Failure of Third-Generation Implantable Cardioverter Defibrillators to Abort Shock Therapy for onsustained Ventricular Tachycardia Due to Shortcomings of the VF Confirmation Algorithm

Unnecessary shocks by ICDs for rhythms other than sustained VT or VF have been described as the most frequent adverse event in ICD patients. To avoid unnecessary shocks for self-terminating arrhythmias, the third-generation Jewel PCD defibrillators 7202, 7219, and 7220 Plus use a specially designed VF confirmation algorithm after charge end. The purpose of this study was to determine the ability of this VF confirmation algorithm to recognize nonsustained VT, and to analyze the reasons for failure of the PCD device to abort shock therapy for nonsustained VT despite use of this VF confirmation algorithm. Analysis of stored electrograms of electrical events triggering high voltage capacitor charging in the programmed VF zone of the device showed 36 spontaneous episodes of nonsustained VT (227 ± 21 beats/mm) during 18 ± 7 months follow-up in 15 patients who had a Jewel PCD implanted at our hospital. Intracardiac electrogram recordings and simultaneously retrieved marker channels demonstrated that the ICD shock was appropriately aborted according to the VF confirmation algorithm in 24 (67%) of 36 episodes of nonsustained VT. Twelve episodes (33%) of nonsustained VT, however, were followed by a spontaneous ICD shock in 6 (40%) of the 15 study patients. The only reason for all 12 shocks for nonsustained VT was the inability of the device to recognize the absence of VT after charge end due to shortcomings of the VF confirmation algorithm: 11 of the 12 shocks for nonsustained VT were triggered by the occurrence of paced beats during the VF confirmation period and 1 shock for nonsustained VT was triggered by the occurrence of 2 premature beats after charge end. Thus, better VF confirmation algorithms need to be incorporated in future PCD devices to avoid unnecessary shocks for nonsustained VT.     

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.     

Antitachycardia pacing for spontaneous rapid ventricular tachycardia in patients with prophylactic cardioverter-defibrillator therapy

AIMS: Antitachycardia pacing (ATP) has not routinely been used in patients who received implantable cardioverter defibrillators (ICDs) for primary prevention of sudden death. This study investigated the efficacy of empirical ATP to terminate rapid ventricular tachycardia (VT) in heart failure patients with prophylactic ICD therapy. METHODS AND RESULTS: Ninety-three patients with a mean left ventricular ejection fraction of 22 +/- 7% (range: 9-35%) due to nonischemic or ischemic cardiomyopathy received prophylactic ICDs with empiric ATP. At least 2 ATP sequences with 6-pulse burst pacing trains at 81% of VT cycle length (CL) were programmed in one or two VT zones for CL below 335 +/- 23 ms and above 253 +/- 18 ms. Ventricular flutter and fibrillation (VF) with CL below 253 +/- 18 ms were treated in a separate VF zone with ICD shocks without preceding ATP attempts. During 38 +/- 27 months follow-up, 339 spontaneous ventricular tachyarrhythmias occurred in 36 of 93 study patients (39%). A total of 232 VT episodes, mean CL 293 +/- 22 ms, triggered ATP in 25 of 36 patients with ICD interventions (69%). ATP terminated 199 of 232 VT episodes (86%) with a mean CL of 294 +/- 23 ms in 23 of 25 patients (88%) who received ATP therapy. ATP failed to terminate or accelerated 33 of 232 VT episodes (14%) with a mean CL of 287 +/- 19 ms in 12 of 25 patients (48%) who received ATP therapy. CONCLUSIONS: Painfree termination of rapid VT with empirical ATP is common in heart failure patients with prophylactic ICD therapy. The occasional inability of empiric ATP to terminate rapid VT in almost 50% of patients who receive ATP for rapid VT warrants restrictive ICD programming with regard to the number of ATP attempts in order to avoid syncope before VT termination occurs.     

