The Value of Electrophysiology Study and Prophylactic Implantation of Cardioverter Defibrillator in Patients with Hypertrophic Cardiomyopathy

Fifty-three consecutive patients with hypertrophic cardiomyopathy (HCM) and no history of sudden death underwent electrophysiology (EP) study. Sustained polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF) was induced in 19 patients (35%). Patients with prior syncope or near syncope had a higher incidence of VT/VF inducibility. An implantable cardioverter defibrillator (ICD) was placed in 14 of the 19 patients. Of the remaining 5 patients with inducible VT/VF, three refused ICD implantation, while two underwent septal myectomy and VT/VF was no longer inducible afier the operation. None of the patients received antiarrhythmic drugs. During a mean follow-up period of 47 ± 31 (2–117) months, no events occurred in the 34 patients with negative EP study. Three events occurred among the 19 patients with inducible VT/VF. One patient died suddenly, one developed wide complex tachycardia which required resuscitation, and one patient received an appropriate ICD shock. In conclusion, sustained polymorphic VT/VF was inducible in about one-third of patients with HCM. Noninducibility of VT/VF appeared to predict a favorable prognosis. Although the overall event rate was low in patients with inducible VT/VF, prophylactic ICD implantation in patients with multiple risk factors may be appropriate.     

Ventricular tachycardia oversensing in S-ICD patients: Case-based brief review

A 76-year-old woman with permanent atrial fibrillation and a mechanical aortic valve came to our attention. Echocardiography showed a 50-55% ejection fraction (EF) with good prosthesis performance. For symptomatic bradyarrhythmia, she received a VVI pacemaker (Proponent MRI L2010 model; Boston Scientific.). During follow-up, frequent symptomatic (presyncopal) episodes of nonsustained episodes of ventricular tachycardia (VT) were detected. Amiodarone proved unsuccessful; she was then offered an upgrade to an implantable cardioverter defibrillator (ICD) and a subcutaneous ICD (S-ICD) was chosen by the patient. A few weeks later, two sustained VT were detected and effectively treated with 80-J shock delivery. In both cases, device interrogation revealed a VT rate around 163 bpm (370 ms cycle length), below the lowest device detection cutoff. The report is a case-based review.     

Reinitiation of ventricular macroreentry within the His-Purkinje system by back-up ventricular pacing - a mechanism of ventricular tachycardia storm

BACKGROUND: We describe immediate reinitiation of macroreentry ventricular tachycardia (VT) involving the His-Purkinje system by ventricular pacing from the electrode of an implantable cardioverter defibrillator (ICD) as a mechanism of VT storm refractory to ICD therapy. METHODS AND RESULTS: Repetitive reinitiation of bundle branch reentry tachycardia (BBRT), interfascicular tachycardia, or both VTs by ventricular pacing was identified in four ICD patients presenting with VT storm or incessant VT. All patients had a pre-existing prolonged HV interval (75 +/- 9 ms) and left bundle branch block (LBBB) or bifascicular block during sinus rhythm. The VTs included BBRT with LBBB in three patients and interfascicular tachycardia with right bundle branch block (RBBB) and left anterior or left posterior fascicular block in two patients. The paced beats from the ICD electrode exhibited a LBBB pattern of depolarization in two patients and a RBBB contour in V1 and V2 with left axis deviation in two patients. The QRS complex during pacing from the ICD electrode closely resembled that of the recurrent VT in all four patients suggesting that the pacing site of the ICD electrode was in proximity to the myocardial exit site of the bundle fascicle used for antegrade conduction during the reinitiated VT. Ventricular pacing from the ICD electrode after termination of the VT apparently encountered the retrograde refractoriness of this bundle fascicle and allowed immediate re-propagation of the wavefront orthodromically along the VT circuit. BBRT was eliminated by ablation of the right bundle branch. Successful ablation of the interfascicular tachycardias was achieved by targeting (1) an abnormal potential of the distal left posterior Purkinje network or (2) a diastolic potential during VT in the midinferior left ventricular (LV) septum. CONCLUSIONS: Repetitive reinitiation of BBRT and interfascicular tachycardia by ventricular pacing from the ICD electrode should be considered as a mechanism of VT storm refractory to ICD therapy in patients with a pre-existing conduction delay within the His-Purkinje system.     

