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Biomedical subjects

Douglas L Packer

Publications and source records attributed to Douglas L Packer.

At least 37 records · Page 2Linked to original sources
PubMed2004

Catheter cryoablation of supraventricular tachycardia: results of the multicenter prospective "frosty" trial.

OBJECTIVE: To study the safety, efficacy, and mapping utility of a new cryoablation catheter. BACKGROUND: The CryoCath Technologies Freezor catheter has been used successfully for cryoablation of supraventricular tachycardia (SVT), but has not been evaluated in a large clinical trial. METHODS: A multicenter clinical trial to evaluate the safety, efficacy, and cryomapping utility of this cryoablation catheter was conducted in 166 subjects. The target of ablation was the slow pathway in patients with SVT due to AV nodal reentry (AVNRT, n = 103), an accessory pathway in patients with AV reentrant SVT (AVRT, n = 51) and the AV junction in patients with atrial fibrillation (AF, n = 12). RESULTS: Acute procedural success (APS) was achieved in 83% of the overall group (95% CI, 76% to 88%). APS in the AVNRT group was 91% (98.3% CI, 82% to 97%), compared to 69% for AVRT (98.3% CI, 51% to 84%) and 67% for AF (98.3% CI, 29% to 93%), a highly significant difference (P < .001 by stepwise logistic regression). In patients with APS, long-term success after 6 months was 91% overall (95% CI, 86% to 96%) and 94% for AVNRT subjects (98.3% CI, 87% to 100%). None of the AVNRT or AVRT subjects required a permanent pacemaker. Cryomapping successfully identified ablation targets in 64% of patients in whom it was attempted. The electrophysiologic effects of cryomapping were completely reversible within minutes in 94% of such attempts. CONCLUSIONS: Catheter cryoablation of SVT is a safe alternative to RF ablation and is clinically effective in patients with AVNRT. Cryomapping can reversibly identify targets for ablation and can help minimize the risk of inadvertent AV block during ablation.

Adult↗
PubMed2004

Trends in treated ventricular fibrillation out-of-hospital cardiac arrest: a 17-year population-based study.

OBJECTIVES: The aims of this study were to describe the trends of ventricular fibrillation (VF) out-of-hospital cardiac arrest in Rochester, Minnesota, since 1985 and to determine coexistent trends in implantable cardioverter defibrillator (ICD) placement and termination of potentially lethal ventricular arrhythmias that might explain, at least in part, a declining incidence trend. BACKGROUND: The incidence of VF out-of-hospital cardiac arrest treated by emergency medical services (EMS) personnel has declined over the past decade. Because VF out-of-hospital cardiac arrest occurs primarily in the setting of severe coronary artery disease, primary and secondary prevention strategies may account in part for the decline. In particular, ICD use in large primary and secondary prevention clinical trials in patients at high risk of sudden death has demonstrated that these devices improve survival. METHODS: All residents of the City of Rochester, Minnesota, who presented with a VF out-of-hospital cardiac arrest from 1985 to 2002, identified and treated by EMS, were included in the study. In addition, residents of the City of Rochester who received their first ICD implant from 1989 to 2002 were identified. From the ICD records, general demographics, etiology of heart disease, comorbid medical disease, and indication for ICD placement were abstracted. Follow-up data obtained from this population included ICD shocks, the underlying rhythm disturbance, and death. RESULTS: The overall incidence of EMS-treated VF out-of-hospital cardiac arrest in Rochester during the study period was 17.1 per 100,000 [95% confidence interval (CI) 15.1-19.4]. The incidence has decreased significantly (P < 0.001) over the study period: 1985-1989: 26.3/100,000 (95% CI 21.0-32.6), 1990-1994: 18.2/100,000 (95% CI 14.1-23.1), 1995-1999: 13.8/100,000 (95% CI 10.4-17.9), 2000-2002: 7.7/100,000 (95% CI 4.7-11.9). One hundred ten patients received an ICD. The placement of ICDs also has increased dramatically over the past 10 years: 1990-1994: 5.0/100,000 to 2000-2002: 20.7/100,000 (P < 0.001). ICDs terminated VF or fast ventricular tachycardia (<270 ms) in 22 patients. Termination of these potentially fatal arrhythmias has shown a trend toward an increase over the study period: 1990-1994: 1.1/100,000 to 2000-2002: 3.5/100,000 (P = 0.06). CONCLUSIONS: The incidence of VF out-of-hospital cardiac arrest is declining. In contrast, the rates of ICD placement and ICD termination of ventricular tachycardia or VF are markedly increasing. Sudden death preventive strategies are multifactorial. These observations suggest that ICD termination of potentially lethal ventricular arrhythmias may contribute to the lower incidence of VF out-of-hospital cardiac arrest.

