Antiadrenergic effects of adenosine on His-Purkinje automaticity. Evidence for accentuated antagonism

The effects of adenosine on the human His-Purkinje system (HPS) were studied in nine patients with complete atrioventricular (AV) block. Adenosine had minimal effect on the control HPS cycle length, but in the presence of isoproterenol increased it from 906 +/- 183 to 1,449 +/- 350 ms, P less than 0.001. Aminophylline, a competitive adenosine antagonist, completely abolished this antiadrenergic effect of adenosine. In isolated guinea pig hearts with surgically induced AV block, isoproterenol decreased the HPS rate by 36%, whereas in the presence of 1,3-dipropyl-8-phenyl-xanthine, a potent adenosine antagonist, the HPS rate decreased by 48% and was associated with an increased release of adenosine. Therefore, by blocking the effects of adenosine at the receptor level, the physiologic negative feedback mechanism by which adenosine antagonizes the effects of catecholamines was uncoupled. The results of this study indicate that adenosine's effects on the human HPS are primarily antiadrenergic and are thus consistent with the concept of accentuated antagonism. These effects of adenosine may serve as a counterregulatory metabolic response that improves the O2 supply-demand ratio perturbed by enhanced sympathetic tone. Some catecholamine-mediated ventricular arrhythmias that occur during ischemia or enhanced adrenergic stress may be due to an imbalance in this negative feedback system.

Automatic external defibrillation of patients after myocardial infarction by family members: practical aspects and psychological impact of training

Automatic external defibrillation (AED) offers the potential for minimally trained individuals to convert life-threatening ventricular arrhythmias prior to arrival of emergency rescue personnel but optimum usage of AED remains undefined. To test the practical aspects of home AED in high risk patients after myocardial infarction, we identified 40 consecutive high risk post-MI patients, who satisfied inclusion and exclusion criteria. Fifteen (38%) patients were eliminated at their physician's request and nine others refused to participate. Twenty-six family members of the remaining 16 patients were trained in AED with follow-up testing at 3 months. Level of skill, especially in CPR performance, decline to unsatisfactory levels in 35% of trainees, including all over age 55. Trainees felt more confident due to availability of AED and 90% felt no strain in intrapersonal relationships. Psychological testing revealed a decrease in patient and trainee depression scores and no change in anxiety or obsessiveness during the study. These observations suggest the following: (1) better awareness of benefits of AED by physicians and lay persons is necessary, (2) retraining at less than 3 month intervals will be required for many spouse trainees and (3) there are no common adverse psychologic sequelae to training in AED.

Current-based versus energy-based ventricular defibrillation: a prospective study

Defibrillation is thought to be mediated by a depolarizing current; however, the present method of defibrillation is based on delivering an empiric dose of energy to all patients. The hypothesis of this study was that for equivalent efficacy rates, a current-based defibrillation method would result in delivering less energy and peak current than would the standard energy-based method. In a group of 86 consecutive patients with ventricular fibrillation, every other patient was prospectively assigned to receive shocks according to method 1 or method 2. Method 1 was current based and delivered successive shocks of 25, 25 and a maximum of 40 A; method 2 was energy based and delivered shocks of 200, 200 and 360 joules. Patients in both groups were similar with respect to age, gender, weight, cardiac diagnosis, ejection fraction, antiarrhythmic therapy, chest circumference, chest depth and transthoracic impedance. Each method had statistically equivalent first shock (79% current-based versus 81% energy-based) and cumulative shock success rates. The mean first shock energy was 120 +/- 30 joules for patients receiving the current-based method and 200 joules for patients receiving energy-based shocks (p = 0.0001). The mean peak current was 24 +/- 2.3 and 33 +/- 5.0 A, respectively (p = 0.0001). Therefore, for equivalent first shock success rates, the energy-based method delivered 67% more energy and 38% more current than the current-based method. High transthoracic impedance (greater than or equal to 90 omega) predicted first shock failure only in patients undergoing defibrillation by the energy-based method (p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of adenosine for arrhythmias in infants and children