Effects of Coronary Artery Bypass Grafting on Ventricular Arrhythmias: Results with Electrophysiological Testing and Long-Term Follow-Up

Myocardial revascularization was performed in 56 patients with coronary artery disease who presented with ventricular tachycardia (VT) (n = 39) or ventricular fibrillation (n = 17). There were 46 men and 10 women, aged 65 ± 10 years. Three vessel (n = 42) or left main disease (n = 4) was present in 82%. Left ventricular ejection fraction averaged 36%± 11%. Electrophysioiogical studies were performed preoperatively in all patients; 50 (89%) had inducible ventricular arrhythmias. Sustained monomorphic VT was induced in 40 patients (cycle length 284 ± 61 msec). Reproducible symptomatic nonsustained VT was induced in four patients and ventricular fibrillation in six patients, while six patients had no inducible arrhythmia. Preoperatively the patients with inducible VT failed 3.3 ± 1.2 drug trials during electrophysiological studies. In addition to coronary bypass, 22 patients also received an automatic implantable cardioverter defibrillator (ICD), 26 patients received prophylactic ICD patches, and 1 patient had resection of a false aneurysm. There were no perioperative deaths. Postoperative electrophysiological studies were performed in all 56 surgical survivors. Ventricular tachyarrhythmia could not be induced in the six patients who had no inducible VT preoperatively and in 13 of 40 (33%) with preoperatively inducible sustained VT or in 19 of 50 (38%) patients with any previously inducible ventricular arrhythmia, thus a totaJ of 25 patients (45%) had no inducible VT postoperatively. Of the remaining, 11 patients were treated with antiarrhythmic drugs alone, 11 had already received an ICD (combined with drugs in 7), and another 9 received the ICD postoperatively (combined with drugs in 4). At a mean foJJow-up of 28 ± 21 months there were 11 deaths (20%): 2 sudden, 5 nonsudden cardiac, and 4 noncardiac deaths. There were 16 nonfatal VT recurrences (29%): 14 among patients with persistently inducible arrhythmias, and onJy 2 among those with no inducible arrhythmia postoperatively (P = 0.004); 13 occurred in patients with an ICD (P = 0.01). Thus among these patients with malignant ventricular arrhythmias who underwent revascuJarization, 45% had no inducible arrhythmia postoperatively with 33% of those with preoperatively inducible sustained VT apparently rendered noninducible by revascularization, while the majority (70%) remained free of major arrhythmic events during long-term follow-up. We conclude that myocardial revascularization alone can result in no ventricular arrhythmia induction in selected patients with VT inducible prior to surgery. Long-term follow-up of such patients indicates a low sudden death and arrhythmia recurrence rate. Furthermore, in patients with persistently inducible ventricular tachyarrhythmias after coronary revascuJarization, the sudden death rate is low despite a high frequency of nonfatal arrhythmia recurrence when antiarrhythmic medications are guided by programmed stimulation or an ICD is used.     

Ventriculoatrial Conduction in Patients with Implantable Cardioverter Defibrillators: Implications for Tachycardia Discrimination by Dual Chamber Sensing

Incorporation of atrial electrograms in the tachycardia detection algorithm may improve tachyarrhythmia discrimination by ICDs but retrograde ventriculoatrial (VA) conduction over the AV node during ventricular tachyarrhythmia may be problematic. The present study analyzed VA conduction characteristics in 66 ICD patients who had evaluation of the VA conduction system by electrophysiological studies before implant. VA conduction was demonstrated in patients during ventricular decremental stimulation. Forty patients had inducible sustained monomorphic VT. The minimum cycle length maintaining 1:1 VA conduction during ventricular stimulation was longer than the cycle of VT in every patient (496 ±100 msec vs 320 ± 81 msec; P < 0.01). Occasional VA conduction during VT was observed in five patients and one patient had 2:1 VA conduction during induced VT. No patient had 1:1 VA conduction during VT. We conclude that brisk VA conduction is uncommon and 1:1 VA conduction during VT is rare in ICD recipients. VA conduction is unlikely to complicate the incorporation of atrial electrograms into tachyarrhythmia detection algorithms.     

