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PubMed1991

Benefits of implantable defibrillators are overestimated by sudden death rates and better represented by the total arrhythmic death rate.

Benefits of the implantable defibrillator on survival were studied in 56 consecutive patients (concomitant coronary bypass or arrythmia surgery in 15) during an 8 year period between 1982 and 1990. During a follow-up period of 29 +/- 25 months, six patients had a sudden death and eight patients had a nonsudden cardiac death. Nonsudden cardiac deaths included three surgical deaths (death within 30 days after the surgery; two in patients without and one in a patient with concomitant cardiac surgery), one arrhythmia-related nonsudden death (death within 24 h after an arrhythmic event despite initial termination of the arrhythmia by the implantable defibrillators) and four nonarrhythmic cardiac deaths. The actuarial survival rate free of events at 1, 2 and 3 years was 96%, 96% and 92%, respectively, for sudden death, 91%, 91% and 87% for sudden death and surgical mortality and 89%, 89% and 85% for total arrhythmic death (sudden death, surgical mortality and arrhythmia-related nonsudden death). Thus, in patients treated with an implantable defibrillator, 1) the rate of sudden death is low (8% at 3 years); 2) 50% of nonsudden cardiac deaths are causally related to arrhythmia (surgical mortality or arrhythmia-related nonsudden death); 3) the total arrhythmic death rate is substantially higher than the sudden death rate; and 4) benefits of an implantable defibrillator are overestimated by reported sudden death and nonsudden cardiac death rates. The benefits may be better represented by the total arrhythmic death and nonarrhythmic cardiac death rates.

Actuarial Analysis↗

PubMed2005

The ethics of deactivating implanted cardioverter defibrillators.

Implantable cardioverter defibrillators are life-saving devices for many patients with cardiac disease. Recipients of these devices, nevertheless, often suffer from progressive comorbid and cardiac conditions. Therefore, physicians should anticipate situations in which the defibrillator is no longer desired by the patient or no longer medically appropriate. Near the end of life, many of these patients may decline cardiopulmonary resuscitation. The comanagement of do-not-resuscitate orders and implanted defibrillators can be confusing to patients and physicians alike since the former proscribe the use of electrical cardioversion while the latter provide this precise treatment. Although the use of implanted defibrillators has important ethical implications, few studies have examined these issues, and guidelines have not yet been developed to assist physicians in caring for patients who have received defibrillators. This paper discusses bioethical considerations in disabling implantable cardioverter defibrillators.

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PubMed2001

Baseline factors predicting early resumption of driving after life-threatening arrhythmias in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial.

BACKGROUND: In the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial, patients with ventricular fibrillation or hemodynamically unstable ventricular tachycardia were randomly assigned to receive either an implantable cardioverter-defibrillator (ICD) or antiarrhythmic drug therapy. As part of the trial, patients were asked to participate in a prospective driving survey. The purpose of the survey was to determine what baseline factors and patient characteristics specifically predicted resumption of driving earlier than advised by current guidelines. METHODS: Patients were surveyed anonymously as to their driving habits in the initial period after random assignment and every 6 months thereafter. AVID study coordinators were independently asked to assess their patients' driving status as well. The relation between baseline factors and time to resumption of driving was explored by means of Kaplan-Meier estimates for univariate analyses and the stepwise Cox proportional hazards regression model for multivariate analyses. RESULTS: There were 802 patients who were eligible for assessment of driving status. The majority of patients (58%) resumed driving an automobile within 6 months of their index arrhythmia regardless of whether they received drug therapy or an ICD. By multivariate analysis, patients who were younger than 65 years of age, male, and college educated were more likely to drive early, as were patients whose index arrhythmia was ventricular tachycardia. CONCLUSIONS: Younger, college-educated men and those whose index arrhythmia is ventricular tachycardia are most likely to resume driving <6 months after the initiation of therapy for a potentially life-threatening ventricular arrhythmia. Patients with an ICD did not appear to resume driving later than those who were discharged on antiarrhythmic drugs alone.

