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PubMed2006

Transthoracic incremental monophasic versus biphasic defibrillation by emergency responders (TIMBER): a randomized comparison of monophasic with biphasic waveform ascending energy defibrillation for the resuscitation of out-of-hospital cardiac arrest due to ventricular fibrillation.

BACKGROUND: Although biphasic, as compared with monophasic, waveform defibrillation for cardiac arrest is increasing in use and popularity, whether it is truly a more lifesaving waveform is unproven. METHODS AND RESULTS: Consecutive adults with nontraumatic out-of-hospital ventricular fibrillation cardiac arrest were randomly allocated to defibrillation according to the waveform from automated external defibrillators administered by prehospital medical providers. The primary event of interest was admission alive to the hospital. Secondary events included return of rhythm and circulation, survival, and neurological outcome. Providers were blinded to automated defibrillator waveform. Of 168 randomized patients, 80 (48%) and 68 (40%) consistently received only monophasic or biphasic waveform shocks, respectively, throughout resuscitation. The prevalence of ventricular fibrillation, asystole, or organized rhythms at 5, 10, or 20 seconds after each shock did not differ significantly between treatment groups. The proportion of patients admitted alive to the hospital was relatively high: 73% in monophasic and 76% in biphasic treatment groups (P=0.58). Several favorable trends were consistently associated with receipt of biphasic waveform shock, none of which reached statistical significance. Notably, 27 of 80 monophasic shock recipients (34%), compared with 28 of 68 biphasic shock recipients (41%), survived (P=0.35). Neurological outcome was similar in both treatment groups (P=0.4). Earlier administration of shock did not significantly alter the performance of one waveform relative to the other, nor did shock waveform predict any clinical outcome after multivariate adjustment. CONCLUSIONS: No statistically significant differences in outcome could be ascribed to use of one waveform over another when out-of-hospital ventricular fibrillation was treated.

Adult↗
PubMed2001

Mechanism of ventricular defibrillation for near-defibrillation threshold shocks: a whole-heart optical mapping study in swine.

BACKGROUND: To study the mechanism by which shocks succeed (SDF) or fail (FDF) to defibrillate, global cardiac activation and recovery and their relationship to defibrillation outcome were investigated for shock strengths with approximately equal SDF and FDF outcomes (DFT(50)). METHODS AND RESULTS: In 6 isolated pig hearts, dual-camera video imaging was used to record optically from approximately 8000 sites on the anterior and posterior ventricular surfaces before and after 10 DFT(50) biphasic shocks. The interval between the shock and the last ventricular fibrillation activation preceding the shock (coupling interval, CI) and the time from shock onset to 90% repolarization of the immediate postshock action potential (RT(90)) were determined at all sites. Of 60 shocks, 31 were SDF. The CI (59+/-7 versus 52+/-6 ms) and RT(90) (108+/-19 versus 88+/-8 ms) were significantly longer for SDF than FDF episodes. Spatial dispersions of CI (36+/-5 versus 34+/-3 ms) and RT(90) (40+/-16 versus 40+/-8 ms) were not significantly different for SDF versus FDF episodes. The first global activation cycle appeared focally on the left ventricular apical epicardium 78+/-32 ms after the shock. CONCLUSIONS: For near-threshold shocks, defibrillation outcome correlates with the electrical state of the heart at the time of the shock and on RT. Global dispersion of RT was similar in both SDF and FDF episodes, suggesting that it is not crucial in determining defibrillation outcome after DFT(50) shocks.

Animals↗
PubMed2003

Effect of cervical vagal nerve stimulation on defibrillation energy: a possible adjunct to efficient defibrillation.

The efficacy of electrical defibrillation is considered to be related to the autonomic status. In search of a possible adjunct to enhance the therapeutic performance of an implantable cardioverter-defibrillator. we investigated whether parasympathetic manipulation by cervical vagal nerve stimulation (VNS) increases defibrillation efficacy. The effects of VNS on transcardiac defibrillation threshold (DFT) were assessed in 55 anesthetized dogs. In neurally intact dogs, right and left unilateral VNS at 10 mA for 7 seconds significantly decreased the DFT after 10 seconds of ventricular fibrillation (control: 3.1 +/- 0.9 J, right: 2.1 +/- 0.9 J [delta-35 +/- 12%, P < 0.0001], left: 2.2 +/- 0.8 J [delta-31 +/- 11%, P < 0.0005]), while bilateral VNS did not (2.8 +/- 1.0 J). In dogs with decentralized vagus nerves, both unilateral and bilateral VNS decreased the DFT. The extent of the VNS-induced decrease in DFT was dependent on the current and the duration of stimulation. We conclude that unilateral VNS decreases the DFT, while bilateral VNS paradoxically has no effect on the DFT unless the vagi are decentralized.

