Antitachycardia Pacing in Patients with Implantable Cardioverter Defibrillators: How Many Attempts Are Useful?

The purpose of this study was to determine the termination and acceleration rates for 1 to 6 attempts of antitachycardia pacing (ATP) delivered by ICD in order to terminate spontaneously occurring VTs. Twenty-four ICD recipients with active ATP programs, including a maximum of six ATP sequences and spontaneously occurring VTs during follow-up, were investigated. During a mean follow-up of 42 ± 15 months (range, 17–63 months) 413 spontaneous VT episodes (17 ± 14; range, 1–49 per patient) resulting in appropriate ATP delivery by the ICD occurred. ATP successfully terminated 328 episodes (80 %) with a mean number of 1.6 ± 1.1 pacing sequences. Eighty episodes (19%) were accelerated by ATP and 5 (1%) were unresponsive to ATP. The ATP success decreased until the third ATP sequence (59%→ 31%→ 24%), but increased again in the fourth to sixth attempt (46%→ 46%→ 29%). The acceleration rate increased from sequence one to sequence three (8%→ 13%→ 28%), but decreased significantly in further ATP attempts (19%→ 0%→ 0%). The mean time delays until redetection or termination after 4, 5, and 6 attempts of ATP were 22 ± 5 seconds, 37 ± 2 seconds, and 41 ± 9 seconds, respectively. Nine patients (37%) used ≥3 ATP attempts during follow-up and all of them had a therapeutic benefit from it. Five out of 13 VTs (38%) treated with ≥4 attempts could ultimately be terminated by ATP. The results of this study demonstrate that the first ATP sequence is the most effective and that > 4 ATP attempts may be useful in a minority of patients. There seems to be a low risk of VT acceleration by the fourth to sixth ATP sequence. Because of the associated time delay, a high number of ATP attempts should only be programmed in patients with hemodynamically well-tolerated stable VTs.     

Ventricular Pacing Induced Ventricular Tachycardia in Patients with Implantable Cardioverter Defibrillators

Appropriately timed noncompetitive ventricular pacing potentially may initiate ventricular tachycardia in patients prone to these arrhythmias. The combination of bradycardia pacing and stored electrograms in a currently available cardioverter defibrillator provides an opportunity to evaluate the occurrence of such pacing induced ventricular tachycardia. During a surveillance period of 18.7 ± 11.4 months, stored electrograms documented 302 episodes of ventricular tachycardia in 77 patients. Five patients (6.5%) demonstrated 25 episodes (1–16 per patient) of ventricular tachycardia that were immediately preceded by an appropriately paced ventricular beat (8.3% of all episodes of ventricular tachycardia). All five patients had prior myocardial infarctions and a history of monomorphic ventricular tachycardia occurring both spontaneously and in response to programmed electrical stimulation. Antitachycardia pacing terminated pacing induced ventricular tachycardia in 22 episodes; in one episode antitachycardia pacing accelerated ventricular tachycardia. In two cases shock therapy was aborted for nonsustained ventricular tachycardia. We conclude that, in selected postinfarction patients with recurrent sustained monomorphic ventricular tachycardia treated with implantable cardioverter defibrillators, appropriately timed ventricular pacing may induce ventricular tachycardia.     

Safety of Antitachycardia Pacing in Patients with Implantable Cardioverter Defibrillators and Severely Depressed Left Ventricular Function

