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PubMed1992

Transtelephonic interrogation of the implantable cardioverter defibrillator.

Third generation implantable cardioverter defibrillators (ICDs) have extensive memory capability to store data about the patient's arrhythmias and the effect of therapies delivered by the ICD. However, this data has so far been accessible only when the patient attends the pacing clinic. Two Medtronic 9421 PCD TeletraceR transmitters have been used to interrogate Medtronic 7216A and 7217B PCD S at distances of up to 300 miles from our hospital and transmit the data to a 9420 PCD TeletraceR receiver. Successful transmission of data has been obtained on 50 occasions with 100% data concordance with repeat transmission. The system can reduce the number of unscheduled clinic visits, reduce delay in making a diagnosis following unexpected delivery of a shock therapy, and reassure patients about to be discharged following ICD implantation. The benefits are magnified where patients reside far away from the implanting center.

Electric Countershock↗
PubMed1997

Experience with implantable cardioverter defibrillator therapy in elderly patients.

AIM: Concern exists about the benefit of implantable defibrillator therapy in elderly patients. We assessed the utility of implantable defibrillator therapy and its effect on mortality in patients 70 years and older and compared results in this group to those in younger patients. METHODS AND RESULTS: Thirty-two out of 200 consecutive patients (16%) were 70 years or older at the time of implantation of a defibrillator. When comparing elderly to younger patients no significant differences were noted with respect to presenting arrhythmia, left ventricular ejection fraction or presence of an old myocardial infarction. Elderly patients had a higher prevalence of ischaemic heart disease, while in the younger group more patients had idiopathic ventricular tachycardia. Cumulative survival curves (Kaplan-Meier method) for all-cause mortality, sudden cardiac death and non-sudden cardiac death were constructed for elderly and younger patients. No significant differences for cumulative survival from all-cause mortality (75 vs 74%), sudden cardiac death (0 vs 4%) and non-sudden cardiac death (97 vs 93%) were found. The incidence of appropriate shocks during follow-up was comparable (65 vs 72%). CONCLUSION: Implantable defibrillator therapy was effective in preventing sudden cardiac death in the elderly. Total mortality was similar to younger patients at a follow-up of 19 +/- 14 and 25 +/- 19 months, respectively. Age itself should be no contraindication to implantable cardioverter defibrillator therapy.

Aged↗
PubMed2005

Value of pre-hospital discharge defibrillation testing in recipients of implanted cardioverter defibrillators.

Opinions vary regarding the need to perform defibrillation testing prior to hospital discharge in recipients of state-of-the-art cardioverter defibrillators (ICDs). Our protocol is to perform predischarge ICD testing 1 day after implant. This report includes 682 consecutive implants. Adverse observations at testing were grouped into (1) risk of defibrillation failure, (2) surgical complications, (3) sensing/pacing issues or narrow defibrillation margin warranting closer follow-up, or (4) findings correctable by device reprogramming. Among the 682 patients, 63% had single-chamber and 37% dual-chamber or biventricular ICDs. In 48 patients (7%) there were 69 concerns and/or interventions, with overlaps among the four categories, including one failure to defibrillate (0.15%), and six other patients at risk. Surgical complications included 11 hematomas (1.6%), and six lead dysfunctions. Closer follow-up was indicated in 19 patients (2.7%), for high pacing thresholds in seven, sensing issues in seven, and <10 J defibrillation margin in five. Device reprogramming was needed in 31 patients (4.5%), for tachycardia detection and therapy settings in 12, and for pacing/sensing functions in 22 patients. In eight patients ventricular fibrillation could not be induced. There was no morbidity or mortality due to testing. The state-of-the-art ICDs delivering biphasic shocks are remarkably reliable. The routine pre-hospital discharge defibrillation testing of such ICDs may be optional and left to the physicians' discretion.

Defibrillators, Implantable↗
PubMed2005

Comparison of defibrillation efficacy using implantable cardioverter-defibrillator with single- or dual-coil defibrillation leads and active can.

