Long-term follow-up of patients with long-QT syndrome treated with beta-blockers and continuous pacing.

BACKGROUND: The long-QT syndrome is associated with sudden cardiac death. Combination of beta-blocker and pacing therapy has been proposed for treatment of drug-resistant patients. The purpose of this study was to summarize our long-term experience with combined therapy in patients with long-QT syndrome. METHODS AND RESULTS: A total of 37 patients with idiopathic long-QT syndrome were treated with combined therapy consisting of continuous cardiac pacing and maximally tolerated beta-blocker therapy and followed up for 6.3+/-4. 6 years (mean+/-SD). The group consisted of 32 female and 5 male patients with a mean age of 31.6 years. The mean paced rate was 82+/-7 bpm (range, 60 to 100 bpm). On follow-up, recurrent symptoms caused by pacemaker malfunction were documented in 3 patients. Four patients died during the follow-up period: 2 adolescents stopped beta-blocker therapy, 1 patient died suddenly while treated with combined therapy, and 1 patient died of unrelated causes. In addition, 3 patients had resuscitated cardiac arrest while on combined therapy, and 1 patient had repeated, appropriate implantable cardioverter-defibrillator discharges on follow-up. CONCLUSIONS: Because 28 of 37 patients remain without symptoms with beta-blocker therapy and continuous pacing, combined therapy appears to provide reasonable, long-term control for this high-risk group. However, the incidence of sudden death and aborted sudden death (24% in all patients and 17% in compliant patients) strongly suggests the use of a "back-up" defibrillator, particularly in noncompliant adolescent patients. Implantable cardioverter-defibrillator therapy, however, may be associated with recurrent shocks in susceptible patients.

Relationship between sinus rhythm activation and the reentrant ventricular tachycardia isthmus.

BACKGROUND: In canine hearts with inducible reentry, the isthmus tends to form along an axis from the area of last to first activity during sinus rhythm. It was hypothesized that this phenomenon could be quantified to predict reentry and the isthmus location. METHODS AND RESULTS: An in situ canine model of reentrant ventricular tachycardia occurring in the epicardial border zone was used in 54 experiments (25 canine hearts in which primarily long monomorphic runs of figure-8 reentry were inducible, 11 with short monomorphic or polymorphic runs, and 18 lacking inducible reentry). From the sinus rhythm activation map for each experiment, the linear regression coefficient and slope were calculated for the activation times along each of 8 rays extending from the area of last activation. The slope of the regression line for the ray with greatest regression coefficient (called the primary axis) was used to predict whether or not reentry would be inducible (correct prediction in 48 of 54 experiments). For all 36 experiments with reentry, isthmus location and shape were then estimated on the basis of site-to-site differences in sinus rhythm electrogram duration. For long and short runs of reentry, estimated isthmus location and shape partially overlapped the actual isthmus (mean overlap of 71.3% and 43.6%, respectively). On average for all reentry experiments, a linear ablation lesion positioned across the estimated isthmus would have spanned 78.2% of the actual isthmus width. CONCLUSIONS: Parameters of sinus rhythm activation provide key information for prediction of reentry inducibility and isthmus location and shape.

Electrophysiological effects of ibutilide in patients with accessory pathways.

BACKGROUND: Atrial fibrillation (AF) may cause life-threatening ventricular arrhythmias in patients with Wolff-Parkinson-White syndrome. We prospectively evaluated the effects of ibutilide on the conduction system in patients with accessory pathways (AP). METHODS AND RESULTS: In part I, we gave ibutilide to 22 patients (18 men, 31+/-13 years of age) who had AF during electrophysiology study, including 6 pediatric patients

Use of electroanatomic mapping to delineate transseptal atrial conduction in humans.