The purpose of this study was to investigate the efficacy and safety of antitachycardia pacing (ATP) in third-generation implantable Cardioverter defibrillators (ICDs) for terminating spontaneously occurring ventricular tachycardias (VTs) in patients with severely depressed left ventricular (LV) function. Ninety-one patients with active ATP were followed for 16 ± 13 months. During this period, 775 VT episodes occurring in 36 patients were treated by ATP. The patients were divided into two groups according to their LV ejection fraction (LVEF): group A with LVEF ± 30% (n = 20), and group B with LVEF ± 30% (n = 16). There were no differences between both groups in age, gender, underlying heart disease, indication for ICD therapy, or drug therapy. The VT rates were comparable (group A: 183 ± 16 beats/min; group B: 180 ± 21 beats/min; P = NS). Eighty-three percent of all episodes (n = 332) in group A and 93% of the VTs (n = 443) in group B were ATP terminated (P ± 0.01). Ten percent of VTs in group A were accelerated by ATP into the ventricular fibrillation zone versus 2% in group B (P ± 0.01). The individual termination rate and acceleration rate per patient were comparable in both groups. All VT episodes unresponsive to ATP were converted by backup shocks. The efficacy of first-shock therapy was similar in both groups (group A: 89%; group B: 97%; P = NS). The proportion of patients who needed at least one backup shock for unsuccessful ATP was comparable in both groups (group A: 65%; group B: 56%; P= NS). We conclude that ATP is effective and safe in patients with recurrent VTs and severely depressed LV function, and it can be safely programmed in this group of patients to minimize the use of shock therapy.     

Remote Monitoring of Implantable Cardioverter Defibrillators:

A prospective study evaluating the functionality and ease of use of the Medtronic CareLink^® Network, "CareLink," was conducted at ten investigational sites. This internet-based remote monitoring service allows clinicians to remotely manage their patients' implantable cardioverter defibrillators (ICDs) and chronic diseases. The network is comprised of a patient monitor, a secure server, and clinician and patient websites. Under clinician direction, patients interrogated their ICDs at home, and transmitted data to secure servers via a standard telephone line. Comprehensive device data and a 10-second presenting rhythm electrogram were captured by the monitor and available for access and review on the clinician website. The information could also be printed using a standard desktop computer with internet access. During this study, patients were asked to transmit device data twice, at least 7 days apart, as scheduled by the clinic. Monitor functionality was assessed, and ease of using the system components was evaluated via questionnaires completed by patients and clinicians following each data transmission and review. Fifty-nine patients (64 ± 14 years, range 22-85 years) completed 119 transmissions with only 14 calls to the study support center. Clinician review of data transmissions revealed several clinically significant findings, including silent AF discovery, assessment of antiarrhythmic drug efficacy in a previously diagnosed AF patient, previously unobserved atrial undersensing, and ventricular tachycardia. ICD patients found the monitor easy to use. Clinicians were pleased with the performance of the network and the quality of the web-accessed data, and found it comparable to an in-office device interrogation. CareLink is a practical tool for routine device management and may allow timely identification of clinically important issues. (PACE 2004; 27[Pt. I]:757–763)     

Morphology Discrimination: A Beat-to-Beat Algorithm for the Discrimination of Ventricular from Supraventricular Tachycardia by Implantable Cardioverter Defibrillators

Inappropriate therapy of SVTs by ICDs remains a major clinical problem despite enhanced detection criteria like "sudden onset" and "rate stability" in third-generation devices. Electrogram morphology discrimination offers an additional approach to improve discrimination of supraventricular tachycardia (SVT) from ventricular tachycardia (VT). In a prospective, multicenter study, patients received an ICD with a beat-to-beat algorithm for morphological analysis of the intracardiac electrogram (Morphology Discrimination, MD). A nominal programmingfor standard enhancement criteria and morphology discrimination was required at implant. Electrogram storage of tachycardia episodes irrespective of delivery of therapy was used to assess sensitivity and specificity of the morphology algorithm alone and in combination with established detection criteria. During a 126 6-month follow-up, 886 episodes of device stored electrograms from 82 of 256patients were evaluated. Atnominal settings, the MD algorithm correctly identified 423 of 551 episodes as VT resulting in sensitivity of 77%. The classification of SVT was met in 239 of 335 episodes resulting in specificity of 71%. In combination with sudden onset, sensitivityincreased to 99.5% at the expense of specificity (48%). In conclusion, SVT-VT discrimination based on morphological analysis alone results in limited sensitivity and specificity. Programming the monitor mode allows individual assessment of the performance of this detection enhancement feature during clinical follow-up without compromising device safety. Only in patients with documented efficacy of morphology discrimination should this feature be subsequently activated.     

