of the eight patients with 20-36 W applied for 15-30 seconds. The His bundle potential at the sites of successful AV junction ablation ranged from 0.06 to 0.99 mV, with a mean of 0.27 +/- 0.32 mV. There was no rise in the creatine kinase-MB fraction and no complications occurred. An intrinsic escape rhythm of 30-60 beats/min was present in seven of the eight patients. Each patient received a permanent pacemaker and has been asymptomatic during 3-13 months of follow-up.

CONCLUSIONS

Catheter ablation of the AV junction can be achieved effectively and safely using radiofrequency energy delivered in the left ventricle when the conventional right-sided approach is unsuccessful.

Recurrence of conduction in accessory atrioventricular connections after initially successful radiofrequency catheter ablation

The purpose of this study was to characterize the incidence and clinical features of accessory pathway recurrence after initially successful radiofrequency catheter ablation and to identify variables correlated with recurrence. Radiofrequency ablation was performed with a 7F deflectable tip catheter with a large (4 mm in length) distal electrode. Left-sided accessory pathways were approached through the left ventricle and right-sided pathways by way of the right atrium. Patients were included in the study if 1) they had an initially successful procedure, defined as the absence of accessory pathway conduction immediately after ablation, and 2) had undergone a 3-month follow-up electrophysiologic test or had documented recurrence of accessory pathway conduction. Accessory pathway conduction recurred after initially successful ablation in 16 (12%) of 130 patients. Almost half (7 of 16) of these recurrences were in the 1st 12 h after ablation, and the last occurred after 106 days. Return of delta waves on the electrocardiogram (ECG) or spontaneous paroxysmal supraventricular tachycardia was the initial indication of recurrence in 15 of the 16 patients. Two patients with manifest accessory pathways exhibited recurrence with exclusively concealed accessory pathway conduction. Accessory pathways ablated from the tricuspid anulus (right free wall or septal accessory pathways) had a much higher recurrence rate (24%) than did those on the mitral anulus (6%). Fourteen of 15 patients have had successful repeat accessory pathway ablation after the initial recurrence. After a mean follow-up period of 4 +/- 3 months, there have been no repeat recurrences of any of these accessory pathways. It is concluded that accessory pathway recurrence is infrequent after successful radiofrequency catheter ablation.(ABSTRACT TRUNCATED AT 250 WORDS)

Repolarization abnormalities after catheter ablation of accessory atrioventricular connections with radiofrequency current

The purpose of this study was to evaluate the serial changes in T wave configuration in patients undergoing successful radiofrequency catheter ablation of accessory atrioventricular (AV) connections. Twenty-nine consecutive patients with overt preexcitation and 16 patients with a concealed accessory atrioventricular (AV) connection were included. An electrocardiogram (ECG) was recorded before ablation and 15 min, 1 or 2 days and 1 and 3 months after ablation. Postablation T wave abnormalities occurred in 22 (76%) of the 29 patients who had overt pre-excitation but in none of the 16 patients with a concealed accessory AV connection. The T wave abnormalities were not related to myocardial necrosis or echocardiographic abnormalities. The ECG location and severity of T wave changes were dependent on the accessory AV connection location and degree of baseline pre-excitation, respectively. Fourteen of 19 patients with a posteriorly located AV connection (left, right or septal) had T wave inversion or flattening in the inferior leads and 3 patients had precordial T wave peaking. Two patients with an anteroseptal AV accessory connection had both inferior T wave inversion or flattening and precordial T wave peaking. Among seven patients with a manifest left lateral accessory AV connection, two had lateral T wave inversion or flattening and two had precordial T wave peaking. There was 95% concordance between the directional change of the T wave after ablation and the direction of the delta wave on the baseline ECG.(ABSTRACT TRUNCATED AT 250 WORDS)

