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PubMed1999

Association of mood disturbance and arrhythmia events in patients after cardioverter defibrillator implantation.

BACKGROUND: Life stresses and negative emotions, such as anxiety and depression, are associated with adverse cardiac events, including arrhythmia. Patients undergoing implantation of an automatic internal cardioverter defibrillator provide a unique opportunity to characterize these relationships since all tachyarrhythmia episodes are recorded by the device. OBJECTIVES: The purpose of this study was to examine the association of emotional status after internal cardioverter defibrillator (ICD) implantation and subsequent arrhythmia events. METHODS: An analysis of data obtained in a prospective longitudinal study of responses to the ICD measured mood disturbance (Profile of Mood States; POMS) before implant and at 1, 3, 6, and 9 months postoperatively. Subjects included 144 men and 32 women with a mean age of 60 +/- 13 years and a mean left ventricular ejection fraction (LVEF) of 33 +/- 12%. Arrhythmia events were measured by self-report of shocks and by ICD device interrogation to obtain the number and type (defibrillation, cardioversion, and antitachycardia pacing) of therapies delivered by the ICD. For each time point, POMS scores of subjects who had arrhythmia events were compared with those who did not. For subjects who had ICD shocks, pre-event and post-event POMS scores were also compared. Multiple logistic regression was used at each time point to determine if clinical, demographic and psychological data could predict arrhythmia events. RESULTS: Patients with arrhythmia events had higher POMS scores throughout the 9 months of follow-up. Higher level of mood disturbance (specifically anxiety, fatigue, and confusion) at 1 and 3 months were independent predictors of subsequent arrhythmia events at 3 and 6 months after controlling for LVEF, the presence of coronary artery disease, pre-implant arrhythmia history, and the use of amiodarone and beta-blocking agents. There were no differences in POMS scores before and after ICD shocks, reinforcing the notion that negative emotions were a cause, rather than a consequence, of arrhythmia events. CONCLUSIONS: Mood disturbances, such as anxiety, may increase the risk for arrhythmia events after ICD insertion.

Adult↗

PubMed2003

Cardiac rehabilitation in patients with implantable defibrillators. Feasibility and complications.

OBJECTIVE: We examined patients with implantable cardioverter defibrillators (ICD) in order to demonstrate their safe participation in a standard rehabilitation program. DESIGN: Prospective cohort study of a consecutive series of patients after ICD implantation. Setting Inpatient rehabilitation center. PATIENTS AND METHODS: A total of 118 patients (73.7% male, mean age 60+/-11 years) took part for 23 +/- 4 days in a standard inpatient rehabilitation program including physical activity, psychological care, heart function seminars, and resuscitation exercises with family members. The following noninvasive tests were performed: symptomlimited exercise testing, two-dimensional echocardiography, Holter monitoring, telemetric ICD interrogation, optional fluoroscopy or X-ray examination of the thorax, and (in some patients) defibrillation threshold testing. RESULTS: Out of 118 patients 101 patients (85.6%) participated in regular ergometer training during which the initial workload of 23 +/- 11 Watts could be increased to 45 +/- 18 Watts. An individual conditioning program was assigned to 15% (n = 17) patients, thereby enabling the inclusion of all patients in the rehabilitation process. Under these conditions 12 patients (10%) experienced ICD malfunctions requiring therapy. As a consequence of all cardiac function tests, ICD reprogramming was necessary in 26 patients (22.1%). CONCLUSION: Following ICD implantation, patients may participate in a standard rehabilitation program without serious complications and with a significant increase in physical capacity. However, ICD malfunction occurs in approximately 10% of patients. Additional tests performed by skilled medical staff and appropriate technical equipment allows the ICD program to be optimized.

Aged↗

PubMed1995

Circadian variation of ventricular arrhythmia recurrences after cardioverter-defibrillator implantation in patients with healed myocardial infarcts.