Basal Exit Site of Clinical Ventricular Tachycardia is an Independent Predictor of Antitachycardia Pacing Failure in Implantable Cardioverter‐Defibrillators Recipients

Background: Little is known about predictors of antitachycardia pacing (ATP) failure in implantable cardioverter defibrillator (ICD) recipients. Distance between the stimulation site and the ventricular tachycardia (VT) site of origin may critically affect ATP effectiveness. We hypothesized that ATP may be less effective in ICD patients who had basal VT than in those who had apical VT. Methods: We reviewed data from 52 patients with sustained monomorphic VT and left ventricular disease referred for ICD implantation. ATP was delivered exclusively at the right ventricular apex. The clinical VTs site of origin (basal, midventricular, or apical) was determined in each patient, using 12‐lead electrocardiogram. VTs episodes treated with ATP during the 1‐year follow‐up were studied. ATP success rate (%), defined as the ratio between the number of successful ATP sequences and the number of delivered ATP sequences, was determined in each patient. Results: VT exit site was apical in 19 patients (36%), basal in 18 patients (35%), and midventricular in 15 patients (29%). In those 52 patients, 1,393 ATP sequences, delivered to treat 761 VT episodes, were analyzed. ATP success rate was found to be associated with the VT site of origin (median [interquartile range]): basal (33%[11–67]), midventricular (50%[37–100]), apical (100%[41–100]) (P = 0.027). Multivariate analysis identified basal VT site of origin as an independent predictor of ATP failure (P = 0.023). Conclusion: ATP is less effective in ICD patients who had basal VT than in those who had apical VT before ICD implantation. (PACE 2012; 35:1209–1216)     

Sustained ventricular tachycardia following alcohol septal ablation for hypertrophic obstructive cardiomyopathy

A 49-year-old man with a history of hypertrophic obstructive cardiomyopathy (HOCM) presented in sustained monomorphic ventricular tachycardia (SMVT) 8 days post-alcohol septal ablation. A dual chamber implantable cardioverter defibrillator ICD was implanted and the patient experienced another episode of VT 3 weeks later, which was terminated by an ICD shock. This case demonstrates probable scar-induced reentrant VT post-alcohol septal ablation, a likely rare but hypothesized complication of this procedure.     

Characteristics and relevance of clustering ventricular arrhythmias in defibrillator recipients

INTRODUCTION: Studies of recurrent ventricular tachycardia and ventricular fibrillation (VT/VF) have been limited to "electrical storms," where recurrent arrhythmias necessitate repeated external cardioversions or defibrillations. Patients with an implantable cardioverter-defibrillator (ICD) may also suffer frequently recurrent arrhythmias. The aim of this study was to analyze the temporal pattern and the clinical relevance of clustering ventricular arrhythmias in ICD recipients. METHODS: The incidence and the type of arrhythmias were determined by reviewing stored electrograms. VT/VF clusters were defined as the occurrence of three or more adequate and successful ICD interventions within 2 weeks. Two hundred and fourteen consecutive ICD recipients were followed during an average of 3.3 +/- 2.2 years (698 patient-years). RESULTS: Fifty-one patients (24%) suffered 98 VT/VF clusters 21 +/- 22 months after ICD implantation, 93% of these clusters consisting of recurrent regular VT. Monomorphic VT as index event leading to ICD implantation was the only factor predicting VT/VF clusters. Kaplan-Meier estimates of the combined end-point of death or heart transplantation showed a 5-year event-free survival of 67% versus 87% in patients with and without clusters, respectively (P = 0.026). Adjusted hazard ratios for death or heart transplantation in the group with arrhythmia clusters was 3.5 (95% confidence interval 1.5-7.9 P = 0.003). CONCLUSIONS: VT/VF clusters are frequent late after ICD implantation particularly in patients who had VT as index-event. As arrhythmias and recurrent ICD interventions are responsible for an important morbidity, there is a possible role for a prophylactic intervention. Furthermore, VT/VF clusters are an independent marker of increased risk of death or need for heart transplantation.     