Adenosine was administered to 25 infants and children (11 patients after presenting with a sustained arrhythmia, and 14 during a diagnostic electrophysiologic study) to determine its electrophysiologic effects. Adenosine was given as an intravenous bolus (starting dose 37.5 micrograms/kg, and increased by 37.5 micrograms/kg increments until an effect was seen). Adenosine caused tachycardia termination or transient increased atrioventricular (AV) block in all 25 patients. Seven patients had tachycardia requiring only the atria for perpetuation and developed increased AV nodal block (minimum effective adenosine dose range 37.5 to 350 micrograms/kg, mean 131). Thirteen had AV reciprocating tachycardia or AV node reentry tachycardia (minimum effective adenosine dose range 37.5 to 225 micrograms/kg, mean 114). Four other patients received adenosine to rule out preexcitation (minimum effective adenosine dose range 37.5 to 375 micrograms/kg, mean 165). One of the 25 patients had junctional ectopic tachycardia and adenosine administration caused retrograde AV block. Six of the 25 (24%) had noticeable but minor side effects. One patient had sustained bradycardia (2 to 3 minutes requiring temporary pacing). Adenosine is a safe and effective agent in the evaluation and treatment of infants and children with arrhythmias.

Surgical ablation of ventricular tachycardia with sequential map-guided subendocardial resection: electrophysiologic assessment and long-term follow-up

A new operative technique of sequential map-guided subendocardial resection (SER) was used in 45 consecutive patients for the treatment of sustained ventricular tachycardia due to coronary artery disease. This technique is characterized by map-guided SER or cryothermic ablation during normothermic cardiopulmonary bypass, followed by repeated sequences of programmed stimulation to assess adequacy of resection. The patients' mean age was 59 +/- 10 years and the mean left ventricular ejection fraction was 34 +/- 12%. Twenty-five (56%) patients had a history of myocardial infarction within the previous 2 months. After ventriculotomy, 34 patients (76%) had inducible monomorphic ventricular tachycardia. These patients underwent repeated sequences of ventricular tachycardia induction and mapping during normothermic bypass followed by successive SER or cryothermic ablation until sustained monomorphic ventricular tachycardia was no longer inducible. Twenty-seven patients had a total of 60 discrete, mappable tachycardias induced and seven patients had 10 discrete tachycardias that were too fast to accurately map. In the remaining 11 patients, no ventricular tachycardia was inducible after ventriculotomy and SER, which included all visually identifiable scar, was performed. The mean cardiopulmonary bypass time was 102 +/- 27 min. Forty-one of 45 patients (91%) survived to hospital discharge, and 35 of 41 patients (85%) had no inducible ventricular tachycardia at postoperative electrophysiologic evaluation performed in the absence of all antiarrhythmic drugs. The remaining six patients had no inducible ventricular tachycardia with drug therapy. All four operative nonsurvivors had refractory cardiac collapse preoperatively. Over 19 +/- 12 months of follow-up, there were four sudden cardiac deaths and no nonfatal recurrences of ventricular tachycardia. There were seven additional cardiac deaths. Actuarial cardiac survival was 0.57, and freedom from arrhythmic events was 0.76 at 42 months. Thus, in the absence of cardiogenic shock, the technique of sequential map-guided SER achieves: (1) a high operative survival with acceptable perfusion times, (2) excellent long-term arrhythmia control, and (3) survival comparable to that in patients with similar left ventricular function and no history of ventricular tachyarrhythmia.