BACKGROUND: Interaction between wave fronts in the right and left atrium may be important for maintenance of atrial fibrillation, but little is known about electrophysiological properties and preferential routes of transseptal conduction. METHODS AND RESULTS: Eighteen patients (age 44+/-12 years) without structural heart disease underwent right atrial electroanatomic mapping during pacing from the distal coronary sinus (CS) or the posterior left atrium. During distal CS pacing, 9 patients demonstrated a single transseptal breakthrough near the CS os, 1 patient in the high right atrium near the presumed insertion of Bachmann's bundle and 1 patient near the fossa ovalis. The mean activation time from stimulus to CS os was 48+/-15 ms compared with 86+/-15 ms to Bachmann's bundle insertion (P<0.01) and 59+/-23 ms to the fossa ovalis (P=NS and P<0.01, respectively). During left atrial pacing, the earliest right atrial activation was near Bachmann's bundle in 5 and near the fossa ovalis in 4 patients. The activation time from stimulus to CS os was 70+/-15 ms compared with 47+/-16 ms to Bachmann's bundle (P<0.01) and 59+/-25 ms to the fossa ovalis (P=NS). Whereas the total septal activation time was not significantly different during CS pacing compared with left atrial pacing (41+/-16 versus 33+/-17 ms), the total right atrial activation time was longer during CS pacing (117+/-49 versus 79+/-15 ms; P<0.05). CONCLUSIONS: Three distinct sites of early right atrial activation may be demonstrated during left atrial pacing. These sites are in accord with anatomic muscle bundles and may have relevance for maintenance of atrial flutter or fibrillation.

Electrophysiologic effects of adenosine in patients with supraventricular tachycardia.

BACKGROUND: We correlated the electrophysiologic (EP) effects of adenosine with tachycardia mechanisms in patients with supraventricular tachycardias (SVT). METHODS AND RESULTS: Adenosine was administered to 229 patients with SVTs during EP study: atrioventricular (AV) reentry (AVRT; n=59), typical atrioventricular node reentry (AVNRT; n=82), atypical AVNRT (n=13), permanent junctional reciprocating tachycardia (PJRT; n=12), atrial tachycardia (AT; n=53), and inappropriate sinus tachycardia (IST; n=10). There was no difference in incidence of tachycardia termination at the AV node in AVRT (85%) versus AVNRT (86%) after adenosine, but patients with AVRT showed increases in the ventriculoatrial (VA) intervals (13%) compared with typical AVNRT (0%), P<0.005. Changes in atrial, AV, or VA intervals after adenosine did not predict the mode of termination of long R-P tachycardias. For patients with AT, there was no correlation with location of the atrial focus and adenosine response. AV block after adenosine was only observed in AT patients (27%) or IST (30%). Patients with IST showed atrial cycle length increases after adenosine (P<0.05) with little change in activation sequence. The incidence of atrial fibrillation after adenosine was higher for those with AVRT (15%) compared with typical AVNRT (0%) P<0.001, or atypical AVNRT (0%) but similar to those with AT (11%) and PJRT (17%). CONCLUSIONS: The EP response to adenosine proved of limited value to identify the location of AT or SVT mechanisms. Features favoring AT were the presence of AV block or marked shortening of atrial cycle length before tachycardia suppression. Atrial fibrillation was more common after adenosine in patients with AVRT, PJRT, or AT. Patients with IST showed increases in cycle length with little change in atrial activation sequence after adenosine.

Atypical right atrial flutter patterns.

BACKGROUND: The purpose of our study was to define the incidence and mechanisms of atypical right atrial flutter. METHODS AND RESULTS: A total of 28 (8%) of 372 consecutive patients with atrial flutter (AFL) had 36 episodes of sustained atypical right AFL. Among 24 (67%) of 36 episodes of lower loop reentry (LLR), 13 (54%) of 24 episodes had early breakthrough at the lower lateral tricuspid annulus, whereas 11 (46%) of 24 episodes had early breakthrough at the high lateral tricuspid annulus, and 9 (38%) of 24 episodes showed multiple annular breaks. Bidirectional isthmus block resulted in elimination of LLR. A pattern of posterior breakthrough from the eustachian ridge to the septum was observed in 4 (14%) of 28 patients. Upper loop reentry was observed in 8 (22%) of 36 episodes and was defined as showing a clockwise orientation with early annular break and wave-front collision over the isthmus. Two patients had atypical right AFL around low voltage areas ("scars") in the posterolateral right atrium. CONCLUSIONS: Atypical right AFL is most commonly associated with an isthmus-dependent mechanism (ie, LLR or subeustachian isthmus breaks). Non-isthmus-dependent circuits include upper loop reentry or scar-related circuits.