Aged↗
PubMed2004

Long-term subjective memory function in ventricular fibrillation out-of-hospital cardiac arrest survivors resuscitated by early defibrillation.

BACKGROUND: Brain injury after a cardiac arrest remains a major cause of morbidity. Programs focusing on early defibrillation have yielded improved survival of patients after hospital discharge following ventricular fibrillation (VF) out-of-hospital cardiac arrest (OHCA). Early defibrillation that promptly restores a circulating rhythm should decrease the hypoxic period and subsequent organ injury. Therefore this study was designed to determine if long-term memory complaints persist in VF OHCA survivors resuscitated in an early defibrillation program when compared with a healthy control population not experiencing cardiac arrest. METHODS: All patients with an OHCA between November 1990 and January 2001 who received defibrillation by emergency medical services personnel in Olmsted County, MN, USA, were included. The memory function questionnaire (MFQ), a 64-item, 7-point Likert-scaled instrument to evaluate the perception of everyday memory functioning was sent to all survivors. The MFQ comprises four scales: general frequency of forgetting (rates general forgetting), retrospective functioning (compares current memory with past ability), seriousness of forgetting (rates how memory impairment impacts daily life), and mnemonics usage (measures adaptation). The MFQ is scaled so that high scores reflect less severe memory complaints. The comparison population comprised members of the Mayo Older Americans Normative Studies (MOANS) cohort. Quality of life was ascertained with a short form (SF)-36 survey. RESULTS: Seventy-nine of the 200 VF OHCA patients (40%) were discharged. Twenty-two patients have died since dismissal, with an overall average length of follow-up of 4.9+/-3.0 years. Thirty-eight (67%) of the survivors completed the MFQ. Compared with the normal, there was a significant decrease in the general frequency of forgetting score of 144.2+/-37.4 versus 168.1+/-27.3 ( P<0.001) and the seriousness of forgetting score of 84.8 +/-26.7 versus 95.2+/-19.7 (P=0.004). The retrospective function-scale scores were not significantly different ( 18.4+/-6.8 versus 18.7+/- 5.0 (P=0.74). Younger patients (lesser than 65 years of age) reported an increase in general forgetting and the seriousness of forgetting compared with older survivors. A comparison with SF-36 scores suggested an association between general forgetting and decreased vitality (P=0.03) and the seriousness of forgetting with a decreased general health (P=0.005), mental health (P=0.009), physical functioning ( P=0.02 ), and vitality ( P=0.05). CONCLUSION: In a cohort of VF OHCA patients, survivors report more memory complaints in comparison with a general healthy older population. There were more long-term-memory complaints in younger patients. Patients with higher long-term quality-of-life score have fewer memory complaints.

Adult↗
PubMed2004

Prediction of short- and long-term outcomes by electrocardiography in survivors of out-of-hospital cardiac arrest.

BACKGROUND: Programs focusing on early defibrillation have improved both short- and long-term survival of patients with VF out-of-hospital cardiac arrest (OHCA). Subsequent long-term management of survivors would be facilitated by a straight-forward, non-invasive method of identifying those at highest risk for recurrence. Therefore, we assessed the predictive value of the standard ECG to determine both short- and long-term outcomes in survivors of VF OHCA to assist in risk stratification of those patients at highest risk of sudden death. METHODS: All patients with an OHCA between November 1990 and December 2000 who received early defibrillation for VF in Olmsted County Minnesota (MN) were included. Cox proportional hazards modeling was used to examine ECG variables and subsequent ICD deployment and death. RESULTS: Two hundred patients presented in VF OHCA; of these 138 (69%) survived to hospital admission (seven died in the emergency department prior to admission) and 79 (40%) were discharged. The QRS duration (141 +/- 41ms in nonsurvivors, 123 +/- 35 in survivors, P = 0.004) was predictive of short-term mortality in patients who did not survive to hospital discharge. The ventricular rate, PR interval, presence of right or left bundle branch block, QTc, ST elevation myocardial infarction, and atrial fibrillation/flutter were nonpredictive. The average length of follow up for hospital dismissal survivors was 4.8 +/- 3.0 years. In univariate analysis, each 30 ms interval increase in the QRS width and PR interval was associated with increased mortality and ICD deployment hazard ratio of 1.6 (CI 1.1-2.5, P = 0.02) and 1.12 (CI 1.0-1.2, P = 0.05), respectively. In multivariate analysis accounting for admission ejection fraction, a PR > 200 ms [HR 4.5 (CI 1.7-11.8, P = 0.022)], QRS width increase greater than 30 ms [HR 1.9 (CI 1.3-2.8, P < 0.001)], and a QRS > 120 ms [HR 2.4 (CI 1.1-5.4, P = 0.032)] were predictive of long-term mortality and ICD shocks. CONCLUSION: Careful evaluation of the admitting and discharge ECG provides prognostic information for in-hospital and long-term outcomes, respectively in this cohort of out-of-hospital cardiac arrest survivors. The QRS duration on the dismissal ECG following VF OHCA provides prognostic information which might be useful to identify those at highest risk long-term, and who would benefit from more aggressive antiarrhythmic therapy and cardiac stabilization.