Sequential endocardial resection for the surgical treatment of refractory ventricular tachycardia

The optimal surgical therapy for refractory ventricular tachycardia is controversial. The usual operation involves induction of tachycardia and endocardial mapping during normothermic cardiopulmonary bypass, followed by systemic hypothermia, aortic cross-clamping, and resection of the identified site of origin of the tachycardia. Our initial experience with this technique in 20 patients (mean age 60 years, mean ejection fraction 29%, mean number of failed antiarrhythmic drugs three) resulted in five (25%) surgical deaths, three caused by ventricular tachycardia and two by respiratory or heart failure. Electrophysiologic study showed that 11 of 15 survivors were free from ventricular tachycardia after operation, for a success rate in the survivors of 73%. Most failures occurred in patients with multiple tachycardia morphologies that were not eradicated by initial resection. Thereafter, the technique of sequential endocardial resection was used. After completion of endocardial mapping, directed normothermic endocardial resection is performed; more attempts to induce ventricular tachycardia are made and followed by further mapping and resection until tachycardia can no longer be induced. Fifty patients (mean age 59 years, mean ejection fraction 33%, mean number of failed antiarrhythmic drugs three) were treated by this method, with a mean of two resections per patient (range one to six). Mean perfusion time in the sequential resection group (101 +/- 28 minutes) was not significantly different from that of the earlier patients (101 +/- 40 minutes). There were four (8%) surgical deaths, one caused by persistent arrhythmia and three caused by respiratory or heart failure. Electrophysiologic study after operation showed that 40 of 46 survivors (87%) were free of ventricular tachycardia. Symptoms in the six with inducible tachycardia on postoperative electrophysiologic study were well controlled with medication. These data suggest that sequential endocardial resection guided by intraoperative mapping is a highly effective operative approach for patients with ventricular tachycardia.

Predictors of efficacy of amiodarone and characteristics of recurrence of arrhythmia in patients with sustained ventricular tachycardia and coronary artery disease

The value of serial electropharmacologic testing during long-term oral amiodarone therapy for prediction of long-term drug efficacy as well as characteristics of arrhythmia recurrence is controversial. One-hundred four consecutive patients with coronary artery disease and sustained ventricular tachyarrhythmias (VT) underwent initial electrophysiologic (EP) evaluation in the drug-free state and again after an amiodarone loading period of 25 +/- 14 days (mean +/- SD). Twenty-six patients (25%) had no inducible ventricular tachyarrhythmia during therapy with amiodarone (VT control group), whereas arrhythmia inducibility persisted in the remaining 78 patients (VT noncontrol group). During 17.4 +/- 13.7 months of follow-up, two patients in the VT control group either had VT recurrence or died suddenly compared with 21 VT recurrences and eight sudden cardiac deaths in the VT noncontrol group (actuarial event rates at 36 months of 0.11 and 0.56, respectively, p = .0065). The cycle lengths of recurrent VT in these 21 patients in the VT noncontrol group were compared with those observed at final EP testing. A significant linear correlation was demonstrated (r = .76, p = .0001). Subgroup analysis of patients in the VT noncontrol group showed no EP predictors of outcome, including cycle length of induced VT. However, patients dying suddenly during the follow-up period had a higher prevalence of new or worsening congestive heart failure (75%) compared with patients with VT recurrence (19%) or those with no arrhythmic event (29%) (p less than .02).2off

Hypertrophic cardiomyopathy and myocardial ischemia with normal coronary arteries

The case reported herein illustrates an unusual form of nonobstructive hypertrophic cardiomyopathy which was associated with Wolff-Parkinson-White syndrome, myocardial ischemia and necrosis despite normal coronary arteries. The patient is unique since the hypertrophied myocardial segment was localized exclusively to the posterolateral free wall. Quantitative thallium-201 scintigraphy demonstrated reversible ischemia that corresponded precisely with this region of posterolateral hypertrophy. While the exact mechanism for ischemia in patients with hypertrophic cardiomyopathy and normal coronary arteries remains controversial, a functional rather than anatomic disturbance of blood flow seems likely.