Mechanisms of atrial fibrillation: is a cure at hand?

The mechanisms of atrial fibrillation relate to the presence of random reentry involving multiple interatrial circuits. Triggers for development of atrial fibrillation include rapidly discharging atrial foci (mainly from pulmonary veins) or degeneration of atrial flutter or atrial tachycardia into fibrillation. Therapy for control of atrial fibrillation includes drugs, atrial pacing for those with sinus node dysfunction, or ablation of the atrioventricular junction. Therapeutic maneuvers for cure of atrial fibrillation include surgical or radiofrequency catheter induced linear lesions to reduce the atrial tissue and prevent the requisite number of reentrant wavelets. We need a much better understanding of basic mechanisms before a true cure is at hand.

Value of electrocardiographic leads MCL1, MCL6 and other selected leads in the diagnosis of wide QRS complex tachycardia.

To compare the modified precordial leads MCL1 and MCL6 with the conventional precordial leads V1 and V6 and assess the diagnostic accuracy of selected leads for continuous bedside electrocardiographic (ECG) monitoring, 121 wide QRS complex tachycardias were recorded from 92 patients during cardiac electrophysiologic study. As ascertained from intracardiac recordings, 86 tachycardias were ventricular and 35 were supraventricular with aberrant conduction. Early or late peaking of the predominant QRS deflection in lead MCL6 or V6 proved valuable in diagnosing wide complex tachycardia. An interval of less than or equal to 50 ms from the onset of the QRS complex to the predominant peak (or nadir) indicated supraventricular tachycardia; an interval of greater than or equal to 70 ms indicated ventricular tachycardia. The QRS complexes in leads MCL1 and MCL6 were comparable to those in leads V1 and V6 during sinus rhythm. Significant discrepancies in QRS configuration occurred between the modified and conventional precordial leads during ventricular tachycardia, especially between leads MCL1 and V1; however. these differences did not affect diagnostic accuracy. A single MCL1, V1, MCL6 or V6 lead was equally valuable in the diagnosis of wide complex tachycardia and far superior to a single lead II. A combination of leads (MCL1 + MCL6), (V1 + V6), (V1 + I + aVF) or (V1 + V6 + I + aVF) was superior to a single lead or the routinely monitored lead V1 + II combination.

Comparison of high energy direct current and radiofrequency catheter ablation of the atrioventricular junction.

OBJECTIVES: The goal of the study was to determine short- and long-term success and complications of radiofrequency atrioventricular (AV) junction catheter ablation and to compare these with those of high energy direct current catheter ablation. BACKGROUND: Catheter ablation of the AV junction with radiofrequency or direct current energy is an accepted treatment for drug-refractory supraventricular tachycardias. Few data are available on the long-term success and effects of radiofrequency ablation or its comparison with direct current ablation. METHODS: Fifty-four patients who underwent attempted AV junction ablation with radiofrequency energy were followed up for a mean of 24 +/- 8.4 months. These patients were retrospectively compared with 49 patients who underwent attempted AV junction ablation with direct current energy and were followed up for a mean of 41 +/- 23 months. RESULTS: The early success rate at the time of discharge for radiofrequency ablation was 81.5%, which was not statistically different from that for direct current ablation (85.7%). Fewer sessions were required to achieve complete AV block in the radiofrequency group (1.05 +/- 0.23) (mean +/- SD) compared with the direct current group (1.21 +/- 0.41) (p = 0.02). Although overall complication rates were similar for both groups (9.3% in the radiofrequency group and 8.2% in the direct current group), there was a trend toward more life-threatening early complications in those patients who received direct-current shocks (6.8%) than in those who underwent radiofrequency ablation alone (2.3%) (p = 0.1). Early sudden death (one patient), early ventricular tachycardia (two patients) and cardiac tamponade (one patient) were seen only in those patients who underwent ablation with direct current energy, whereas pulmonary embolism (one patient) was the only early life-threatening complication in the radiofrequency group. During follow-up, the rate of recurrence of AV conduction was the same (5%) for both the direct current and radiofrequency groups. In the direct current group, one patient died suddenly 2 weeks after the procedure and another had a cardiac arrest due to ventricular tachycardia 6 h after the procedure. In the radiofrequency group, two patients died suddenly at 11 and 7 months, respectively. Two patients, one who had unsuccessful radiofrequency ablation and required direct current ablation, were resuscitated from ventricular tachycardia. CONCLUSIONS: Radiofrequency energy appears to be as efficacious as and perhaps safer than direct current energy for AV junction ablation.