Animals↗
PubMed2001

Successful treatment with an implantable cardioverter defibrillator for spontaneous ventricular fibrillation in dilated cardiomyopathy with very high defibrillation thresholds.

A 72-year-old male patient with idiopathic dilated cardiomyopathy who had shown recurrent episodes of drug refractory ventricular fibrillation underwent implantation of a transvenous implantable cardioverter defibrillator (ICD). Ventricular fibrillation (VF) was induced by a T wave shock at the implantation. However, the ICD device with a maximum energy of 30 J failed to terminate the VF. Reversing defibrillation polarity and/or adding a defibrillation electrode lead at the site of a high superior vena cava were also ineffective. The ICD was programmed to a maximum energy of 30 J when the device sensed spontaneous VF. During the follow-up period of 5 months, two episodes of spontaneous VF were recorded from ICD telemetry, and the ICD device terminated VF successfully with the first therapy shock in both episodes. No previous reports have shown failure to terminate induced VF at implantation of the ICD with successful termination of spontaneous VF during follow-up. Careful follow-up is needed in ICD patients, especially those with very high defibrillation thresholds.

Aged↗
PubMed2005

[Successful defibrillation by disconnection of superior vena cava electrode for high defibrillation threshold: a case report].

A 72-year-old man with dilated cardiomyopathy and sustained ventricular tachycardia was treated with amiodarone. He visited another hospital because of loss of consciousness. Electrocardiography showed 2: 1 atrioventricular block. Ambulatory electrocardiography showed total heart beats were 59,700 per day. He was referred to our hospital to evaluate his heart. Several types of ventricular tachycardia and ventricular fibrillation were induced by program stimulation during the electrophysiological study. Therefore, an implantable cardioverter-defibrillator was introduced. During defibrillation threshold tests, ventricular fibrillation could not be terminated by the maximal output of 31J. Despite changing the polarity and lead position, stable defibrillation could not be obtained. Finally, successful defibrillation could only be achieved by disconnection of the superior vena cava electrode.

Aged↗
PubMed1989

Success rate versus defibrillation energy: temporal profile and the most efficient defibrillation threshold.

To determine the temporal profile of the energy requirement for defibrillation, shocks were delivered to canine hearts after 5, 10, or 20 seconds from the onset of fibrillation with a combination of patch and catheter electrodes. A total of 956 fibrillation-defibrillation sequences were performed at one of four energy levels appropriately selected for each period of fibrillation in 10 anesthetized dogs. The energy values related to 50% (E50) and 80% (E80) of the predicted success were calculated from a logistic regression curve. The E50 and E80 values at 10 seconds after the onset of fibrillation were less than those at 20 seconds after the onset by 7.1% +/- 18.3% and 9.7% +/- 21.4%, respectively; differences were not significant. At 5 seconds after the onset, the differences were 15.3% +/- 14.2% (p less than 0.02) and 16.4% +/- 12.7% (p less than 0.01), respectively. The defibrillation energy efficiency was assessed by dividing the success rate (SR) of fibrillation by the applied energy (E). The maximal SR/E at 5, 10, and 20 seconds of fibrillation was achieved at the energy corresponding to the SRs of 88.8% +/- 4.5%, 90.4% +/- 3.9%, and 88.1% +/- 4.6%, respectively. We conclude that the energy requirement for defibrillation increases with the duration of fibrillation, even shortly after the onset of fibrillation, and the maximal energy efficiency is attained at the energy associated with the SR of approximately 90%.

Animals↗
PubMed1994

Mechanisms of electrical defibrillation: impact of new experimental defibrillator waveforms.

Six possible explanations for why some biphasic waveforms have lower defibrillation thresholds than monophasic waveforms of the same duration are as follows: (1) the impedance for the second phase of the biphasic shock is very low because electrode polarization develops during the first phase; (2) the large change in voltage between the first and second phases of a biphasic waveform is responsible for the increased defibrillation efficacy; (3) biphasic waveforms cause less severe detrimental effects in regions of high potential gradient; (4) the first phase of the biphasic waveform restores activity of the sodium channels, which makes defibrillation easier for the second phase; (5) the potential gradient required for defibrillation is less for biphasic waveforms than for monophasic waveforms; and (6) biphasic waveforms are better able to stimulate the myocardium to induce new action potentials or to cause refractory period prolongation. Evidence shows that, while a few of these proposed mechanisms are incorrect, several of the others may together contribute to the general superiority of biphasic waveforms.

