Worldwide clinical experience with a new dual-chamber implantable cardioverter defibrillator system

INTRODUCTION: Management of atrial tachyarrhythmias represents a significant challenge in patients with implantable cardioverter defibrillators (ICDs). Drug therapy of these arrhythmias is limited by moderate efficacy, ventricular proarrhythmia, and drug-device interactions. This study tested the safety and efficacy of a new dual-chamber ICD to detect and treat atrial as well as ventricular tachyarrhythmias. METHODS AND RESULTS: A dual-chamber ICD (Medtronic 7250 Jewel AF) was implanted in 293 of 303 patients at 49 centers in Europe, Canada, and North America. Specific data were collected at implant and during a mean follow-up period of 7.9+/-4.7 months. There were no clinically evident failures to detect and treat ventricular arrhythmias. In patients with at least one of the dual-chamber detection criteria activated, 1,056 of 1,192 episodes of ventricular tachycardia or fibrillation detected were judged to be appropriate (89% positive predictive accuracy). Therapy efficacy was 100% in the ventricular fibrillation zone and 98% in the ventricular tachycardia zone. Positive predictive accuracy for detection of atrial episodes was 95% (1,052/1,107). For episodes classified as atrial tachycardia by the device, the efficacy of atrial antitachycardia pacing and high-frequency (50-Hz) burst pacing was 55% and 17%, respectively. High-frequency burst pacing terminated 16.8% of episodes classified as atrial fibrillation, and atrial defibrillation had an estimated efficacy of 76%. The actuarial estimates of 6-month complication-free survival and total survival were 88% and 94%, respectively. CONCLUSION: This novel dual-chamber ICD is capable of safely and effectively discriminating atrial from ventricular tachyarrhythmias and of treating atrial tachyarrhythmias without compromising detection and treatment of ventricular tachyarrhythmias.     

Circadian variation of malignant ventricular arrhythmias in patients with ischemic and nonischemic heart disease after cardioverter defibrillator implantation. European 7219 Jewel Investigators.

OBJECTIVES: The purpose of this study was to examine the circadian variation of ventricular arrhythmias detected by an implantable cardioverter defibrillator in patients with and without ischemic heart disease. BACKGROUND: Previous studies have shown a circadian variation of ventricular arrhythmias, sudden death and myocardial infarction with a peak occurrence in the morning hours. The circadian pattern, which is similar for both arrhythmic and ischemic events, suggests that ischemia may play a critical role in the genesis of ventricular arrhythmias and sudden death. We hypothesized that, if ischemia plays an important role in the triggering of ventricular arrhythmias, the circadian pattern should be different in patients with ischemic heart disease compared with patients with nonischemic heart disease. METHODS: The circadian variation of ventricular arrhythmias recorded by an implantable cardioverter defibrillator was studied in 310 patients during a mean follow-up of 181 +/- 163 days. Two hundred four patients had a history of ischemic heart disease and 106 patients had nonischemic heart disease. The times of the episodes of ventricular arrhythmias were retrieved from the data log of each device during follow-up, and the circadian pattern was compared between the two groups. RESULTS: During follow-up, 1,061 episodes of ventricular arrhythmias were recorded by the device in the 310 patients. Six hundred eighty-two episodes occurred in the group of patients with ischemic heart disease and 379 occurred in the nonischemic heart disease group. The circadian variation of the episodes showed a typical pattern with a morning and afternoon peak in both groups of patients with ischemic and nonischemic heart disease, but there was no significant difference between the two groups. CONCLUSIONS: The circadian rhythm of ventricular arrhythmias in patients with ischemic heart disease is similar to patients with nonischemic heart disease, suggesting that the trigger mechanisms of the initiation of ventricular tachyarrhythmias may be similar, irrespective of the underlying heart disease.     