Electrophysiologic testing and follow-up of patients with aborted sudden death.

Clinical, electrophysiologic and follow-up data were analyzed for 108 patients with aborted sudden death. The mean follow-up interval was 2 years. All patients underwent baseline drug-free invasive electrophysiologic studies. Seventy-five patients (group I) had inducible ventricular arrhythmias (including nonsustained and sustained ventricular tachycardia and ventricular fibrillation) and 33 patients (group II) had no inducible arrhythmias. Noninducibility was not predictive of a favorable outcome, because the incidence of both sudden death and recurrent ventricular tachycardia was similar in the two groups. Treatment guided by electrophysiologic testing was used in 17 patients; in 13 (17%) in group I arrhythmias became noninducible, and in 4 (5%) sustained ventricular arrhythmias became nonsustained after administration of conventional drugs. There was a significantly higher incidence of sudden death and recurrent ventricular tachycardia in the 4 patients with inducible arrhythmias (n = 3, 75%) compared with the 13 patients whose arrhythmias were noninducible (n = 2, 15%) (p less than 0.05). For the group as a whole, 11% died suddenly and 15% had recurrence of ventricular tachycardia. Sixty-four patients were treated with amiodarone and, of these, four (6%) died suddenly during the follow-up period and nine (14%) had recurrent ventricular tachycardia. Ventricular arrhythmias could be induced in 69% of patients with aborted sudden death but inducibility could be suppressed in only 20% of them. The role of therapy guided by electrophysiologic testing could therefore not be fully assessed. The findings reveal a significant recurrence rate of symptomatic, potentially life-threatening ventricular arrhythmias in medically treated patients with aborted sudden death.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical features and prognosis of patients with out of hospital cardiac arrest and a normal electrophysiologic study.

Nineteen patients survived a cardiac arrest not associated with an acute myocardial infarction, and had a normal electrophysiologic study with no inducible ventricular tachycardia despite programmed stimulation with one to three extrastimuli at two or more ventricular sites. Among 14 patients who had obstructive coronary artery disease, cardiac arrest occurred during exertion or an episode of angina pectoris in 11; 24 hour ambulatory electrocardiographic recordings demonstrated infrequent or no premature ventricular complexes in 10 and an ischemic response occurred during stage I or II (Bruce protocol) in 6 of 9 patients who underwent exercise testing. Treatment of these patients consisted of myocardial revascularization (eight patients) or antianginal medications (six patients). Only three patients were also treated with an antiarrhythmic drug. Over a follow-up period of 26 +/- 15 months (mean +/- standard deviation), only one patient died suddenly. Two patients who had coronary artery spasm were treated with coronary vasodilator medications and had no recurrence of cardiac arrest over 7 and 36 months of follow-up, respectively. Three patients who had cardiomyopathy or no identifiable structural heart disease were treated with nadolol or amiodarone and had no recurrence of cardiac arrest over 3 to 27 months of follow-up. Among patients who survive a cardiac arrest and have a normal electrophysiologic study, those with obstructive coronary artery disease or coronary artery spasm generally have an excellent prognosis with treatment directed primarily at the underlying heart disease. The clinical features of these patients suggest that cardiac arrest was related to ischemia rather than a primary arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and efficacy of central intravenous bolus administration of adenosine for termination of supraventricular tachycardia.