Implantation of Submammary Implantable Cardioverter Defibrillators

Implantable cardioverter defibrillators (ICDs) are routinely placed in the left pectoral area using a transvenous approach. This approach may result in poor cosmetic outcome and cause psychological problems, especially in younger patients. To avoid this, several alternative implantation techniques have been developed. For cosmetic reasons, we used a submammary technique to implant ICDs into three young women. Apart from defibrillation threshold testing, the procedures were performed under local anesthesia. Threshold testing was done under general anesthesia. Appropriate defibrillation thresholds were obtained in all three cases, and all the patients tolerated the procedure well. There were no complications in a mean of 22 months of follow-up, and the cosmetic results were very good.(PACE 2004; 27[Pt. I]:779–782)     

A Fuzzy Logic-Controlled Classifier for Use in Implantable Cardioverter Defibrillators

Purpose: Implantable cardioverters defibrillators (ICDs) are increasingly used in the management of life-threatening arrhythmias. Correct recognition of a treatable arrhythmia is crucial to this application. However, the computational power of microprocessors currently used in ICDs limits the range of traditional algorithms available for this application. Methods: Classification based on fuzzy inference systems (FIS) were trained to recognize different cardiac rhythms (AF, VF, SVT, VT) from the Ann Arbor Electrogram Library. The FIS used were designed using adaptive-network-based fuzzy inference methods to optimize the classification procedure. Only computational techniques suitable for ICD design were used. Results: After pretraining with the ANFIS correct rhythm classification was observed for the rhythms studied. Conclusion: In this preliminary study, successful rhythm classification was demonstrated using fuzzy logic techniques. In view of the computational efficiency this may have application in ICD design.     

Use of an Implantable Cardioverter Defibrillator in an Eight-Month-Old Infant with Ventricular Fibrillation Arising from a Myocardial Fibroma

We report our experience with use of a ICD in a 7-month-old infant who presented with VF. We utilized an epicardial patch and active generator in the abdomen. Development of mediastinitis required explantation and eventual replacement with a subcutaneous patch and active generator in the abdomen.     

Impact of Dual Chamber Pacing on the Incidence of Atrial and Ventricular Tachyarrhythmias in Recipients of Implantable Cardioverter Defibrillators

Recent observations suggest that frequent dual-chamber pacing in recipients of implantable cardioverter defibrillators (ICD) may adversely influence clinical outcomes. This prospective, multicenter study examined the relationship between the frequency of atrial (%AP) and ventricular pacing (%VP) and the incidence of atrial (AT) and/or ventricular tachyarrhythmias (VT) in a standard ICD population. A total of 141 consecutive patients with primary and secondary ICD indications were studied. Continuous arrhythmia detection with a dual-chamber ICD revealed paroxysmal AT in 60 (43%) and VT in 72 (51%) patients within 6 months of device implantation. Far-field oversensing of ventricular signals occurred in 13% of all "atrial tachy response" mode switches. Without adjustment for covariates, a higher %AP was associated with an increased incidence of AT (P < 0.05). However, this association remained only weakly significant after adjustment for covariates using a multivariate model. High New York heart failure functional classes correlated significantly with AT (P = 0.02) and VT (P = 0.007). Rate-modulated pacing, programmed in 1/3 of patients, correlated with occurrence of AT (P = 0.006), but not with occurrence of VT. With respect to dual-chamber pacing, a %AP ≥ 48% combined with a %VP > 40% was associated with an increased probability for VT. In conclusion, AT and VT occurred frequently within 6 months after dual-chamber ICD implantation. High rates of DDD/R stimulation were associated with a trend toward higher incidence of AT, VT, or both.     

