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PubMed1984

Functional cardiac depression caused by defibrillator shocks. Quantitation of the safety factor for electrical defibrillation.

The overdose shock strengths required to depress ventricular contraction were determined for damped sinusoidal current in 7 metabolically supported, isolated contracting canine hearts. Each heart was suspended in an isoresistive and isotonic solution-through which the defibrillating shocks were delivered. Defibrillation thresholds were determined with standard damped sine wave shocks of 4.4-5.5 msec duration. Then overdose shocks were delivered and the depressant effect on systolic left ventricular pressure was measured for shocks of 3-12 times threshold current. The minimum (threshold) current and energy densities required to defibrillate were 59.5 +/- 4.6 mA/cm2 (average) and 3.12 +/- 0.2 mJ/cm3. Increasing the shock strength above threshold produced a concomitant reduction of postshock left ventricular systolic pressure. The current and energy densities required to produce 50% depression (TD50) of left ventricular systolic pressure were 5.0 and 24.1 times the threshold current and energy densities respectively, indicating a wide safety margin using this criterion.

Animals↗
PubMed2000

Elevation of defibrillation thresholds with propofol during implantable cardioverter-defibrillator testing.

A 26-year-old man with severe dilated cardiomyopathy and frequent ventricular tachycardia treated with propafenone plus mexiletine underwent implantable cardioverter-defibrillator testing one day after dual chamber defibrillator implantation. There were no significant changes in the R-wave and lead position on chest x-ray. Routine defibrillator threshold (DFT) testing after 320 mg intravenous propofol demonstrated high DFTs (greater than 31 Joules and requiring 360 Joules externally for termination). Change in polarity failed to improve DFTs. After about 20 minutes of washout, conscious sedation was performed with 20 mg of midazolam and repeat DFTs were equal to 21 Joules. This case demonstrates the potential for an acute dose dependent rise in DFT with propofol.

Adult↗
PubMedDate not supplied

[A possibility of significant lowering the defibrillation current by determining the right time for application of a defibrillating pulse. A mathematical model].

The effect of defibrillating pulses on the functionally determined re-entries (leading circles) was studied by computer simulation. Arrhythmias caused by different numbers of leading circles (from 1 to 18) were investigated. The defibrillation threshold was found to vary 2-4-fold, depending on the time of application of a pulse. At small currents the defibrillation mechanism is principally different from the commonly known one and is linked to the movement of leading circles towards each other or towards the boundary of the excitable tissue.

Arrhythmias, Cardiac↗
PubMed2002

Dual-chamber pacing or ventricular backup pacing in patients with an implantable defibrillator: the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial.

CONTEXT: Implantable cardioverter defibrillator (ICD) therapy with backup ventricular pacing increases survival in patients with life-threatening ventricular arrhythmias. Most currently implanted ICD devices provide dual-chamber pacing therapy. The most common comorbid cause for mortality in this population is congestive heart failure. OBJECTIVE: To determine the efficacy of dual-chamber pacing compared with backup ventricular pacing in patients with standard indications for ICD implantation but without indications for antibradycardia pacing. DESIGN: The Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial, a single-blind, parallel-group, randomized clinical trial. SETTING AND PARTICIPANTS: A total of 506 patients with indications for ICD therapy were enrolled between October 2000 and September 2002 at 37 US centers. All patients had a left ventricular ejection fraction (LVEF) of 40% or less, no indication for antibradycardia pacemaker therapy, and no persistent atrial arrhythmias. INTERVENTIONS: All patients had an ICD with dual-chamber, rate-responsive pacing capability implanted. Patients were randomly assigned to have the ICDs programmed to ventricular backup pacing at 40/min (VVI-40; n = 256) or dual-chamber rate-responsive pacing at 70/min (DDDR-70; n = 250). Maximal tolerated medical therapy for left ventricular dysfunction, including angiotensin-converting enzyme inhibitors and beta-blockers, was prescribed to all patients. MAIN OUTCOME MEASURE: Composite end point of time to death or first hospitalization for congestive heart failure. RESULTS: One-year survival free of the composite end point was 83.9% for patients treated with VVI-40 compared with 73.3% for patients treated with DDDR-70 (relative hazard, 1.61; 95% confidence interval [CI], 1.06-2.44). The components of the composite end point, mortality of 6.5% for VVI-40 vs 10.1% for DDDR-70 (relative hazard, 1.61; 95% CI, 0.84-3.09) and hospitalization for congestive heart failure of 13.3% for VVI-40 vs 22.6% for DDDR-70 (relative hazard, 1.54; 95% CI, 0.97-2.46), also trended in favor of VVI-40 programming. CONCLUSION: For patients with standard indications for ICD therapy, no indication for cardiac pacing, and an LVEF of 40% or less, dual-chamber pacing offers no clinical advantage over ventricular backup pacing and may be detrimental by increasing the combined end point of death or hospitalization for heart failure.