Aged↗
PubMed2004

Impact of age on long-term survival and quality of life following out-of-hospital cardiac arrest.

OBJECTIVE: Early defibrillation programs have improved long-term outcomes following out-of-hospital cardiac arrest from ventricular fibrillation. Although long-term collective quality of life and survival are favorable, there are subsets of these patients who may be predisposed to worse outcomes. In particular, elderly patients may present with more comorbid medical conditions affecting their outcome. However, the impact of age on mortality rate and quality of life after rapid defibrillation is unknown. DESIGN: Observational study. SETTING: Hospital. SUBJECTS: All patients with an out-of-hospital cardiac arrest between November 1990 and January 2001 who received rapid defibrillation for ventricular fibrillation in Olmsted County, Minnesota. All patients received treatment at one hospital. INTERVENTIONS: Long-term outcome and quality of life were followed. Survival was estimated using the Kaplan-Meier method. The quality of life was established by an SF-36 survey. MEASUREMENTS AND MAIN RESULTS: Two hundred patients presented in ventricular fibrillation out-of-hospital cardiac arrest; of these, 138 (69%) survived to hospital admission, seven (4%) died in the emergency department, and 79 (39%) were discharged neurologically intact. The average age was 62+/-16 yrs, with 51% (n = 40) of the population > or =65. The average length of follow-up was 4.8+/-3.0 yrs. The 5-yr survival in patients <65 was 94% (confidence interval, 86-100%) and 66% (confidence interval, 52-84%) in patients > or =65 (p <.001). The observed survival in the younger group was not different from that expected in a U.S. age- and gender-matched population. However, in the older group, the expected survival was significantly lower compared with an age- and gender-matched U.S. population (p =.01) but similar to an age-, gender-, and disease-matched cohort of patients from Olmsted County not experiencing an arrest. In both age-dependent cohort populations, the quality of life scores crossed the norm in all categories with exception of vitality in patients >65 yrs old (42.6+/-7.2). In direct comparison between the two patient groups, the older cohort reported lower levels of physical functioning (p =.002), role-emotional score (p =.03), and role-physical score (p =.007). Other SF-36 scores were not different between the groups. Sixty-five percent of patients <65 yrs returned to work compared with 56% of older patients. CONCLUSIONS: The survival rate for ventricular fibrillation out-of-hospital cardiac arrest is significantly improved by the presence of a rapid defibrillation program. In patients <65 yrs old, long-term survival is equal to that of normal individuals and quality of life is similar to the general population. The survival, although high, in older patients is less than that in age-matched healthy controls, and physical and emotional quality of life scores are decreased.

Academic Medical Centers↗
PubMed2004

Mechanisms for enlarging lesion size during irrigated tip radiofrequency ablation: is there a virtual electrode effect?