Differential electrophysiologic properties of decremental retrograde pathways in long RP' tachycardia

Long RP' supraventricular tachycardias (SVT) often demonstrate both slow and decremental conduction properties in the retrograde pathway of the reentrant circuit. The electrophysiologic properties of these pathways are poorly understood. We studied 10 patients with long RP' SVT (RP'/RR, 0.52 to 0.71); five had the unusual form of atrioventricular nodal reentry (fast-slow) and five patients had accessory AV pathways with slow, decremental retrograde conduction properties. During SVT, the effects of intravenous adenosine (37.5 to 150 micrograms/kg), which increases potassium current (iK) in supraventricular tissue and hyperpolarizes membrane potential toward Ek (-90 mV), and the response to slow-inward channel blockade with verapamil (0.10 to 0.20 mg/kg iv) were evaluated. Adenosine and verapamil has similar effects in the presence of fast-slow AV nodal reentry since both agents terminated SVT by producing block in the retrograde slow AV nodal pathway. In contrast, adenosine and verapamil had differential effects on retrograde conduction in decremental accessory pathways. Adenosine terminated all episodes of SVT in the retrograde decremental pathway, whereas verapamil had a direct effect on this tissue in only two of five patients. Decremental retrograde accessory pathways can therefore demonstrate at least two types of electrophysiologic responses. Pathways that respond only to adenosine-induced hyperpolarizing K+ current likely comprise depressed fast-Na+ channel tissue, i.e., partially depolarized (greater than -60 to -70 mV) atrial tissue. In contrast, decremental accessory pathways that respond to both modulation of the slow-inward calcium current and K+ conductance have pharmacologic properties similar to those of the AV node and may represent more completely depolarized atrial fibers with resting membrane potentials of -60 mV or less.

Relation between amiodarone and desethylamiodarone plasma concentrations and electrophysiologic effects, efficacy and toxicity

Because the value of monitoring amiodarone plasma concentrations remains undefined, this study was performed to evaluate its role during the management of patients receiving amiodarone. The early electrophysiologic effects of amiodarone were assessed in 40 consecutive patients with coronary artery disease and sustained ventricular tachycardia or fibrillation who underwent electrophysiologic studies and measurement of amiodarone plasma concentration before and 29 +/- 15 (mean +/- SD) days after initiation of therapy. Amiodarone and desethylamiodarone plasma levels did not correlate with changes in either sinus cycle length, QTc interval, ventricular effective refractory period, AH and HV intervals or ventricular tachycardia cycle length. Amiodarone and desethylamiodarone plasma concentrations and the effects of the drug on conduction intervals or right ventricular effective refractory periods were not related to suppression of arrhythmia induction by ventricular stimulation after 1 month of therapy. The relation between amiodarone plasma concentrations and both toxicity and efficacy during long-term therapy were prospectively assessed in a larger series of 114 consecutive patients with either symptomatic supraventricular or ventricular arrhythmias who were followed up on long-term amiodarone therapy for 26 +/- 15 months. Sixty-three patients (55%) had one or more adverse effects attributed to amiodarone. By life-table analysis, 40, 69 and 80% of patients had experienced an adverse reaction after 1, 2 and 3 years of therapy, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of ischemia by quantitative thallium-201 scintigraphy in patients with ventricular tachycardia or fibrillation inducible by programmed stimulation

The prevalence of exercise-induced ischemia was determined by thallium-201 (TI-201) scintigraphic criteria in patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) inducible by programmed electrical stimulation. Thirty-eight patients (age 57 +/- 19 years), of whom 87% had angiographic coronary artery disease, underwent quantitative TI-201 exercise scintigraphy within 14 days of invasive electrophysiologic testing. The mean rest ejection fraction was 38 +/- 9%. Eighty percent of patients had 1 or more regions with akinetic or dyskinetic wall motion. Thallium-201 scan segments were scored as normal or containing redistribution defects or mild or severe persistent defects. Only 4 patients (10%) had only redistribution defects and 9 (24%) had both redistribution defects and persistent defects; 32 of 38 patients (84%) had 1 or more persistent defects, of which 26 had at least 1 severe, persistent defect (more than 50% reduction in TI-201 activity). Patients with and without exercise-induced VT had a similar prevalence of redistribution. Redistribution defect prevalence was similar in patients with polymorphic VT (3 of 13) and monomorphic VT (10 of 25) during programmed electrical stimulation (difference not significant). Thus, patients with VT or VF induced by programmed ventricular stimulation have extensive TI-201 scintigraphic abnormalities on exercise scintigrams, predominantly those suggesting scar, with associated severe regional wall motion abnormalities at rest. The scintigraphic prevalence of exercise-induced ischemia is low and TI-201 redistribution and exercise ST depression are observed with equal frequency in patients with and those without VT induced during exercise.