INTRODUCTION: The reduction of defibrillation threshold (DFT) in patients treated with an implantable cardioverter-defibrillator increases patients' safety and prolongs ICD battery life. AIM: To evaluate the possibility of reducing the defibrillation threshold in ICDs with an active can and an additional atrial defibrillation coil instead of the typical intracardiac single-coil lead. METHOD: This study involved 138 patients (36 F and 102 M, mean age 54+/-15 years) including 62 subjects with dual-coil defibrillation lead (group A) and 76 ones with single-coil defibrillation lead (group B). No statistically significant differences with respect to age, left ventricular function, main disease or exacerbation of heart failure according to the NYHA functional class were observed between groups. The defibrillation threshold was measured using the DFT+ protocol. RESULTS: No significant differences between groups were identified with respect to pacing and sensing parameters. The comparison of DFT values between the two studied groups revealed significant improvement (by 14% mean) of defibrillation efficacy in group A. In group A, the mean DFT was 9.8+/-4.6 J (3-20 J) and mean defibrillation resistance - 45+/-7 W (32-73 W), whereas in group B: 11.45+/-5.25 J (3-28 J) and 72+/-12.8 W (38-106 W), respectively. In 93% of patients from group A, DFT was below 15 J, in comparison to 81% of patients from group B (p=0.046). The odds ratio of a higher defibrillation threshold (ł15 J) in group A vs. group B was 0.3 (95% confidence interval: 0.09-0.98). The DFT reduction associated with modified ICD system use was independent of following clinical parameters: patient age, gender, main disease, end-diastolic left ventricular diameter, left ventricular ejection fraction, NYHA functional class and concomitant treatment with antiarrhythmic agents. CONCLUSIONS: Modification of the electric field during defibrillation, achieved with the use of active-can ICDs with dual-coil defibrillation leads, allows a reduction of DFT by 14%. At the same time, it reduces the risk of a higher (> or =15 J) DFT by three times compared to patients with a standard single-coil defibrillation lead.

Adolescent↗
PubMed1993

A subcutaneous lead array for implantable cardioverter defibrillators.

Two patients received an implantable cardioverter defibrillator with the combination of a transvenous lead and a subcutaneous lead array with three branches. This approach allowed us to find low defibrillation thresholds in both patients (< or = 10 and < or = 15 joules [J], respectively), which was impossible with a transvenous catheter. In a third patient, a crinkled subcutaneous patch was replaced by an array. The defibrillation threshold with the array was < or = 20 J, as opposed to > 24 J with the patch. No surgical problems occurred. The subcutaneous array is a technical improvement for the therapy with implantable defibrillators, when a single catheter system is not sufficient to ensure a safety margin for defibrillation, or when surgical or postsurgical problems occur with a subcutaneous patch.

Adult↗
PubMed1988

Automatic implantable cardioverter defibrillators and survival of patients with left ventricular dysfunction and malignant ventricular arrhythmias.

STUDY OBJECTIVE: To assess survival after insertion of automatic implantable cardioverter defibrillators in high-risk patients who have malignant ventricular arrhythmias and left ventricular dysfunction. DESIGN: Actual survival time compared with arrhythmia-free time in a single group of patients. SETTING: Inpatient services of a tertiary referral center and outpatient follow-up. PATIENTS: Seventy consecutive patients with clinical sustained ventricular tachycardia or fibrillation whose arrhythmia could not be controlled by medication as determined by programmed electrical stimulation, and who had an automatic cardioverter defibrillator implanted. INTERVENTION: All patients received an implantable defibrillator. MEASUREMENTS AND MAIN RESULTS: Two-year survival was 93.4% (95% CI, 87 to 99.8) and projected survival based on recurrence of malignant arrhythmias was 60.3% (CI, 47.3 to 73.3; P less than 0.001). In the 25 patients with left ventricular ejection fraction less than 30%, actual survival was 86.7% (CI, 72.3 to 91.1) and projected survival was 56.9% (CI, 35.9 to 77.9; P = 0.025). Projected survival percentages are similar to survival figures reported in the literature for such high-risk patients. There was only one sudden death; the remaining deaths were not arrhythmic in nature. Of the 65 patients who were alive at the end of follow-up, 13 were in New York Heart Association Class I; 44, Class II; 5, Class III; and 3, Class IV. CONCLUSIONS: The automatic implantable cardioverter defibrillator is probably highly effective in preventing arrhythmic mortality even in high-risk patients. Such treatment does not appear to significantly impair a patient's functional status.