INTRODUCTION: Irrigated tip radiofrequency ablation of cardiac arrhythmias was developed to increase the size of the radiofrequency-induced lesion, since cooling of the electrode tip allows use of higher power settings. The purpose of this study was to determine if the increased lesion size during irrigated tip ablation is caused by the cooling effect solely or if increased electrical conductivity around the tip also contributes by increasing the "current-delivering size" of the tip: the so-called "virtual electrode effect." METHODS AND RESULTS: In vitro strips of left ventricular porcine myocardium and in vivo canine left ventricles were ablated. In vitro closed loop tip and showerhead irrigated tip catheters were compared. In vitro and in vivo showerhead tip catheters irrigated with solutions having different ionic content were compared. We found no difference in lesion size for closed loop and showerhead-type catheters (998 +/- 345 vs. 811 +/- 313 mm(3) during power-controlled ablation and 227 +/- 76 vs 318 +/- 127 mm(3) during temperature-controlled ablation). For irrigation with liquids having increasing ionic strength we found a decrease in lesion volume in vitro (361 +/- 249 vs. 812 +/- 229 mm(3) (P < 0.001) for power-controlled and 156 +/- 78 vs. 318 +/- 127 mm(3) (P < 0.05) for temperature-controlled ablation and nonsignificant differences in vivo. CONCLUSIONS: The mechanism for enlarging lesion size during radiofrequency irrigated-tip ablation is that higher power levels can be used. There is no virtual electrode effect caused by the highly conductive surroundings of the tip during irrigation. In vitro this effect is shown to be opposite: it decreases lesion size.

Animals↗
PubMed2004

Outcomes and in-hospital treatment of out-of-hospital cardiac arrest patients resuscitated from ventricular fibrillation by early defibrillation.

OBJECTIVE: To describe and evaluate the in-hospital treatment of ventricular arrhythmias and underlying structural heart disease in patients who survive ventricular fibrillation (VF) out-of-hospital cardiac arrest (OHCA) in a region with a high survival rate after hospital discharge. PATIENTS AND METHODS: The study included all patients presenting in Olmsted County, Minnesota, who had experienced OHCA between November 1990 and December 2000 and who underwent defibrillation of VF by an emergency medical service system. RESULTS: Of 200 patients who experienced VF arrest, 138 (69%) survived to hospital admission (7 died in the emergency department before admission), and 79 (40%) were discharged. Of patients who were discharged, 37 (47%) had a reversible cause of the arrest (perimyocardial infarction) and received treatment of the primary process. The other 42 patients who were discharged had ischemic coronary heart disease (CHD) (n=25), nonischemic CHD (n=10), or idiopathic VF (n=7). Four of the patients with CHD but no left ventricular dysfunction were treated with coronary artery bypass grafting or percutaneous coronary intervention alone. A total of 52 patients (66%) were candidates for electrophysiologic testing. Of these patients, 48 (92%) underwent electrophysiologic testing; of these patients, 10 received amiodarone alone, and 35 received an implantable cardioverter-defibrillator (ICD) (of whom 3 also received amiodarone). Patients who did not receive ICD therapy typically presented before 1998 with CHD and underwent coronary artery bypass grafting or percutaneous coronary intervention only. Of 79 patients who were discharged, 14 (18%) with an ICD have received subsequent shocks. Nineteen (24%) of 79 patients have died, 5 of a primary cardiac etiology (including 2 with repeated OHCA). CONCLUSIONS: The VF OHCA survival rate is high in the setting of rapid defibrillation, with 40% of patients being discharged from the hospital. By the end of the 10-year study, more patients were receiving antiarrhythmic therapy, in particular ICD implantation, after hospital admission. Overall, the long-term survival in patients with VF OHCA is favorable.

Aged↗
PubMed2003

Thoracoscopic extracardiac obliteration of the left atrial appendage for stroke risk reduction in atrial fibrillation.

OBJECTIVES: We evaluated left atrial appendage obliteration in high-risk patients with atrial fibrillation (AF). BACKGROUND: Left atrial appendage thrombosis and embolization is the principal mechanism of stroke in AF. Anticoagulation is underutilized and often contraindicated. METHODS: Thoracoscopic Left Appendage, Total Obliteration, No cardiac Invasion (LAPTONI) was undertaken with a loop snare in eight patients and a stapler in seven patients, median age 71 years, with clinical risk factors for stroke and with an absolute contraindication to or failure of prior thrombosis prevention with warfarin. Eleven patients had a history of prior thromboembolism. One patient took sustained warfarin during follow-up. RESULTS: The LAPTONI procedure was completed in 14 of 15 patients, and 1 patient required urgent conversion to open thoracotomy because of bleeding. Patients have been followed up for 8 to 60 months, mean 42 +/- 14 months. One fatal stroke occurred 55 months after surgery, and one non-disabling stroke three months after surgery. Two other deaths occurred, one after coronary bypass surgery and the other from hepatic failure. The subgroup of 11 patients with prior thromboembolism had an annualized rate of stroke of 5.2% per year (95% confidence interval [CI] 1.3 to 21) after LAPTONI, which compares to a rate of 13% per year (95% CI 9.0 to 19) for similar aspirin-treated patients from the Stroke Prevention in Atrial Fibrillation trials (p = 0.15). CONCLUSIONS: The LAPTONI procedure appears technically feasible without immediate disabling neurologic morbidity or mortality, and it demonstrates low post-operative event rates and a statistical trend toward thromboembolic risk reduction in high-risk AF patients.