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PubMed1994

Antiarrhythmic drugs versus implantable defibrillators: the need for a randomized controlled study.

The implantable cardiac defibrillator was first used in 1980 and has gained widespread acceptance. However, no randomized controlled trials have been reported that compare the implantable cardiac defibrillator with antiarrhythmic drugs. Most published studies have used historical control subjects or nonrandomized concurrent patients for comparison with patients who received an implantable defibrillator. To reduce bias, studies are needed that compare therapies randomized between antiarrhythmic drugs and implantable defibrillators. The Antiarrhythmics Versus Implantable Defibrillators (AVID) Study was designed to evaluate the nonthoracotomy, tiered-therapy implantable defibrillator compared with drug therapy (amiodarone or sotalol). Patients are eligible for randomization if they have a history of recent cardiac arrest caused by ventricular fibrillation or have hemodynamically serious ventricular tachycardia. A pilot study to enroll 200 patients began on June 1, 1993, before the start of the main study of 1000 patients. Analysis of the main study by intention to treat will assess the primary endpoint of total mortality.

Amiodarone↗

PubMed1998

[Implantable defibrillators in the management of malignant ventricular tachyarrhythmias. Experience at the Arrhythmia National Center].

BACKGROUND: Implantable defibrillators are the most effective means to prevent sudden death in patients with malignant ventricular tachyarrhythmias. The availability of this type of devices is limited in Chile, due to their high price. AIM: To report the first patients treated with implantable defibrillators in our hospital. PATIENTS AND METHODS: Nine males and one female aged 13 to 65 years old are reported. Three presented with ventricular fibrillation (presenting out of the hospital in three) and the rest had ventricular tachycardia resistant to drugs or radiofrequency ablation. RESULTS: All implants were performed using intracardiac electrodes. The generator was implanted in the pectoral region in nine and in the abdomen in one. A successful defibrillation was obtained with less than 15 J in four patients, with 20 J in three and with 24 J in three. There were no complications during the procedure. After a 12 months follow up, four patients have been treated by the implantable device. One of these subjects had a ventricular fibrillation in two occasions. One patient died of a bronchopneumonia two years after the implant. CONCLUSIONS: Implantable defibrillators are an effective therapy for the treatment of malignant ventricular arrhythmias with a high risk of sudden death.

Adolescent↗

PubMed1998

Prospective evaluation of new and old criteria to discriminate between supraventricular and ventricular tachycardia in implantable defibrillators.

This study was designed to evaluate the ability to distinguish between supraventricular tachycardias (SVTs) and ventricular tachycardias (VTs) based on onset, stability, and width criteria in an implantable defibrillator. Inappropriate detection of atrial fibrillation and sinus tachycardia is a common problem in patients with implantable defibrillators. The onset, stability, and width criteria were studied in 17 patients who underwent implantation of a Medtronic 7218C implantable defibrillator by inducing sinus tachycardia and atrial fibrillation. Additional data on the width criteria was obtained by pacing at separate sites in both the left and right ventricle. Patients were studied at different times for up to 6 months to determine any changes in the criteria. The onset and stability criteria caused inappropriate detections in 36% and 12% of the episodes, respectively. The addition of the width criteria decreased the inappropriate detection using the onset and stability criteria to 5% and 2%, respectively. Pacing from the RV apex, RV outflow tract, and LV apex was appropriately detected as wide in 76%, 41%, and 94%, respectively. The width criteria changed over time in individual patients, but was stable by 6 months in all but one patient. No single criterion is satisfactory for distinguishing between SVT and VT in this patient population, but the combination of criteria seems to provide better discrimination. The width criteria can change dramatically over time and needs to be monitored carefully. Newer algorithms will need to be developed to allow better detection of supraventricular tachycardias.

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PubMed2003

Nonthoracotomy implantable defibrillator lead extraction: results and comparison with extraction of pacemaker leads.

