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At least 703 records · Page 39Linked to original sources
PubMed2000

Determination of pacing capture in implantable defibrillators: benefit of evoked response detection using RV coil to can vector.

Automatic detection of capture in ICDs would be useful for ensuring normal pacing function and lead integrity and may increase device longevity. Evoked response detection can be difficult due to postpace polarization. Polarization on the RV coil to can vector, however, should be absent when pacing with a true bipolar lead (pace tip to ring). Polarization on the RV coil to can vector should be low in an integrated bipolar lead due to the large surface area of the coil. Ventricular-paced responses were prospectively recorded in 20 patients during ICD implantation or replacement. Capture and loss of capture responses were noted during threshold searches with electrograms recorded between the RV coil and can. A detector was designed to discriminate between capture and noncapture-paced responses using data from the first 11 patients and validated on the remaining 9. The detector had a sensitivity of 99.9% (detected capture on capture beats), and had a specificity of 100% (detected no capture on noncapture beats) for all lead configurations. There was no measurable polarization with true bipolar leads. In integrated bipolar leads, maximum polarization ranged from 0.0 to 16.7 mV. In conclusion, paced evoked responses can be detected in ICDs using the RV coil to can vector using standard pacing waveforms. Special polarization reducing pacing waveforms are not required. These observations could be used to design ICDs with automatic pacing threshold detection.

Adolescent↗
PubMed1996

Right ventricular implantable cardioverter defibrillator lead implantation through a persistent left superior vena cava.

A 60-year-old woman required implantation of an ICD because of a hypotensive ventricular tachycardia refractory to four different antiarrhythmic drugs. Preoperative diagnostics revealed a persistent left SVC as the only major venous return from the upper part of the body to the heart. Under local anesthesia, a tripolar lead was advanced through the left SVC into the right ventricular apex. Following successful testing, an active can ICD device was implanted, which is functioning well during a follow-up period of 9 months.

Defibrillators, Implantable↗
PubMed2004

T wave oversensing by a cardioverter defibrillator implanted in a patient with the Brugada syndrome.

Oversensing of electrical signals in recipients of ICDs is a common complication causing the delivery of inappropriate therapy. The Brugada syndrome has a characteristic ECG pattern with dynamic temporal changes in response to various physiological or environmental conditions. This case report presents a patient with the Brugada syndrome and intermittent T wave oversensing by an ICD due to changes in T wave amplitude which could not be resolved by device reprogramming and required repositioning of the electrode.

Aged↗
PubMed2002

Variability of Holter electrocardiographic findings in patients fulfilling the noninvasive MADIT criteria. Multicenter Automatic Defibrillator Implantation Trial.

In the MADIT study, a selected group of postinfarction patients with asymptomatic nonsustained ventricular tachycardia (NSVT) has been shown to benefit from prophylactic ICD treatment. The present study analyzed the variability of NSVT in a patient population fulfilling the non-invasive MADIT criteria. Three consecutive Holter ECGs were performed in weekly intervals in 68 postinfarction patients with an LVEF < or = 0.35. Patients with NSVT underwent programmed ventricular stimulation (PVS); patients were implanted with an ICD if sustained VT or VF was inducible. If NSVT was found in at least two recordings, the arrhythmia was defined as reproducible. In 28 (41%) of the 68 patients, NSVT was found in at least one recording. Seventeen patients revealed NSVT in the first, the remaining 11 in the second registration; no patient had NSVT only in the third Holter. Of the patients with NSVT, 50% had only one, 39% had two, and 11% had three positive recordings. Thus, reproducible NSVT was found in only 50% of the patients with NSVT. Predictors for reproducibility were LVEF > 0.27, NYHA Class I, absence of digitalis therapy, and > 2 NSVT per 24-hour period. Reproducible NSVT was not associated with risk factors such as elevated mean heart rate, reduced heart rate variability, late potentials, or inducibility of sustained VT during PVS. During 17 +/- 9 months of follow-up, seven (10%) patients experienced arrhythmic events: two without and five with previously documented NSVT. In the latter patients, first occurrence of NSVT was consistently in the first Holter; only two of them had reproducible NSVT. In postinfarction patients, the risk factor NSVT exhibits marked spontaneous variability, especially in those with a low number of NSVT per 24-hour period, LVEF < 0.27 or NYHA III, which limits its clinical value as a selection criterion for PVS. Reproducibility of NSVT itself does not seem to be an independent risk factor.

Death, Sudden, Cardiac↗
PubMed1988

Automatic implantable defibrillator discharge resulting from routine pacemaker programming.