Impedance Monitoring During Radiofrequency Catheter Ablation in Humans

Radiofrequency catheter ablation of accessory pathways and the atrioventricular junction often requires multiple applications of energy. The inability to determine the effects of any given application on the underlying tissue may contribute to this problem. In the present study, impedance was monitored in 20 patients undergoing radiofrequency catheter ablation, and the relationship between an initial decrease in impedance and subsequent effects were examined. An initial fall in impedance of more than 10 omega was 78% sensitive and 88% specific for predicting subsequent evidence of tissue heating (interruption of conduction or an abrupt rise in impedance due to coagulum formation). In contrast, initial values of voltage, current, or impedance did not distinguish between effective and ineffective applications of radiofrequency energy. Continuous monitoring of impedance may facilitate radiofrequency catheter ablation.

Incidence of loss of consciousness during automatic implantable cardioverter-defibrillator shocks

OBJECTIVE

To determine the incidence of loss of consciousness occurring in association with shocks delivered by automatic implantable cardioverter-defibrillators (AICD) in patients who had undergone implantation as treatment for ventricular tachycardia or ventricular fibrillation.

DESIGN

Cohort study.

SETTING

Two major tertiary medical care facilities.

PATIENTS

A total of 180 patients who had undergone implantation of an AICD for treatment of ventricular tachycardia or ventricular fibrillation.

INTERVENTION

Implantation of an AICD that delivered only high-energy shock.

MEASUREMENTS

During a mean (+/- SD) follow-up period of 16 +/- 12 months, the incidence of loss of consciousness occurring in association with spontaneous AICD shocks was determined. Various clinical factors were analyzed to identify predictors of loss of consciousness that occurred during AICD shocks.

MAIN RESULTS

Of the 180 patients who received an AICD, 106 patients (59%) experienced AICD shocks during follow-up. Sixteen of the 180 patients (9%) experienced loss of consciousness; 13 of these 16 patients had syncope and 3 died suddenly, in association with AICD shocks. The absence of syncope during one AICD shock did not always predict the absence of syncope during subsequent shocks. Syncope could not be predicted by age, sex, history of syncope, left ventricular function, type of underlying heart disease, electrophysiologic findings, rate of ventricular tachycardia, antiarrhythmic medications, and type of pulse generator implanted.

CONCLUSIONS

Patients with sustained ventricular tachycardia or ventricular fibrillation who receive an AICD that delivers only high-energy shock therapy are at moderate risk for experiencing loss of consciousness during AICD shocks. No clinical variables were found to be predictors of syncope. Therefore, driving and other activities that require patients to be extra vigilant should not be assumed to be safe after implantation of an AICD that delivers only high-energy shock.

Effect of epinephrine on the efficacy of the internal cardioverter-defibrillator

To evaluate the effect of sympathetic activation on the efficacy of the implantable cardioverter-defibrillator (ICD) in converting ventricular tachycardia (VT) or ventricular fibrillation (VF), 32 patients who received an ICD because of life-threatening VT/VF underwent 1 week postimplant ICD testing both before and after infusion of 25 (16 patients) or 50 (16 patients) ng/kg/min of epinephrine for greater than or equal to 12 minutes. These infusion rates are known to result in plasma epinephrine concentrations comparable to mild-moderate stress. The patients' mean age was 63 +/- 10 years; 26 had coronary artery disease, 2 had dilated cardiomyopathy and 4 had no evidence of structural heart disease. VT and VF were induced in 16 patients each by programmed stimulation or alternating current. Among the 16 patients with VT, the first ICD discharge (26 to 30 J) was effective in 15 patients in the baseline state and in all 16 patients during epinephrine infusion. Among patients with VF, the first ICD discharge (26 to 30 J) terminated VF in all patients in the baseline state, compared with 12 of 16 patients during epinephrine infusion (p less than 0.05). In 4 patients, VF was terminated during epinephrine infusion only by the second or third ICD discharge (30 J). In conclusion, physiologic increases in the plasma epinephrine concentration may increase the number and energy of shocks needed to terminate VF.