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.     

Intraoperative Mapping is Not Necessary for VT Surgery

Surgical ablation of ventricular tachycardia is generally guided by the results of pre- and intraoperative cardiac mapping. However, in certain situations intraoperative cardiac mapping may not be possible and, therefore, surgery has to be based on information obtained preoperatively. This raises the question whether intraoperative mapping is necessary for the success of this approach. We describe our experience with encircling endocar-dial cryoablation for ischemic VT and examine the contribution of intraoperative mapping for this procedure. Thirty-three patients with inducibie VT refractory to medical therapy and a well defined anatomic scar were considered for surgery. All patients underwent baseline electrophysiology study and intraoperative mapping was attempted during normothermic cardiopulmonary bypass. In 14 patients, VT was inducibie intraoperatively (Group 1) and surgical ablation was guided by this information, whereasin 19patients, VT could not be mapped for various reasons (Group 2). Reasons for failure to obtain intraoperative map included noninducibility (3), nonsustained VT (8), polymorphic VT (4), VF (3), and incessant VT with hemodynamic collapse and cardiac arrest (1). The two groups did not differ with respect to age, location of myocardial infarction, or preoperative left ventricular ejection fraction. The operative procedures were similarin the twogroups with respect to aortic cross clamp time, cardiopulmonary bypass time, number of cryoablation lesions, concomitant revascularization, aneurysmectomy, and ICD implantation. Encircling endocardial cryoablation was performed in 32 patients and one patient underwent partial right ventricular free wall disconnection (RV infarct). Thirteen patients underwent concomitant coronary artery bypass grafting (5 in Group 1 and 8 in group 2). One patient had prophylactic ICD patches (Group 1). The mean LVEF pre- and postoperatively were similar in the two groups. One patient died postoperatively. Three patients had recurrent VT perioperatively: one patient was treated with amiodarone and two had an ICD implantation. During long-term follow-up (mean 5 years), survival was similar in the two groups. Conclusions: Encircling endocardial cryoablation for ventricular tachycardia is a useful surgical technique in selected patients. Preoperative cardiac mapping is useful in defining a surgical plan, but intraoperative mapping is not crucial to the success of encircling endocardial cryoablation.     

Sustained polymorphic arrhythmias induced by programmed ventricular stimulation have prognostic value in patients receiving defibrillators

BACKGROUND: Patients with ischemic cardiomyopathy (ICM) who have monomorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation (PVS) are at increased risk of sudden cardiac death (SCD). Among a primary prevention population, the prognostic significance of induced polymorphic ventricular arrhythmias is unknown. METHODS: A total of 105 consecutive patients who received an implantable cardioverter-defibrillator (ICD) for primary prevention of SCD in the setting of ICM and non-sustained VT were retrospectively evaluated. Seventy-five patients (group I) had induction of monomorphic VT and 30 patients (group II) had a sustained ventricular arrhythmia other than monomorphic VT (ventricular flutter, ventricular fibrillation, and polymorphic VT) induced during PVS. RESULTS: Baseline characteristics were similar between group I and group II except for ejection fraction (25% vs. 31%, P = 0.0001) and QRS duration (123 milliseconds vs. 109 milliseconds, P = 0.04). Sixteen of 75 (21.3%) patients in group I and 6 of 30 (20%) patients in group II received appropriate ICD therapy (P = 0.88). Survival free from ICD therapy was similar between groups (P = 0.54). There was a trend toward increased all-cause mortality among patients in group I by Kaplan-Meier analysis (P = 0.08). However, when adjusted for age, EF, and QRS duration mortality was similar (P = 0.45). CONCLUSIONS: There is no difference in rates of appropriate ICD discharge or mortality between patients dichotomized by type of rhythm induced during PVS. These results suggest that patients in this population who have inducible VF or sustained polymorphic VT have similar rates of subsequent clinical ventricular tachyarrhythmias as those with inducible monomorphic VT.     