Past studies using Holter monitoring and retrospective reviews of death certificates have documented peak occurrence of sudden death and nonsustained ventricular tachycardia (VT) in the morning hours. We used the Ventritex Cadence device (Ventritex, Sunnyvale, California) which documents the date and time of all stored arrhythmias leading to device therapy to evaluate the circadian pattern of sustained ventricular arrhythmia recurrence. Mean follow-up after defibrillator implantation was 628 +/- 285 days. All 390 patients had at least 1 episode (range 1 to 43) of sustained VT documented from analysis of the stored electrograms associated with an arrhythmia event. Stored electrograms were available for review and analysis in 3,041 device detections; 349 stored events were excluded because they did not fulfill the diagnostic criteria for VT or failed to document the onset of the ventricular arrhythmia at the beginning of the recorded event of the arrhythmia episode. Criteria for the diagnosis of VT or ventricular fibrillation were met in 2,692 arrhythmia episodes occurring in 390 patients. There was circadian variation for ventricular arrhythmia recurrence for the whole patient group with the data fit to the sinusoidal density function: f(t) = 126 - 51 x cos (-57 + 2 pi t/24) - 25 x sin (63 + 2 pi t/12) (p < 0.0001). Ventricular arrhythmia occurrence rate was lowest between 2:00 and 3:00 A.M., and highest between 10:00 and 11:00 A.M. In addition, the same circadian pattern was demonstrated regardless of patient age, gender, left ventricular ejection fraction (< 35% or > or = 35%), and VT cycle length (< 300 or > or = 300 ms).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1992

The automatic implantable defibrillator is the most realistic and cost-effective way of preventing sudden cardiac death.

Judgement about cost-effectiveness of medical treatments depends upon the criteria used to define effectiveness. The most rational single criterion is the Quality Adjusted Life Year gained (QALY). Comparisons of cost-effectiveness of treatments may be made by comparing the dollar costs per QALY. Both the dollar and the QALY comparisons are subject to all errors of biological variable measurement and bias introduced by experimental design seen in other biological experiments. The proper methodology for comparison is the prospective randomised controlled clinical trial. Such trials using the automatic implantable defibrillator (AICD) as prophylaxis against sudden cardiac death (SCD) have not yet been performed. The major underlying cause of SCD is coronary artery disease with previous myocardial infarction (MI) and provocative tests for ventricular arrhythmias are the most powerful predictors of SCD in infarction survivors. AICD implantation carriers a mortality of about 2%, and survival after successful implantation is about 89% at one, and 84% at two years. By comparison, infarction survivors with left ventricular ejection fraction < 0.4 and inducible slow monomorphic ventricular tachycardia have a survival rate of 70% at one, and 54% at two years. Antiarrhythmic drugs have not proven effective. There is an urgent need to confirm the advantage of the AICD by proper randomised controlled trial.

Australia↗

PubMed2004

Performance of a dual-chamber implantable defibrillator algorithm for discrimination of ventricular from supraventricular tachycardia.

BACKGROUND: Inappropriate therapies remain a major problem in patients with implantable cardioverter defibrillators (ICDs). Decreasing the proportion of inappropriate therapies is a major objective. With the addition of atrial detection and advanced algorithms, dual-chamber ICDs are designed to offer better discrimination of ventricular (VT) and supraventricular (SVT) arrhythmias. The present multicentre, open study aimed to evaluate the performance of a dual-chamber detection algorithm, the Atrial View algorithm, incorporated in a dual-chamber ICD, the Ventak AV (Guidant Inc., St. Paul, Minnesota, USA). METHODS AND RESULTS: Fifty-one patients (45 males, 62+/-11 years, ejection fraction 42+/-15%) with standard indications received a Ventak AV ICD which analyzes, within the VT zone RR stability, tachycardia onset, atrial rate and AV relationship. Predischarge enhanced-detection algorithms were prospectively programmed: stability 24 ms, onset 9%, atrial fibrillation threshold 200 beats/min, and Vrate>Arate. An additional sustained rate duration criterion was programmed at least at 30 s. ICDs were interrogated every 3 months or when patients received shocks. A blinded review of electrograms for arrhythmia diagnosis and appropriateness of therapy was performed by 2 experts. Over the follow-up period (12+/-3.6 months), a total of 400 tachycardia episodes was recorded within the VT zone. After the review of stored electrograms, 237 (59%) true positive, 143 (36%) true negative, 17 (4%) false positive and 3 (1%) false negative episodes were diagnosed. Considering the 3 VTs incorrectly detected by the detection algorithms, therapy was delivered in 2 cases after sustained rate duration and 1 VT reverted spontaneously. Inappropriate therapy occurred in 17 cases. All but 1 were related to SVT with 1:1 atrioventricular relationship. Finally, on a per episode basis, the detection algorithm sensitivity was 99% and specificity was 89%. CONCLUSIONS: Programming of detection criteria based on stability, onset, atrial fibrillation rate threshold and Vrate>Arate allows a 99% sensitivity and an 89% specificity in Guidant ICDs. Discrimination of SVT with 1:1 atrioventricular relationship, however, remains a challenge for which new algorithms have to be designed.