Actuarial Analysis↗
PubMed1998

Relationship between the upper limit of vulnerability determined in normal sinus rhythm and the defibrillation threshold in patients with implantable cardioverter defibrillators.

The upper limit of vulnerability is the strength above which ventricular fibrillation is no longer inducible with a shock delivered during the vulnerable phase of the cardiac cycle. It has been demonstrated that the upper limit of vulnerability correlates with the defibrillation threshold in a paced rhythm. The purpose of this study is to evaluate the correlation of the upper limit of vulnerability determined in normal sinus rhythm with the defibrillation threshold using a simplified protocol in patients undergoing placement of an ICD. We studied 28 patients who underwent ICD implantation. CPI generators and Endotak leads were used in all patients. Device-based testing was used to determined the defibrillation threshold and the upper limit of vulnerability. The upper limit of vulnerability was tested with three shocks delivered at 0, 20, and 40 ms before the peak of the T wave during normal sinus rhythm. The defibrillation threshold was determined by a simple step up-down protocol. The upper limit of vulnerability (9.0 +/- 4.5 J) did not significantly differ from the defibrillation threshold (9.9 +/- 4.0 J), P = NS. A close correlation was present, correlation coefficient = 0.75, P < 0.0001. The upper limit of vulnerability was within 5 J of the defibrillation threshold in 27 (96%) of the 28 patients. The upper limit of vulnerability underestimated the defibrillation threshold by 10 J in one patient who had a defibrillation threshold of 15 J. The upper limit of vulnerability determined in normal sinus rhythm correlates significantly with the defibrillation threshold in patients undergoing ICD implantation. The protocol is simple and easily implemented clinically.

Anti-Arrhythmia Agents↗
PubMed1999

Use of sedation during cardioversion with the implantable atrial defibrillator.

BACKGROUND: The low shock energy used during internal atrial defibrillation may decrease the need for sedation during defibrillation with an implantable atrial defibrillator. METHODS AND RESULTS: The atrial defibrillator (Metrix Atrioverter) was implanted in 12 patients. During the in-hospital treatment of atrial fibrillation (AF) episodes, intravenous sedation was given only on patient request. The Atrioverter was programmed for ambulatory therapy in 4 patients. Efficacy, number of shocks delivered, and sedation requirements were recorded. A total of 393 shocks (1.8+/-1. 6 shocks/AF episode) were delivered to treat 213 AF episodes; 85 of 213 AF episodes (40%) were treated away from the hospital. Sinus rhythm was restored in 195 AF episodes (92%). Five patients never requested sedation. No sedation was needed for ambulatory-treated AF episodes. During the treatment of 26 of 213 AF episodes (12%), 75 shocks were delivered after patients received sedation. The number of shocks required to treat an AF episode determined the need for sedation (4.3+/-2.1 shocks for AF episodes requiring sedation versus 2+/-1 shocks for AF episodes requiring no sedation; P<0.001). These additional shocks were needed to treat immediate reinitiation of AF (14 episodes) or initial failure to cardiovert (4 episodes). For 8 AF episodes, sedation was requested before the first shock. CONCLUSIONS: This study suggests that, in a selected group of patients, AF can be treated with Atrioverter therapy without sedation. Successful ambulatory treatment of AF episodes with the Atrioverter, programmed to deliver </=2 shocks, did not require sedation. When multiple shocks were required to treat an AF episode, the need for sedation increased and included patients initially not requesting sedation.

Aged↗
PubMed1981

Lead systems for internal ventricular fibrillation.

We examined the feasibility of using a standby automatic implantable defibrillator and established thresholds for internal defibrillation. The implantable defibrillator senses ventricular fibrillation and delivers an electrical impulse for defibrillation. Two lead systems for the device have been investigated. System I consists of two 12-cm2 silicone-covered titanium mesh patches attached to the atrial and diaphragmatic pericardial surfaces. System II has an identical diaphragmatic patch and a titanium spring catheter, with a 12-cm2 surface area of conductivity, placed transvenously in the right atrium. Both systems were implanted by thoracotomy in 12 dogs (mean weight 20 kg) and by a subxiphoid approach in 10 pigs (mean weight 20 kg). The defibrillation threshold (lowest energy required for 80% success) was determined periodically for 54 weeks in the dogs (615 trials) and at 6 weeks for the pigs (100 trials). In dogs, the mean defibrillation threshold with system I leads at 4 weeks was 10.5 J and did not change significantly over a 54-week period (p greater than 0.05). Similar results were obtained in the pig at 4 weeks. The defibrillation thresholds for both lead systems in dogs and pigs using a transpleural thoracotomy or a subxiphoid approach are satisfactory for an implantable defibrillator that produces 20-35 J.