Clinical Experience with a Dual-Chamber Implantable Cardioverter Defibrillator to Treat Atrial Tachyarrhythmias

INTRODUCTION: This study evaluated the safety and efficacy of a new dual-chamber implantable cardioverter defibrillator (ICD) to detect and treat atrial tachyarrhythmias in patients with drug-refractory atrial fibrillation (AF) and no indication for a ventricular ICD. METHODS AND RESULTS: A dual-chamber ICD (Medtronic 7250 Jewel AF) was implanted in 144 of 146 patients. The device discriminates atrial tachycardia from AF based on cycle length and regularity, and uses atrial overdrive pacing as well as shocks to terminate tachyarrhythmia episodes. Patients were followed for an average of 12.6+/-6.2 months. Use of antiarrhythmic drugs was 63% at baseline and did not change over time. Kaplan-Meier estimates of 12-month complication-free survival, device therapy survival, and patient survival were 85%, 91%, and 98%, respectively. Positive predictive accuracy of spontaneous atrial tachyarrhythmia detection was 99%, while atrial overdrive pacing and shocks terminated 40% and 87% of treated episodes, respectively. Median duration of successfully treated episodes was 8.9 minutes versus 144 minutes for the therapy failures. There was no reduction in the use of patient-activated shock therapy over time; at the 12-month follow-up evaluation, 94% of patients were in sinus rhythm. Ventricular tachyarrhythmias (67 episodes) were detected and appropriately treated in 7.6% of patients. CONCLUSION: This dual-chamber ICD appears to be safe and well tolerated in patients with drug-refractory symptomatic atrial tachyarrhythmias. The device, used in combination with drugs, effectively treats atrial tachyarrhythmias with pacing and/or shock therapies and decreases the median episode duration. In addition, the device protects from ventricular tachyarrhythmias in patients with AF and structural heart disease.     

Low recurrence of syncope in patients with inducible sustained ventricular tachyarrhythmias treated with an implantable cardioverter-defibrillator.

AIMS: To determine the effectiveness of the implantable cardioverter defibrillator (ICD) in preventing recurrence of syncope in patients with structural heart disease, previously unexplained syncope and inducible ventricular arrhythmias. METHODS: Thirty-eight patients with syncope, structural heart disease and inducible arrhythmias had an ICD implanted. All ICDs delivered antitachycardia pacing and shocks of adjusted energy. Detection and therapy were programmed according to uniform criteria. RESULTS: The mean age of the patients was 63+/-11 years and most of them were male (36/38). After a mean follow-up of 28+/-15 (4-61) months, six patients died and one underwent heart transplantation. Syncope recurred in three patients, but in none of them was it caused by an arrhythmic event. In 18 patients, 113 episodes of ventricular tachycardia/ventricular fibrillation were detected and appropriately treated by the ICD. The mean time from implant until first appropriate therapy was 18+/-14 months. The actuarial probability of receiving appropriate therapy was 20% and 42% at 12 and 24 months, respectively. CONCLUSIONS: In patients with unexplained syncope, structural heart disease and inducible arrhythmias, ICD prevents syncope associated with arrhythmic events. Frequent effective use of antitachycardia pacing and shocks of adjusted energy seem essential to this aim.     

Risk Stratification and Prevention of Sudden Death in Patients with Heart Failure