Extraction of pacemaker leads has been demonstrated to be successful and safe in experienced hands using current tools. Whether application of such techniques and tools yield similar results among patients undergoing extraction of nonthoracotomy implantable defibrillator leads is unknown. This report describes a retrospective analysis of indications, techniques used, and outcome of patients who had a single ventricular nonthoracotomy implantable defibrillator lead extracted at The Cleveland Clinic Foundation. Results were compared to a matched population of patients undergoing extraction of ventricular pacemaker leads from a national registry and to the experience with pacemaker lead extraction at The Cleveland Clinic Foundation. Successful complete extraction of ventricular nonthoracotomy implantable defibrillator leads, in the absence of major complications, was achieved in 96.9% of attempts to extract leads from 161 patients. Clinical success was achieved in 98.1% of patients. Failure occurred in three patients. Two patients had major complications, including one death. The most common indication for extraction was infection (46.6%), followed by lead failure (34.2%). Procedure (140.8 vs 171.2 minutes, P<0.01) and fluoroscopy (9.9 vs 11.0 minutes, P<0.01) times compared favorably with those obtained from the pacemaker lead extraction database. Use of LASER did not influence the safety of the procedure or fluoroscopy times. Extraction of ventricular nonthoracotomy implantable defibrillator leads using currently available tools is a complex but effective procedure. In experienced hands, excellent success rates should be achieved with a low incidence of complications.

Adolescent↗

PubMed1995

Implantable defibrillators for high-risk patients with heart failure who are awaiting cardiac transplantation.

The objective of this study was to assess the operative risk and efficacy of implantable defibrillators for preventing sudden death in patients with heart failure awaiting transplantation. The average waiting time for elective cardiac transplantation is 6 months to 1 year. Sudden cardiac death is the major source of mortality in outpatients in stable condition awaiting cardiac transplantation. The efficacy of implantable defibrillator therapy in this population is not established. We analyzed the operative risk, time to appropriate shock, and sudden death in 15 patients determined to be at high risk of sudden death who were accepted onto the outpatient cardiac transplant waiting list. Nonfatal postoperative complications occurred in two (13%) subjects with epicardial defibrillating lead systems and in none with transvenous lead systems. Defibrillation energies were 16 +/- 2 J versus 24 +/- 2 J with epicardial and transvenous lead systems, respectively. Sudden death free survival until transplantation was 93%. Most of the patients (60%) had an appropriate shock during a mean follow-up of 11 +/- 12 months. The mean time to an appropriate shock was 3 +/- 3 months. Hospital readmission was required in three (20%) subjects to await transplantation on an urgent basis. However, two of these subjects had received appropriate shocks before readmission. In selected patients at high risk for sudden death while on the outpatient cardiac transplant waiting list, the operative risk is low and adequate defibrillation energies can be obtained to allow implantable defibrillator placement. Most subjects will have an appropriate shock as outpatients before transplantation, and sudden death free survival is excellent.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗

PubMed1999

Design and results of the antiarrhythmics vs implantable defibrillators (AVID) registry. The AVID Investigators.

BACKGROUND: The Antiarrhythmics Versus Implantable Defibrillators (AVID) Study compared treatment with implantable cardioverter-defibrillators versus antiarrhythmic drugs in patients with life-threatening ventricular arrhythmias (VAs). AVID maintained a Registry on all patients, randomized or not, with any VA or unexplained syncope who could be considered for either of the treatment strategies. Trial-eligible arrhythmias were the categories of VF cardiac arrest, Syncopal VT, and Symptomatic VT, below. METHODS AND RESULTS: Of 5989 patients screened, 4595 were registered and 1016 were randomized. Mortality follow-up through 1996 was obtained on the 4219 Registry patients enrolled before 1997 through the National Death Index. Crude mortality rates (mean+/-SD, follow-up, 16.9+/-11.5 months) were: VF cardiac arrest, 17.0% (n=1399, 238 deaths); Syncopal VT, 21.2% (n=598, 127 deaths); Symptomatic VT, 15.8% (n=1065, 168 deaths); Stable (asymptomatic) VT, 19.7% (n=497, 98 deaths); VT/VF with transient/correctable cause, 17.8% (n=270, 48 deaths); and Unexplained syncope, 12.3% (n=390, 48 deaths). CONCLUSIONS: Patients with seemingly lower-risk or unknown-risk VAs (asymptomatic VT, and VT/VF associated with a transient factor) have a (high) mortality similar to that of higher-risk, AVID-eligible VAs. The similar (and poor) prognosis of most patients with VT/VF suggests the need for reevaluation of a priori risk grouping and raises the question of the appropriate arrhythmia therapy for a broad range of patients.