A middle-aged gentleman with an idiopathic dilated cardiomyopathy, drug-refractory sustained ventricular arrhythmia, and high-degree AV block was managed with an automatic implantable cardioverter-defibrillator (AICD) and a Cordis Multicor II VVI pacemaker. During a routine follow-up visit, the pacemaker threshold was determined. Seven seconds after reprogramming the Cordis pacemaker to the "stat" VVI mode, the AICD discharged. The time to discharge after reprogramming the pacemaker equalled the previously determined AICD charge time. No other rhythm disturbance was documented and the rate with double counting of pacemaker stimulus and QRS complex was less than the triggering rate for the AICD. In conclusion, the AICD can be triggered by pacemaker programming signals unrelated to subsequent pacemaker function.

Electric Countershock↗
PubMed2000

Debate: Do all patients with heart failure require implantable defibrillators to prevent sudden death?

Sudden death is a major cause of mortality in patients with ventricular dysfunction. The highest risk occurs among patients with less severe functional impairment. Current methods of risk stratification are inadequate, and a rational therapy for prevention of sudden death is not available. The implantable cardioverter-defibrillator (ICD) has proven to be more effective than drugs in reducing sudden-death risk in some subsets of patients. Empiric ICD therapy, targeting the general population with mild to moderate heart failure, will maximize the impact of such a strategy to prevent sudden death and improve long-term survival.

Journal Article↗
PubMed2000

Meta-analysis of the implantable cardioverter defibrillator secondary prevention trials. AVID, CASH and CIDS studies. Antiarrhythmics vs Implantable Defibrillator study. Cardiac Arrest Study Hamburg . Canadian Implantable Defibrillator Study.

AIMS: Three randomized trials of implantable cardioverter defibrillator (ICD) therapy vs medical treatment for the prevention of death in survivors of ventricular fibrillation or sustained ventricular tachycardia have been reported with what might appear to be different results. The present analysis was performed to obtain the most precise estimate of the efficacy of the ICD, compared to amiodarone, for prolonging survival in patients with malignant ventricular arrhythmia. METHODS AND RESULTS: Individual patient data from the Antiarrhythmics vs Implantable Defibrillator (AVID) study, the Cardiac Arrest Study Hamburg (CASH) and the Canadian Implantable Defibrillator Study (CIDS) were merged into a master database according to a pre-specified protocol. Proportional hazard modelling of individual patient data was used to estimate hazard ratios and to investigate subgroup interactions. Fixed effect meta-analysis techniques were also used to evaluate treatment effects and to assess heterogeneity across studies. The classic fixed effects meta-analysis showed that the estimates of ICD benefit from the three studies were consistent with each other (P heterogeneity=0.306). It also showed a significant reduction in death from any cause with the ICD; with a summary hazard ratio (ICD:amiodarone) of 0.72 (95% confidence interval 0.60, 0.87;P=0.0006). For the outcome of arrhythmic death, the hazard ratio was 0.50 (95% confidence interval 0.37, 0.67;P<0.0001). Survival was extended by a mean of 4.4 months by the ICD over a follow-up period of 6 years. Patients with left ventricular ejection fraction < or = 35% derived significantly more benefit from ICD therapy than those with better preserved left ventricular function. Patients treated before the availability of non-thoracotomy ICD implants derived significantly less benefit from ICD therapy than those treated in the non-thoracotomy era. CONCLUSION: Results from the three trials of the ICD vs amiodarone are consistent with each other. There is a 28% reduction in the relative risk of death with the ICD that is due almost entirely to a 50% reduction in arrhythmic death.

Amiodarone↗
PubMed2004

Life-years gained from defibrillator implantation: markedly nonlinear increase during 3 years of follow-up and its implications.

BACKGROUND: Although treatment benefit in randomized controlled trials of defibrillators is often summarized by the numbers of lives saved (absolute risk difference), this may not be a good representation of what matters most to patients, namely, the amount of life they should expect to gain from implantation. The estimate of gain in life-years may depend on duration of follow-up. In this study, we examine this dependency. METHODS AND RESULTS: We estimated, from published data of 8 landmark defibrillator trials, the cumulative benefit in life-years gained at time points from 3 months to 3 years. Because the trial populations, clinical status, and prognosis varied widely between studies, we expressed for each study the benefit at each time point as the proportion of benefit at 3 years. The average dependency of the benefit on duration of follow-up was then calculated. We found that the number of life-years gained from 1 device implantation increases with length of follow-up considered. Importantly, this increase is markedly nonlinear. Within the 3-year span addressable, the benefit rises with the square of time (gain infinity t(1.94), R2=0.998, P<0.001). CONCLUSIONS: Measurable benefit from a defibrillator to patients' life spans (life-years gained) is dramatically dependent on the time window over which the benefit is assessed. Because the effort of implantation is front loaded, yet benefit grows with time, the choice of an early time point artificially reduces apparent benefit and artificially increases the apparent number needed to treat to prevent an event. These are useful considerations for the formulation of treatment policy (and even for planning of the follow-up phase of clinical trials).