Safety and Diagnostic Yield of Noninvasive Ventricular Stimulation Performed Via Tiered Therapy Implantable Defibrillators

Extensive electrophysiological testing is critical for the effective utilization of sophisticated tachycardia detection and termination algorithms available in tiered therapy ICDs. To evaluate the safety and diagnostic yield of electrophysiological testing via noninvasive ventricular stimulation, we performed 294 electrophysiological studies in 154 patients (age 65 ± 10; left ventricular ejection fraction 0.36 ± 0.15) with tiered therapy ICDs. Stimulation was performed under methohexital anesthesia. A total of 928 sustained ventricular tachyarrhythmias were induced (3.1 ± 2.5 per procedure); monomorphic VT, 550; ventricular flutter, 74; and VF, 246. The results of invasive and noninvasive programmed stimulation were compared for 79 patients wbo had both studies under similar treatment. Overall concordance iras 83%, and did not differ significantly between patients who bad the noninvasive stimulation via epicardial or endocardial pacing leads. VF could be induced in 206 of 257 studies (82%), and it was less likely to be induced in patients on amiodarone (74% vs 85%; P = 0.02), or beta blockers (55% vs 83%; P = 0.017). No patient presented a serious complication. Minor complications occurred during 39 studies; transient laryngospasm in 1, unintended delivery of an ICD sbock to a conscious patient in 4; induction of sustained atrial fibrillation in 8; need for external rescue defibrillation sbocks in 13; and delivery of inappropriate sbocks for supraventricular rhythms in 14 studies. Noninvasive ventricular stimulation performed under methobexital anestbesia is safe. Its diagnostic yield compares favorably with that of conventional electropbysiological studies. VF can be induced in a majority of patients. There is good correlation between invasive and noninvasive programmed stimulation for induction of VT. Noninvasive ventricular stimulation may emerge as standard procedure for the initial programming and follow-up of ICDs.     

Do Traditional VT Zones Improve Outcome in Primary Prevention ICD Patients?

Aims: We reviewed outcomes in our primary prevention implantable cardioverter defibrillator (ICD) population according to whether the device was programmed with a single ventricular fibrillation (VF) zone or with two zones including a ventricular tachycardia (VT) zone in addition to a VF zone. Methods: This retrospective study examined 137 patients with primary prevention ICDs implanted at our institution between 2004 and 2006. Device programming and events during follow‐up were reviewed. Outcomes included all‐cause mortality, time to first shock, and incidence of shocks. Results: Eighty‐seven ICDs were programmed with a single VF zone (mean >193 ± 1 beats per minute [bpm]) comprising shocks only. Fifty ICDs had two zones (mean VT zone >171 ± 2 bpm; VF zone >205 ± 2 bpm), comprising antitachycardia pacing (100%), shocks (96%), and supraventricular (SVT) discriminators (98%) . Discriminator “time out” functions were disabled. Mean follow‐up was 30 ± 0.5 months and similar in both groups. All‐cause mortality (12.6% and 12.0%) and time to first shock were similar. However, the two‐zone group received more shocks (32.0% vs 13.8% P = 0.01). Five of 16 shocks in these patients were inappropriate for SVT rhythms. The single‐zone group had no inappropriate shocks for SVTs. Eighteen of 21 appropriate shocks were for ventricular arrhythmias at rates >200 bpm (three VF, 15 VT). This suggests that primary prevention ICD patients infrequently suffer ventricular arrhythmias at rates <200 bpm and that ATP may play a role in terminating rapid VTs. Conclusions: Patients with two‐zone devices received more shocks without any mortality benefit. (PACE 2010; 1353–1358)     

Discriminatory therapy for very fast ventricular tachycardia in patients with implantable cardioverter defibrillators