For almost the past decade, recommendations for the use of implantable cardioverter defibrillators (ICDs) for primary prevention of sudden cardiac death have been based upon the left ventricular ejection fraction (LVEF). Current guidelines recommend an ICD for heart failure patients with LVEF ≤35% and NYHA functional class of II or III; however, because the majority of heart failure patients who qualify for ICD implantation based on these criteria will never have an event requiring ICD therapy over several years of follow-up, additional methods of risk stratification for sudden death are clearly needed. Additionally, most of the nearly 300,000 cardiac arrests that occur each year occur in patients without heart failure or significant left ventricular dysfunction. To improve the identification of patients at risk for sudden death, several criteria other than ejection fraction have been proposed and studied. Markers of autonomic tone, including heart rate turbulence and QT dynamicity, have shown some ability to predict total mortality but not arrhythmic events. Microvolt T-wave alternans testing was initially thought to be highly predictive of life-threatening arrhythmias, but prospective large sub-studies of the MADIT II and SCD-HeFT trials have failed to show a predictive value for T-wave alternans testing. Newer markers for risk are based upon the detection of myocardial fibrosis, which forms the substrate for re-entrant and malignant ventricular tachyarrhythmias. Markers of collagen turnover or quantification of myocardial scar by MRI may hold the best promise for identifying patients at highest risk for sudden cardiac death and may also identify patients at high risk but with an ejection fraction above 35%, who are not currently recommended for ICD implantation.     

Association between atrial fibrillation and appropriate implantable cardioverter defibrillator therapy: results from a prospective study

INTRODUCTION: Atrial fibrillation (AF) is associated with significant morbidity and mortality that may be related to hemodynamic impairment, thromboembolic events, or enhanced electrical instability of the ventricular myocardium. There is, however, a lack of data concerning the association of AF and ventricular tachyarrhythmias. METHODS AND RESULTS: Consecutive patients with indication for an implantable cardioverter defibrillator (ICD) were classified for the presence or absence of persistent AF at the time of device implantation. Incidence of device therapy, stored electrograms, and clinical events during follow-up were evaluated prospectively. Two hundred fifty patients were included. During follow-up (20+/-14 months), patients in AF experienced appropriate device therapy for recurrent ventricular arrhythmias more frequently compared with patients in sinus rhythm (SR) (63% vs 38%, P = 0.01). On multivariate analysis, AF was an independent predictor of appropriate ICD therapy (relative risk 1.8; 95% confidence interval [CI] 1.2 to 2.9) and inappropriate device therapy (relative risk 2.3; 95% CI 1.2 to 4.5). Predefined clinical events (cluster endpoint: death, syncope, and hospitalizations) were observed more frequently in AF than in SR patients (55% vs 31%, P = 0.01). Analysis of device-stored electrograms revealed a higher incidence of short-long-short cycles preceding ventricular arrhythmias in AF compared with SR patients (50% vs 16%, P = 0.002). Baseline heart rate preceding ventricular arrhythmias did not differ between the two groups. CONCLUSION: AF is an independent predictor of recurrent ventricular arrhythmias in ICD recipients. The underlying electrophysiologic mechanism seems to be irregular rather than rapid ventricular activation, with a high incidence of short-long-short sequences preceding ventricular tachyarrhythmias in AF patients.     

植入型心律转复除颤器不恰当放电的临床分析

目的 分析植入型心律转复除颤器(ICD)不恰当放电发生情况及常见原因.方法 2001年11月至2007年10月植入ICD并长期随访的43例患者.通过定期随访查询ICD中存储的事件信息,根据腔内电图判断事件是否为不恰当放电.结果 43例患者中有7例发生了96次不恰当放电.6 例患者是室上性心动过速引起,1 例是干扰引起.5 例患者第1次不恰当放电发生在植入ICD后1年内.植入ICD前有心房颤动(房颤)病史是发生不恰当放电的独立预测因子.结论 植入ICD前有房颤病史的患者较易出现不恰当放电,临床应多予以重视.     

Repolarization variability in the risk stratification of MADIT II patients.