Retrospective Analysis of Patients Undergoing One- or Two-Stage Strategies for Myocardial Revascularization and Implantable Cardioverter Defibrillator Implantation

Internal defibrillation leads were placed at time of coronary revascularization in 79 patients. In 34, an implantable cardioverter defibrillator (ICD) was placed simultaneously (group I). A two-stage strategy (selective implantation of the ICD in patients with postoperative spontaneous or inducible ventricular tachycardia [VT]) was followed in 45 patients (group II). Group I patients had failed more antiarrhythmic drug trials (2.9 +/- 1.6 vs 1.5 +/- 1.6; P = 0.02), including amiodarone (62% vs 20%; P less than 0.001). There were four operative deaths in each group. Postoperatively, VT was present in 27 group II patients (60%), 25 of whom received an ICD (two refused device implantation). Patients with postoperative VT had a lower left ventricular ejection fraction than those without VT (33 +/- 9 vs 47 +/- 16; P = 0.01). Actuarial survival at 1, 2, and 3 years was 88 +/- 6, 88 +/- 7, and 88 +/- 10 in group I; and 83 +/- 6, 76 +/- 7, and 76 +/- 11 in group II (NS). No patient without an ICD (based on the postoperative electrophysiological study [EPS]) died suddenly. Five patients (6%) had ICD system infection. Sudden death was largely prevented by either strategy, but relatively high rates of operative mortality and ICD system infection were observed. Prospective studies should identify patients more likely to benefit from one or another strategy.     

Late Retesting of System Performance in ICD Patients Without Spontaneous Shocks

One hundred five implantable cardioverter defibrillator (ICD) patients (71 ± 9 years of age, 83% men) without spontaneous ICD discharges for ≥ 12 months were tested to assess high voltage (HV) circuit integrity and the system's ability to recognize and terminate ventricular fibrillation (VF). Indications for ICD implantation were sustained ventricular tachycardia (VT) (35%), cardiac arrest (27%), and inducible VT (38%). Eighty-two percent of the patients had coronary artery disease (CAD), and the mean left ventricular ejection fraction (LVEF) was 36%± 13%. Results: One hundred patients had inducible VF and five did not. Testing led to ICD reprogramming in 50 (49%) patients. Two (1.9%) patients required ICD replacement: (1) a 45-year-old patient with a Ventritex 110 ICD implanted for 13 months interfaced with a CPI 0062 lead implanted for 46 months could not be defibrillated internally (impedance nonmeasurable); (2) an 82-year-old patient with a 23-month-old Medtronic 7219 ICD interfaced with 6936 and 6933 leads whose defibrillation threshold (DFT) had doubled since implantation (24 J from 12 J). Lead fractures were found in both cases (proximal coil of the 0062, and subcutaneously in the 6933). Based on DFT determinations, the first shock output was programmed lower in 37 patients and higher in 10 patients. Shock pulse width was changed in one patient and the ventricular refractory period in another. No programming changes were made in 54 (51%) patients. Conclusions: (1) Late testing of HV circuit integrity in ICD patients without an ICD shock in ≥ 12 months identifies previously unsuspected HV lead fractures; (2) chronic DFT testing resulted in HV output reprogramming in one-half of the patients.     

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.     