Objectives: We assessed the efficacy of antitachycardia pacing (ATP) and low-energy (5J) shock for very fast ventricular tachycardia (VFVT), cycle length 200–250 ms, in patients with implantable cardioverter defibrillators (ICDs).
Methods and Results: One hundred and fifty-two consecutive patients with standard indications for ICD therapy were enrolled. Before discharge from the hospital each patient had an electrophysiological study (EPS) performed through the device, to assess the efficacy of ATP and low-joule shock at terminating VFVT. Initial therapy for VFVT consisted of three bursts of ATP followed by low-energy shock, and high-energy shocks as required. The mean age of enrolled patients was 63 ± 13 years, and the mean left ventricular ejection fraction (LVEF) was 31 ± 13%. During the predischarge EPS, a total of 125 VT episodes were induced in 64 patients. In patients with VFVT, the success rate of ATP was 30% (14/46), the acceleration rate was 26% (12/46), and the success rate of low-energy shock was 86% (25/29). In patients with fast ventricular tachycardia (FVT), cycle lengths 251–320 ms, the success rate of ATP was 62% (24/39), the acceleration rate was 18% (7/39), and the success rate of low-energy shock was 94% (17/18).
Conclusions: This study has demonstrated for the first time that ATP and low-energy shock are effective, as an alternative to high-energy shock, to revert induced VFVT. Low-energy shock has a very high success rate for VT slower than VFVT. Clinical studies are required prior to consideration for empiric programming.     

Comparison of Clinical Benefits and Outcome in Patients with Programmable and Nonprogrammable Implantable Cardioverter Defibrillators

Technological advances in implantable cardioverter defibrillators (ICDs) have provided a variety of programmable parameters and antitachycardia therapies whose utility and impact on clinical outcome is presently unknown. ICDs have capabilities for cardioversion defibrillation alone (first generation ICDs), or in conjunction with demand ventricular pacing (second generation ICDs), or with demand pacing and antitachycardia pacing (third generation ICDs). We examined the pattern of antitachycardia therapy use and long-term survival in 110 patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Group I included 62 patients with nonprogrammable first generation ICDs that delivered committed shock therapy after ventricular tachyarrhythmia detection based on electrogram rate and/or morphology was satisfied. Group II included 48 patients with multiprogrammable ICDs (including second and third generation ICDs) that had programmable tachyarrhythmia detection based on rate and tachycardia confirmation prior to delivery of electrical treatment with either programmable shocks and/or, as in the third generation ICDs, antitachycardia pacing. Incidence and patterns of antitachycardia therapy use and long-term survival were compared in the two groups. The incidence of appropriate shocks in patients who completed 1 year of follow-up was significantly greater in group I (30 of 43 patients = 70% vs 11 of 26 patients = 42%; P less than 0.05). In the total follow-up period, a significantly larger proportion of group I patients as compared to group II patients used the shock therapies (46 of 62 patients = 74% vs 25 of 48 patients = 52%; P less than 0.01), with the majority doing so within the first year of implantation (96% and 92%, respectively). Although the frequency of antitachycardia therapy activation was similar, the number of shocks delivered per patient was lower in group II, particularly in the initial 3 months of follow-up (P = 0.06). No clinical variable aided in identifying users from nonusers of antitachycardia therapy. Arrhythmic mortality was virtually eliminated in both groups. Two-year actuarial cardiac survival in the two groups was similar (group I = 78% vs group II = 84%; P greater than 0.2). Survival from cardiac mortality in users and nonusers of antitachycardia therapies was also similar in both groups (P greater than 0.2) and in the total patient group (P greater than 0.2). We conclude that programmable ICDs continue to confer advantages in prevention of sudden death that were observed with nonprogrammable ICDs and can be expected to improve patient tolerance and physician acceptance of device therapy for VT/VF.     

Amiodarone in the Management of Patients with Ventricular Tachycardia and Ventricular Fibrillation