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PubMed2004

Anesthetic management for cardioverter-defibrillator implantation in a patient with Kearns-Sayre syndrome.

Kearns-Sayre syndrome (KSS) is a rare mitochondrial myopathy and often involves cardiac conduction abnormality and muscle weakness. We report a patient with KSS who had an implantable cardioverter-defibrillator (ICD) implanted during general anesthesia with propofol and nitrous oxide (N2O). These anesthetics did not show any effects on respiration, cardiac conduction, or neuromuscular transmission in this case. The surgery was performed successfully, and the postoperative period was uneventful. The authors recommend that propofol and N2O are suitable general anesthetics for ICD implantation in KSS patients.

Adult↗

PubMed1999

Evidence-based medicine and the implantable defibrillator.

Evidence from recent randomized clinical trials now strongly supports the use of the implantable defibrillator, as treatment of first choice, in patients who have experienced symptomatic, sustained ventricular tachyarrhythmias. Little or no controversy remains on this question, either among physicians or third-party players. The evidence-based use of the defibrillator as primary preventative therapy (that is, for patients who have an increased risk for lethal arrhythmias, but who have not yet experienced them) is far more limited. Two randomized trials have now demonstrated a survival benefit with the defibrillator in patients who have ischemic heart disease; reduced left ventricular ejection fraction; documented nonsustained ventricular tachycardia; and inducible sustained ventricular tachycardia during electrophysiologic testing that is not suppressed by at least one drug trial. Based on the strength of this recently available information, the screening of appropriate patients, while admittedly inconvenient, ought to be strongly considered. The broader use of the implantable defibrillator in the primary prophylaxis of arrhythmic sudden death will have to await the results of future trials.

Amiodarone↗

PubMed2001

Long-term infection rates associated with the pectoral versus abdominal approach to cardioverter- defibrillator implants.

Infection is an uncommon (0% to 6.7%) but serious complication after implantable cardioverter-defibrillator (ICD) implantation. All ICD primary implants, replacements, or revisions performed at the Massachusetts General Hospital between April 1983 and May 1999 were reviewed. A total of 21 ICD-related infections (1.2%) were identified among 1,700 procedures affecting 1.8% of the 1,170 patients who underwent a primary implant, a generator change, or a revision of their systems. The mean follow-up time was 35 +/- 33 months. Of the 959 patients with long-term follow-up, 19 of the 584 patients (3.2%) with abdominal and 2 of the 375 patients (0.5%) with pectoral systems developed ICD-related infections (p = 0.03). There was no significant difference between the infection rate among the 959 primary ICD implants and the 447 replacements or system revisions. Only 5 of the patients (24%) had systemic signs of infection, including fever (T>100.5) and elevated white blood count >12,000. Cultures from the wound revealed staphylococcal species in 16 patients (76%). Nineteen patients were treated with removal of the entire ICD system in addition to intravenous antibiotics for 2 to 4 weeks. A decrease in the incidence of ICD-related infection has occurred since the advent of transvenous pectoral systems. The main organism responsible for ICD infection is Staphylococcus. The mainstay of ICD infection management consists of complete removal of the entire implanted system.

Antibiotic Prophylaxis↗

PubMed2006

Survival in octogenarians receiving implantable defibrillators.