Aged↗

PubMedDate not supplied

Implantable defibrillators are preferable to pharmacologic therapy for patients with ventricular tachyarrhythmias: an antagonist's viewpoint.

Despite their intuitive appeal, implantable cardioverter defibrillator s (ICDs) will require testing in randomized studies to establish their relative value as compared with antiarrhythmic drugs in patients with life-threatening ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]). In these studies, only total mortality is an acceptable primary end point. Lessons from recent drug studies (CAST, ESVEM, CASCADE) have shown that class-III/beta-receptor antagonist therapy is superior to class-I drugs selected by electrophysiologic or Holter monitor testing. Thus, sotalol or amiodarone should now be considered first-line drugs for VT/VF therapy. Advantages of contemporary drug therapy for VT/VF include wide experience among clinicians, progressively better drugs, lower cost, universal availability, greater flexibility in use (easy to start, titrate, and stop), ability to suppress (not just terminate) events, and favorable effect on disease progression (eg, beta-blockade effects in cardiomyopathy and ischemic heart disease). Recent matched observational studies and a small randomized experience (CASH) suggest near equivalence in total mortality in ICD and drug-treated groups. Until or unless modified by the results of large, ongoing, randomized trials (AVID, CIDS), contemporary antiarrhythmic drug therapy has much to be recommended as first-line, standard treatment for patients with VT/VF. Even in patients receiving ICDs, added drug therapy is frequently indicated.

Anti-Arrhythmia Agents↗

PubMed1996

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

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

Adolescent↗

PubMed1998

Gross and microscopic pathological changes associated with nonthoracotomy implantable defibrillator leads.

BACKGROUND: Although the effects of epicardial implantable cardioverter-defibrillator (ICD) leads on underlying cardiac tissue have been reported, the gross and microscopic changes associated with endocardial ICD leads are less well described. This study describes the gross and microscopic changes associated with endocardial ICD leads in humans. METHODS AND RESULTS: The hearts from 8 patients were examined. At the time of ICD implantation, the patients' mean age was 47+/-11 years, and the left ventricular ejection fraction was 0.24+/-0.10. Four patients had ischemic heart disease, and 4 had dilated cardiomyopathy. Five hearts were examined after transplantation; 3, after death. The electrode-myocardial interfaces were characterized by intense endocardial fibrosis and were remarkably consistent. Each lead was encased by a ring of fibroelastic tissue, and there was fibrosis of the right ventricular myocardium adjacent to the leads. Fibrosis involved the tricuspid valve in 5 patients, and 1 had perforation of the valve by the lead. Microscopically, interstitial fibrosis was adjacent to each lead in the current path of ICD shocks. Acute cell injury was present only in the hearts that had received recent shocks. CONCLUSIONS: The ICD electrode-myocardial interface is characterized by intense fibrosis. The fibrosis associated with endocardial ICD leads and the cumulative acute damage produced by defibrillation discharges may explain changes in the defibrillation and pacing thresholds and the difficulty of lead extraction that can be encountered with transvenous ICD systems.

Adult↗

PubMed2004

Implantable defibrillators for the prevention of mortality in patients with nonischemic cardiomyopathy: a meta-analysis of randomized controlled trials.