Action Potentials↗
PubMed1995

Towards early defibrillation--a nurse training programme in the use of automated external defibrillators.

It is essential that all health care professionals are regularly trained in the practice of basic life support (BLS). In most cases of cardiac arrest, the chances of a favourable outcome depend not only on efficient BLS, but also on the early use of defibrillation. In a hospital environment, the first responders are most likely to be members of the nursing staff. The potential advantage of these personnel being able to perform early defibrillation, as well as BLS, is considerable. We describe an initiative in which instruction in the use of automated external defibrillators (AEDs) was introduced into routine BLS training sessions, with the aim of developing this capability. Using specifically-acquired training aids, 43 nurses and nine other members of the non-medical staff were trained in 12 teaching sessions over a period of 4 months. Refresher training was carried out after 6 months and 37 nurses were retrained during six sessions using a similar syllabus. The programme was well-received by all students, and a higher than expected level of motivation and competence was achieved. Throughout retraining all nurses appreciated the key importance of early defibrillation. We conclude that, although the initial workload is high, it is entirely feasible to augment BLS training for health care professionals with instruction in the use of AEDs. We recommend that this potentially life-saving tuition programme be widely adopted.

Automation↗
PubMedDate not supplied

Law Enforcement Agency Defibrillation (LEA-D): proceedings of the National Center for Early Defibrillation Police AED Issues Forum.

Why does LEA-D intervention seem to work in some systems but not others? Panelists agreed that some factors that delay rapid access to treatment, such as long travel distances in rural areas, may represent insurmountable barriers. Other factors, however, may be addressed more readily. These include: absence of a medical response culture, discomfort with the role of medical intervention, insecurity with the use of medical devices, a lack of proactive medical direction, infrequent refresher training, and dependence on EMS intervention. Panelists agreed that successful LEA-D programs possess ten key attributes (Table 6). In the end, the goal remains "early" defibrillation, not "police" defibrillation. It does not matter whether the rescuer wears a blue uniform--or any uniform, for that matter--so long as the defibrillator reaches the victim quickly. If LEA personnel routinely arrive at medical emergencies after other emergency responders or after 8 minutes have elapsed from the time of collapse, an LEA-D program will be unlikely to provide added value. Similarly, if police frequently arrive first, but the department is unwilling or unable to cultivate the attributes of successful LEA-D programs, efforts to improve survival may not be realized. In most communities, however, LEA-D programs have tremendous lifesaving potential and are well worth the investment of time and resources. Law enforcement agencies considering adoption of AED programs should review the frequency with which police arrive first at medical emergencies and LEA response intervals to determine whether AED programs might help improve survival in their communities. It is time for law enforcement agency defibrillation to become the rule, not the exception.

Cardiopulmonary Resuscitation↗
PubMed2004

Recurrent ventricular fibrillation in out-of-hospital cardiac arrest after defibrillation by police and firefighters: implications for automated external defibrillator users.

OBJECTIVE: To determine the prevalence and frequency of recurrent ventricular fibrillation (VF) in patients defibrillated by police and firefighters only and to determine its relation to survival. DESIGN: Retrospective observational study. SETTING: Out of hospital. PATIENTS: Individuals with witnessed VF arrest in the Rochester, MN, ambulance public service area who had defibrillatory shocks delivered by police and firefighters and return of spontaneous circulation with shocks only. MEASUREMENTS AND MAIN RESULTS: Electrocardiograms were recovered from data cards in automated external defibrillators used by police (n = 49) or firefighters (n = 18) to deliver shocks from December 1996 through December 2003 in the Rochester, MN, ambulance public service area. Patients with witnessed VF arrest were identified for recurrent VF after initial shock success (first one to three shocks). Both police and firefighters deployed automated external defibrillators delivering nonescalating 150-J biphasic truncated exponential waveform shocks (ForeRunner Automated External Defibrillator, Phillips/Heartstream Operation, Seattle, WA). Among 67 patients, 30 (45%) survived to neurologically intact discharge (overall performance category score of 1 in 29 patients and score of 2 in one patient). Twenty-nine patients (43%) regained spontaneous circulation with shocks only and 25 of 29 (86%) survived. VF recurred in 35 of the 67 patients (52%) while being cared for by police or firefighters. Of these 35 patients, no relation was found between the prevalence or frequency of VF recurrence and survival. CONCLUSIONS: VF recurrence is frequent, variable in time of onset, and unrelated to the performance of bystander CPR. The prevalence and frequency of VF recurrence were unpredictable and do not adversely affect survival. Thus, vigilance for recurrent VF is essential to ensure the survival of patients who are in the care of first responders, even after initial restoration of pulses with shocks.