AIMS: QT variability has been reported to be associated with ventricular arrhythmias and sudden cardiac death. There is limited data regarding variability in T-wave morphology and its prognostic value. In this study, we present a novel approach for the measurement of T-wave variability (TWV) reflecting changes in T-wave morphology, and we investigate the prognostic significance of Holter-derived TWV in patients with and without ventricular arrhythmias requiring appropriate implantable cardioverter defibrillator (ICD) therapy from the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II). Methods Study population consisted of 275 ICD patients from MADIT II after excluding patients with intraventricular conduction abnormalities or atrial fibrillation. TWV was measured based on amplitude variance of T-wave amplitude. Results During 2-year follow-up, 58 (21%) patients had appropriate ICD therapy for ventricular tachycardia or fibrillation. Patients with appropriate ICD therapy had higher levels of TWV measures than those without arrhythmic events. After adjustment for heart rate, ejection fraction, and significant clinical predictors of arrhythmic events, a Cox proportional-hazards regression model revealed that dichotomized TWV values were predictive for ventricular tachyarrhythmias requiring appropriate ICD therapy (hazard ratio, 2.0; 95% CI; 1.2-3.5; P=0.01). On the basis of the comprehensive testing, TWV value >59 microV was found predictive for arrhythmic events in MADIT II population. CONCLUSION: Our newly designed method for the assessment of repolarization variability in ambulatory Holter recordings detected transient variability of T-wave morphology, which was predictive for ventricular tachyarrhythmias in the MADIT II population.     

A perspective on ventricular arrhythmias: patient assessment for therapy and outcome

Clinical management of patients with ventricular arrhythmias continues to evolve. It is generally accepted that patients with sustained ventricular tachyarrhythmias (ventricular tachycardia [VT] or fibrillation) require treatment. It is also generally accepted that patients with frequent or complex ventricular ectopy or nonsustained VT, in the absence of underlying heart disease, do not require treatment unless relief of symptoms is warranted. Whether patients with frequent or complex ventricular ectopy or nonsustained VT require treatment in the presence of underlying organic heart disease remains uncertain. The concern is that these ventricular arrhythmias may be a precursor for sustained, potentially life-threatening ventricular tachyarrhythmias. Available data suggest that patients with underlying heart disease, particularly coronary artery disease and a previous myocardial infarction, who manifest frequent or complex ventricular ectopy or nonsustained VT are at increased risk for sudden cardiac death. However, no studies have shown that treatment of these arrhythmias will affect outcome. Data are accumulating to suggest that use of the principles of risk stratification permits identification of patients at very high risk for developing sustained ventricular tachyarrhythmias. Carefully designed clinical trials are required before one can provide firm guidelines for the management of these patients. Nevertheless, when several risk factors for sudden cardiac death (e.g., abnormal ejection fraction, a late potential on a signal-averaged electrocardiogram, and frequent or complex ventricular ectopy or nonsustained VT) are present in a patient, especially after a recent myocardial infarction, invasive electrophysiologic testing may help identify those who need treatment (sustained VT is inducible) and those who do not (no sustained VT is inducible).     

Inflammation of the myocardium as an arrhythmia trigger

In patients with acute or chronic myocarditis, arrhythmias are a common and often the only clinical symptom in the natural course of the disease. The potentially malignant tachy- and bradyarrhythmias are of particular significance in the differential diagnosis of sudden cardiac death in myocarditis. Factors responsible for the increased incidence of cardiac arrhythmias are structural changes, parameters of ventricular dynamics and vascular changes. On the one hand, inflammatory processes in the cardiac myocytes and interstitium can lead directly to fluctuations in membrane potential. Fibrosis and scarring of the myocardial tissue and secondary hypertrophy and atrophy of the myocytes favor the development of ectopic pacemakers, late potentials and reentry as a result of inhomogeneous stimulus conduction. Furthermore, parameters of ventricular dynamics such as increased wall tension, increased myocardial oxygen consumption and diminished coronary reserve in the case of disturbed systolic or diastolic left ventricular function also contribute to the increased incidence of arrhythmias. Lastly, vascular factors can further increase the arrhythmogenicity of the inflamed myocardium through the disturbance of micro- and macrovascular perfusion and the resulting myocardial ischemia. Non-invasive rhythmological evaluation by 24 h Holter ECG, measurement of ventricular late potentials and heart rate variability can be used for orienting risk stratification of the at-risk patient with myocarditis. Programmed atrial and ventricular electrophysiological stimulation also has a relatively high predictive value for spontaneous ventricular tachyarrhythmias. It should be emphasized that, at the present time, optimal electrophysiological parameters with a high predictive value do not exist. In a selected patient population, immunosuppressive therapy in addition to conventional antiarrhythmic therapy can lead to the reduction or complete suppression of spontaneous and inducible arrhythmias. Nevertheless, in the interim, further precautionary antiarrhythmic measures such as serial antiarrhythmic treatment, VT ablation and ACID implantation are necessary in patients with malignant cardiac arrhythmias. Right ventricular myocardial biopsy for demonstration or exclusion of myocarditis is an important additional examination which can improve the differential diagnosis and treatment of patients with cardiac arrhythmias of unclear etiology.     