BACKGROUND: Although clinical trials have expanded implantable defibrillator (ICD) indications, octogenarians have been poorly represented in these studies. Overall, survival in this subgroup is ill-defined. METHODS: Consecutive patients > or = 80 years of age at ICD implant between July 1995 and September 2003 were retrospectively analyzed. Kaplan-Meier survival analysis was performed, and mortality predictors were identified. Consecutive nonelderly patients aged 60 to 70 years (60-70 group) who received ICDs over the same period were analyzed as a reference. Mortality predictors in the > or = 80 group were compared to the 60-to-70 group. RESULTS: A total of 348 patients (age, > or = 80 years [n = 107]; age, 60-70 years [n = 241]) were included. Mean follow-up time for the entire cohort was 3.3 +/- 2.2 years. Other than the estimated glomerular filtration rate (eGFR) (58 +/- 22 vs 66 +/- 22 mL/min) in the > or = 80 group versus the 60-to-70 group, no other differences in baseline characteristics were observed. Median survival was 4.2 years after implant in the > or = 80 group versus 7 years in the 60-to-70 group (P < .01). Mortality predictors in the > or = 80 group included ejection fraction (EF) < or = 30% (hazard ratio [HR], 2.2; 95% confidence interval [CI], 1.3-4.0) and eGFR < 60 mL/min (HR, 2.2; 95% CI, 1.3-3.7). In the 60-to-70 group, EF < or = 30% (HR, 2.7; 95% CI, 1.6-4.5), eGFR < 60 mL/min (HR, 3.4; 95% CI, 2.2-5.3), diabetes (HR, 1.8; 95% CI, 1.9-2.9), and QRS width > 120 ms (HR, 2.1; 95% CI, 1.4-3.3) predicted mortality. QRS > 120 ms and diabetes were not predictors in octogenarians (HR, 1.1 and 1.5, respectively; 95% CI, 0.7-1.9 and 0.8-2.7, respectively). Analysis of octogenarians subgrouped by EF < or = 30% and eGFR < 60 mL/min identified patients whose median survival was 6.1 years (neither predictor present; n = 28), 4.7 years (either predictor present; n = 46), and 19 months (both predictors present; n = 33) (P < .01 between groups). Survival analysis in the > or = 80-year-old cohort grouped by eGFR quartile identified groups with median survival of 5.6, 4.7, 3.5 years, and 18 months, respectively, in the highest to the lowest eGFR quartile (> 75, 61-75, 41-60, and < 41 mL/min). CONCLUSIONS: Median survival in octogenarian ICD recipients is greater than 4 years. In addition to baseline EF, eGFR is a strong predictor of mortality in elderly ICD candidates. These easily identifiable clinical variables may assist clinical decision making and help to provide appropriate post-ICD implant survival expectations in this elderly patient group.

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PubMed2004

Feasibility and accuracy of pre-procedure imaging of the proximal cephalic vein by duplex ultrasonography in pacemaker and defibrillator implantation.

BACKGROUND: Failure of the cephalic venous approach in pacemaker and defibrillator implantation is always due to the small size and difficulty in isolation of the cephalic vein. We propose that pre-procedure imaging of the proximal cephalic vein is valuable to achieve successful access of cephalic vein. However, the feasibility and accuracy of duplex ultrasonographic imaging of the proximal cephalic vein are unknown. METHODS: The study enrolled 30 consecutive patients who underwent new implantation of permanent pacemakers or defibrillators at our institute. An ultrasound probe scanned along the plane 2 cm beneath the inferior margin of the clavicle to locate the cephalic vein before device implantation. If the vein was well visualized, the venous diameter and the vertical depth were measured. The corresponding surface location of the vein on the chest wall was also identified and recorded by duplex ultrasonography. The echo-derived vertical depths and vascular findings were compared with those measured during surgery. RESULTS: All proximal cephalic veins were well visualized in the infraclavicular region by duplex ultrasonography. They were compressible, patent in color Doppler ultrasound imaging, and displayed phasic change of Doppler signal during respiration, indicating patency in all study veins. The average diameter of the target cephalic vein was 7.7 +/- 1.6 mm (range, 5.0-11.1 mm). The echo-derived vertical depth of the proximal cephalic veins was highly correlated with the depth measured during surgery (28.4 +/- 5.5 vs. 28.4 +/- 5.6 mm, r = 0.93, P < 0.0001). All target cephalic veins were isolated after exploration via the estimated surface location of the chest wall by pre-procedure duplex ultrasonography. Seven (23%) of the studied patients did not have their cephalic vein cannulated successfully. CONCLUSION: The target proximal cephalic vein in pacemaker and defibrillator implantation can be precisely imaged and localized by duplex ultrasonography. Although further studies are needed, our findings pave a way to further study and clarify the implantation problems of cephalic vein approach.