CONTEXT: Implantable cardioverter defibrillator (ICD) therapy is effective in primary and secondary prevention of sudden cardiac death among patients with prior myocardial infarction and depressed ejection fraction. However, conclusive evidence of survival benefit in patients with nonischemic cardiomyopathy (NICM) is still lacking. OBJECTIVE: To determine whether ICD therapy reduces all-cause mortality in patients with NICM. DATA SOURCES: MEDLINE (1966-2004), EMBASE (1991-2004), the Cochrane Central Register of Controlled Trials (through first quarter, 2004), reports presented at scientific meetings (2003-2004), and bibliographic review of secondary sources. Search terms included defibrillator, randomized controlled trials, clinical trials, and sudden death. STUDY SELECTION: Eligible studies were prospective randomized controlled trials of ICD or combined cardiac resynchronization therapy and defibrillator (CRT-D) vs medical therapy enrolling at least some individuals with NICM and reporting all-cause mortality as an outcome. Of 675 potentially relevant articles screened initially, 8 reports of randomized trials enrolling a total of 2146 patients with NICM were included. DATA EXTRACTION: Included studies were reviewed to determine the number of patients randomized, mean duration of follow-up, primary end point, mortality of ICD cohort, and mortality of control cohort. DATA SYNTHESIS: Five primary prevention trials enrolling 1854 patients with NICM were identified; pooled analysis suggested a significant reduction in total mortality among patients randomized to ICD or CRT-D vs medical therapy (risk ratio [RR], 0.69; 95% confidence interval [CI], 0.55-0.87; P = .002). Mortality reduction remained significant even after elimination of CRT-D trials. Two of the 3 secondary prevention trials presented subgroup estimates for ICD efficacy in NICM. Pooled analysis of these secondary prevention trials (n = 256 patients with NICM) indicated an equivalent but nonsignificant mortality reduction with ICD therapy (RR, 0.69; 95% CI, 0.39-1.24; P = .22). Analysis of all 7 trials combined demonstrated a statistically significant 31% overall reduction in mortality with ICD therapy (RR, 0.69; 95% CI, 0.56-0.86; P = .002). CONCLUSION: ICD therapy appears to significantly reduce mortality in selected patients with NICM.

Cardiomyopathies↗

PubMed1996

[Shock-induced, but not terminated ventricular tachycardia in a patient with implantable defibrillator].

A 62-year-old male patient with coronary artery disease and drug refractory sustained ventricular tachycardia received an implantable cardioverter defibrillator (PRX III, model 1720, CPI) with a transvenous lead system (Endotak, model 0115, CPI) in combination with a subcutaneous array electrode (SQ array, model 049, CPI). The intraoperative defibrillation threshold was 15 J and was confirmed 1 week later at the hospital discharge test. Three months after discharge from hospital the patient reported 5 shocks during moderate physical exertion followed by a tachycardia associated with dizziness which terminated spontaneously. The print out of the stored electrogram showed a supraventricular tachycardia (probably sinus tachycardia) with a heart rate of 154/min which activated the device. Antitachycardia pacing did not terminate the supraventricular tachycardia, and hence shock therapy was delivered. The first shock (34 J) converted the supraventricular tachycardia to a ventricular tachycardia with a heart rate of 178/min, which was not terminated by four consecutive 34 J DC shocks. There was no hint of a device or lead failure. Determination of the defibrillation threshold reconfirmed the 15 J value for termination of ventricular fibrillation. However, neither a 1 J shock nor a 34 J shock terminated a monomorphic sustained ventricular tachycardia (cycle length 340 ms) induced by noninvasive programmed electrical stimulation. The ventricular tachycardia was, however, reproducibly terminate by antitachycardia pacing. It is concluded that an inappropriate high-energy DC shock might induce a sustained ventricular tachycardia. However, a sufficient defibrillation threshold for the termination of ventricular fibrillation does not necessarily mean that a sustained ventricular tachycardia will be terminated by a high-energy DC shock.

Coronary Disease↗

PubMed1994

Longitudinal recovery following sudden cardiac arrest and internal cardioverter defibrillator implantation: survivors and their families.

OBJECTIVE: To describe psychological reactions, neurological sequelae, and family adjustment following sudden cardiac arrest during the first year of recovery. METHODS: 15 sudden cardiac arrest survivors and 1 member of each family were interviewed and completed questionnaires five times within the first year following sudden cardiac arrest (hospital discharge, 1, 3, 6, and 12 months). Psychological reactions assessed included anxiety, depression, anger, denial, and global stress. Neurological sequelae assessed included confusion and neurocognitive functioning. Family adjustment assessed included marital adjustment and family coping. All sudden cardiac arrest survivors suffered primary ventricular fibrillation outside the hospital and had an internal cardioverter defibrillator implanted during hospitalization. RESULTS: Anxiety, depression, anger, stress, and confusion were highest at hospital discharge and decreased over 1 year, with survivors reporting higher levels than spouses. Denial was high throughout the entire year in survivors. Memory and construction ability were impaired throughout the entire year in survivors. Family coping and dyadic satisfaction were highest at hospital discharge and decreased throughout 1 year. Spouses reported fewer coping strategies and lower dyadic satisfaction than survivors. Family social support was lower than previously established norms at all periods during the first year of recovery. CONCLUSION: To develop intervention programs to aid adjustment, healthcare providers need to take into account psychological reactions, neurological deficits, and family coping of sudden cardiac arrest survivors and their family members.