Adrenergic beta-Antagonists↗
PubMed2001

Patients at lower risk of arrhythmia recurrence: a subgroup in whom implantable defibrillators may not offer benefit. Antiarrhythmics Versus Implantable Defibrillator (AVID) Trial Investigators.

OBJECTIVES: The goal of this study was to identify subgroups of arrhythmia patients who do not benefit from use of the implantable cardiac defibrillator (ICD). BACKGROUND: Treatment of serious ventricular arrhythmias has evolved toward more common use of the ICD. Since estimates of the cost per year of life saved by ICD therapy vary from $25,000 to perhaps $125,000, it is important to identify patient subgroups that do not benefit from the ICD. METHODS: Data for 491 ICD patients enrolled in the Antiarrhythmics Versus Implantable Defibrillators Study were used to create a hazards model relating baseline factors to time to first recurrent arrhythmia. The model was used to predict the hazard for recurrent arrhythmia among all trial patients. A priori cut points provided lower and higher recurrent arrhythmia risk strata. For each stratum the incremental years of life due to ICD versus antiarrhythmic drug therapy were calculated. RESULTS: Factors that predicted recurrent arrhythmia were: ventricular tachycardia as the index arrhythmia, history of cerebrovascular disease, lower left ventricular ejection fraction, a history of any tachyarrhythmia before the index event and the absence of revascularization after the index event. Survival times (over a follow-up of three years) were identical in each arm of the lowest risk sextile (survival advantage 0.03 +/- 0.12 [se] years), while the survival advantage for patients above the first sextile was 0.27 +/- 0.07 (se) years (two-sided p = 0.05). CONCLUSIONS: Patients presenting with an isolated episode of ventricular fibrillation in the absence of cerebrovascular disease or history of prior arrhythmia who have undergone revascularization or who have moderately preserved left ventricular function (left ventricular ejection fraction > 0.27) are not likely to benefit from ICD therapy compared with amiodarone therapy.

Aged↗
PubMed2003

[The impact of the Multicenter Automatic Defibrillator Implantation Trial II in a university hospital--do all patients with myocardial infarction and reduced left ventricular function need an implantable cardioverter-defibrillator?].

BACKGROUND AND OBJECTIVES: Patients with coronary artery disease (CAD) and severely compromised left ventricular ejection fraction are at high risk to die from sudden cardiac death. The Multicenter Automatic Defibrillator implantation Trial II (MADIT II) shows a significant benefit of a cardioverter-defibrillator (ICD) therapy compared to standard treatment alone in this selected group of patients. The objective of the present study was to investigate the number of patients who will fulfil the MADIT II criteria and are candidates for prophylactic ICD implantation. METHODS AND MATERIAL: From January to December 2001 a total of 2653 patients underwent coronary angiography at our institution due to angina pectoris, positive exercise stress testing, pathological SPECT myocardial perfusion images, suspected dilated cardiomyopathy or ventricular arrhythmias. According to the MADIT II inclusion criteria patients with significant coronary artery disease (diameter stenosis > 50%), ejection fraction < 0.31% and previous myocardial infarction were included. Exclusion criteria were acute coronary syndromes, patients with ventricular tachyarrhythmias or an existing indication for ICD therapy, and patients with coronary artery bypass graft surgery or percutaneous transluminal coronary angioplasty within the past or following three months. RESULTS: Out of 2653 patients 185 (7%) had an ejection fraction less than 0.31, 149 (5.6%) showed significant coronary artery stenosis and 70 (2.6%) patients fulfilled the MADIT II criteria. The mean age of these patients was 68 +/- 9 years, the left ventricular ejection fraction 24 +/- 6. In 37 patients an ICD system was implanted according to the existing guidelines. 70 patients met the MADIT II inclusion criteria, resulting in an increase of 189% of ICD implantations per year. CONCLUSION: 2.6% out of 2653 patients who were referred to coronary angiography fulfilled the criteria of MADIT II. The expanding indication for ICD therapy will result in an annual increase of 70 (189%) prophylactic ICD implantations in our study population.