Defibrillators, Implantable↗

PubMed2005

The relation between patients' outcomes and the volume of cardioverter-defibrillator implantation procedures performed by physicians treating Medicare beneficiaries.

OBJECTIVES: The purpose of this study is to determine if implantable cardioverter-defibrillator (ICD) implantation should be limited to physicians with high procedural volume. BACKGROUND: Expanding indications for ICDs will result in an increasing number of physicians implanting these devices. METHODS: Using the 20% Part B Medicare files for 1999 through 2001, we identified new ICD implantations and the corresponding denominator files. We used Medicare Provider Analysis and Review hospital records and the appropriate International Classification of Diseases-9 diagnosis and procedure codes to define complications within 90 days. We defined physician volume categories by assigning one-quarter of the patients to each quartile. A logistic regression model was used to adjust outcomes for potential confounders. RESULTS: Ninety-day mortality did not differ between patients who had their ICD implanted by physicians with the highest volume of implants and those who had their ICD implanted by physicians with the lowest volume of implants (6.2% vs. 5.9%; odds ratio [OR] 0.99; 95% confidence interval [CI] 0.75 to 1.30). Within 90 days, mechanical complications were significantly higher in the lowest volume quartile (OR 1.47; 95% CI 1.09 to 1.99) but were comparable for physicians who implanted at least 11 ICDs per year. The risk of ICD infection was significantly higher in patients who had their ICD implanted by physicians with the lowest volume of implants (OR 2.47; 95% CI 1.18 to 5.17). CONCLUSIONS: We observed an association between a higher volume of ICD implants and a lower rate of mechanical complications and infections. This association suggests that ICD implantation should not be performed by physicians without regard to their procedural volume.

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PubMed2006

[Positive microvolt T-wave alternans as a marker of ventricular arrhythmia trigering during cardioverter-defibrillator implantation].

Microvolt T-wave alternans (MTWA) is promising method for noninvasive assessment of arrhythmic risk, but its role hasn't established yet. The aim of this study was to establish the MTWA potency to predict the ventricular arrhythmia triggering during implantable cordioverter-defibrillator (ICD) implantation. Material and metods. The study group consisted of 21 patients, aged 63.0+/-8.0 years; EF was 38.0+/-12.8%. Seventeen of them had a history of myocardial infarction and 4 had non-ischemic cardiomyopathy. The reason for ICD implantation were secondary prevention due to nonfatal cardiac arrest caused by VF/VT in nineteen patients and in two patients ICD was implanted because of unexplained syncope and low EF (< or =35%). All patients underwent VT/VF triggering during device implantation caused by electrophysiological study (EPS). If this proved ineffective aggressive protocol of 50 Hz BURST and T SHOCK was applied. After ICD implantation the following tests were performed: ECG with HR, QRS and QTc evaluation, 24-hour ECG Holter monitoring with HRV assessment and MTWA evaluation during treadmill exercise test. Results. In the group with VT/VF induced by less aggressive protocol (EPS), group I (n = 10) MTWA was present in nine patients, in one the result of MTWA was indeterminate. In the group with VT/VF induced by more aggressive protocol, group II (n = 11) MTWA was present in four patients, indeterminate in four and absent in three. There was a significant (p = 0.017) difference between group I and II in the frequency of positive result of MTWA. There were no differences between the two groups according to time domain parameters of HRV such as SDNN, RMSSD and PNN50 and QTc. There was a significant difference between the two groups in time duration of QRS complexes, 118.9+/-14.7 vs. 105.6+/-11.5 accordingly (p < 0.04). Conclusions. MTWA may help identify patients in whom VTNVF is more easily inducible by electrophysiologic study during ICD implantation. It is easier to induce ventricular arrhythmia when QRS complexes are wider, irrelevant to left ventricular dysfunction and autonomic function of the heart.

