A comparison of biphasic and monophasic shocks for external defibrillation. Physio-Control Biphasic Investigators

BACKGROUND AND OBJECTIVE

The ability of a shock to defibrillate the heart depends on its waveform and energy. Past studies of biphasic truncated exponential (BTE) shocks for external defibrillation focused on low energy levels. This prospective, randomized, double-blind clinical trial compared the first-shock efficacies of 200-joule (J) BTE, 130-J BTE, and 200-J monophasic damped sine wave shocks.

METHODS

Ventricular fibrillation (VF) was induced in 115 patients during evaluation of implantable cardioverter-defibrillator function and 39 patients during electrophysiologic evaluation of ventricular arrhythmias. After 19 +/- 10 seconds of VF, a randomized transthoracic shock was administered. Mean first-shock success rates of the three groups were compared using a "Tukey-like" statistical test, adjusting for multiple comparisons. Blood pressures and arterial oxygen saturations were measured before VF induction and 30, 90, and 150 seconds after successful defibrillation.

RESULTS

First-shock success rates were 61/68 (90%) for 200-J monophasic, 39/39 (100%) for 200-J biphasic, and 39/47 (83%) for 130-J biphasic shocks. The 200-J biphasic shocks were simultaneously superior in first-shock efficacy to both 200-J monophasic and 130-J biphasic shocks (experimentwise error rate, alpha < 0.01). There was no significant difference between the efficacies of 200-J monophasic and 130-J biphasic shocks, nor was there any significant difference between the three groups in hemodynamic parameters after successful shocks.

CONCLUSIONS

Biphasic shocks of 200 J provide better first-shock defibrillation efficacy for short-duration VF than 200-J monophasic and 130-J biphasic shocks and thus may allow earlier termination of VF in cardiac arrest patients.

Biventricular pacing diminishes the need for implantable cardioverter defibrillator therapy. Ventak CHF Investigators

OBJECTIVES

We sought to test the postulate that biventricular pacing diminishes the need for appropriate tachycardia therapy. We reviewed the frequency of therapy in patients, serving as their own controls, who were enrolled in the Ventak CHF (congestive heart failure) biventricular pacing study.

BACKGROUND

It is well established that both acute and chronic CHF contribute to the need for tachyarrhythmia therapy in recipients of an automatic implantable cardioverter defibrillator (ICD). Synchronized biventricular (BV) pacing is a new and promising therapy for symptomatic improvement of CHF in selected patients (low ejection fraction, intraventricular conduction delay). We postulate that this pacing therapy will diminish the need for tachyarrhythmia therapy.

METHODS

Participants in the Ventak CHF trial received a triple-chamber biventricular ICD with a transvenous right ventricular lead and a left ventricular (LV) lead placed via thoracotomy. Of 54 patients enrolled in the Ventak CHF trial, 32 could be analyzed, with each completing three blinded months programmed to BV VDD pacing and a second randomly assigned three-month period of no pacing.

RESULTS

Of the 32 patients, 13 (41%) received appropriate therapy for a ventricular tachyarrhythmia at least once in the six-month monitoring period postimplant. Five patients (16%) had at least one tachyarrhythmic episode while programmed to BV pacing, whereas 11 (34%) had at least one episode while programmed to no pacing. Three patients (9%) received therapy in both pacing periods, two with BV pacing only. The decrease in necessary tachycardia therapy during the BV pacing period was statistically significant (p = 0.035).

CONCLUSIONS

In patients with standard ICD indications who also have CHF, LV dysfunction, and an intraventricular conduction delay, ICD therapy is less common with BV pacing. The mechanism for this improvement is unclear but may be related to hemodynamic improvement in CHF. Although BV pacing does not obviate the need for an ICD, it does diminish the need for appropriate tachyarrhythmia therapy in selected patients.