Aged↗
PubMed1996

The impact of repeated short episodes of circulatory arrest on cerebral function. Reassuring electroencephalographic (EEG) findings during defibrillation threshold testing at defibrillator implantation.

The impact of circulatory arrest on EEG features during defibrillation threshold testing for implantation of a cardioverter defibrillator has been disputed. Cumulation of cerebral ischemic effects during threshold testing has been observed, and consequently the advice was given to avoid short intervals between tests and to limit the test number. This study investigated the duration of EEG signs of cerebral ischemia as well as the occurrence of cumulation. EEGs were recorded during standardized general anesthesia. Subsequent tests were performed after recovery of EEG, electrocardiogram, systemic arterial blood pressure, and heart rate. In 36 consecutive survivors of out-of-hospital cardiac arrest 286 episodes of induced circulatory arrest were analyzed. Ischemic EEG changes were present in all episodes of circulatory arrest, consisting of slowing, progressing to absence of activity. The relation between the onset time or recovery time and the test number and test interval was studied. A highly significant correlation between circulatory arrest and recovery time was found (P < 0.001). A significant negative correlation existed between test number and recovery time (P < 0.05). Test interval was not related with either onset or recovery time. We conclude that repeated threshold tests which are monitored by assessment of EEG and hemodynamics are not associated with cumulative EEG changes as a result of ischemia. Our results do not support the advice that the number of tests should be limited.

Adolescent↗
PubMed2005

Time to resumption of driving after implantation of an automatic defibrillator (from the Dual chamber and VVI Implantable Defibrillator [DAVID] trial).

The time to resumption of driving after insertion of an implantable cardioverter-defibrillator (ICD) was evaluated in the Dual Chamber And VVI Implantable Defibrillator trial. Most patients were advised not to drive for 3 to 6 months after the ICD was implanted. Patients were surveyed at 3-, 6-, or 9-month intervals to characterize their driving habits, with 101 of 137 (73.7%), 98 of 146 (67.1%), and 79 of 135 (58.5%) responding. Of respondents, 82% recalled being told not to drive for a specified time after ICD implantation. These patients generally obeyed recommendations (association between recommended time and time of resumption, p <0.001) from medical personnel.

Arrhythmias, Cardiac↗
PubMed2005

Relation of echocardiographic wall motion score index and response to dobutamine stress to defibrillation threshold at the time of implantation of a cardiac defibrillator.

Predictors of defibrillation threshold (DFT) at implantation remain poorly defined. It was hypothesized that a greater wall motion score index (WMSI) at rest on echocardiography and an ischemic or biphasic response on dobutamine stress echocardiography (DSE) would predict a greater DFT. Consecutive patients who underwent implantable cardiac-defibrillator implantation underwent echocardiography and DSE. DFT at implantation was assessed using the step-down method. Thirteen men aged 68 +/- 10 years with left ventricular ejection fractions of 28 +/- 10% participated in the study. DFTs ranged from 5 to 25 J (mean 14 +/- 8). A WMSI at rest of > or = 2.5 had a 71% positive predictive value and an 83% negative predictive value for a DFT > or = 15 J. An ischemic or biphasic response during DSE did not predict a greater DFT at implantation.