Adult↗
PubMed2003

Significant effects of atrioventricular node ablation and pacemaker implantation on left ventricular function and long-term survival in patients with atrial fibrillation and left ventricular dysfunction.

Control of ventricular rate by atrioventricular node ablation and pacemaker implantation in patients with drug-refractory atrial fibrillation (AF) is associated with improved left ventricular (LV) function. The objective of this study was to determine the effect of atrioventricular node ablation on long-term survival in patients with AF and LV dysfunction. Survival was determined by the Kaplan-Meier method for 56 study patients with LV ejection fraction (EF) < or =40% who underwent atrioventricular node ablation and pacemaker implantation and 56 age- and gender-matched control patients with AF and LVEF >40%, and age- and gender-matched control subjects from Minnesota. Groups were compared using the log-rank test. In study patients (age 69 +/- 10 years; 45 men), LVEF was 26% +/- 8% and 34% +/- 13% (p <0.001) before and after ablation, respectively. During follow-up (40 +/- 23 months), 23 patients died. Observed survival was worse than that of normal subjects (p <0.001) and control patients (p = 0.005). After ablation, LVEF nearly normalized (> or =45%) in 16 study patients (29%), in whom observed survival was comparable to that of normal subjects (p = 0.37). Coronary artery disease, hyperlipidemia, chronic renal failure, previous myocardial infarction, and coronary artery operation were independent predictors for mortality. Near normalization of LVEF occurred in 29% of study patients, suggesting that AF-induced EF reduction is reversible in many patients. Normal survival in patients with reversible LV dysfunction highlights potential survival benefits of rate control. Poor survival in patients with persistent LV dysfunction confirms the importance of optimal medical therapy.

Aged↗
PubMed2003

Long-term outcomes of out-of-hospital cardiac arrest after successful early defibrillation.

BACKGROUND: Mortality after out-of-hospital cardiac arrest from ventricular fibrillation is high. Programs focusing on early defibrillation have improved the rate of survival to hospital discharge. We conducted a population-based analysis of the long-term outcome and quality of life of survivors. METHODS: All patients who had an out-of-hospital cardiac arrest between November 1990 and January 2001 who received early defibrillation for ventricular fibrillation in Olmsted County, Minnesota, were included. The survival rate was compared with that of an age-, sex-, and disease-matched (2:1) control population of residents who had not had an out-of-hospital cardiac arrest and with that of age- and sex-matched controls from the general U.S. population. The quality of life was assessed with use of the Medical Outcomes Study 36-item Short-Form General Health Survey (SF-36) and compared with U.S. population norms. RESULTS: Of 200 patients who presented with an out-of-hospital cardiac arrest with ventricular fibrillation, 145 (72 percent) survived to hospital admission (7 died in the emergency department) and 79 (40 percent) were neurologically intact (good overall capability or moderate overall disability) at discharge. The mean (+/-SD) length of follow-up was 4.8+/-3.0 years. Nineteen patients died after discharge from the hospital. The expected five-year survival rate (79 percent) was identical to that among age-, sex-, and disease-matched controls (P=0.68) but lower than that among the age- and sex-matched U.S. population (86 percent, P=0.02). Fifty patients completed SF-36 surveys at the end of follow-up, and the majority had a nearly normal quality of life, with the exception of reduced vitality. CONCLUSIONS: Long-term survival among patients who have undergone rapid defibrillation after out-of-hospital cardiac arrest is similar to that among age-, sex-, and disease-matched patients who did not have out-of-hospital cardiac arrest. The quality of life among the majority of survivors is similar to that of the general population.

Aged↗
PubMed2003

Familial atrial fibrillation is a genetically heterogeneous disorder.