The first year experience with the dual chamber ICD

In July 1997, a dual chamber pacemaker combined with a tiered therapy implantable cardioverter defibrillator (ICD) first became available in the United States. We report the first-year experience of one center in the United States with this dual chamber ICD. Of a total of 174 ICDs, 95 (55%) were dual chamber devices and 79 (45%) were single chamber. New dual chamber ICD insertions averaged 57.4 +/- 8.9 minutes, though there was a learning curve as the last 30 implants averaged 45.1 +/- 6.1 minutes with a negative slope to the regression line of procedure duration (-0.52, P < 0.05). New single chamber ICD implants were 18.5 minutes quicker (38.9 +/- 7.2 minutes). The most challenging implants were dual chamber upgrades (mean procedure duration 64.9 +/- 15.8 minutes), especially if there was a previously implanted pacemaker and ICD at separate sites. Indications for a new dual chamber device were grouped into classic pacemaker indications (52.5%), which comprised the Class I ACC/AHA guidelines, ICD-specific indications (24.6%), and other (23.0%). In the 34 patients undergoing dual chamber upgrade, the classic and ICD-specific groups were equal (47.0% each). Complications were rare (2.8%), though 3 (8.8%) of 34 undergoing a dual chamber upgrade developed late infections requiring explantation. In its first year, the dual chamber ICD has become a common device at our institution comprising 55% of new implants. As experience grows, we anticipate similar usage at most institutions.

Impact of the Multicenter Automatic Defibrillator Implantation Trial on implantable cardioverter defibrillator indication trends

Since publication of the Multicenter Automatic Defibrillator Implantation Trial (MADIT) in 1996, indications for implantation of implantable cardioverter defibrillators (ICDs) have expanded. Initial criticisms of the study have been addressed, including the need to await the conclusion of several additional ICD clinical trials. These other trials have generally shown an improved survival with ICD therapy when compared with antiarrhythmic agents. As a result, ICD implantation volumes have increased worldwide. However, ICD usage has regional variation with 120 implants per million population in the United States, 45 per million in Germany, but only 7 and 8 per million in France and the United Kingdom, respectively. Although many factors affect implant decisions, reimbursement issues are particularly important. Other factors may explain the slower growth in Europe when compared with the United States including greater skepticism regarding MADIT, less industry-sponsored marketing, and lack of unified cardiology society support for the MADIT recommendations. Nevertheless, it is anticipated that > 50,000 ICDs have been implanted worldwide in 1998, with a growing percentage in the countries of Europe.

Indications for implantation of a dual-chamber pacemaker combined with an implantable cardioverter-defibrillator

Of 122 patients with single-chamber implantable cardioverter-defibrillators (ICDs) reviewed retrospectively, 35 had traditional indications, 14 had other indications, and 18 had ICD-specific indications for dual-chamber pacing therapy. Thus, 67 patients (55%) were potential candidates for dual-chamber pacing, which has only recently become available combined with ICD therapy.

ICD restudy: results and potential benefit from routine predischarge and 2-month evaluation

Evaluation of ICD function can now be performed noninvasively with intravenous sedation. To determine the value of follow-up electrophysiological studies for ICD implants, we performed a retrospective review of predischarge and 2-month ICD re studies, identifying critical problems uncovered. Of the 123 patients implanted, 122 had a predischarge study, 105 had both predischarge and elective 2-month follow-up studies, and 1 patient expired prior to restudy. Patients who underwent 2-month studies for nonelective indications (e.g., frequent shocks) were excluded from analysis. Programming changes were made in 62% of the predischarge studies (n = 122) and 70% of the elective 2-month studies (n = 105). The average number of programming changes per study was 1.3 for predischarge testing and 1.1 for 2-month testing. The most common changes at predischarge testing were adjustment of the tachyarrhythmia rate cutoff (35%) and at 2-month study, reprogramming of bradycardia pacing parameters (41%). Of the patients who underwent both predischarge and 2-month testing, 91% had programming changes in at least one of their re studies. Of 227 re studies performed, 18 studies in 14 patients yielded 24 critical findings which included: DFT increases to > or = 25 J (n = 13); sensing abnormalities of induced ventricular arrhythmia (n = 6); dislodged lead (n = 2); and serious pacemaker interactions (n = 3). Six of these critical cases (5% of total patients) required reoperation. The data suggests that routine ICD restudy is a valuable tool for management of the ICD patient. Additionally, ICD restudy is likely to increase the diagnostic yield of clinically silent critical system problems that could result in device failure.