Aged↗
PubMed2005

Effects of beta-blockers on implantable cardioverter defibrillator therapy and survival in the patients with ischemic cardiomyopathy (from the Multicenter Automatic Defibrillator Implantation Trial-II).

This study examined the effects of beta blockers on (1) appropriate implantable cardioverter defibrillator (ICD) therapy for ventricular tachycardia (VT) or ventricular fibrillation (VF), (2) inappropriate ICD therapy for atrial fibrillation or supraventricular tachycardia, and (3) survival in 691 patients who received ICDs in the Multicenter Automatic Defibrillator Implantation Trial-II. The study population involved 258 patients who were not receiving beta blockers and 433 who were receiving metoprolol (n = 192), atenolol (n = 58), or carvedilol (n = 182). Patients receiving beta blockers were divided into the upper quartile and lower 3 quartiles of the drug doses they were taking. Patients receiving the higher doses of beta blockers (those in the top quartile of doses) had a significant reduction in the risk for VT or VF requiring ICD therapy compared with patients not receiving beta blockers (hazard ratio 0.48, p = 0.02). The frequency of inappropriate ICD therapy for supraventricular tachyarrhythmias was not significantly different among the 3 treatment groups (p = 0.32). Beta-blocker use at the 2 dosage levels was associated with significant improvement in survival compared with the nonuse of beta blockers (hazard ratios 0.42 to 0.44, p <0.01). In conclusion, beta blockers reduce the risk for VT or VF and improve survival in ICD-treated patients with ischemic cardiomyopathy.

Adrenergic beta-Antagonists↗
PubMed2004

Improving the acceptability of the atrial defibrillator for the treatment of persistent atrial fibrillation: the atrial defibrillator sedation assessment study (ADSAS).

BACKGROUND: To compare the acceptability and effectiveness of three pre-medication regimens for manually activated cardioversion of recurrent persistent atrial fibrillation. METHODS: Eighteen patients implanted with the Jewel AF atrial defibrillator for drug-resistant persistent atrial fibrillation only were studied in an open-labelled randomised crossover study. Patients were assigned to sedation (S) with midazolam elixir, analgesia (A) with morphine sulphate or combination therapy (C) with dextromoramide and lorazepam. Pre-medication was taken up to 1 h before cardioversion. Patients rotated through each type of medication after undertaking at least one cardioversion. Visual analogue scales were completed immediately post-cardioversion and 24 h later for pain, anxiety and 'unpleasantness'. Higher scores represented a worse outcome. RESULTS: After 2 years' follow-up, 238 cardioversions were performed with S, 17 with A and 35 with C. The mean immediate combined score for S (10.9, 95% confidence interval (CI) 8.2-13.6) was significantly lower than for A (17.3, 95% CI 15.1-19.5, P = 0.01) and for C (15.9, 95% CI 12.3-19.6, P = 0.02). All patients who used S chose it as the most favourable pre-medicant. All patients who used A found it the least acceptable. CONCLUSION: Sedation rather than analgesia enhanced the acceptability of manually activated atrial defibrillation.

Adult↗
PubMed2005

Factors influencing appropriate firing of the implanted defibrillator for ventricular tachycardia/fibrillation: findings from the Multicenter Automatic Defibrillator Implantation Trial II (MADIT-II).