Clinical Trials as Topic↗
PubMed2001

Value of programmed ventricular stimulation for prophylactic internal cardioverter-defibrillator implantation in postinfarction patients preselected by noninvasive risk stratifiers.

OBJECTIVES: The aim of this prospective study was to evaluate the role of programmed ventricular stimulation (PVS) after noninvasive risk stratification to identify a subgroup of acute myocardial infarction (AMI) survivors considered at risk for ventricular arrhythmias and whether these patients could benefit from internal cardioverter-defibrillators (ICDs). BACKGROUND: The predictive value of noninvasive and invasive risk stratifiers after AMI has been questioned. The question of whether the group of patients with inducible monomorphic ventricular tachycardia (VT) after AMI could profit from ICD implantation is unanswered. METHODS: A consecutive series of 1,436 AMI survivors was screened noninvasively by Holter monitoring, heart rate variability, ventricular late potentials, and ejection fraction. A subgroup of 248 patients (17.3%) were identified as high-risk patients and scheduled for PVS. Due to the study design, 54 patients >75 years were excluded; thus, 194 patients were eligible for PVS. Triple extrastimuli at two paced cycle lengths (600 ms and 400 ms) were applied. RESULTS: In a subgroup of 98 (51%) high-risk patients, PVS was performed; 21 patients had an abnormal response, and in 20 patients an ICD was implanted. During a mean follow-up of 607 days the arrhythmic event rate (sudden cardiac death, symptomatic VT, cardiac arrest) was 33% with a positive electrophysiological test versus 2.6% (p < 0.0001) with a negative electrophysiological test. A subgroup of 96 high-risk patients declined electrophysiological study. In this nonconsent group, cardiac mortality (combined sudden and nonsudden) was significantly higher (log-rank chi-square 9.38, p = 0.0022, relative risk 4.7, 1.6 to 13.9) compared to the group guided by electrophysiological testing and consecutive ICD implantation. CONCLUSIONS: After a two-step risk stratification, PVS is helpful in selecting a subgroup of AMI survivors without spontaneous ventricular arrhythmias who benefit from prophylactic ICD implantation.

Defibrillators, Implantable↗
PubMed1984

Unipolar electrode system for an implantable defibrillator: new experimental approaches.

Defibrillation thresholds are studied in normal dog hearts after induction of ventricular fibrillation by alternating current. Shocks of progressively increasing energies are tried after a period of 10 seconds of sustained ventricular fibrillation. The endocardial electrode system may be either unipolar or bipolar, the distal electrode being situated at the right ventricular apex. The results suggest that for an optimal capacitor in the range of 9-20 uF, unipolar shocks are more effective than bipolar shocks (3-10 versus 10-30 Joules). In addition, several cardiac arrhythmias, including rapid ventricular tachycardia, accelerated idioventricular rhythm, and transient AV block are frequently observed. We conclude that (1) an implantable unipolar endocardial defibrillator seems feasible; and (2) the design should include the appropriate circuits to treat the arrhythmias observed after the shocks.

Animals↗
PubMed2001

Minimally invasive cardioverter defibrillator implantation for children: an animal model and pediatric case report.

The smaller venous capacitance in infants and small children may hamper transvenous ICD lead implantation, and epicardial approaches require thoracotomy and have associated complications. The study evaluated the feasibility and performance of subcutaneous arrays and active can ICDs without transvenous shocking coils or epicardial patches. An immature and mature pig were anesthetized and ventilated. A pacing lead was inserted in the right ventricle for fibrillation induction and rate sensing. Subcutaneous arrays were positioned in the right and left chest walls. An ICD emulator was placed in abdominal and prepectoral pockets. Fluoroscopic images were acquired for each electrical vector configuration (array --> can, can --> array, array --> array, array + array --> can). Ventricular fibrillation was induced and DFT testing performed. Defibrillation was achieved in all ten trials in the immature piglet, with DFT < or = 9 J, regardless of vector configuration. Using a single subcutaneous array and active can, the shock impedance ranged from 28-36 ohms. With two arrays, shocking impedance fell to 15-22 ohms. In the adult pig, defibrillation was not accomplished with maximum energy of 40 J, using all vector configurations. Using data garnered from these experiments, this technique was then successfully performed in a 2-year-old child with VT and repaired congenital heart disease, needing an ICD. This study demonstrates the feasibility of leadless ICD implantation in an immature animal and successful implementation in a small child. A single subcutaneous array and active can resulted in excellent implant characteristics and DFTs with a minimally invasive approach. Defibrillation was not possible in a larger animal, possibly due to maximal available energy. This may be of value for small children requiring ICD implantation.

Animals↗