Mechanism of atropine-resistant atrioventricular block during inferior myocardial infarction: possible role of adenosine

Mechanisms responsible for atrioventricular (AV) block during acute inferior myocardial infarction are only partially understood. Increased parasympathetic tone is the factor usually postulated; however, persistence of AV block after atropine administration is frequently observed. Adenosine, an endogenous ischemic metabolite, has well established depressant effects on AV node conduction. In this report, an episode of atropine-resistant AV block was reversed by aminophylline, a competitive adenosine antagonist, in a patient with an acute inferior myocardial infarction. This observation suggests a role for adenosine in the mediation of ischemia-induced AV node block.

Adenosine-sensitive ventricular tachycardia: evidence suggesting cyclic AMP-mediated triggered activity

Catecholamine-induced triggered activity is thought to be caused by intracellular calcium overload mediated by elevation of intracellular cyclic AMP (cAMP). Although shown to occur in isolated preparations, evidence supporting its clinical existence has been lacking. Electrophysiologic studies were performed in four patients with structurally normal hearts who had exertionally related sustained ventricular tachycardia (VT). Programmed stimulation reproducibly initiated and terminated VT in all patients. Induction of tachycardia was also facilitated by infusion of isoproterenol. Adenosine, an endogenous nucleoside, whose only known electrophysiologic effect on ventricular myocardium and Purkinje fibers is antagonism of catecholamine-induced stimulation of intracellular cAMP production, reproducibly terminated all episodes of VT. The tachycardia was also terminated by intravenous verapamil and by the Valsalva maneuver and/or carotid sinus massage. Beta-Adrenergic receptor blockade with propranolol either terminated or prevented induction of VT during programmed stimulation or catecholamine challenge. Adenosine was also administered during VT to 14 patients whose arrhythmias fulfilled standard criteria for reentry, two of whom also had exercise-induced VT. Adenosine, at a dose (112.5 to 225 micrograms/kg iv) sufficient to cause either sinus slowing/arrest or ventriculoatrial block during ventricular pacing, failed to slow or terminate any episode of VT in these patients. Verapamil and autonomic modulation were also ineffective in this group of patients. Adenosine, verapamil, vagal maneuvers (acetylcholine), and beta-adrenergic receptor blockade are all known to decrease the slow-inward calcium current either directly by modulating calcium channels or indirectly by inhibiting production of cellular cAMP. Therefore the observation in this study that interventions that lower intracellular cAMP either terminate or prevent induction of VT in patients with structurally normal hearts and exercise-induced VT suggests that the mechanism of tachycardia may be cAMP-mediated triggered activity.

Adverse reactions to antiarrhythmic drugs during therapy for ventricular arrhythmias