Recurrent Twiddler's syndrome in a nonthoracotomy ICD system despite a Dacron pouch

Twiddler's syndrome is a highly recognized yet rare complication of pacemaker and cardioverter defibrillator (i.c.d.) implantation. We present a case in which persistent generator rotation resulted in lead dislodgment and inappropriate shocks in an initial ICD and recurrent lead fracture in a second ICD system. This case is unusual in that even with extensive surgical precautions including use of a Dacron pouch, generator rotation could not be prevented. Submuscular implantation and use of a smaller generator may prevent Twiddler's syndrome.

Improved survival with an implanted defibrillator in patients with coronary disease at high risk for ventricular arrhythmia. Multicenter Automatic Defibrillator Implantation Trial Investigators

BACKGROUND

Unsustained ventricular tachycardia in patients with previous myocardial infarction and left ventricular dysfunction is associated with a two-year mortality rate of about 30 percent. We studied whether prophylactic therapy with an implanted cardioverter-defibrillator, as compared with conventional medical therapy, would improve survival in this high-risk group of patients.

METHODS

Over the course of five years, 196 patients in New York Heart Association functional class I, II, or III with prior myocardial infarction; a left ventricular ejection fraction < or = 0.35; a documented episode of asymptomatic unsustained ventricular tachycardia; and inducible, nonsuppressible ventricular tachyarrhythmia on electrophysiologic study were randomly assigned to receive an implanted defibrillator (n = 95) or conventional medical therapy (n=101). We used a two-sided sequential design with death from any cause as the end point.

RESULTS

The base-line characteristics of the two treatment groups were similar. During an average follow-up of 27 months, there were 15 deaths in the defibrillator group (11 from cardiac causes) and 39 deaths in the conventional-therapy group (27 from cardiac causes) (hazard ratio for overall mortality, 0.46; 95 percent confidence interval, 0.26 to 0.82; P=0.009). There was no evidence that amiodarone, beta-blockers, or any other antiarrhythmic therapy had a significant influence on the observed hazard ratio.

CONCLUSIONS

In patients with a prior myocardial infarction who are at high risk for ventricular tachyarrhythmia, prophylactic therapy with an implanted defibrillator leads to improved survival as compared with conventional medical therapy.

Classification of death in antiarrhythmia trials

OBJECTIVES

We sought to develop and apply a new scheme for the classification of death to be used in trials of antiarrhythmia treatments.

BACKGROUND

Because presently accepted classifications of death do not fully describe or tabulate all significant aspects of terminal events, nor do they consider unique aspects of arrhythmia investigations, a new classification scheme that addresses these issues is desirable.

METHODS

A classification scheme of deaths that occur in antiarrhythmia trials was developed using the following categories: 1) primary organ cause (cardiac [arrhythmic, nonarrhythmic or unknown], noncardiac or unknown); 2) temporal course (sudden, nonsudden or unknown); 3) documentation (witnessed, monitored [yes, no or unknown]); 4) operative relation (preoperative, perioperative or postoperative); and 5) system relation (procedure related, pulse generator related and lead related [yes, no or unknown]).

RESULTS

The classification scheme was used in a clinical trial of a new implantable cardioverter-defibrillator (1,250 patients, of whom 79 died) and used in an application for device market approval. Application of the classification to data reported using an older classification scheme is demonstrated.

CONCLUSIONS

We propose a descriptive classification scheme that 1) fully describes and tabulates all significant aspects of terminal events; 2) incorporates previously used categorizations of death and new categorizations that address unique aspects of arrhythmia investigations; and 3) tabulates sufficient data to allow comparison with other studies. Events in a clinical trial of implantable defibrillator therapy were classified using the new classification scheme.

Stability: an ICD detection criterion for discriminating atrial fibrillation from ventricular tachycardia

INTRODUCTION

The purpose of this study was to review a new implantable cardioverter defibrillator (ICD) detection criterion, stability, to determine if it can effectively discriminate rapid rhythms of atrial fibrillation from ventricular tachycardia. Inappropriate shocks for rapid atrial fibrillation limit the acceptance of ICDs. The advent of an additional detection criterion, stability, has been postulated to be of value in discriminating rapid atrial fibrillation, which may not warrant treatment, from ventricular tachycardia, which obviously does warrant therapy deliver.