OBJECTIVES: This study was done to quantify the dosing differences between central and peripheral adenosine administration for treatment of supraventricular tachycardia. BACKGROUND: Earlier studies that evaluated the safety and efficacy of adenosine primarily utilized a peripheral site of administration. Although it has been recommended that lower doses should be given centrally, dosing recommendations have not been provided. METHODS: Thirty adults with supraventricular tachycardia underwent invasive electrophysiologic study and were treated with central and peripheral intravenous administration of adenosine. Peripheral injections were administered through a venous catheter in an upper extremity and central infusions were accomplished by means of a catheter positioned in or near the right atrium. The site of administration was randomized and each subject received adenosine by both routes. Adenosine was administered every minute in increasing increments of 3, 6, 9 and 12 mg until the tachycardia terminated. Peripheral responses were compared with those obtained centrally. RESULTS: The minimal effective peripheral dose was distributed among the four doses: Tachycardia was terminated in 11 patients with 3 mg (37%), in 10 (33%) with 6 mg, in 4 (13%) with 9 mg and in 5 (17%) with 12 mg. In contrast, after central administration, 23 episodes of tachycardia (77%) were terminated with 3 mg, 6 (20%) with 6 mg and 1 (3%) with 9 mg; none required 12 mg. Lower doses of adenosine were more effective after central than after peripheral administration, with 63% of the subjects requiring a lesser dose. There was no difference between the two routes of drug administration in the incidence of side effects or transient arrhythmias at the time of tachycardia termination. CONCLUSIONS: Adenosine can be safely given centrally for termination of supraventricular tachycardia. The initial dose should be 3 mg.

Exercise-induced double (atrial and ventricular) tachycardia: a report of three cases.

Exercise-induced double tachycardia, i.e., the simultaneous occurrence of atrial and ventricular tachycardia, is described in three patients: one patient had coronary artery disease; the other two were young and had no apparent heart disease. One of the latter patients later died suddenly. Double tachycardia could not be initiated by programmed atrial or ventricular stimulation. In two patients atrial tachycardia always preceded ventricular tachycardia and, in one patient, ventricular tachycardia was terminated by the administration of adenosine triphosphate. Reentry does not seem to be the underlying mechanism for these arrhythmias; abnormal automaticity or triggered activity may be the mechanism.

Usefulness of sotalol for drug-refractory malignant ventricular arrhythmias.

Fifty patients with recurrent sustained symptomatic ventricular tachycardia (43 patients) or ventricular fibrillation (7 patients) resistant to a mean of 2.8 + 1.4 antiarrhythmic drugs were treated with sotalol, a beta-adrenergic receptor antagonist, and 45 underwent invasive electrophysiologic testing before and after sotalol therapy. The arrhythmia became noninducible in 10, was slower and hemodynamically well tolerated in 12 and was poorly tolerated in 23. Four patients were empirically treated with long-term administration of oral sotalol as were 21 patients who either had noninducible arrhythmia (10 patients) or had hemodynamically stable ventricular tachycardia (11 patients). In these 25 patients treated with long-term administration of sotalol, there was no recurrence of ventricular tachycardia in the group with noninducible arrhythmia, whereas 37% of patients with inducible ventricular tachycardia had new ventricular tachycardia or sudden death. Programmed ventricular stimulation with up to three extrastimuli proved to be an excellent predictor of drug efficacy and a good predictor of inefficacy. A positive prior response to amiodarone was not a reliable indicator of a positive response to sotalol. Side effects included those attributed to both beta-adrenergic blockade as well as proarrhythmic effects. The latter were observed in two of four patients with a QT interval greater than 600 ms. Sotalol was found to be effective therapy for a subset of patients with ventricular tachycardia unresponsive to type IA drugs.

Effects of catheter-delivered electrical discharges near the tricuspid anulus in dogs.