Fifty-eight patients with symptomatic ventricular tachycardia (VT) or ventricular fibrillation (VF) were treated with amiodarone. All had clinical episodes of VT/VF or inducible VT during electropharmacologic testing despite treatment with maximumtolerated doses of conventional antiarrhythmic agents. Chronic treatment with amiodarone was begun at a dose of 800–1000 mg per day. Thirty-two patients were also treated with a previously ineffective conventional agent. Thirty patients underwent programmed ventricular stimulation after 2.6 ± 1.7 months (mean ± S. D.) of treatment with amiodarone at a mean daily dose of 588 ± 155 mg. VT was induced in 25 patients (sustained in 20, nonsustained in five). Seventeen patients had a recurrence of VT or VF after 0.5–9 months of treatment with amiodarone (fatal in seven, non-fatal in 10). Forty-one patients (71%) had no recurrence of symptomatic VT or VF while being treated with amiodarone (mean follow-up period, 17.1 ± 12.4 months). Among the 25 patients who had inducible VT with programmed ventricular stimulation while being treated with amiodarone, 19 patients (76%) have had no recurrence of symptomatic VT or VF overa follow-up period of 21.5 ± 7.3 months. Ambulatory electrocardiographic recordings obtained after one week of treatment with amiodarone were not helpful in predicting clinical response. Twenty-two patients (38%) developed ataxia and/or an intention tremor which improved with a decrease in the amiodarone dose. Amiodarone, either by itself or in combination with conventional antiarrhythmic drugs, has a significant therapeutic effect in high risk patients with refractory VT. The finding of inducible VT during electropharmacologic testing in patients taking amiodarone does not preclude a favorable clinical response. Neurologic toxicity is common in patients treated with 600–800 mg per day of amiodarone.     

The Mean Ventricular Fibrillation Cycle Length: A Potentially Useful Parameter for Programming Implantable Cardioverter Defibrillators

In programming the implantable cardioverter defibrillator (ICD), the ventricular tachycardia (VT) detection cycle length (CL) is based on the CL of the documented tachycardia but the ventricular fibrillation (VF) detection CL is set arbitrarily. Appropriate programming of VF detection may not only reduce the incidence of inappropriate ICD shocks for non-VF rhythms but can also avoid the fatal underdetection of VF. The mean VFCL may provide a useful parameter for optimal ICD programming for VF detection if it is reproducible. This study examined the intrapatient reproducibility and interpatient variation of the mean VFCL in 30 ICD patients (25 men and 5 women, mean age 63 ± 13 years). A total of 210 VF episodes (7 ± 4 per patient, range 3–17) induced by T-wave shocks (166) or AC (44) at the ICD implant (30 patients) and the predischarge test (12 of 30 patients) were analyzed. The mean VFCL was calculated from the stored V-V intervals in the ICDs. Although the mean VFCL varied significantly from 171 ± 6 to 263 ± 11 ms (P < 0.01) among different patients, it was reproducible among different VF episodes in an individual patient (maximal variation 4–50 ms, P > 0.05). The mean VFCL was not significantly different between patients with and without antiarrhythmic drugs (210 ± 32 vs 210 ± 23 ms, P > 0.05) and was correlated with the ventricular effective refractory period (r = 0.5, P < 0.05). The mean VFCL varies greatly among different patients but remains reproducible in an individual patient, suggesting that the mean VFCL may serve as a reference for ICD programming of VF detection.     

Termination of ventricular tachycardia by far-field stimulation in humans: a feasibility study

Background: Although a low‐energy cardioversion (LEC) shock from an implantable cardioverter‐defibrillator (ICD) can terminate ventricular tachycardia (VT), it frequently triggers ventricular fibrillation (VF) and is therefore not used in clinical practice. We tested whether a modified LEC shock with a very short duration (0.12–0.36 ms), termed “field stimulus,” can terminate VT without triggering VF. Methods: In 13 sedated patients with implanted ICDs, we attempted to induce VT and to terminate the arrhythmias by field stimuli during hospital predischarge tests. Results: In eight patients, 27 VT episodes were induced and treated with a total of 46 high‐voltage (25–200 V) field stimuli, which terminated 11 VT episodes (41% efficacy) and never accelerated VT into VF. VT episodes slower than 230 beats per minute (bpm) (median rate) were terminated more successfully than faster arrhythmia episodes (69% vs 15%, P < 0.01). The strength of the field stimulus had no major influence on the effectiveness. We therefore postulate that suboptimal timing of field stimuli (delivered simultaneously with a sensed event in the right ventricular apex) was the main reason for failed VT terminations. Conclusion: A short (0.12–0.36 ms), high‐voltage (50–100 V) field stimulus delivered from the shock coil of an implanted ICD system can safely terminate VT, especially for VT rates below 230 bpm. We believe that it would be reasonable to test the effectiveness of automatic field‐stimulus therapy from implanted ICDs in VT episodes up to 230 bpm that are not susceptible to termination by antitachycardia pacing. (PACE 2010; 33:1540–1547)     