T-wave alternans in microwave frequency as a new indicator of disordered ventricular repolarization: pathophysiology, methodology, clinical results

Primary prevention of sudden cardiac death is hampered by the inability to accurately identify high risk patients. Various noninvasive methods such as determination of left ventricular function or heart rate variability as well as invasive electrophysiologic testing are currently used for risk stratification. Noninvasive measurement of microvolt T wave alternans (TWA) is a promising new method to assess repolarization abnormalities; in experimental studies, TWA was associated with an increased incidence of ventricular tachyarrhythmias. Since the occurrence of TWA is heart rate-dependent, it is measured either during atrial pacing or during exercise stress testing. The first clinical validation of the method was performed in patients undergoing invasive EP testing to assess prediction of inducibility of ventricular tachyarrhythmias. A first prospective validation of the noninvasive method was performed in patients surviving out-of-hospital cardiac arrest fitted with an ICD. Further studies have shown a good concordance between invasive and noninvasive TWA determination. The occurrence of TWA in this population was of predictive value with respect to arrhythmia recurrence. Recently published data confirm the value of TWA assessment with respect to identification of patients with congestive heart failure at high risk of malignant ventricular tachyarrhythmias. The use of this method in post myocardial infarction risk stratification is currently under prospective evaluation.     

Relation between heart rate variability and spontaneous and induced ventricular arrhythmias in patients with coronary artery disease

Objectives. The aim of this study was to determine the relation between autonomic control of heart rate and the spontaneous occurrence and inducibility of ventricular arrhythmias in patients with coronary artery disease.Background. Low heart rate variability increases the risk of arrhythmic events. It is not known whether impaired autonomic heart rate control reflects alterations in functional factors that contribute to the initiation of spontaneous arrhythmias or whether it is the consequence of an anatomic substrate for reentrant tachyarrhythmias.Methods. Fifty-four patients with coronary artery disease with a history of sustained ventricular tachycardia (n = 25) or cardiac arrest (n = 29) were studied by 24-h ambulatory electrocardiographic recording and by programmed electrical stimulation. Heart rate variability was compared among the patients with and without spontaneous ventricular arrhythmias and with and without inducibility of sustained ventricular tachyarrhythmias.Results. Eight patients had a total of 21 episodes of sustained ventricular tachycardia on Holter recordings. Standard deviation of RR intervals and low frequency and very low frequency components of heart rate variability were significantly blunted in patients with sustained ventricular tachycardias compared with those without repetitive ventricular ectopic activity (p < 0.05, p < 0.01 and p < 0.05, respectively). However, no significant alterations were observed in heart rate variability before the onset of 21 episodes of sustained ventricular tachycardia. Heart rate variability did not differ between the patients with or without nonsustained episodes of ventricular tachycardia. In patients with frequent ventricular ectopic activity, low frequency and very low frequency power components were significantly blunted compared with those with infrequent ventricular ectopic activity (p < 0.01 and p < 0.001, respectively). Heart rate variability did not differ significantly between the patients with and without inducible sustained ventricular tachyarrhythmias.Conclusions. Impaired very low and low frequency oscillation of heart rate reflects susceptibility to the spontaneous occurrence of ventricular arrhythmias but may not reflect the instantaneous triggers for life-threatening arrhythmias or a specific marker of the arrhythmic substrate for ventricular tachyarrhythmias.     