We analyzed the incidence of adverse reactions to antiarrhythmic drugs in 123 consecutive patients with a history of sustained ventricular tachycardia or ventricular fibrillation. Blood levels were measured serially and were maintained within the usual therapeutic range. Minor reactions were defined as those that required dosage reduction and major reactions as those that required drug discontinuation or permanent pacing for bradycardia. A total of 237 individual, oral drug trials were evaluated in the 123 patients. Adverse reactions were noted in 79 trials (33%). Fifty-nine (48%) of the 123 patients had one or more adverse reaction. Major reactions were noted in 36 patients (29%). Adverse effects occurred during 49% of trials with mexiletine hydrochloride, 44% of trials with amiodarone, 24% of trials with procainamide hydrochloride, and 18% of trials with quinidine sulfate or gluconate. In conclusion, clinically significant adverse reactions are common during drug therapy for ventricular arrhythmias. These observations indicate that with the drugs used in this study, an acceptable risk-benefit ratio will be possible only in patients at a significant risk for a symptomatic arrhythmia. Antiarrhythmic drug therapy in patients at low risk for serious arrhythmia should be discouraged.

Surgical management of sustained ventricular arrhythmias presenting within eight weeks of acute myocardial infarction

When it occurs after a recent (less than eight weeks) myocardial infarction, sustained ventricular tachycardia (VT) or fibrillation (VF) has resulted in a high one-year mortality despite antiarrhythmic drug therapy. We have operated on 29 patients with this syndrome either on an emergency basis because they had medically refractory VT or VF (19 patients) or electively if they had persistent congestive heart failure or angina and VT or VF (10 patients). Ages ranged from 36 to 82 years (mean, 60 years), and the mean left ventricular ejection fraction was 31 +/- 13%. Each patient had failed a trial of one or more (average, four) antiarrhythmic drugs and because of VT, required electrical cardioversion on an average of five occasions. Intraoperative mapping was complicated by multiple VT morphologies (9 patients), the rapid degeneration of VT to VF (5 patients), and the inability to induce VT reliably (5 patients). Subendocardial excision was performed at the site of the earliest electrical activity, or if no single site could be identified, a wide subendocardial excision of all visible scar was performed. There were 4 perioperative deaths (14%). All operative survivors underwent postoperative electrophysiological studies. Twenty of them required no further antiarrhythmic therapy, but 5 patients required drug therapy because of either spontaneous (2 patients) or electrically induced (3 patients) VT. During follow-up (average, 16 months) of these 25 patients, there have been 3 late deaths, 2 of them sudden. Two of the 3 late deaths were those of patients taking antiarrhythmic drugs. Our results demonstrate the effectiveness of early operative intervention when sustained ventricular arrhythmias complicate recovery after myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial pacing for conversion of atrial flutter

Fifty-seven episodes of atrial flutter in 46 consecutive medically treated patients (aged 60 +/- 17 years) were treated by rapid atrial pacing. Thirty-three patients (72%) had structural heart disease. Most pacing trials were conducted in patients receiving digoxin (88%) and antiarrhythmic drugs (77%). In 51 of 57 trials (89%), patients were successfully converted to normal sinus rhythm. Multivariate analysis revealed that patients who had congestive heart failure and who were older were more likely to be refractory to pacing. Left atrial size did not influence outcome. Confirmation of local atrial capture with a bipolar atrial electrogram and use of multiple atrial pacing sites enhanced the success rate. Eight patients (17%) demonstrated sinus node suppression after atrial pacing; sinus node disease was previously unsuspected in 4 of these patients. These bradyarrhythmias were easily managed because a pacing catheter was already in place. The only significant complication was femoral vein thrombosis in 1 patient. It is concluded that atrial pacing is an effective, safe and convenient method for the elective conversion of atrial flutter in the general population of medically treated patients. This technique is an attractive alternative to transthoracic cardioversion, and may be preferable in many patients.