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PubMed2002

Impaired detection of ventricular tachyarrhythmias by a rate-smoothing algorithm in dual-chamber implantable defibrillators: intradevice interactions.

INTRODUCTION: Rate smoothing is an algorithm initially designed to prevent rapid changes in pacemaker rates. In this study, we sought to determine the potential of the rate-smoothing mechanism in preventing detection of ventricular tachyarrhythmias. METHODS AND RESULTS: Clinical testing of rate smoothing was performed at the time of defibrillator arrhythmia induction in 16 patients with implantable defibrillators during 65 episodes of ventricular tachyarrhythmias. We also performed simulator-based testing to assess detection of ventricular tachycardia between 170 and 220 beats/min with systematic sequential change of rate-smoothing percent, AV delay, and maximal rate. During clinical testing of 54 ventricular fibrillation/polymorphic ventricular tachyarrhythmia episodes, there were no cases of nondetection and 3 episodes (5%) of minimally delayed detection. Of 10 monomorphic ventricular tachyarrhythmias, 6 had either delayed (2 cases) or absent (4 cases) detection. During simulator testing, complex interrelationships were demonstrated in AV delay, upper rate, and rate-smoothing percent in determining the severity of the effect on detection. Generally, long AV delay, higher upper rate, and smaller (more aggressive) rate smoothing were associated with increased risk of ventricular tachyarrhythmia underdetection. Importantly, use of parameters that impaired detection was always accompanied by a programmer warning message. CONCLUSION: Rate smoothing may result in delay or failure of ventricular tachycardia detection. It is important to consider warning messages when programming rate smoothing and to test for appropriate detection when rate smoothing is used despite warning messages.

Algorithms↗

PubMed2001

Survival benefit with an implanted defibrillator in relation to mortality risk in chronic coronary heart disease.

Although improved patient survival has been reported in several randomized trials with the implanted cardioverter-defibrillator, <15% of patients treated with defibrillators during trials receive life-saving benefit from this therapy. We evaluated the survival benefit from defibrillator therapy in relation to the severity of the mortality risk in patients with coronary heart disease. Using data from the Multicenter Automatic Defibrillator Implantation Trial, we partitioned the study population into high- and low-risk subsets for each of 3 physiologically meaningful risk factors (ejection fraction, QRS duration, and history of heart failure requiring therapy). Risk of death was evaluated by Cox proportional-hazards regression analyses in patients with single and multiple risk factors. The defibrillator was associated with a significant (p = 0.002) reduction in mortality only in high-risk subsets with ejection fraction <0.26, QRS duration > or =0.12 second, and history of heart failure requiring treatment. The Cox hazard ratio for the risk of death progressively increased >1.0 as a function of the number of risk factors present. Defibrillator therapy was associated with a progressive reduction in the hazard ratio <1.0 (improved survival) at each increased level of mortality risk. Patients at the highest mortality risk (all 3 risk factors; hazard ratio 4.33) achieved the largest mortality reduction (hazard ratio 0.20) from defibrillator therapy. In patients with chronic coronary heart disease, the magnitude of the survival benefit from the implanted defibrillator is directly related to the severity of cardiac dysfunction and its associated mortality risk.

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