Ventricular Arrhythmia Inducibility Predicts Subsequent ICD Activation in Nonischemic Cardiomyopathy Patients: A DEFINITE Substudy

Objectives: We evaluated whether electrophysiologic (EP) inducibility predicts the subsequent occurrence of spontaneous ventricular tachycardia (VT) or ventricular fibrillation (VF) in the Defibrillators in Nonischemic Cardiomyopathy Treatment Evaluation (DEFINITE) trial.
Background: Inducibility of ventricular arrhythmias has been widely used as a risk marker to select implantable cardioverter defibrillator (ICD) candidates, but is believed not to be predictive in nonischemic cardiomyopathy patients.
Methods: In DEFINITE, patients randomized to the ICD arm, but not the conventional arm, underwent noninvasive EP testing via the ICD shortly after ICD implantation using up to three extrastimuli at three cycle lengths plus burst pacing. Inducibility was defined as monomorphic or polymorphic VT or VF lasting 15 seconds. Patients were followed for a median of 29 ± 14 months (interquartile range = 2–41). An independent committee, blinded to inducibility status, characterized the rhythm triggering ICD shocks.
Results: Inducibility, found in 29 of 204 patients (VT in 13, VF in 16), was associated with diabetes (41.4% vs 20.6%, P = 0.014) and a slightly higher ejection fraction (23.2 ± 5.9 vs 20.5 ± 5.7, P = 0.021). In follow-up, 34.5% of the inducible group (10 of 29) experienced ICD therapy for VT or VF or arrhythmic death versus 12.0% (21 of 175) noninducible patients (hazard ratio = 2.60, P = 0.014).
Conclusions: In DEFINITE patients, inducibility of either VT or VF was associated with an increased likelihood of subsequent ICD therapy for VT or VF, and should be one factor considered in risk stratifying nonischemic cardiomyopathy patients.     

Time to First Shock in Implantable Cardioverter Defibrillator (ICD) Patients with Chagas Cardiomyopathy

The time to first ICD shock has been extensively studied in patients with coronary artery disease (CAD). However, there are no published data on ICD shocks in patients with Chagas cardiomyopathy (ChC). The occurrence of the first appropriate ICD shock during the first 6 months of follow-up in 20 patients with ChC (group 1) and 35 CAD patients (group 2) was analyzed retrospectively. All patients had received a third-generation pectoral ICD for ventricular tachycardia or fibrillation (VT/VF). Indications for ICD implantation were refractoriness to drug therapy or noninducibility of VT/VF at EPS in cardiac arrest survivors. Results: The mean age, left ventricular ejection fraction (LVEF), and sex in groups I and II were 57.4 ± 7 years versus 64 ± 9 (P < 0.01), 30.9%± 10% versus 32.9%± 10% (P = NS), and 10 men versus 31 women (P < 0.005), respectively. Six months after ICD implantation, 85% (17/20) group I patients received appropriate ICD shocks versus 51 % (18/35) in group 2, a statistically significant difference (P < 0.02, RR: 1.65, OR: 5.35). Conclusions: The incidence of appropriate ICD shocks within the first 6 months postimplantation was significantly higher in ChC patients than in CAD patients. ChC patients were younger and more often women than CAD patients.     

Shock on T versus direct current voltage for induction of ventricular fibrillation: a randomized prospective comparison