Adaptation, Psychological↗

PubMed1992

Serum creatine kinase activity and sensing characteristics after intraoperative arrhythmia induction using implantable defibrillator rate sensing leads.

In 29 patients (24 men, 5 woman, mean age 57 +/- 14 years) we evaluated the effect of intraoperative arrhythmia induction during implantable defibrillator (ICD) placement using alternating current (AC) applied through the epicardial rate sensing leads on acute and chronic pacing thresholds, electrogram amplitudes, slew rates and serum creatine kinase levels. In 15 patients undergoing new ICD implantation, pacing thresholds, electrogram amplitudes, slew rates, and resistances were measured before and following at least three inductions of ventricular fibrillation (VF) using AC applied through the epicardial rate sensing leads. Fourteen patients who underwent VF induction using AC through the epicardial leads during initial implant (mean time of 31 months previously) underwent ICD pulse generator replacement only with parameters measured as above before and after at least two inductions, and these compared to the values at initial implant. In all 29 patients serum creatine kinase levels were obtained before, immediately following, and at 8, 16, and 24 hours after surgery. No significant change in acute pacing threshold, electrogram amplitude, slew rate or resistance occurred. Chronically there was an expected 154% increase in pacing threshold but no significant change in electrogram amplitude or resistance. Serial serum creatine kinase and MB isoenzyme determinations demonstrated no evidence of myocardial necrosis. We conclude that intraoperative arrhythmia induction during ICD implantation using AC applied through the rate sensing leads is a safe and effective technique.

Cardiac Pacing, Artificial↗

PubMed2003

Comparison of arrhythmia recurrence in patients presenting with ventricular fibrillation versus ventricular tachycardia in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial.

Because many episodes of ventricular fibrillation (VF) are believed to be triggered by ventricular tachycardia (VT), patients who present with VT or VF are usually grouped together in discussions of natural history and treatment. However, there are significant differences in the clinical profiles of these 2 patient groups, and some studies have suggested differences in their response to therapy. We examined arrhythmias occurring spontaneously in 449 patients assigned to implantable cardioverter-defibrillator (ICD) therapy in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial to determine whether patients who receive an ICD after VT have arrhythmias during follow-up that are different from patients who present with VF. ICD printouts were analyzed both by a committee blinded to the patients' original presenting arrhythmia and by the local investigator. During 31 +/- 14 months of follow-up, 2,673 therapies were reported. Patients who were enrolled in the AVID trial after an episode of VT were more likely to have an episode of VT (73.5% vs 30.1%, p <0.001), and were less likely to have an episode of VF (18.3% vs 28.0%, p = 0.013) than patients enrolled after an episode of VF. Adjustment for differences in ejection fraction, previous infarction, and beta-blocker and antiarrhythmic therapy did not appreciably change the results. Ventricular arrhythmia recurrence during follow-up is different in patients who originally present with VT than in those who originally present with VF. These findings suggest there are important differences in the electrophysiologic characteristics of these 2 patient populations.

Adrenergic beta-Antagonists↗

PubMed2002

Effect of surgical revascularization in patients with coronary artery disease and ventricular tachycardia or fibrillation in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Registry.

BACKGROUND: Patients who undergo resuscitation from near-fatal ventricular arrhythmias often have significant coronary artery disease, and revascularization has been shown to reduce myocardial ischemia and cardiac arrest episodes in this patient population. The magnitude of benefit attributed to revascularization has varied by study, and the use of adjunct implantable cardioverter defibrillator (ICD) therapy has not been well-characterized. METHODS AND RESULTS: The Antiarrhythmics Versus Implantable Defibrillators (AVID) registry included 3117 patients with life-threatening ventricular arrhythmias, of whom 2321 (77%) had documented coronary artery disease and 281 (17%) underwent a coronary artery bypass grafting revascularization procedure after the index event. Patients who underwent a revascularization procedure were younger, had a lower incidence rate of prior myocardial infarction and ventricular arrhythmia, had a higher left ventricular ejection fraction, had less congestive heart failure, and were more likely to have had ventricular fibrillation as the presenting arrhythmia. Patients who underwent revascularization had a better survival rate than did those who did not undergo such a procedure after the index event, and adjustment for differing baseline patient covariates did not alter the relative survival rate benefit. Further, ICD implantation offered a similar survival rate advantage to those patients in the AVID registry with coronary artery disease independent of revascularization. CONCLUSION: Coronary revascularization in the AVID registry patients with coronary artery disease effected a survival rate benefit that was not attributable to differences in baseline patient characteristics. The benefit of ICD on patient survival rate was not attenuated by a revascularization procedure.