Animals↗
PubMed1982

Ultrastructural alterations in the fibrous sheath, endocardium, and myocardium of dogs shocked with chronically implanted automatic defibrillator leads.

Catheter-mounted automatic implantable defibrillator leads were implanted in 10 dogs for 11 to 21 months (mean 15.0 months). Single shocks of 10 A, 20 A, or 30 A (peak current) were then delivered through the chronically implanted leads. Two days after the shock, the dogs were euthanatized and necropsied. The intracardiac segment of the lead was covered by a fibrous sheath, the endocardium in contact with the lead was thickened by fibrous tissue, and shock-induced myocardial necrosis was present surrounding the distal pair of electrodes, with the largest amount of damage found in the dogs given the large shocks. Ultrastructurally, the fibrous sheath was covered by endothelium and contained numerous spindle cells and identified as smooth muscle cells by their prominent cytoplasmic filaments and external laminae or myofibroblasts with prominent endoplasmic reticulum. The spindle cells were surrounded by abundant collagen fibrils but not by elastic fibers. The thickened endocardium contained numerous fibroblasts, abundant collagen fibrils, and a few small elastic fibers. The shock-induced myocardial alterations included necrosis of cardiac muscle cells with prominent mitochondrial mineralization, interstitial edema, and infiltration of macrophages.

Animals↗
PubMed2005

Risk stratification for arrhythmic death after myocardial infarction: current perspective and future direction.

The number of patients eligible for implantable cardioverter defibrillator implantation is large and growing. Results of the Multicenter Automatic Defibrillator Implantation Trial-II, Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure trial, and Sudden Cardiac Death in Heart Failure Trial will have a major impact on health care expenditure and economics in all countries. Therefore, one of the most important challenges in today's cardiology is finding more specific and accurate risk stratification strategies (rather than simply ejection fraction) for primary prevention of sudden cardiac death in patients who have suffered myocardial infarction. We hereby reviewed the existing data on potential risk stratifiers and assessed their impact on every day decision making and patient selection for ICD implantation.

Algorithms↗
PubMed1992

Superiority of endocardial versus epicardial implantation of the implantable cardioverter defibrillator (ICD).

The implantable cardioverter-defibrillator (ICD) has proved to be an efficient device for the treatment of severe ventricular tachyarrhythmias (VT). From May 1985 to August 1991, the ICD was implanted in 107 patients of whom 72% suffered from coronary artery disease, 17% from cardiomyopathy, 5% from long QT-syndrome and 6% from other heart disease. All patients had a life threatening episode of VT or at least one episode of ventricular fibrillation. Of 107 implants, 12% were combined with other heart surgery, 55% were isolated epicardial implantations (epi I) and in 33%, the novel endocardial (endo I) approach was chosen. Between epi I and endo I we found no difference in operation time, but time for ICU and in-hospital stay was significantly shorter using the transvenous approach. In addition, sensing and pacing capability of the endocardial screw-in electrode was superior and the need for thoracotomy was avoided, a particular advantage in patients with previous heart surgery. Complications after epi I were: temporary low cardiac output, 1; perioperative death, 2; infection, 3, and after endo I: electrode dislocation, 2. Hence, endo I may become the method of choice for patients without concomitant surgery.

Adult↗
PubMed2006

Relations among renal function, risk of sudden cardiac death, and benefit of the implanted cardiac defibrillator in patients with ischemic left ventricular dysfunction.