Cardiopulmonary Resuscitation↗
PubMed1996

Estimating defibrillation efficacy using combined upper limit of vulnerability and defibrillation testing.

It is frequently necessary, both clinically and in the laboratory, to estimate how strong a stimulus is required to defibrillate. Current techniques for forming such estimates require the repeated induction of ventricular fibrillation (VF) and subsequent attempts at defibrillation (DF testing). DF testing can be time consuming and in the operating room may increase the patient risks. A novel scheme is presented which combines DF testing with upper limit of vulnerability (ULV) testing. ULV testing is a relatively safe procedure which yields data well correlated with defibrillation efficacy. A Bayesian statistical model of combined ULV/DF testing is presented which is both powerful and concise. The model is used in two examples to design minimum rms error protocols and estimators for the DF95 (the stimulus strength which defibrillates 95% of the time). A simulation for humans of one example solution shows that a single VF episode of combined ULV/DF testing (rms error = 23% of the mean DF95) is better than two VF episodes with DF testing alone (25%). The simulation results for a second example are directly compared with laboratory results from six pigs, showing a less than 1.0% average difference between the simulated and measured rms errors.

Algorithms↗
PubMed2000

Pacing following shocks stronger than the defibrillation threshold: impact on defibrillation outcome.

INTRODUCTION: A recent study of shocks near defibrillation threshold (DFT) strength demonstrated that at least three rapid cycles always occur after failed shocks but not after successful shocks, suggesting that the number and rapidity of postshock cycles are important in determining defibrillation success. To test this hypothesis, rapid pacing was performed following a shock stronger than the DFT that by itself did not induce rapid cycles and ventricular fibrillation (VF). METHODS AND RESULTS: Epicardial activation was mapped in six pigs using a 504-electrode sock. The DFT was determined by an up/down protocol with S1 shocks (right ventricle-superior vena cava, biphasic). Ten shocks that were 100 to 200 V above the DFT (aDFT) were delivered after 10 seconds of VF to confirm they always defibrillated. Then, S2, S3, etc., pacing at 5 to 10 times diastolic threshold was performed from the left ventricular apex after aDFT shocks during VF. First, the postshock interval after aDFT shocks was scanned with an S2 stimulus to find the shortest S1-S2 coupling interval (CI) that captured. This was repeated for S3, S4, etc., until VF was induced. To induce VF after aDFT shocks, three pacing stimuli (S2, S3, S4) with progressively shorter CIs were always required; S2 or S2,S3 never induced VF. For the S2-S4 cycles, the intercycle interval was shorter (P < 0.01), and the wavefront conduction time was longer (P < 0.01) for episodes in which VF was induced (n = 57) than for episodes in which it was not (n = 60). Following the S4 cycle that induced VF, two types of spontaneous activation patterns appeared: focal (88%) and reentrant (12%). CONCLUSION: VF induction after aDFT shocks always required at least three rapid successive paced-induced cycles. Thus, the number and rapidity of the first several postshock cycles rather than just the first postshock cycle may be determining factors for defibrillation outcome.

Animals↗
PubMed1987

Relationship between canine transthoracic impedance and defibrillation threshold. Evidence for current-based defibrillation.

The electrical parameter used to define defibrillation strength is energy. Peak current, however, may more accurately reflect the field quantities (i.e., electric field strength and current density) that mediate defibrillation and therefore should be a better clinical descriptor of threshold than energy. Though transthoracic impedance is a major determinant of energy-based threshold and is sensitive to operator-dependent changes in impedance (electrode-subject interface), an ideal threshold descriptor should be invariant with respect to these changes in impedance. We therefore compared the relative invariance of energy- and current-based thresholds when transthoracic impedance was altered by one of two methods: (a) change in electrode size (protocol A) or (b) change in electrode force (protocol B). In protocol A, impedance was altered in each dog by a mean of 95%. Energy thresholds determined at both low and high impedance were 44 +/- 21 J (mean +/- SD) and 105 +/- 35 J, respectively, P less than 0.0001. In contrast, peak current (A) thresholds were independent of transthoracic impedance, 22 +/- 5 A (low impedance) vs. 24 +/- 6 A (high impedance), P = NS. Energy and current thresholds showed a similar relationship for animals tested in protocol B. Therefore, current-based thresholds, in contrast to energy thresholds are independent of operator-dependent variables of transthoracic impedance and are invariant for a given animal. These results suggest that redefining defibrillation threshold in terms of peak current rather than energy provides a superior method of defibrillation.