Physical properties of chitosan pellets produced by extrusion–spheronisation: influence of formulation variables

Pellets comprising chitosan, cellulose microcrystalline, povidone, filler excipient and diclofenac sodium as model drug were prepared by extrusion-spheronisation. The effects of chitosan load (zero, 0%, low, 4% and high, 16% levels), type of filler (lactose, tribasic calcium phosphate and beta-cyclodextrin) and composition of the binding liquid (ethanol/water mixtures 20 and 50%) on physical characteristics of pellets were evaluated. A three-factor factorial design was employed in the study. Analysis of variance (ANOVA) indicated that single factors had significant effect on the physical characteristics of the pellets. The type of filler followed by polymer load markedly affected the density. The type of binding liquid had negligible effect on the shape and surface roughness of the pellets. Increase in the chitosan load resulted in pellets of lower porosity values. This could be attributed to the binding capacity of chitosan and povidone leading to more compacted structures. Chitosan load and type of filler had significant influence on the surface roughness. The surface of pellets became rougher as the chitosan load increased, however, there was no significant difference between zero and low contents of chitosan. Pellets prepared using tribasic calcium phosphate showed a smoother surface when compared with formulations including lactose or beta-cyclodextrin. Chitosan was useful to provide pellets of acceptable physical characteristics when employing an alcohol/water mixture 50% (v/v) as binding liquid for the extrusion-spheronisation process.

Reduction in medical care cost associated with radiofrequency catheter ablation of accessory pathways

The cost of definitive therapy was compared in 25 patients who underwent radiofrequency catheter ablation of accessory pathways in 1990 and 25 patients who underwent surgical ablation of accessory pathways in 1989. In the radiofrequency group, 23 of 25 patients had a single accessory pathway and the remaining 2 patients each had 2 accessory pathways. In the surgical group, 20 patients had a single accessory pathway and 5 patients each had 2 accessory pathways. The success rate was 96% in each group. The mean duration of hospitalization was 3 +/- 1 days in the radiofrequency group and 9 +/- 4 days in the surgical group (p less than 0.0001). All the cost data are expressed in fiscal year 1990/1991 dollar values. The total cost of therapy in the radiofrequency group was $14,919 +/- $6,740 compared with $53,265 +/- $12,755 in the surgical group (p less than 0.0001). The cost of radiofrequency ablation consisted of a hospital charge of $7,753 +/- $3,472 and physician fees of $7,166 +/- $3,439. The hospital charge included charges for use of the electrophysiology laboratory, hospital stay, electrocardiograms, echocardiograms and blood studies. The cost of surgery consisted of a hospital charge of $37,708 +/- $10,179 and physician fees of $15,557 +/- $3,149. The hospital charge in the surgical group included the costs of a baseline electrophysiology study, in-hospital care and a follow-up office visit. In conclusion, radiofrequency catheter ablation of accessory pathways results in a dramatic reduction in the cost of definitive therapy in patients with the Wolff-Parkinson-White syndrome.

Distribution and impacts of microplastic incorporation within sea ice

Microplastics (plastic particles <5 mm) are an emerging concern in Arctic sea ice with measured concentrations orders of magnitude higher than in surface seawater. However, incorporation of microplastics into sea ice, and their impact on sea ice properties, is unknown. We added microplastic particles in a microcosm experiment to determine microplastic distributions and effects on sea ice properties. Microplastic additions did not affect sea ice growth, but high concentrations of microplastics at the ice surface resulted in high ice salinity and changes in sea ice albedo. Field studies in the Gulf of Bothnia (Baltic Sea) showed sea ice concentration of microplastics from 8 to 41 particles per liter of melted ice, wich were much lower than those found to impact sea ice properties in the microcosm experiments. However, should microplastic concentrations increase, microplastic incorporation in sea ice may impact sea ice albedo.