Troponin-I elevation in a young man with arrhythmogenic right ventricular dysplasia/cardiomyopathy

Ventricular arrhythmias occur frequently in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) as well as those with ischemic heart disease. We present the case of a 29-year-old man with ARVD/C and multiple episodes of symptomatic ventricular tachycardia terminated by implantable cardioverter defibrillator (ICD) discharges. Phasic elevation of troponin-I prompted repeated coronary angiograms, all of which were normal. The patient was successfully treated with radiofrequency ablation. This case illustrates that ARVD/C may result in elevated cardiac enzymes in the absence of coronary artery disease.     

Diagnosis and therapy of atrial tachyarrhythmias in the dual chamber implantable cardioverter defibrillator

INTRODUCTION: Devices capable of monitoring and treating atrial tachyarrhythmias provide information about the natural history of the arrhythmias and potentially can influence their natural course by electrical therapy early after onset. METHODS AND RESULTS: Types of atrial arrhythmias and efficacy of device therapies were evaluated in 30 patients implanted with the Medtronic model 7250 Jewel AF implantable cardioverter defibrillator (ICD). All patients had structural heart disease and documented sustained ventricular and atrial arrhythmias (27 with atrial fibrillation [AF]) before implant. Twenty patients were taking amiodarone, and three were taking sotalol. During 20+/-10 months of follow-up, 600 atrial arrhythmia recurrences were documented in 50% of patients. AF was diagnosed in 19%, fast polymorphic atrial tachycardia (AT) in 20%, fast monomorphic AT in 57%, and slow AT in 4% of episodes. The two adaptive pacing therapies, burst and ramp, together with the 50-Hz burst, were successful in 57% of detected atrial arrhythmias. Burst and ramp were responsible for 49% and 50-Hz burst for 51% of successfully treated arrhythmias; 33% of the episodes terminated spontaneously. No ventricular proarrhythmia was observed due to atrial pacing therapies. In 30% of episodes, dual chamber pacing was required due to post termination bradycardia. Atrial arrhythmia recurrences in patients with dilated cardiomyopathy were not amenable to pacing therapies. Several aspects of atrial arrhythmia diagnosis, therapy, and documentation that are specific for functioning of the Jewel AF are discussed. CONCLUSION: Atrial arrhythmias in ICD patients with diseased hearts who are taking Class III antiarrhythmics frequently had longer cycle lengths than AF. Half of these arrhythmias could be terminated with pacing therapies; one third terminated spontaneously.     

Microvolt level T wave alternans: a new marker for noninvasive risk stratification

Prospective identification of patients with structural heart disease who could profit from prophylactic ICD therapy is hampered by the low predictive power of the currently available risk stratification parameters. Microvolt T wave alternans measured noninvasively is a new promising parameter to assess impaired ventricular repolarization which has been associated with an increased incidence of ventricular tachyarrhythmias. T wave alternans is rate-dependent; to induce alternans, heart rate may be increased by atrial stimulation during invasive EP testing or noninvasively by exercise stress testing. The first clinical validation with respect to prediction of inducibility of ventricular tachyarrhythmias and of arrhythmic events during follow-up in patients undergoing invasive EP testing was reported in 1994. Subsequently, a good concordance between the results of invasive and noninvasive assessment of T wave alternans was demonstrated by our group. The first prospective evaluation of the noninvasive alternans measurement using submaximal exercise testing was performed in patients surviving prehospital ventricular fibrillation or sustained ventricular tachycardia referred to our institution. The occurrence of T wave alternans in this patient population was predictive of future tachyarrhythmic events with subsequent appropriate ICD therapy. The results of the currently performed prospective trials in various patient populations will help to establish the utility of T wave alternans assessment as a risk stratifier in clinical practice.     