Animals↗
PubMed2006

Causes and consequences of heart failure after prophylactic implantation of a defibrillator in the multicenter automatic defibrillator implantation trial II.

BACKGROUND: Implantable cardioverter-defibrillator (ICD) therapy may be associated with an increased risk for heart failure (HF). The present study evaluated the frequency, causes, and consequences of HF after ICD implantation. METHODS AND RESULTS: We performed a retrospective analysis of the clinical factors and outcomes associated with postenrollment HF events in 1218 patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial II. The adjusted hazard ratios (HRs) of ICD:conventional therapy for first and recurrent HF events were 1.39 (P=0.02) and 1.58 (P<0.001), respectively. The risk was increased among patients who received single-chamber or dual-chamber ICDs. Development of HF was associated with an increased mortality risk (HR, 3.80; P<0.001). Among patients who received a single-chamber ICD, there was a similar survival benefit before and after the development of HF (HR, 0.59 and 0.61, respectively; P=0.92 for difference), whereas among patients with dual-chamber devices, there was a significant reduction in survival benefit after HF (HR, 0.26 and 0.83, respectively; P=0.01 for difference). Within the defibrillator arm of the trial, patients who received life-prolonging therapy from the ICD had an increased risk for first and recurrent HF events (HR, 1.90; P=0.01 and 1.74; P<0.001, respectively). CONCLUSIONS: Patients with chronic ischemic heart disease who are treated with either single-chamber or dual-chamber ICDs have improved survival but an increased risk of HF. The present data suggest that ICD therapy transforms sudden death risk to a subsequent HF risk. These findings should direct more attention to the prevention of HF in patients who receive an ICD.

Adrenergic beta-Antagonists↗
PubMed1994

The development of implantable cardioversion defibrillation systems: the clinical chronicle of defibrillation leads.

Clinical experience suggests that there is a significant advantage from both the standpoint of survival and thoracotomy morbidity in the use of cardioverter defibrillator implantation strategies with transvenous and subcutaneous leads. Bioengineering achievements making the latter possible remains somewhat preliminary in comparison with the highly advanced analytic technology from which the leads for bradycardia pacing have issued. Accordingly, a good deal remains to be accomplished in the technology evolution of leads for implantable cardioverter defibrillators (ICDs). While second- and third-generation leads have proved to be clinically useful, their development remains far from complete. To date most lead studies have focused on endocardial shock pathways, waveforms, and the linkage thereof affecting defibrillation thresholds. Experience suggests that asymmetric biphasic waveforms that use dual pathways (versus monophasic unidirectional shocks) yield a greater margin of safety for effective control of arrhythmias with existing ICD systems. The critical mass and region of myocardium encompassed by energy pathways, the simultaneous versus sequential pulsing of ICD antiarrhythmic discharges, as well as electrode combinations, locations, and polarity, remain under study. Although final adjudication of the superiority of endocardial systems that exclude the need for thoracotomy over those that use epicardial electrodes remains to be determined by further observational and randomized trials, it is reasonable to conclude at this juncture that ICDs with endocardial leads are feasible and facile, providing a highly promising alternative to other antiarrhythmic strategies.

Animals↗
PubMed2006

Elevated defibrillation thresholds in patients undergoing biventricular defibrillator implantation: incidence and predictors.