Resection of scarred papillary muscles improves outcome after surgery for ventricular tachycardia

Papillary muscle scarring is encountered frequently during operations for sustained ventricular tachycardia (VT). Indications for excision of the papillary muscle scar and mitral valve replacement (MVR) are controversial. The findings in 46 consecutive patients undergoing operative electrophysiologic map-directed endocardial resections for VT were reviewed. There was papillary muscle scarring in 15 patients (average age: 59 years; sex: 11 male, 4 female; average ejection fraction: 31 +/- 14%). Eleven patients had a VT with the site of origin on a scarred papillary muscle; four had another VT site of origin. Six patients underwent papillary muscle scar resection (5 with MVR); six underwent papillary muscle cryotherapy (-60 C X 2 min); and three had neither papillary muscle resection nor MVR. All six patients with papillary muscle resection +/- MVR are alive and free of arrhythmia after 14.3 +/- 7.6 months of follow-up. Five of six patients treated by papillary muscle cryotherapy alone manifested spontaneous (4 patients) or inducible (1 patient) VT during early postoperative evaluation. Two of the three patients with untreated papillary muscle scarring developed late complications requiring reoperation. One patient developed mitral regurgitation requiring MVR 5 months later. The other developed a previously undocumented VT 2 years after operation. Significant papillary muscle scarring visualized at the time of operation for arrhythmia is an indication for resection of the scar and the papillary muscle, even if this necessitates MVR. In this series, attempts to preserve the papillary muscle, by incomplete resection of the scar or by cryotherapy, resulted in a high failure rate owing to recurrent VT or mitral regurgitation.

Repetitive supraventricular tachycardia: clinical manifestations and response to therapy with amiodarone

Repetitive supraventricular tachycardia is an uncommon arrhythmia which usually occurs in patients free of structural heart disease. It is characterized by incessant short salvos of supraventricular tachycardia separated by only one or two normal sinus beats. Therapy with conventional antiarrhythmic drugs is usually ineffective. This report describes three patients with repetitive supraventricular tachycardia in whom evidence for associated sinus node dysfunction was observed. Amiodarone therapy, with ventricular pacing in two patients, has provided effective control of this arrhythmia in all three patients.

Extended subendocardial resection. A surgical approach to ventricular tachyarrhythmias that cannot be mapped intraoperatively

The optimal surgical management of patients with sustained, uniform-morphology ventricular tachycardia is endocardial activation sequence mapping during ventricular tachycardia and directed resection and/or cryoablation of the involved endocardium. The results of these procedures are superior to those obtained with nondirected aneurysmectomy. The optimal operative procedure when stable uniform ventricular tachycardia cannot be induced intraoperatively is uncertain. Between April, 1982, and April, 1984, intraoperative endocardial mapping was attempted on 33 patients with prior ventricular tachycardia. There were six perioperative deaths. Completely satisfactory intraoperative electrophysiologic maps were obtained in only 17 of the remaining 27 patients (63%). In 10 of these 27 patients, stable ventricular tachycardia could not be induced in the operating room, and satisfactory mapping thus could not be performed. In the first three of these 10 patients, limited subendocardial resection was performed either in regions with fractionated activity during sinus rhythm (two patients) or in regions suggested by preoperative catheter mapping (one patient). Ventricular tachycardia recurred postoperatively in two of these three patients. In the next seven patients, all visible endocardial scar around the border of the aneurysm was resected. Clinical ventricular tachycardia could not be induced at postoperative electrophysiologic study and has not recurred in these seven patients. These results suggest that complete endocardial resection provides an acceptable operative approach when intraoperative electrophysiologic mapping is not satisfactory.

Sustained ventricular tachyarrhythmias within 2 months of acute myocardial infarction: results of medical and surgical therapy in patients resuscitated from the initial episode