Hybrid Therapies for Ventricular Arrhythmias

In recent years several trials demonstrated the efficacy of implantable cardioverter-defibrillation (ICD) therapy in reducing cardiac and total mortality in patients affected by rapid ventricular tachycardia (VT) and/or ventricular fibrillation. Nevertheless, ICD do not prevent arrhythmia recurrences, thus being a palliative and not a curative treatment modality. The tolerance to ICD therapy varies greatly, and within individuals, this leading to a nonuniform acceptance of this form of therapy. The very frequent occurrence of VT, defined as an arrhythmic storm, may be a life threatening condition. The majority of ICD patients is under antiarrhythmic drug therapy, to reduce episodes of VT or to make antitachycardia pacing more effective by slowing the tachycardia rate. Drug therapy, however, may cause additional problems, and does not represent the optimal solution. The prevention of VT and/or ventricular fibrillation episodes and excessive ICD therapy, remains a worthwhile goal. Radiofrequency catheter ablation (RFCA) is a curative approach, and can be expected to reduce the frequency of recurrent VT episodes in the majority of patients. The combination of these treatment modalities (ICD and RFCA) is often described as hybrid therapy, implying that the two treatments act providing some form of synergism. In experienced centers, RFCA is now performed, regardless of whether the VT rate is rapid and/or is hemodynamically unstable. Newer mapping and ablation techniques are now available, enhancing the acute success rate of the procedure. In this review the most recent application of VT catheter ablation and the use of advanced mapping and ablation techniques will be discussed.     

The Impact of Antitachycardia Pacing with Defibrillation

Chronic recurrent ventricular tachycardia (VT) can be reproducibly terminated by programmed endocardiaJ right ventricular stimulation. However, antitachycardia pacing can be associated with possible acceleration of VT, while frequent episodes of VT and patient discomfort can limit treatment by an implantable cardioverter defibrillator (ICD). The combined use of antitachycardia pacing and the AICD (automatic implantable cardioverier defibrillator) was evaluated in 6 out of 51 patients (age 57 ± 11 years) in whom the AICD had been implanted because of recurrent VT. In each instance VT could be terminated by temporary overdrive pacing. The interactive mode of VT termination by a pacemaker (Tachylog) as well as by the AICD was assessed after implantation. In the automatic mode, the Tachylog functioned as a bipolar, ventricular inhibited (VVI) device with antitachycardia burst stimulation capability, allowing two to five stimuli at intervals of 260–300 ms and one or two interventions. During follow-up of 47 ± 24 months, the Tachylog terminated VT reliably 50–505 times per patient. When burst stimulation accelerated VT, termination was achieved by AICD discharge. Thus, drug resistant VT can be terminated by antitachycardia pacing to avoid patient discomfort. In the event of tachycardia acceleration, VT was terminated by the AICD. A universal pacemaker-defibrillafor should combine antibradycardia and antitachycardia pacing with back-up cardioversion defibrillation.     

Are Electrophysiological Studies Needed Prior to Defibrillator Implantation?

At present, patients with documented sustained VT or resuscitated cardiac arrest (CA) are treated with ICDs. The aim of this study was to retrospectively evaluate if a routine electrophysiological study should be recommended prior to ICD implantation. In 462 patients referred for ICD implantation because of supposedly documented VT (n = 223) or CA (n = 239), electrophysiological study was routinely performed. In 48% of the patients with CA, sustained VT or VF was inducible. Electrophysiological study suggested conduction abnormalities (n = 11) or supraventricular tachyarrhythmias (n = 3) in conjunction with severely impaired left ventricular function to have been the most likely cause of CA in 14 (5.9%) of 239 patients. Likewise, sustained VT was only inducible in 48% of patients with supposedly documented VT. Of these inducible VTs, nine were diagnosed as right ventricular outflow tract tachycardia or as bundle branch reentry tachycardia. Supraventricular tachyarrhythmias judged to represent the clinical event were the only inducible arrhythmia in 35 (16%) patients (AV nodal reentrant tachycardia [n = 7], AV reentry tachycardia [n = 4], atrial flutter [n = 19], and atrial tachycardia [n = 5]). Based on findings from the electrophysiological study, ICD implantation was withheld in 14 (5.9%) of 239 patients with CA and in 44 (19.7%) of 223 patients with supposedly documented VT. During electrophysiological study, VT or VF was only reproducible in about 50% of patients with supposedly documented VT or CA. Electrophysiological study revealed other, potentially curable causes for CA or supposedly documented VT in 12.6% (58/462) of all patients, indicating that ICD implantation can potentially be avoided or at least postponed in some of these patients. Based on these retrospective data, routine electrophysiological study prior to ICD implantation seems to be advisable.     