VF is induced during ICD implantation to determine efficacy of therapy. Establishing the best clinical method of induction of VF would potentially be beneficial in reducing the number of induction attempts and reducing the frequency of inadvertent induction of VT. Commonly used methods to induce VF include shock in the T wave vulnerable period (T shock) and high frequency stimulation. This study compared the efficacy of T shock with a new induction method using a 9-V DC pulse. The study was a randomized, prospective, case crossover trial in patients receiving ICDs. VF was induced by T shock and DC in a randomized sequence during an ICD implant. VF was induced at least four times in each patient (two T shocks and two DC inductions) and with each induction; attempts were continued with modifications until successful. A paired evaluation between the T shock/DC induction was performed in 37 patients (28 men, age 64 +/- 12 years) with a left ventricular ejection fraction of 0.40 +/- 0.20. Arrhythmia indications were VT (n = 23), VF (n = 10), and VT/VF (n = 4). Drug therapy included amiodarone (n = 10), metoprolol (n = 6), digoxin (n = 1), and lidocaine (n = 1). The average T shock voltage was 207.0 +/- 16.1 V. The S1 cycle drive length was consistently 400 ms, and the mean S2 coupling interval was 317.8 +/- 19.6 ms. The length of time DC applied averaged 3.8 +/- 1.4 seconds. A total of 148 episodes of VF were included in the analysis. T shock induced VF with a cycle length of 213.5 +/- 35.1 ms, and DC induced VF with a cycle length of 214.6 +/- 34.5 ms (P = 0.86). Although VF was eventually induced for each randomization, the number of attempts required were dependent on the method of induction. The successful DC first attempt VF induction rate was 96%, with three patients requiring two attempts during one of the DC inductions. T shock had a 68% first attempt success rate with 21 patients requiring multiple T shocks to induce VF. All nine female patients had at least one unsuccessful first attempt T shock, which contributed to an overall unsuccessful first attempt induction rate significantly higher in women then men (36.1% vs 12.5%, P = 0.001). A constant DC voltage induction of VF may be more effective than T shock for induction of VF in a clinical setting because it reduces the number of attempts required to induce VF. By either method, VF appears to be more difficult to induce in women. DC induction has the advantage of simple programming of only duration of stimulation. These findings have implications particularly for ICD implantation with conscious sedation.     

Implantable Cardioverter Defibrillator Events in Patients with Asymptomatic Nonsustained Ventricular Tachycardia:

Primary prevention trials have demonstrated that patients with coronary disease, reduced left ventricular function, and nonsustained ventricular tachycardia (NSVT) have improved survival with implantable cardioverter defibrillator (ICD) therapy, presumably secondary to effective termination of life-threatening arrhythmias. However, stored intracardiac electrograms were not always available and specific arrhythmias leading to ICD therapy were not always known. We examined the occurrence of ICD events in 51 consecutive patients who match the described patient profile to determine the frequency of appropriate and inappropriate ICD therapy. ICD detections were noted in 18 (35%) patients during a median follow-up period of 13.1 months. Appropriate therapy for sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) occurred in 11 (22%) patients, with appropriate shocks in 8 (16%) patients and appropriate antitachycardia pacing (ATP) in 4 (8%) patients. The time to first appropriate therapy occurred at a mean of 17 +/- 12 months (median 18 months, range 3-36 months). Inappropriate therapy occurred in 5 (10%) patients with inappropriate shocks in 4 patients and inappropriate ATP in 2 patients. Inappropriate therapy was delivered for supraventricular arrhythmias (SVAs) in 4 patients and for T wave oversensing in 1 patient. The reason for shock therapy was unknown in 1 patient (2%) due to ICD malfunction. The mean arrhythmia rate leading to appropriate therapy for VT/VF was 232 +/- 72 beats/min (range 181-400 beats/min), and the mean rate leading to inappropriate therapy for SVT was 168 +/- 10 beats/min (range 160-180 beats/min). Patients with coronary disease and asymptomatic NSVT commonly receive appropriate defibrillator therapy. These results support the need for ICD implantation for primary prevention, with attention to careful programming of the detection rate to prevent inappropriate therapy.     