The possibility of using electrical discharges to ablate right free wall accessory pathways by delivering a series of catheter shocks near the tricuspid anulus was assessed in a canine model. Before the shock, the amplitudes of the atrial and ventricular electrograms recorded from the distal electrodes were compared (A/V ratio), and the atrial pacing threshold was determined. To assess effects on function and arrhythmogenicity, right heart pressures were measured and programmed ventricular stimulation was performed before the shock and prior to sacrifice 7 to 10 days after the shock. Nine dogs received a total of 24 discharges at varying energies (50 to 400 J). Nonsustained ventricular tachycardia occurred with 13 shocks (62%) and transient atrioventricular block with 9 shocks (43%). There was no worsening in cardiac or valvular function as determined by right heart pressure measurements or right ventriculography. Programmed ventricular stimulation performed before the shocks and repeated before sacrifice failed to induce ventricular arrhythmias. The endocardial lesion produced by the shock was roughly circular and its area correlated with both the magnitude of the shock as well as the atrial pacing threshold. Transmural necrosis always occurred at the anulus when the A/V ratio was between 1.00 and 1.50 and preshock atrial pacing threshold suggested adequate wall contact (less than 1.5 mA). There was mild inflammation of the adventitia of the right coronary artery near two discharge sites (both 200 J) and inflammation of the media near one discharge site (400 J); no intimal involvement was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Catheter-induced His bundle ablation in a patient with reentrant tachycardia associated with a nodoventricular tract.

A patient with refractory tachycardia associated with a nodoventricular tract in whom tachycardia was successfully controlled with catheter-induced ablation of the His bundle is reported. Tachycardia was always initiated by ventricular impulses that blocked retrogradely in the nodoventricular tract and conducted by way of the His-Purkinje system. The His bundle ablation was successfully accomplished by delivering two direct current countershocks of 400 J each in the region of the His bundle. Postablation, the patient manifested stable 1:1 anterograde conduction via the atrioventricular (AV) node-nodoventricular fiber over a wide range of heart rates (50 to 180 beats/min). A permanent pacemaker was not implanted at the patient's request. During 16 months of follow-up, the patient has had stable sinus rhythm with no sustained tachycardia. Brief asymptomatic episodes of ectopic atrial tachycardia have been recorded on ambulatory electrocardiographic monitoring. This case 1) demonstrates the potential role of ablation of the His bundle in patients with refractory tachycardia associated with a nodoventricular tract provided that the His bundle is a critical component in the initiation of the tachycardia or a part of the tachycardia circuit; 2) reveals stable 1:1 AV conduction over a nodoventricular tract; and 3) emphasizes the utility of the phase image technique for diagnosis of a Mahaim tract.

Dissociation of atrial electrograms by right and left atrial pacing in patients with atrioventricular reciprocating tachycardia.

Seventeen patients had atrioventricular (AV) reciprocating tachycardia incorporating an AV bypass tract as the retrograde limb of the tachycardia circuit. High right atrial pacing during tachycardia dissociated the low septal right atrial electrogram in four of seven patients with a left free wall bypass tract, neither of two patients with a right free wall bypass tract, four of six patients with a posteroseptal bypass tract and both patients with an anteroseptal bypass tract. Pacing from the coronary sinus during tachycardia dissociated the atrial electrogram recorded at the os of the coronary sinus in no patient with a left free wall bypass tract, both patients with a right free wall bypass tract, two patients with a posteroseptal bypass tract and one patient with an anteroseptal bypass tract. These findings suggest two distinct inputs to the AV node, with the left-sided input being part of the tachycardia circuit in patients with a left free wall bypass tract and the right-sided input being part of the tachycardia circuit in patients with a right free wall bypass tract. However, in some patients with a septal bypass tract, neither the right- nor the left-sided atrial input appears to be a necessary link in the tachycardia circuit.

Long-term follow-up of patients with recurrent unexplained syncope evaluated by electrophysiologic testing.