METHODS AND RESULTS

Twenty-six patients were studied during 32 episodes of rapid atrial fibrillation and 24 episodes of monomorphic ventricular tachycardia below 220 beats/min. Each rhythm was repeatedly evaluated by the device at each of the seven stability values available (8, 16, 23, 31, 39, 47, and 55 msec) and then classified as stable or unstable. Upon completion of this acute study, 32 ICD patients had the stability feature activated and were followed for proper arrhythmia treatment by the device. Using stability windows from 8 to 47 msec, all atrial fibrillation rhythms were appropriately classified as unstable. Three of 6 were classified correctly for the 55-msec window. All ventricular tachycardia rhythms were appropriately classified as stable from all stability windows from 8 to 55 msec. Clinical follow-up confirmed appropriate therapy delivery when coupled with sustained rate duration (SRD). Thirty-two patients followed for 292 patient-months had no episodes of untreated ventricular tachycardia with 428 successfully classified as stable and treated. Only three episodes of suspected atrial fibrillation resulted in therapy delivery as the rhythm duration exceeded the SRD of 30 seconds.

CONCLUSIONS

The CPI Ventak PRx ICD is highly reliable in appropriately classifying atrial fibrillation as unstable and monomorphic ventricular tachycardia as stable for most stability windows evaluation tachycardias below 220 beats/min. As a result, when testing of atrial fibrillation is not possible, we recommend the routing programming of this stability feature at the 31-msec window with an SRD of 30 seconds. The reliability of this device in discriminating atrial fibrillation from monomorphic ventricular tachycardia may have important clinical implications for other tiered therapy ICDs with this feature as well as for future ICDs in development.

The subcutaneous array: a new lead adjunct for the transvenous ICD to lower defibrillation thresholds

Despite the benefits of transvenous implantable cardioverter defibrillators (ICDs), concern exists that patients with high defibrillation thresholds (DFTs) have an inadequate safety margin between the DFT and the maximum defibrillator energy. A new transvenous ICD lead adjunct, a subcutaneous lead array (SQ Array), was developed to increase safety margins by lowering DFTs. Composed of three lead elements joined in a common yoke, the SQ Array is tunneled subcutaneously in the left lateral chest. Serving as their own controls, 20 patients were studied intraoperatively comparing transvenous lead-alone DFTs with lead-SQ Array DFTs. Seventeen males and three females were randomized to receive the SQ Array through the CPI Ventak PRx/Endotak 70 series protocol. Mean patient age was 63.7 +/- 2.5 years and mean ejection fraction 0.34 +/- 0.04. DFTs were determine using a precise protocol of step-down/step-up testing commencing at 20 joules. Lead-alone DFTs were tested using the proximal coil as the anode (+). For the lead-SQ Array, the proximal coil and the array were linked as a common anode. The lead-SQ Array resulted in a statistically significant reduction in mean monophasic DFT from 23.3 +/- 2.3 joules (lead-alone) to 13.5 +/- 1.9 joules (lead-SQ Array) (P < 0.001). Six patients had lead-alone DFTs > 25 joules but did not require thoracotomy because of adequate DFT reduction with the SQ Array. We conclude that the SQ Array adjunct to the transvenous ICD lead lowers monophasic DFTs an average of 9.8 joules (40.6%) obviating the need for a thoracotomy in selected patients.

Effects of quinidine versus procainamide on the QT interval

Eighteen patients were given quinidine and procainamide separately to evaluate whether prolongation of the QT interval by type Ia antiarrhythmic agents is a drug-specific phenomenon. Doses were titrated to achieve standard trough therapeutic levels of quinidine (2 to 5 micrograms/ml) and procainamide (4 to 12 micrograms/ml). In 16 of the 18 patients, the increase in corrected QT interval (QTc) was greater with quinidine than with procainamide, averaging 78 +/- 10 ms (+/- standard error of the mean) with quinidine and 39 +/- 7 ms with procainamide (p less than 0.001). The greater degree of QTc prolongation with quinidine than with procainamide was not due to differences in sinus cycle length, QRS duration, serum potassium level or concomitant drug therapy. Differences in relative drug level did not appear to account for the greater effect of quinidine. Thus, at frequently used plasma levels, quinidine prolongs QTc to a greater degree than does procainamide. This effect does not appear to be due to the comparison of "nonequivalent" drug levels.