Clinical Efficacy and Safety of the New Cardioverter Defibrillator Systems

Clinical efficacy and safety of two new third-generation implantable cardioverter defibrillators (ICD) were studied in 38 patients with ventricular tachycardia (VT) or fibrillation (VF). There were 31 patients with coronary disease, three patients with right ventricular dysplasia, one patient with dilated cardiomyopathy, and three patients with valvular disease. Twenty-four patients (group I) received an ICD with monophasic (Ventak PRx 1700, CPI) and 14 patients (group II) with biphasic shocks (Cadence V 100, Ventritex). Intraoperatively, the mean defibrillation threshold was significantly lower in group II than in group I, both in patients with induced VT (group I 11.0 ± 6.3 joules: group N 5.8 ± 1.3 joules) (P < O.01) and induced VF (group I 17.5 ± 4.6 joules; group II 9.6 ± 5.2 joules) (P < O.O1). During the mean follow-up of 12 ± 7 months four patients (11%) died. 865 arrhythmia events (AE) occurred and were terminated by ATP (671 VTs, 78%). Acceleration of VTs was observed in 28 AE (3%) and ATP was unable to interrupt 58 AE (7%). ICD shocks were delivered as a first therapy in 108 AE (13%).     

Potential Hazards of Fixed Gain Sensing and Arrhythmia Reconfirmation for Implantable Cardioverter Defibrillators

Appropriate sensing of ventricular tachycardia (VT) and ventricular fibrillation (VF)is of paramount importance for safety of patients with implanted cardioverter defibrillators (ICDs). Recently, the Guardian^R ATP 4210, a new third generation ICD that uses programmable but fixed sensing during sinus rhythm and doubles its sensitivity settings when VF is detected, to a maximum programmable sensitivity of 1 mV, has been tested in phase I and II clinical trials. A reconfirmation algorithm of this ICD confirms the presence of VT or VF prior to therapy. This case report describes undersensing of VF in a patient with the Guardian^R ATP 4210 at the maximum programmed sensitivity of 1 mV. Inappropriate episodes of asystole and prolonged bradycardias were also observed in this patient due to shortcomings in the reconfirmation algorithm design. Reoperation was required, with positioning of a new endocardial sensing lead to correct the undersensing of VF. This, however, did not correct asystolic pauses following antitachycardia pacing or spontaneous tachycardio termination prior to therapy. This case report highlights the hazards of fixed gain sensing for implantable ICDs and a potential limitation of a specific tachyarrhythmia reconfirmation algorithm used in this device.     

Inappropriate shock delivery by implantable defibrillators with dual chamber pacing during nonsustained ventricular tachycardia in patients with heart block

Transvenous implantable cardioverter defibrillators (ICDs) have improved the management of patients with ventricular tachycardia/ventricular fibrillation (VT/VF). Many patients with sustained VT/VF have bradyarrhythmias and nonsustained VT. Shock delivery due to nonsustained VT would be an undesirable feature. Abortive shock capability (noncommitted shocks) is a feature available in devices to prevent delivery of shocks for nonsustained VT. Recently, the availability of dual chamber pacing capability has improved the efficacy of ICDs by obviating the need of separate pacemaker implantation in patients with VT/VF and concomitant bradyarrhythmias. However, interaction between bradyarrhythmias and VT/VF has not been described and has important clinical implications. We report a case in which a patient with complete atrioventricular (AV) block and ventricular arrhythmias received an inappropriate shock following spontaneous termination of nonsustained VT, showing an important shortcoming of devices with these features.     

Efficacy of Antitachycardia Pacing in Patients Presenting with Cardiac Arrest

The efficacy of antitachycardia pacing (ATP) incorporated into implantable cardioverter defibrillators (ICDs) was assessed in 29 consecutive survivors of cardiac arrest, not attributable to acute myocardial infarction, ischemia, or drug and electrolyte effects. The cohort included 25 men and 4 women with a mean age of 65 years and a mean left ventricular ejection fraction of 29%. Seventeen patients had coronary artery disease, 11 had nonischemic dilated cardiomyopathy, and 1 had long QT syndrome. Programmed stimulation yielded monomorphic ventricular tachycardia (VT) in 17 patients, polymorphic VT in 6, and no inducible VT in 6. During a mean follow-up of 22 months, a total of 91 episodes of monomorphic VT occurred, 73 of which were successfully pace terminated (83%). Monomorphic VT amenable to pace termination recurred only in the group that had this arrhythmia inducible. The recurrent arrhythmias in the 12 patients having either no inducible VT or polymorphic VT were all rapid VTs, having a cycle length < 220 ms; and therefore, not amenable to pace termination. These results suggest that ATP incorporated into ICDs is useful in survivors of cardiac arrest and may significantly reduce the number of shocks that these patients would otherwise receive. Programmed stimulation may also help to define those patients who would receive the maximum benefit from ATP.     