Clinical Significance of Consecutive Shocks in Patients with Left Ventricular Dysfunction Treated with Implantable Cardioverter Defibrillators

The purpose of the present study was to determine the clinical significance of consecutive automatic shocks delivered by implantable cardioverter defibrillators (ICDs). Sixty-four patients who received ICDs at our institution between January 1990 and July 1997 were included in this study. There were 53 men and 11 women with a mean age of 50 ± 14 years. During a follow-up period ranging between 0.2 and 73 months (mean 23 ± 21 months), 17 patients received consecutive shocks (group A), 29 patients received single shocks (group B), and 18 patients received no ICD therapy (group C). Clinical characteristics, episodes of ICD therapy, and prognosis were compared among the three groups. There were no significant differences among the three groups with regard to clinical characteristics, time to first ICD therapy, number of antitachycardia pacing episodes, or frequency of inappropriate discharges. The mortality rate was higher in group A than in groups B and C (P = 0.0021). The sensitivity of consecutive shocks in predicting death was 70%, the specificity was 88%, and the predictive accuracy was 81% in patients with left ventricular ejection fractions < 35%. In summary, consecutive shocks are a clinically important event in patients with ICDs. Specifically, patients who receive consecutive shocks and have a depressed left ventricular function should be considered particularly high risk.     

植入型心律转复除颤器的临床应用及随访观察

目的 :观察我院 8例次植入型心律转复除颤器 (implantablecardioveterdefibrillatorICD)患者的临床疗效及随访情况。方法 :自 1996年 7月至 2 0 0 3年 9月 ,共有 7例患者 (其中 1例更换 1次 )在我院成功安装了ICD。 4例为扩张型心肌病 ,1例为长QT间期综合症 ,1例为多形性室性心     

Implantable Cardioverter Defibrillators in Patients with Chagas' Disease: Are They Different from Patients with Coronary Disease?

Chagas' disease is a parasitic affliction, endemic to certain regions of South America, which may lead to a chronic dilated nonischemic cardiomyopathy. Ten Chagasic patients were compared to 18 coronary patients undergoing transvenous ICD implantation for ventricular tachycardia (VT), ventricular fibrillation (VF), or aborted cardiac arrest. Indications for ICD implantation were either drug intolerance or refractoriness, or no inducible tachyarrhythmia at EPS. There were no statistically significant differences between the Chagas and coronary artery disease groups with respect to age (60.2 vs 62.6 yrs], NYHA Class II (50% vs 62%), ejection fraction (31.1% vs 29.7%), and incidence of cardiac arrest (20% vs 33%), respectively. The following ICD implant and long-term follow-up variables were compared between the two groups: pacing threshold (0.94 V vs 0.95V), defibrillation threshold (19.5 J vs 19.6 J), number of VT episodes (414 vs 435), number of spontaneous VT terminations (86 vs 187), percent efficacy of antitachycardia pacing (93.9% vs 92.1 %), and total number of shocks (112 vs 145). These differences were not statistically significant. We conclude that patients with Chagas' disease, compared with coronary artery disease patients, have similar clinical characteristics leading to ICD implantation. Furthermore, no differences were found with respect to ICD and long-term follow-up characteristics between the two groups.     

Combination of Antitachycardia Pacemaker and Automatic Implantable Cardioverter/Defibrillator for Ventricular Tachycardia

Antitachycardia pacing for ventricular tachycardia (VT) is associated with the possibility of fibrillating the heart; on the other hand, the frequency of VT and patient discomfort can limit treatment with the automatic implantable cardioverter/defibrillator (AICD). To contribute to the further development of a universal pacemaker, we evaluated the combined use of the antitachycardia pacemaker ("tachylog") and the AICD in five patients with recurrent VT. In the automatic mode, the "tachylog" worked as a bipolar VVI pacemaker. For antitachycardia pacing, a burst of rapid ventricular pacing was delivered at about 80% of the cycle length. During a follow-up period of 5 +/- 2 months (range, 3 to 8) two to 291 successful interventions of antitachycardia pacing were counted from diagnostic data which had been collected by the pulse generator during the course of treatment. When the antitachycardia pacemaker failed to terminate VT, the AICD was activated. In the individual case, between 0 and 41 discharges of the AICD were delivered. The high pulse energy of the AICD did not damage the antitachycardia pacemaker; no interference of the two devices was observed. Future antitachycardia systems should be more flexible with regard to detection and termination modes, combining antitachycardia pacing with back-up defibrillation.     