Identification of patients at increased risk for potentially malignant arrhythmias

Summary This review discusses the substrate and triggers of ventricular tachyarrhythmias or fibrillation and highlights the concepts that underlie risk stratification. Topics covered include the risks posed by arrhythmias in patients with: a) postinfarction, b) cardiomyopathy c) mitral valve prolapse, d) Wolff-Parkinson-White syndrome, and e) the long QT syndrome. Appropriate identification of patients at high risk for malignant ventricular arrhythmias requires subclassification by disease entity, historic information about syncopal episodes, noninvasive testing, and invasive electrophysiologic studies in selected patients.     

Ventricular tachyarrhythmias,myocardial ischemia,and sudden cardiac death in patients with hypertensive heart disease

Hypertensive heart disease is increasingly considered to be a strong and independent risk factor for sudden cardiac death. Ventricular tachyarrhythmias in these patients are common and mainly the result of electrophysiologic abnormalities and increased electrical vulnerability of the hypertrophic myocardium. However, proarrhythmia in the hypertrophic heart often is facilitated and aggravated by electrolyte disturbances, the sympathoadrenergic tone, transient blood pressure crisis, and especially by the occurrence of myocardial ischemia. Myocardial ischemia in the setting of hypertensive heart disease may result from stenotic lesions in large and/or small coronary artery vessels and, in the absence of both, will result from the altered cellular oxygen supply and consumption in the hypertrophic myocardium. Recent studies have shown that acute and transient myocardial ischemia are common in many hypertensives, often fail to be symptomatic, and that the dynamic interaction of left ventricular hypertrophy, transient myocardial ischemia, and ventricular tachyarrhythmias may provide a crucial link for the high incidence of sudden cardiac death in patients with hypertensive heart disease.     

Delayed and indirect effects of antiarrhythmic drugs in reducing sudden cardiac death

In the USA, two-thirds of sudden cardiac deaths (SCDs) are caused by sustained ventricular tachycardia and ventricular fibrillation. Implantable cardioverter defibrillator (ICD) therapy has been demonstrated to decrease mortality caused by these arrhythmias, when used both for primary and secondary prevention. However, ICD use is expensive, has proarrhythmic effects and does not prevent ventricular arrhythmias. Antiarrhythmic drugs (AADs) can be used for acute or chronic therapy to prevent ventricular arrhythmias and SCD. Most commonly, AADs are often used in patients with an ICD who have recurrent ICD shocks due to ventricular arrhythmias. Class I AADs are used in patients with a structurally normal heart and are contraindicated in patients with structural heart disease. β-blockers have been demonstrated to be beneficial in preventing mortality and malignant tachyarrhythmias in postmyocardial infarction and congestive heart failure patients, and in patients who have an ICD. Amiodarone has a neutral effect on mortality, while other class III drugs may increase mortality in certain subgroups of patients. Dronedarone, a new class III drug, may reduce mortality, but sufficient data are not available to allow for its use in the prevention of malignant tachyarrhythmias. Few drugs that are not classified as AADs can also prevent arrhythmias, via their beneficial effects on cardiovascular remodeling. These non-ADDs have delayed and indirect effects, which are mediated by the renin-angiotensin-aldosterone system and lipid metabolism - n-3 polyunsaturated fatty acids (fish oil), and statins, and can thus can reduce the likelihood of future malignant ventricular arrhythmias in patients with coronary artery disease or congestive heart failure. The role of chronic drug therapy alone for primary and secondary prevention of SCD is less than desirable because of proarrhythmic and adverse side effects. The non-ADDs are well tolerated and have no proarrhythmic actions, thus their benefit could outweigh risks, although currently there are no concrete data to suggest this.     