Aged↗

PubMed1983

The implantable defibrillator in ventricular arrhythmias.

The most common cause of sudden cardiac death appears to be electrical instability that culminates in ventricular fibrillation. The implantable defibrillator, a self-contained diagnostic-therapeutic system, provides automatic detection and correction of malignant ventricular tachyarrhythmias. Principles involved in its development are reviewed, as are initial clinical results.

Animals↗

PubMed1997

Utility of predischarge and one-month transvenous implantable defibrillator tests.

We evaluated the utility of performing predischarge implantable cardioverter-defibrillator (ICD) testing and ICD testing at 1 month in detecting ICD-related problems, identifying 4 patients with an unacceptable increase in defibrillation threshold. Given that ICD testing is noninvasive and has minimal (if any) associated risk, we recommend that predischarge and 1-month follow-up ICD testing should be performed after implantation.

Aged↗

PubMed2003

Initiation of monomorphic ventricular tachycardia: electrophysiological, clinical features, and drug therapy in patients with implantable defibrillators.

At least 2 distinct patterns of sustained monomorphic ventricular tachycardia (MVT) have been ascribed during analysis of stored intracardiac electrograms retrieved from implantable cardioverter defibrillators and Holter recordings in patients with ventricular arrhythmia. We aimed to investigate the electrophysiological features of MVT with different initiation patterns in patients with implantable cardioverter defibrillators and to assess whether there is a relationship of the initiation patterns of sustained MVT with clinical characteristics and efficacy of antiarrhythmic therapy. Seventy-four stored intracardiac electrograms in 21 patients (mean age of 68.2 +/- 4.2 years) with MVT were evaluated. Cardiovascular diagnosis included coronary artery disease in 85.7% of the patients. All MVT episodes were classified as those initiating with ventricular premature beats (nonsudden onset MVT) and those without ventricular ectopy preceding tachycardia (sudden onset MVT). There was significant difference in left ventricular ejection fraction between MVTs with different initiation pattern, being the lower in those with nonsudden onset (33.6% +/- 38.4% vs. 38.4 +/- 7.0%, P <.04). Ventricular tachycardia cycle length was shorter in group of MVT with nonsudden onset as compared with sudden onset (338.5% +/- 48.1% vs. 376.8% +/- 57.0%, P <.02). Tachycardia with sudden onset was associated with shorter preceding RR interval than tachycardia with nonsudden onset (821.8 +/- 136.2% vs. 748.7 +/- 107.7%, P <.01). There were no significant differences in the type of antiarrhythmic drug therapy used between groups (P >.05). Monomorphic ventricular tachycardias with nonsudden onset occurred more frequently than with sudden onset, without precipitating RR cycles shortening, are faster in rate, associating with lower ejection fraction. Monomorphic ventricular tachycardias with sudden onset are characterized by preceding shortening of RR intervals, slower cycle length, and less worsening of ejection fraction.

Aged↗

PubMed1991

Radiation-induced effects in multiprogrammable pacemakers and implantable defibrillators.

Twenty-three multiprogrammable pacemakers and four implantable cardioverter defibrillators (ICDs) containing either complementary metal-oxide semiconductor (CMOS) or CMOS/Bipolar integrated circuit (IC) technology were exposed to 6-MV photon and 18-MeV electron radiation at various dose levels. Of the 17 pacemakers exposed to photon radiation eight failed before 50 Gy, whereas four of the six pacemakers exposed to electron radiation failed before 70 Gy. Photon scatter doses were well tolerated. For the ICDs detection and charging time increased with accumulated radiation dose, the charging time increased catastrophically at less than 50 total pulses delivered when compared with the charging time of six implanted ICDs. Sensitivity and output energy delivered by the ICD pulse were constant during the test. It was found that devices using the shorter channel length IC technology (i.e., 3 microns CMOS) were per se harder to ionizing radiation than the devices using larger channel length IC technologies (i.e., either 8 microns CMOS or combined 5 microM CMOS/20 V Bipolar). In fact, none of the devices based on 3 microns CMOS IC technology failed before 76 Gy, which is above the highest dose level (70 Gy) normally used in radiation oncology treatments.

Electric Countershock↗