OBJECTIVES: The purpose of this study was to prospectively examine the role of clinical, laboratory, echocardiographic, and electrophysiological variables as predictors of appropriate initial implantable cardioverter-defibrillator (ICD) therapy for ventricular tachycardia (VT) or ventricular fibrillation (VF) or death in the Multicenter Automatic Defibrillator Implantation Trial II (MADIT-II) population. BACKGROUND: There is limited information regarding the determinants of appropriate ICD therapy in patients with reduced ventricular function after a myocardial infarction. METHODS: We used secondary analysis in one arm of a multicenter randomized clinical trial in patients with a previous myocardial infarction and reduced left ventricular function. RESULTS: We analyzed baseline and follow-up data on 719 patients enrolled in the ICD arm of the MADIT-II study. Appropriate ICD therapy was observed in 169 subjects. Clinical, laboratory, echocardiographic, and electrophysiological variables, along with measures of clinical instability such as interim hospitalization for congestive heart failure (IH-CHF) and interim hospitalization for coronary events (IH-CE), were examined with proportional hazards models and Kaplan-Meier time-to-event curves before and after first interim hospitalization. Interim hospitalization-CHF, IH-CE, no beta-blockers, digitalis use, blood urea nitrogen (BUN) >25, body mass index (BMI) > or =30 kg/m2, and New York Heart Association functional class >II were associated with increased risk for appropriate ICD therapy for VT, VF, or death. In a multivariate (stepwise selection) analysis, IH-CHF was associated with an increased risk for the end point of either VT or VF (hazard ratio [HR] 2.52, 95% confidence interval [CI] 1.69 to 3.74, p < 0.001) and for the combined end point of VT, VF, or death (HR 2.97, 95% CI 2.15 to 4.09, p < 0.001). Interim hospitalization-CE was associated with an increased risk for VT, VF, or death (HR 1.66, 95% CI 1.09 to 2.52, p = 0.02). CONCLUSIONS: These results provide important mechanistic information, suggesting that worsening clinical condition and cardiac instability, as reflected by an IH-CHF or IH-CE, are subsequently associated with a significant increase in the risk for appropriate ICD therapy (for VT/VF) and death.

Aged↗
PubMed2006

Time dependence of defibrillator benefit after coronary revascularization in the Multicenter Automatic Defibrillator Implantation Trial (MADIT)-II.

OBJECTIVES: The study was designed to assess the effect of elapsed time from coronary revascularization (CR) on the benefit of the implantable cardioverter-defibrillator (ICD) and the risk of sudden cardiac death (SCD) in patients with ischemic left ventricular dysfunction. BACKGROUND: The ICD improves survival in appropriately selected high-risk cardiac patients by 30% to 54%. However, in the Coronary Artery Bypass Graft (CABG)-Patch trial no evidence of improved survival was shown among a similar population of patients in whom an ICD was implanted prophylactically at the time of elective CABG. METHODS: The outcome by time from CR was analyzed in 951 patients in whom a revascularization procedure was performed before enrollment in the Multicenter Automatic Defibrillator Implantation Trial (MADIT)-II. RESULTS: The adjusted hazard ratio (HR) of ICD versus conventional therapy was 0.64 (p = 0.01) among patients enrolled more than six months after CR, whereas no survival benefit with ICD therapy was shown among patients enrolled six months or earlier after CR (HR = 1.19; p = 0.76). In the conventional therapy group, the risk of cardiac death increased significantly with increasing time from CR (p for trend = 0.009), corresponding mainly to a six-fold increase in the risk of SCD among patients enrolled more than six months after CR. CONCLUSIONS: In patients with ischemic left ventricular dysfunction, the efficacy of ICD therapy after CR is time dependent, with a significant life-saving benefit in patients receiving device implantation more than six months after CR. The lack of ICD benefit when implanted early after CR may be related to a relatively low risk of SCD during this time period.

Aged↗
PubMed1996

Clinical predictors of defibrillation energy requirements in patients treated with a nonthoracotomy defibrillator system. The ResQ Investigators.

Many factors can influence defibrillation energy requirements (DER) in patients with a nonthoracotomy defibrillator. No large studies, however, have correlated clinical characteristics with the DER. In this study, 124 patients underwent the same DER protocol with the identical biphasic waveform, nonthoracotomy lead system, and lead configuration. These patients were 63 +/- 12 years old (mean +/- SD); 99 were men; the ejection fraction was 0.32 +/- 0.13, and 36 were taking an antiarrhythmic medication. New York Heart Association congestive heart failure class I was present in 28, class II in 70, and class III in 26 patients. Male sex (454 +/- 94 V vs 406 +/- 91 V for female sex) was associated with a significantly higher DER (p = 0.02) and an increased risk of a DER > 550 V (p = 0.047). No other clinical variable was associated with the DER or a DER > 550 V. In conclusion, women tend to have lower DERs than men.