Implanted cardioverter defibrillator therapy has been shown to be associated with a significant reduction in the risk of sudden cardiac death (SCD) in patients with ischemic left ventricular dysfunction. However, data on the relation between renal function and SCD in this population are limited, and the effect of renal dysfunction on the implanted cardioverter defibrillator benefit has not been determined. We performed a retrospective analysis of the outcome associated with renal dysfunction, as determined by the estimated glomerular filtration rate (eGFR), in patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial-II. Multivariate analysis in conventionally treated patients showed that for each 10-U reduction in eGFR, the risk of all-cause mortality and SCD increased by 16% (p = 0.005) and 17% (p = 0.03), respectively. Defibrillator therapy was associated with a survival benefit in each eGFR category of > or = 35 ml/min/1.73 m2 (overall risk reduction for all-cause mortality 32%, p = 0.01 and for SCD 66%, p < 0.001). However, no implanted cardioverter defibrillator benefit was shown among patients with an eGFR < 35 ml/min/1.73 m2 (all-cause mortality hazard ratio 1.09, p = 0.84; SCD hazard ratio 0.95, p = 0.95). In conclusion, in patients with high-risk cardiac disease enrolled in the Multicenter Automatic Defibrillator Implantation Trial-II, a significant increase was found in the risk of SCD with declining renal function. Defibrillator therapy was associated with a significant survival benefit among the study patients with mild to moderate or no renal disease, but no benefit was shown among patients with more advanced renal dysfunction.

Aged↗
PubMed1995

[Clinical value of intracavitary electrograms stored by implantable automatic defibrillator in patients resuscitated after cardiac arrest].

A major limitation of implantable defibrillators in the past has been the inability to document the arrhythmia precipitating discharge of the device. Although symptoms can be of some help in identifying the arrhythmia, symptomatic supraventricular arrhythmias and asymptomatic ventricular tachycardia (VT) have been documented in some cases before device discharge. The aim of this study was to systematically assess the value of stored intracardiac electrograms by implantable cardioverter-defibrillator in survivors of cardiac arrest during an antiarrhythmic drug free-period, in order to better define the arrhythmic profile determining device activation. The stored intracardiac electrograms of a fourth-generation cardioverter-defibrillator, implanted in 18 survivors of cardiac arrest were retrieved. The number of device activations, and the characteristics of any stored arrhythmic events were analyzed. A total number of 249 arrhythmic events were detected and stored over a mean follow-up of 378 +/- 107 days. These resulted in 78 delivered shocks, 84% of which were appropriate. Most of the detected events were episodes of unsustained VTs (33%), and atrial fibrillation or flutter (31%), which led to inappropriate shocks in 16% of the cases. The remaining recorded events were: sustained VT or fibrillation (66 episodes, 26%), sinus rhythm (11 events, 4%), not classified episode (6%). Of the 171 (69%) arrhythmic episodes not resulting in shocks, 73 events aborted before shock delivery by the device's reconfirmation algorithm, and the remaining 98 (39%) were detected but unsustained in duration, thus terminating before charging. In some cases, sustained and unsustained episodes of both supraventricular and ventricular arrhythmias gave symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2002

Shock coordinated with high power of morphology electrogram improves defibrillation success in patients with implantable cardioverter defibrillators.

Animal studies have suggested that the success of defibrillation may depend on the properties of VF waveform obtained from the morphology electrogram (ME) at the time of the shock. The reliable identification of depolarization events in the fibrillatory signal can be achieved using adaptive estimation of the instantaneous signal power (P). The aim of this study was to investigate if a high P of the ME (P(ME)) was related to ventricular DFT and if the upslope in ME can be associated with the depolarization event. A total of 575 VF (mean duration 10 s) episodes recorded and stored during ICD implantation in 77 patients with ventricular arrhythmias were used for analysis. The DFT was defined using a double step-down test. The values of P(ME) immediately before pulse delivery (P(shock)) and shock outcomes were registered. The differences between P(shock) of successful and failed defibrillation were tested with the Mann-Whitney U test. The relationship between individual medians of P(shock) (P(med)) and DFT was analyzed using the Kruskall-Wallis H-test. The coincidence between identified depolarization and upslope in ME was tested using the chi-square test. A P value of 0.05 was set for an error probability. The P(shock) in case of failed defibrillation was significantly lower than P(shock) in successful cases by the pulses of any strength (P < 0.001). The test revealed a significant inverse correlation between P(med) and DFT with P < 0.001. The depolarization corresponded to the upslope of ME in 85% of cases. This study demonstrated that a high value of instantaneous power of ME indicates the optimal time for shock delivery. The implementation of this algorithm in ICDs may improve the defibrillation efficacy.