Hydroperoxyl, superoxide and pH gradients in the mitochondrial matrix: a theoretical assessment

The negative surface charge of many cellular membranes concentrates protons and rarefies superoxide in their vicinity. It was speculated that the low pH near membranes should facilitate superoxide protonation, thereby concentrating hydroperoxyl radical in this region. This process would exacerbate both lipid peroxidation and the transfer of oxidative damage between cellular compartments, as hydroperoxyl is a good initiator of lipid peroxidation and permeates lipid bilayers. Surface-charge-enhancement of hydroperoxyl production in mitochondria--which are main intracellular sources of superoxide--should be particularly relevant. Using a simple model of superoxide metabolism in the mitochondrial matrix, we calculated the gradients of pH, superoxide, and hydroperoxyl, and assessed the previous hypothesis in the light of available experimental data. The following predictions ensued: (i) Near the mitochondrial inner membrane, gradients of superoxide concentration with amplitude up to 36% of the maximal concentration, and pH gradients of up to 0.19 units between membrane and bulk. (ii) These electrostatically induced gradients die out within approximately 4 nm of the membrane. (iii) At high (hundreds of nanometres) inter-cristae separations, owing to enzyme-catalyzed dismutation of superoxide, both superoxide and hydroperoxyl become rarefied towards the midpoint between cristae. (iv) Surface charge should neither enhance superoxide protonation nor concentrate hydroperoxyl near biological membranes.

A mathematical analysis of TCR serial triggering and down-regulation

Despite the increasing knowledge on the pathways involved in TCR signal transduction and T cell activation, the molecular mechanism of TCR triggering by ligand, MHC-peptide complexes, is still elusive and controversial. The present paper addresses the controversy on the early events of TCR engagement and triggering. Mathematical modelling techniques are applied to experimental data to infer plausible molecular mechanisms of TCR triggering and down-regulation. A similar approach has been followed by Bachmann et al. (Eur. J. Immunol. 1998, 28: 2571 - 2579), who concluded that the TCR triggering requires the formation of MHC-TCR dimers or trimers. We report here the failure to generalize this conclusion to the data reported by Valitutti et al. (Nature 1995, 375: 148 - 151). We show that there are several kinetic features in these experimental curves of TCR down-regulation that cannot be explained by the simple model proposed by Bachmann et al. unless some phenomenological extensions are considered. These extensions are: (1) a ligand independent turnover of the TCR; (2) a transient accumulation of triggered TCR; (3) a high order of TCR triggering kinetics; and (4) two pools of membrane TCR in dynamic equilibrium.

Reversal of antiarrhythmic drug effects by epinephrine: quinidine versus amiodarone

Although previous studies have demonstrated that the electrophysiologic effects of many antiarrhythmic agents can be reversed by catecholamines, the susceptibility of amiodarone to such reversal is unknown. The objective of this study was to compare the relative degree of reversal of the electrophysiologic effects of quinidine and amiodarone by epinephrine infusions that result in plasma epinephrine levels similar to those achieved during various physiologic stresses. Twenty-nine patients who had inducible sustained monomorphic ventricular tachycardia and underwent electropharmacologic testing with quinidine and amiodarone were enrolled in the study. The variables measured before and during an epinephrine infusion (25 or 50 ng/kg per min) included the sinus cycle length, mean arterial pressure, QT interval and effective refractory period at drive train cycle lengths of 600 and 400 ms. The effective refractory period measured at a drive train cycle length of 600 ms shortened less during amiodarone therapy (2 +/- 2%) than during quinidine therapy (6 +/- 4%) or than in the baseline state (6 +/- 4%; p less than 0.01). Similar results were obtained during evaluation of the effective refractory period at a cycle length of 400 ms. Epinephrine infusion, at both 25 and 50 ng/kg per min, completely reversed the effects of quinidine and partially reversed the effects of amiodarone on the effective refractory period. The effects of epinephrine on the sinus cycle length and QT interval were similar in the baseline state and in conjunction with quinidine and amiodarone. Twenty-four patients underwent programmed ventricular stimulation during amiodarone therapy alone and in conjunction with either a 25- or a 50-ng/kg per min infusion of epinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)