Postextrasystolic U Wave Augmentation, a New Marker of Increased Arrhythmic Risk in Patients Without the Long QT Syndrome

Objectives. We attempted to determine the correlation between the presence of postextrasystolic changes in the STU segment and a history of sustained ventricular arrhythmias.

Background. Postextrasystolic U wave augmentation (a marked increment in U wave amplitude after premature ventricular complexes [PVCs]) is an adverse prognostic sign in the “pause-dependent long QT syndrome.” However, the prevalence of postextrasystolic changes in patients without the long QT syndrome is unknown.

Methods. We compared the configuration of the STU segment of the postextrasystolic beat (the sinus beat after a PVC) with the STU configuration during sinus rhythm in three patient groups: 1) 41 patients with spontaneous ventricular tachycardia/fibrillation (VT/VF) (VT/VF group), 2) 63 patients with heart disease and high grade ventricular arrhythmias (control group), and 3) 29 patients with high grade ventricular arrhythmias but no heart disease (reference group).

Results. Postextrasystolic T wave changes did not correlate with a history of ventricular tachyarrhythmias. However, postextrasystolic U wave changes were more common among the patients with VT/VF than among control subjects (39% vs. 8.7%, p < 0.001). By logistic multiple regression analysis, a low left ventricular ejection fraction (p < 0.001) and postextrasystolic U wave changes (p < 0.005) were independent predictors of ventricular tachyarrhythmias.

Conclusions. Postextrasystolic T wave changes are common and lack predictive value. Postextrasystolic U wave changes may be a specific marker of a tendency to the development of spontaneous ventricular arrhythmias. Prospective studies should be performed to confirm this association.

(J Am Coll Cardiol 1996;28:1746–52)>     

First worldwide clinical experience with a new dual chamber implantable cardioverter defibrillator. Advantages and complications. The Ventak AV II DR investigators.

AIMS: The need for physiological pacing and for improving the ability to discriminate atrial from ventricular tachyarrhythmias has prompted the development of dual chamber implantable cardioverter/defibrillators (ICDs). METHODS: Fifty-two patients were implanted with a newly developed dual-chamber ICD providing rate-responsive physiological pacing (Ventak AV II DR). The device possesses two new arrhythmia detection algorithms ('atrial fibrillation rate threshold' and 'ventricular to atrial rate relationship') in addition to commonly used features such as 'onset' and 'stability'. During implantation, the atrial and ventricular lead impedances and pacing thresholds were determined together with the defibrillation threshold. Prior to discharge, attempts were made to induce both atrial and ventricular tachyarrhythmias in order to test those new detection criteria. All patients were followed for at least 3 months. RESULTS: The device was successfully implanted in all 52 patients. Placement of the atrial lead was successful in 50/52 patients (96%; P-wave 3.2 +/- 1.4 mV; impedance 576 +/- 123 omega; atrial pacing threshold 1.2 +/- 0.9 V). Prior to discharge, 32 episodes of atrial fibrillation (AF) alone, 38 episodes of AF with ventricular fibrillation and 10 episodes of AF with monomorphic ventricular tachycardia were induced in 33/50 patients (66%) and all were appropriately classified by the detection algorithm. During the 3 months follow-up, 12 patients (23%) had appropriate and successful therapies for ventricular arrhythmias, while four patients (8%) experienced inappropriate ICD therapies. Although all these episodes were detected correctly as supraventricular arrhythmias by the device, therapy was delivered because of incorrect or incomplete programming. In all cases reprogramming of the device resolved the problem. CONCLUSION: Implantation of dual chamber ICDs is feasible and appears to improve discrimination of supraventricular from ventricular tachyarrhythmias. In addition, patients with tachyarrhythmias and concomitant bradyarrhythmias may benefit from simultaneous physiological pacing. However, implantation and follow-up of such patients should be performed at experienced centres since both surgical handling and programming of these devices is more difficult and complex than conventional ICDs.