Anti-Arrhythmia Agents↗
PubMed1997

Comparison of clinical characteristics and frequency of implantable defibrillator use between randomized patients in the Antiarrhythmics Vs Implantable Defibrillators (AVID) trial and nonrandomized registry patients.

In the Antiarrhythmics Vs Implantable Defibrillators (AVID) trial, all patients who meet the study entry criteria are followed in a registry. During the period between June 1993 and June 1995, of 1,117 patients who were enrolled in the registry and met the study entry criteria, 476 were randomized to receive either implantable cardioverter-defibrillators (ICDs) or drug therapy (amiodarone or sotalol), and 641 patients were not randomized for a variety of reasons including: patient refusal (42%); physician refusal (43%); concerns about ability to maintain follow-up over several years (10%), and others (6%). There were no significant differences between the 476 randomized and 641 nonrandomized patients with regard to clinical characteristics, left ventricular function, history of congestive heart failure, medical history, and previous cardiac procedures performed before the index event, except that randomized patients were slightly older (65 vs 62 years) and had a slightly higher prevalence of coronary artery disease and previous myocardial infarction. The index event and location of the index event were not significantly different between the 2 groups. Although 14% of registry patients received neither ICD nor antiarrhythmic drug therapy, ICDs were no more frequently used in the registry patient than antiarrhythmic drugs (45% for ICD vs 42% for drugs). Thus, randomized AVID patients have very similar clinical characteristics, cardiac history, and presenting arrhythmias as to nonrandomized eligible patients. Therefore, the results of the AVID trial may be generalized for all patients with AVID-eligible arrhythmias.

Adolescent↗
PubMed1997

Induction of atrial fibrillation with low-energy defibrillator shocks in patients with implantable cardioverter defibrillators.

In a population of 151 consecutive patients who received an implantable cardioverter defibrillator, we found that atrial fibrillation was induced by low-energy shocks in 19% and was most common in patients with lead systems that included a right atrial electrode. Our finding that there was a fixed relation between the energy required to fibrillate (< or = 3 J) and defibrillate (> 3 J) suggests the presence of an upper limit of vulnerability in the human atrium.

Aged↗
PubMed1999

Navigation in the mega-trials waters: reflections on the Multicenter Automatic Defibrillator Implantation Trial and the Antiarrhythmics Versus Implantable Defibrillators Study.

Today, cardiology seems to be driven by mega-trials and meta-analyses. Guidelines published by scientific and professional cardiovascular societies, such as the American Heart Association, the American College of Cardiology, and the European Society of Cardiology, follow the rules of evidence-based medicine. Such evidence is not always sufficiently conclusive to practice clinically helpful medicine. Sometimes, relatively small trials, such as the Multicenter Automatic Defibrillator Implantation Trial and the Antiarrhythmics Versus Implantable Defibrillators study, may be taken as guides for current clinical decisions and as inspiration for future investigations. Large mega-trials with a great lack of homogeneity among the recruited patients are less important for clinically helpful medicine than studies enrolling well-defined, high-risk patients. It is probably important to acknowledge that the best possible treatment for many patients with ventricular tachyarrhythmias remains obscure. Among these situations are the following: (1) sustained ventricular tachycardia (VT) in patients without coronary artery disease; (2) sustained, nonsyncopal VT in patients with coronary artery disease and left ventricular dysfunction; (3) post myocardial infarction survivors with an ejection fraction < or = 35%, frequent/complex ventricular arrhythmias, depressed heart rate variability, and inducible sustained ventricular tachyarrhythmias during electrophysiologic study. Many studies are being conducted to add light where uncertainty exists, but probably only a few will contribute to the practice of clinically helpful medicine, although some will be used to produce meta-analysis to sustain evidence-based medicine.

Anti-Arrhythmia Agents↗
PubMed1999

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.

Anti-Arrhythmia Agents↗