Algorithms↗
PubMed1999

Relation of atrial refractoriness to upper and lower limits of vulnerability for atrial fibrillation/flutter following implantable ventricular defibrillator shocks.

BACKGROUND: Implantable ventricular cardioverter defibrillator (ICD) shocks can cause atrial fibrillation/flutter (AF). This study investigated the pathogenesis of AF after ICD shocks in a canine model. METHODS AND RESULTS: The study was conducted in 8 dogs. In 5 dogs (group 1), truncated exponential (8 ms, 78% tilt) monophasic and biphasic shocks were delivered through a bipolar epicardial (patch) or endocardial lead. After the last S1 of atrial pacing at a cycle length of 350 ms, shocks of 0.1 to 7.6 A (0.005 to 27.7 J) were delivered, timed to the atrial effective refractory period (AERP). Ventricular defibrillation thresholds were also determined. In 3 dogs (group 2), the effect of the open versus closed chest technique on AF induction was tested in the endocardial biphasic shock configuration. AF was induced in all 8 dogs and in all waveforms and configurations. Mean AF duration was 11.5+/-6 s, with a mean ventricular rate of 184+/-37 bpm. Ventricular shocks could induce AF only if they were timed between an AERP of -60 to 40 ms, -40 to 60 ms, -40 to 60 ms, and -20 to 60 ms in the epicardial monophasic, epicardial biphasic, endocardial monophasic, and endocardial biphasic configurations, respectively. The mean+/-SD of the upper limit of vulnerability (ULV) for AF induction (in J) was 5. 2+/-0.6, 3.5+/-0.4, 5.2+/-1.2, and 2.5+/-0.1 for the epicardial monophasic, epicardial biphasic, endocardial monophasic, and endocardial biphasic configurations, respectively (P<0.05). The lower limit of vulnerability (LLV) was 0.8+/-0.1, 0.8+/-0.1, 0.9+/-0, and 0.6+/-0 for the epicardial monophasic, epicardial biphasic, endocardial monophasic, and endocardial biphasic configurations, respectively (P=NS). The ventricular defibrillation threshold (in J) for all wave forms and configurations was higher than the ULV (P<0. 05). CONCLUSIONS: (1) An atrial LLV and ULV exist for ventricular ICD shock-induced AF; (2) the shock-induced AF is related to both shock intensity and its timing to AERP; and (3) avoiding this atrial window of vulnerability may minimize the risk of post-ICD shock AF.

Animals↗
PubMed2006

Genetic profiling as a marker for risk of sudden cardiac death.

PURPOSE OF REVIEW: Clinical trials provide evidence that an empirical approach of implantable cardioverter-defibrillator implantation in all heart failure patients (ejection fraction </= 35%) with mild to moderate symptoms effectively reduces mortality rate as compared to the best available medical therapy. At least 50% of patients, however, will succumb to a non-arrhythmic demise and over half of all patients will not require device therapy over long-term follow-up. Thus, the approach of empiric implantable cardioverter-defibrillator implantation is costly in light of the considerable expense of device cost, implantation, and patient follow-up. This review discusses the prospect of genomic medicine as an approach to assess genetic susceptibility to sudden arrhythmic death in at-risk populations. RECENT FINDINGS: Through the past 10 years of primary prevention implantable cardioverter-defibrillator trials, the number of patients needed to treat to prevent a sudden death has risen from one in four patients to one in 14. Although numerous clinical tests exist for stratification, they are of low positive predictive value in assessing arrhythmic risk, and have not been prospectively validated as effective strategies in identifying arrhythmia-prone patients. Recent data from genetic studies identifying genes responsible for sudden cardiac death have compiled a list of relatively common genetic variations (polymorphisms). These polymorphisms, encoding for proteins known to be involved in cardiac electrophysiology, may contribute to arrhythmic risk in the milieu of heart failure. SUMMARY: Current clinical indications for implantable cardioverter-defibrillator implantation in primary prophylaxis of sudden cardiac death necessarily include a significant number of patients who may not benefit. The identification of common genetic variations causing an increased risk of vulnerability to ventricular arrhythmia in heart failure patients may optimize the use of medical resources through rapid identification of sub-populations at highest risk.

Arrhythmias, Cardiac↗