Direct Current Application: Easy Induction of Ventricular Fibrillation for the Determination of the Defibrillation Threshold in Patients with Implantable Cardioverter Defibrillators

For the determination of the defibrillation threshold, the induction of ventricular fibrillation is mandatory. However, in severely damaged hearts it is sometimes difficult to induce ventricular fibrillation by rapid stimulation or alternating current. Only rapid nonclinical ventricular tachycardias may result, and their cardioversion threshold may be different from the defibrillation threshold. Therefore, it was the purpose of this study to test the potential of direct current (DC) application to rapidly induce ventricular fibrillation in patients with an implanted cardioverter defibrillator. The defibrillation threshold had to be determined in 13 patients (9 with coronary heart disease, 4 with dilative cardiomyopathy, ejection fraction 35%) during and 2 weeks after the implantation of a cardioverter defibrillator. DC was applied 37 times by a commercially available 9-V DC battery via a bipolar catheter for about 3 seconds. Ventricular fibrillation was induced 23 times (62%) and rapid nonclinical ventricular tachycardias were induced six times (16%). In one patient clinical ventricular tachycardia was observed. In seven instances (19%) sinus rhythm remained. In 12 of the 13 patients, ventricular fibrillation could be induced by DC. Thus, the induction of ventricular fibrillation by DC application may serve as an additional tool to induce ventricular fibrillation, determining the defibrillation threshold in implantable cardioverter defibrillator patients.     

Outcomes of Elderly Recipients of Implantable Cardioverter Defibrillators

Aims of the Study: To examine the patterns of use, complication rates, and survival in elderly recipients of implantable cardioverter defibrillators (ICD).
Methods and Results: We followed 500 consecutive patients included in the Marburg Defibrillator database for 48 ± 39 months. There were 40 patients (8%) ≥75 and 460 (92%) <75 years of age at the time of implant. The 5-year Kaplan-Meier estimate for appropriate treatment of VT or VF by ICD was 49% among patients <75- versus 57% among patients ≥75-years-old (P = 0.17). The 5-year sudden death rate was similarly low in both groups of patients (2% versus 3%). The 5-year overall mortality rate was significantly higher in patients ≥75 than in patients <75 years of age (55% versus 21%, P = 0.001), due to a higher mortality from heart failure (HF). All procedure-related, lead-related, and pulse generator-related complications were similar in both patient groups (23% versus 25%).
Conclusions: ICD therapy was equally effective in patients ≥75 and patients <75 years of age in the prevention of sudden cardiac death. While the complication rates were similar in both age groups, the long-term mortality was considerably higher in elderly patients, due to a higher mortality from HF. The current ICD therapy guidelines appear applicable to elderly patients who are otherwise medically stable and without advanced HF.     

Significant Differences in Charge Times Among Currently Available Implantable Cardioverter Defibrillators

Capacitor charging accounts for most of the delay between arrhythmia detection and therapy delivery in ICDs. Long capacitor charge times may increase the risk of syncope in patients with poorly tolerated arrhythmias. To determine if there are clinically important differences in charge time among currently available devices, we analyzed charge times at various delivered energy levels in three manufacturers'devices: Medtronic, CPI, and Ventritex, Charge times were measured for shocks delivered for spontaneous or induced arrhythmias occurring from time of implant to 4 months after implant. A total of 343 shocks were assessed in 63 patients with ICDs: 16 Medtronic (Microfewel II, model 7223Cx). 14 CPI (Mini II, model 1762), and 33 Ventritex (Cadet and Contour, models V-115 and V-145). The curves of the relationship between charge time and delivered energy for the three types of devices were significantly different, with Medtronic charge times shorter than CPI or Ventritex (P < 0.0001), and CPI charge times shorter than Ventritex (P - 0.002). The difference in mean charge times between the Ventritex and Medtronic devices ranged from 1.7 seconds at a delivered energy of 10 ± 2.5 J to 8,0 seconds at a delivered energy of 30 ± 2.5 J. Thus, clinically important differences in charge time exist among the three types of defibrillators studied. These results should be considered in selecting an ICD for patients with poorly tolerated arrhythmias .