Transtelephonic Monitoring and Transmission of Stored Arrhythmia Detection and Therapy Data From an Implantable Cardioverter Defibrillator

A new transtelephonic monitoring device designed for use with implantable Cardioverter defibrillators (ICDs) was evaluated. It is capable of interrogating ICDs and transmitting the following data via telephone: programmed parameters (e.g., ventricular tachycardia [VT] and ventricular fibrillation [VF] detection, therapies), number of VT and VF episodes, identification of successful therapies, the 20 cycle lengths preceding the last episode detected, the 10 cycle lengths after the last delivered therapy, battery voltage, and real-time transmission of the patient's rhythm. Eighteen patients (mean age 64 ± 17years; 15 males) were implanted with an ICD and epicardial lead system. The patients who did not live near the primary hospital were provided with this transmitter and instructed to transmit monthly and whenever presyncope, syncope, or a shock were experienced. Five hundred ten episodes of spontaneous arrhythmia (495 VT, 15 VF) were detected in 14 of 18 patients in a 24-month period and the success of each therapy (antitachycardia pacing, cardioversion 0.4-34 J, defibrillation 34 J) was analyzed. The number of therapies delivered and their success (%) in terminating the arrhythmia were: 380 ramp/86%, 116 burst/84%, 119 cardioversion/57%, and 15 defibrillations/ 100%. Sixty-three (42%) of the 152 transmissions indicated an arrhythmia. Twenty-five (16%) of the 152 were transmitted because of symptoms. Sixteen (9.7%) of 165 VT episodes could not be terminated by the full set of programmed VT therapies. Analysis of the pre- and post-episode intervals along with the patient's transmitted rhythm indicated that sinus tachycardia or atrial fibrillation were likely responsible for these episodes. The transmitted data included the real-time ECG, which provided acute rhythm status plus stored data from the ICDs memory identifying the chronic arrhythmias detected, the therapies delivered, and the number and type of successful and ineffective therapies. This information provided the clinical data to the primary physician in order to determine the effectiveness of the programmed detection and therapy parameters and in some cases recommend to the home physician modifications to the device parameters or medication adjustments for enhanced arrhythmia control. We conclude that telephone transmission of stored ICD data is feasible and useful for patient management. It may obviate the need for patients experiencing symptoms to return to a site capable of device interrogation.     

Transcutaneous T Wave Shock: A Universal Method for Ventricular Fibrillation Induction

Our objective was to develop a universal noninvasive method for VF induction. ICD implantation requires VF induction. Conventional rapid ventricular stimulation may fail to induce VF. Some ICDs can deliver low energy shocks on the T wave to induce VF. We hypothesized that an external dual chamber pacemaker and an external defibrillator could be configured to allow reliable VF induction with any ICD system. A surface ECC signal was delivered to the atrial channel of an external dual chamber DDD pacemaker. The 'AV' delay was adjusted so that the ventricular output of the pacemaker was delivered to an external defibrillator synchronized to deliver 5–50 J. Twenty-six patients at ICD implant or follow-up had VF induced in native rhythm (sinus rhythm or atrial fibrillation), or during a ventricular pacing train (3–8 beats at cycle length 500–880 ms). VF was successfully induced in 14 of 25 (56%) patients in native rhythm; and in 16 of 17 (94%) patients during pacing (P = 0.013). VF induction success rate was 36% in native rhythm (31/86 attempts) and 88% during pacing (69/78 attempts) (P < 0.001). The 'R' to shock interval was 269 ± 31 ms in native rhythm and 257 ± 48 ms during pacing. Energy delivered from the external defibrillator was 19 ± 3 J in native rhythm and 21 ± 6 J during pacing. We concluded that VF induction by synchronizing a small external shock to the T wave is a fast, effective way to reliably ensure arrhythmia induction with any ICD at implant or follow-up. This method is more successful during pacing than in sinus rhythm.