OBJECTIVES: The aims of this study were to identify and characterize familial cases of atrial fibrillation (AF) in our clinical practice and to determine whether AF is genetically heterogeneous. BACKGROUND: Atrial fibrillation is not generally regarded as a heritable disorder, yet a genetic locus for familial AF was previously mapped to chromosome 10. METHODS: Of 2,610 patients seen in our arrhythmia clinic during an 18-month study period, 914 (35%) were diagnosed with AF. Familial cases were identified by history and medical records review. Four multi-generation families with autosomal dominant AF (FAF 1 to 4) were tested for linkage to the chromosome 10 AF locus. RESULTS: Fifty probands (5% of all AF patients; 15% of lone AF patients) were identified with lone AF (age 41 +/- 9 years) and a positive family history (1 to 9 additional relatives affected). In FAF 1 to 3, AF was associated with rapid ventricular response. In contrast, AF in FAF-4 was associated with a slow ventricular response and, with progression of the disease, junctional rhythm and cardiomyopathy. Genotyping of FAF 1 to 4 with deoxyribonucleic acid markers spanning the chromosome 10q22-q24 region excluded linkage of AF to this locus. In FAF-4, linkage was also excluded to the chromosome 3p22-p25 and lamin A/C loci associated with familial AF, conduction system disease, and dilated cardiomyopathy. CONCLUSIONS: Familial AF is more common than previously recognized, highlighting the importance of genetics in disease pathogenesis. In four families with AF, we have excluded linkage to chromosome 10q22-q24, establishing that at least two disease genes are responsible for this disorder.

Adult↗
PubMed2002

Relation of ejection fraction and inducible ventricular tachycardia to mode of death in patients with coronary artery disease: an analysis of patients enrolled in the multicenter unsustained tachycardia trial.

BACKGROUND: Fifty percent of deaths in patients with coronary disease occur suddenly. Although many factors correlate with increased mortality, there is little information regarding the influence of these factors on mode of death. As such, optimum methods to determine patients most likely to benefit from implantable defibrillator therapy are unclear. METHODS AND RESULTS: We analyzed the relation of ejection fraction and inducible ventricular tachyarrhythmias to mode of death in all 1791 patients enrolled in the Multicenter Unsustained Tachycardia Trial who did not receive antiarrhythmic therapy. Total mortality and arrhythmic deaths/cardiac arrests occurred more frequently in patients with ejection fraction <30% than in those with ejection fraction of 30% to 40%. The percentage of deaths classified as arrhythmic was similar in patients with ejection fraction <30% or > or =30%. The relative contribution of arrhythmic events to total mortality was significantly higher in patients with inducible tachyarrhythmia (58% of deaths in inducible patients versus 46% in noninducible patients, P=0.004). The higher percentage of events that were arrhythmic among patients with inducible tachyarrhythmia appeared more distinct among patients with an ejection fraction > or =30% (61% of events were arrhythmic among inducible patients with ejection fraction > or =30% and only 42% among noninducible patients, P=0.002). CONCLUSIONS: Both low ejection fraction and inducible tachyarrhythmias identify patients with coronary disease at increased mortality risk. Ejection fraction does not discriminate between modes of death, whereas inducible tachyarrhythmia identifies patients for whom death, if it occurs, is significantly more likely to be arrhythmic, especially if ejection fraction is > or =30%.

Canada↗
PubMed2002

Effect of implantable defibrillators on arrhythmic events and mortality in the multicenter unsustained tachycardia trial.

BACKGROUND: The Multicenter Unsustained Tachycardia Trial (MUSTT) was designed to evaluate an antiarrhythmic treatment strategy, including drugs and implantable defibrillators (ICDs), guided by electrophysiological (EP) testing. We performed several statistical analyses to assess the contribution of defibrillators to the observed treatment benefit. METHODS AND RESULTS: First, the effects of defibrillators were indirectly examined by comparing the randomized treatment arms (EP-guided therapy versus no antiarrhythmic therapy) within subgroups that varied according to ICD usage. Use of ICDs increased during the trial; hence, the randomized treatments were compared according to date of enrollment. There were also site-specific differences in ICD use; hence, the randomized arms were compared within groups of sites defined by level of ICD use. There was a distinct "dose response" in relation to ICD use. Where ICD use was high, EP-guided therapy produced significant reductions in arrhythmic death or cardiac arrest (P<0.004). Where ICD use was low, there was no benefit of EP-guided therapy. Finally, outcomes of EP-guided therapy patients who received an ICD were directly compared with outcomes of other patients using the Cox proportional hazards model with receipt of an ICD as a time-dependent covariate. Adjusted for other prognostic factors, patients who received an ICD had risk reductions of >70% in arrhythmic death or cardiac arrest and >50% in total mortality (P<0.001 for both end points). CONCLUSIONS: The benefit of EP-guided antiarrhythmic therapy observed in MUSTT was due to improved outcomes among patients who received an ICD but not among patients who received antiarrhythmic drugs.

Anti-Arrhythmia Agents↗