Long-Term Efficacy of an Antitachycardia Pacemaker and Implantable Defibrillator Combination

Antitachycardia pacemakers and implantable cardioverter defibrillators (ICD) were implanted in 14 patients to control recurrent hemodynamically stable ventricular tachycardia (VT), All patients underwent extensive preimplant testing in the elecrrophysiology laboratory documenting that in each patient at least 50 episodes of VT could be reliably terminated by an external model of the antitachycardia pacemaker. The burst scanning mode of anfitachycardia pacing was used in all patients. ICDs were implanted solely as a back up should acceleration of VT occur, and all had high nonprogrammable rate cutoffs (mean 191 ± 12 beats/min). During a mean follow-up of 25 ± 6 months, 6,029 episodes of VT were treated in the 14 patients. Only 103 ICD discharges were required (approximately one discharge per 60 episodes of VT). Ten of the 14 patients received discharges from their ICDs. No deaths have occurred. All devices remain active and in the automatic mode. Thus, an antitachycardia pacemaker and ICD combination can safely and effectively terminate VT in highly selected patients who are subjected to extensive preimplant testing. In such patients, the vast majority of episodes of VT can be terminated with antitachycardia pacing, and only rarely is a discharge required from the ICD.     

The Effect of Coronary Bypass Graft Surgery for the Prevention of Sudden Cardiac Death: Recurrent Episodes After ICD Implantation and Review of Literature

Sudden cardiac death (SCD) accounts for at least 50% of the mortality of patients with ischemic heart failure. Ventricular arrhythmias are responsible for most cases of sudden cardiac death. There is some evidence that coronary artery bypass graft (CABG) surgery may reduce the incidence of recurrent episodes of SCD by prevention of myocardial ischemia. To test the hypothesis that CABG surgery is effective in the prevention of SCD, we compared the recordings of implantable cardioverter defibrillators (ICD) in patients who underwent ICD implantation alone (n = 64) or ICD implantation and concomitant CABG surgery respectively (n = 11). All patients had experienced out of hospital cardiac arrest. ICD recordings were obtained every 3 months and the number of recurrent episodes of ventricular tachycardia (VT) for each time period was noted. Three months foilowing ICD implantation patients in the surgically treated group had an average of one episode of VT per patient as compared to 2.7 episodes in the nonsurgical group. This difference was observed during the following months as well. However, at nlo time (up to 18 months of follow-up) this difference reached statistical significance. There were no deaths in the surgically treated group. Although we could not demonstrate a statistical significant difference between the two groups, there was a tendency in the surgically treated group to have less episodes of recurrent VT than in the medically treated group. We, therefore, conclude that survivors of SCD presenting with multivessel coronary artery disease (CAD) should undergo coronary artery bypass grafting to prevent myocardial ischemia as the triggering event for lethal ventricular arrhythmias.     

Inadequacy of Qualitative Implantable Cardioverter Defibrillator Electrogram Analysis to Distinguish Supraventricular from Ventricular Tachycardia Due to Electrogram Changes During Normally Conducted Complexes

Stored electrograms (EGMs) recorded from ICD leads are used to evaluate the appropriateness of ICD therapies. Stored EGMs different from sinus have been interpreted as ventricular in origin. We present a patient with a n ICD for VT wh o received multiple shocks for a tachycardia with a stored EGM different than sinus, suggesting VT. An electrophysiological study demonstrated EGMs different than sinus during atrial pacing and induced supraventricular arrhythmias. This case points out the limitations of stored EGMs and suggests complete electrophysiological study with analysis of ECMs during induced arrhythmias should be performed prior to discharge.