BACKGROUND: The biventricular implantable cardioverter-defibrillator (ICD) is an important therapy for select patients with severe heart failure. Given reported risk factors for elevated defibrillation thresholds (DFTs), patients undergoing biventricular ICD placement would be suspected of having a higher incidence of elevated DFT. OBJECTIVES: The purpose of this study was to examine the clinical predictors and mortality risk of elevated DFTs in patients receiving a biventricular ICD. METHODS: Characteristics of patients undergoing biventricular ICD placement with an elevated DFT were compared to those without an elevated DFT. RESULTS: An elevated DFT was found in 14 (12%) of 121 patients. Mean QRS duration was 210 +/- 50 ms in the elevated DFT group and 171 +/- 36 ms in the normal DFT group (P = .01). Patients with a QRS duration >or=200 ms were more likely to have an elevated DFT than those with a duration <200 ms (odds ratio 13.4, 95% confidence interval 3.1-66.7, P <.01). No other clinical characteristics were associated with an elevated DFT. More than 90% of patients with an elevated DFT achieved an adequate safety margin through system modification or manipulation of their drug regimen. An elevated DFT did not have an impact on 2-year mortality. CONCLUSION: Patients with a biventricular ICD had a 12% incidence of elevated DFT in our sequential patient cohort. QRS duration prior to biventricular ICD placement is the most powerful predictor of patients at risk for an elevated DFT. An elevated DFT does not have an impact on mortality, perhaps because of successful implementation of system modifications to ensure an adequate defibrillation safety margin.

Adult↗
PubMed2005

Providing automated external defibrillators to urban police officers in addition to a fire department rapid defibrillation program is not effective.

OBJECTIVE: The aim of this study was to determine if providing automated external defibrillators (AEDs) to urban police officers would increase the proportion of patients with out-of-hospital cardiac arrest (OOH-CA) who were discharged alive from the hospital. METHODS: This prospective, controlled study was conducted in a city with about 332,000 persons. The EMS system included paramedic ambulances and fire department based first responders equipped with defibrillators, but police officers did not respond routinely to medical emergencies. Between March 1997 and February 1999, all OOH-CAs in four police districts were identified and followed until death or hospital discharge. All 35 police cars in one police district were provided with AEDs, and all police officers in that district were trained in CPR and the use of AEDs. Police and fire first response units were dispatched simultaneously in district 3 (intervention group). Fire first response was dispatched without police in districts 2, 4, and 5 (control group). RESULTS: A total of 645 OOH-CAs occurred over the 2 years. Sixty-two were outside of the study area. Two did not have accurate address information to determine the police district. Of the remaining cases, 154 (27%) occurred in the intervention district and 427 (73%) were in the control area. Survival to hospital discharge was similar; it was 11/154 (7.1%) in the intervention and 16/427 (3.8%) in the control districts (odds ratio=1.98; 95% CI 0.90--4.36). Survival to hospital discharge for witnessed OOH-CA events occurring prior to EMS arrival and found to be in ventricular fibrillation or ventricular tachycardia was 4/27 (15%) in the intervention area and 9/73 (12%) in the control area (odds ratio=1.2; 95% CI 0.4-4.4). CONCLUSION: Equipping police cars with AEDs in an urban area where the fire department-based first response system also carries defibrillators did not improve the hospital discharge survival rate for victims of OOH-CA.

Automation↗
PubMed2000

Therapeutic decision tree for patients with sustained ventricular tachyarrhythmias or aborted cardiac arrest: a critical review of the Antiarrhythmics Versus Implantable Defibrillator trial and the Canadian Implantable Defibrillator Study.

Antiarrhythmic drugs, mainly amiodarone and sotalol, radiofrequency catheter ablation, and the implantable cardioverter defibrillator (ICD) are the 3 therapeutic options in patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Idiopathic VT, incessant VT, frequently recurring, hemodynamically stable VT, and VT based on bundle branch reentry, are candidates for radiofrequency catheter ablation. Patients with high-risk ventricular tachyarrhythmias should receive ICDs as initial therapy. Two studies, the Antiarrhythmics Versus Implantable Defibrillator trial (AVID) and the Canadian Implantable Defibrillator Study (CIDS) have tried to approach the problem of these high-risk ventricular tachyarrhythmias. Although at 3 years, the ICD in AVID demonstrated a significant relative risk reduction over amiodarone of 31.5%, CIDS could not duplicate this finding. At 3 years, the relative risk reduction conferred by the ICD over amiodarone in CIDS was only 13.7%. A careful analysis of both studies suggests that CIDS was insufficiently powered to demonstrate statistically significant benefits similar to those shown by AVID, and furthermore, seemed to include an undetermined number of low-risk VT patients. The problem in the CIDS trial in this regard was the recruitment of patients in whom the inclusion criteria were met by the arrhythmias induced during the electrophysiology stimulation study, but which did not exist in real life. In addition CIDS included 14% of patients with (1) undocumented syncope and inducible monomorphic sustained VT; or (2) long runs of spontaneous nonsustained VT. Under these circumstances, the therapeutic implications of AVID remain unchallenged.

Anti-Arrhythmia Agents↗