Sustained ventricular tachycardia or fibrillation that develops during the early recovery period after acute myocardial infarction is a common clinical problem whose management remains controversial. Fifty-three patients who survived an initial episode of sustained ventricular tachycardia or fibrillation occurring between 3 and 60 days (mean +/- SD 21 +/- 16) after myocardial infarction were evaluated. Most of these patients had had a large (peak creatine kinase = 1,729 +/- 882 IU) complicated infarction. Forty-two (79%) of the 53 patients had had repetitive sustained ventricular arrhythmias and the condition of 19 of these could not be stabilized with drug therapy. Twenty-eight patients received medical therapy only. Twenty-four survived and were discharged from the hospital. Twenty-five patients underwent infarctectomy or aneurysmectomy either on an emergency basis (16 patients) or electively because of coexistent heart failure or angina (9 patients). Intraoperative mapping was attempted in these patients but was completely successful in only 13 (52%). Operative mortality was 16% with all deaths occurring in patients who were in shock before surgery. Five of 21 surgically treated survivors required long-term antiarrhythmic therapy. Twenty-one of 24 patients medically treated remain alive and well after 15 +/- 10 months of follow-up. Nineteen of 21 surgically treated patients remain alive and well after 17.9 +/- 11 months. One of these patients required reoperation for severe mitral regurgitation. These results confirm the poor medical prognosis of sustained ventricular tachyarrhythmias that present during the first 2 months after myocardial infarction but demonstrate that an acceptable rate of survival can be achieved with a combined medical and surgical approach to therapy.

Effect of prostacyclin on vascular capacity in the dog

Since the discovery of prostacyclin (PGI2) in 1976, there has been great interest in its vascular effects and potential clinical applications. High infusion rates of PGI2 markedly depress arterial blood pressure both in animal studies and in clinical trials. This fall in pressure may result entirely from a decrease in arterial resistance. However, it is possible that the administration of PGI2 may decrease ventricular filling due to an increase in vascular capacity. To investigate whether or not PGI2 affects vascular capacity, we infused PGI2 intraarterially at both 10 and 25 micrograms/min into 15 dogs on total cardiopulmonary bypass. These infusions were associated with a 25 +/- 3 mmHg decrease in arterial pressure and an increase in vascular capacity of 155 +/- 29 ml (SE, P less than 0.005). This increase in capacity was greater (P less than 0.02) than the increase of 23 +/- 42 ml resulting from infusions of nitroglycerin into eight dogs at 2 mg/min, which produced a decrease in arterial pressure of 23 +/- 4 mmHg, which was the maximal effect that could be achieved. Neither bilateral cervical vagotomy nor beta adrenergic blockade with propranolol significantly diminished the increase in vascular capacity associated with infusions of PGI2. The results from studies in four eviscerated dogs indicated that PGI2 acts on both splanchnic and extrasplanchnic capacity vasculature. To compare the direct effects of PGI2 with those of nitroglycerin and nitroprusside on venous tone, we used an isolated canine spleen preparation. Infusions of PGI2 (100 mcg/min) increased spleen weight in this preparation by 9.0 +/- 2.4% (n = 10, P less than 0.001); this increase was significantly greater than increases of 3.6 +/- 2.2% (P less than 0.001) and 3.5 +/- 2.3% (P less than 0.001) caused by high dose infusions of nitroglycerin (1 mg/min) and nitroprusside (400 micrograms/min), respectively. Thus, PGI2 substantially increases vascular capacity by a mechanism that appears to involve a direct action on vascular smooth muscle. Furthermore, these results suggest that PGI2 might be useful in clinical conditions in which an increase in vascular capacity is indicated.

Role of invasive electrophysiologic studies in the evaluation and treatment of supraventricular tachycardia

Electrophysiologic studies have provided new insights into the mechanisms responsible for supraventricular arrhythmias and have enabled investigators to evaluate with precision the acute effects of pharmacologic, physiologic, electrical, and surgical interventions. Not all patients with supraventricular arrhythmias require invasive studies, however, since empiric drug trials will often be adequate for management. At present, the clinical indications for study include the following: (1) for diagnosis of tachycardia mechanism when scalar ECG analysis is uncertain; (2) for assessment of risk of future life-threatening arrhythmia; and (3) as a rapid means of assessing future therapy when sporadic arrhythmias are likely to be poorly tolerated. Innovations that include surgical and catheter ablations of tachycardia pathways and antitachycardia pacing devices hold great promise and in the future, will provide nonpharmacologic options for patients poorly controlled by or intolerant of drug therapy.