Electrophysiologic testing was performed in 53 patients with recurrent syncope that remained unexplained despite a thorough neurologic and noninvasive cardiac evaluation. Fifteen patients had no structural heart disease, 9 had mitral valve prolapse and 29 had structural heart disease other than mitral valve prolapse. Nonsustained ventricular tachycardia was induced in 15 patients (28%), sustained ventricular tachycardia was induced in 9 (17%), ventricular fibrillation was induced in 4 (8%) and sinus node function was abnormal in 2 (4%). Female sex and lack of structural heart disease were independently associated with a negative electrophysiologic study (p less than 0.001). Patients with inducible ventricular tachycardia or ventricular fibrillation were treated with drugs selected on the basis of the results of electropharmacologic testing. The recurrence rate of syncope was 43% over a 31 +/- 10 month period (mean +/- standard deviation) of follow-up in patients with a negative electrophysiologic study, 40% over a 22 +/- 6 month period in patients with inducible nonsustained ventricular tachycardia, 0% over a 30 +/- 12 month period in patients with inducible sustained ventricular tachycardia and 25% over a 21 +/- 10 month period in patients with inducible ventricular fibrillation. In patients with recurrent unexplained syncope undergoing electrophysiologic testing, a potential cause of syncope is least likely to be found in women without structural heart disease. The results of programmed ventricular stimulation must be interpreted with regard to the method of induction of ventricular tachycardia and the type of ventricular tachycardia induced. The excellent response rate in patients with inducible sustained ventricular tachycardia whose therapy is guided by the results of electropharmacologic testing suggests that sustained ventricular tachycardia is a clinically significant response.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of patch electrode position for the internal cardioverter-defibrillator by cine computed tomography and its relation to the defibrillation threshold.

Cardioverter-defibrillator implantation in 22 consecutive patients after aborted sudden cardiac death was followed by prospective determination of the correct anatomic position of epicardial patch electrodes by chest X-ray study and cine computed tomography; the data were compared with the defibrillation threshold obtained intraoperatively. Patch electrode position was qualitatively graded. Computed tomography improved the assessment as compared with X-ray study in 13 patients (59%), visualizing electrodes in relation to the underlying myocardial and vascular structures. Although the computed tomographic technique provided more precise visualization, its grading of patch position correlated as poorly as that of the X-ray study with the measured acute defibrillation threshold. Three-dimensional reconstruction by computed tomography made it possible to determine quantitatively left ventricular mass (free wall and septum) and the mass encompassed by the patch electrodes. The 34.6 +/- 13.7% (range 12.6 to 61.1%) of the left ventricular mass encompassed by both patch electrodes showed a linear relation to the defibrillation threshold (r = 0.64, p = 0.01). Differentiation of free wall and septal mass in these measurements revealed that the proportion of septal mass encompassed by patch electrodes correlated closely with the defibrillation threshold (r = -0.6, p = 0.019), whereas that of the free wall mass, although significantly larger (35.4 +/- 15.8 vs. 20.6 +/- 15.4 g, p = 0.007), did not. Thus, the position of epicardial patch electrodes could be reliably determined by computed tomography.(ABSTRACT TRUNCATED AT 250 WORDS)

A new single catheter technique for simultaneous measurement of action potential duration and refractory period in vivo.

In vivo correlations of action potential duration measured by a monophasic action potential catheter and effective refractory period measured by a separate pacing catheter have been poor, probably because of the known variability of both action potential duration and effective refractory period between different ventricular sites. In this study, a new quadripolar contact electrode catheter designed for simultaneous pacing and monophasic action potential recording at closely adjacent sites (2 mm separation between recording electrodes and pacing electrodes) was tested in five closed chest dogs and four patients. Dog studies: Pacing thresholds were extremely low, ranging from 0.02 to 0.25 mA (mean +/- SD 0.099 +/- 0.051, n = 36) and were stable over time (less than 20% increase during 1 h of continuous pacing). Because of the close proximity of pacing and recording electrodes, the pacing artifact nearly coincided with the monophasic action potential upstroke. Because of the low pacing threshold, however, pacing artifacts were small (33 +/- 17% of the monophasic action potential amplitude at twice diastolic threshold strength) and did not affect the duration or configuration of the simultaneously recorded monophasic action potential. The short stimulus response time and the undisturbed monophasic action potential signal fidelity during pacing allowed precise simultaneous measurements of action potential duration and effective refractory period at the same endocardial site.(ABSTRACT TRUNCATED AT 250 WORDS)