Identification and management of ventricular tachycardia

Recognising ventricular origin of a broad QRS tachycardia helps to appropriately identify and manage patients with ventricular tachycardia (VT) in the emergency. Relatively simple clinical and ECG clues help in reaching the correct diagnosis in the majority of patients. Management strategies vary with the clinical diagnosis and an implantable cardioverter defibrillator (ICD) is indicated for chronic prophylactic therapy in patients with coronary artery disease and serious ventricular arrhythmias, especially in those with ventricular dysfunction. The role of this device in patients with stable VT and ejection fractions > 0.35 deserves closer scrutiny. Radiofrequency ablation mostly plays an adjunctive role. Anti-arrhythmic drugs (amiodarone/sotalol and beta-blockers) are required to prevent frequent recurrences. A hybrid approach combining all these therapeutic modalities is often needed. Prognosis in patients with specific VT syndromes such as right ventricular outflow VT, left ventricular fascicular VT and left ventricular outflow VT is excellent with drugs. Radiofrequency ablation is curative in such syndromes.

Successful implantation of cardiac defibrillators without induction of ventricular fibrillation using upper limit of vulnerability testing

INTRODUCTION

Conventionally, the implantable cardioverter-defibrillator (ICD) is tested at implantation by measurement of defibrillation threshold (DFT), which involves repeated induction of ventricular fibrillation (VF). We report our data on successful ICD implantation without VF induction using a modified upper limit of vulnerability (ULV) testing method, compared to standard DFT testing.

METHODS

Fourteen patients underwent ICD implantation using a modified ULV testing method by delivering a 15 J shock during the vulnerable period on the peak of the T wave, and if VF was not induced 15 J shocks were repeated at -20 and -40 msec before the peak of T wave. Failure to induce VF, indicating a ULV <15 joules (J), suggested a DFT < or =20 J based on previous studies demonstrating a close correlation (+/-5 J) between ULV and DFT. If VF was induced, a 20 J rescue shock was delivered. ICD therapy was then programmed on the basis of ULV testing. All patients underwent pre-discharge DFT testing to confirm adequate DFT.

RESULTS

Using a modified ULV testing method, ICD implantation was completed without induction of VF in 8 patients and only a single episode of VF in 6 patients. The mean number of VF episodes (0.42 +/- 0.5) induced with ULV testing was significantly lower (p <.001) than the number induced during DFT testing (3.9 +/- 0.8). Pre-discharge DFT testing did not alter ICD programming in any patient. During follow-up of 14.85 +/- 12.31 months, three patients had seven episodes of VT/VF, six of whom were converted with the programmed first-shock strength, while one required a second high-energy shock to convert. This patient had a pre-discharge DFT of 10 joules.

CONCLUSIONS

Successful ICD implantation can be safely performed with no or fewer episodes of VF induction using a modified ULV testing method.

Primary and secondary prevention of sudden cardiac death: the role of the implantable cardioverter defibrillator

Sudden cardiac death (SCD) affects nearly 300,000 people each year in the U.S., and out-of-hospital rates for survival range from only 2% to 25%. A substantial reduction in SCD requires primary prevention through risk-stratification and secondary prevention of sustained ventricular tachycardia (VT-S) and ventricular fibrillation (VF). Because frequent premature ventricular complexes (PVCs) appeared to be associated with an increased risk for SCD in patients with significant ventricular dysfunction, it was thought that suppression of PVCs would prevent SCD. The implantable cardioverter defibrillator (ICD) electrically treats life-threatening VT-S and VF, and it can be implanted readily in the pectoral area. Two randomized, prospective, controlled trials demonstrated conclusively that the ICD is the treatment of choice in the primary prevention of SCD in patients with a previous MI. In addition, three randomized, controlled trials found the ICD to be superior to antiarrhythmic drugs in the secondary prevention of SCD. Physicians should learn to recognize patients who are candidates for the ICD and refer them to an electrophysiologist so that they can get this life-saving therapy.

[Tachyarrhythmias--when rapid pace is pathological]

Tachycardias are classified as supraventricular and ventricular tachycardias. Supraventricular and ventricular tachycardias may occur as a complication of almost any underlying cardiac disease and many extracardiac causes. In addition, patients without any detectable structural heart disease may present with these arrhythmias. In this overview, we discuss the clinical presentations, the pathophysiological mechanisms and the therapeutical strategies in patients with tachyarrhythmias.

Percutaneous Cardiopulmonary Support Aids Resuscitation From Sustained Ventricular Tachycardia

A 67-year-old man was transferred to hospital because of acute circulatory failure resulting from sustained left ventricular tachycardia (LVT) and dysfunction. Transthoracic echocardiography revealed severely impaired left ventricular contraction and dyskinesis of the apical wall. Neither anti-arrhythmic agents nor direct current cardioversion was effective; the patient was resuscitated by immediate use of percutaneous cardiopulmonary support and intraaortic balloon counterpulsation. Ventricular contraction returned to normal following restoration of normal sinus rhythm with amiodarone and cibenzoline. The pathogenesis of LVT accompanied by transient ventricular dyskinesis is discussed with regard to the efficient use of a mechanical circulatory support system in resuscitation.

Catecholaminergic polymorphic ventricular tachycardia: electrocardiographic characteristics and optimal therapeutic strategies to prevent sudden death

OBJECTIVE

To investigate the clinical outcome, ECG characteristics, and optimal treatment of catecholaminergic polymorphic ventricular tachycardia (CPVT), a malignant and rare ventricular tachycardia.

PATIENTS AND METHODS

Questionnaire responses and ECGs of 29 patients with CPVT were evaluated. Mean (SD) age of onset was 10.3 (6.1) years.

RESULTS

The initial CPVT manifestations were syncope (79%), cardiac arrest (7%), and a family history (14%). ECGs showed sinus bradycardia and a normal QTc. Mean heart rate during CPVT was 192 (30) beats/min. Most cases were non-sustained (72%), but 21% were sustained and 7% were associated with ventricular fibrillation. The morphology of CPVT was polymorphic (62%), polymorphic and bidirectional (21%), bidirectional (10%), or polymorphic with ventricular fibrillation (7%). There was 100% inducement of CPVT by exercise, 75% by catecholamine infusion, and none by programmed stimulation. No late potential was recorded. Onset was in the right ventricular outflow tract in more than half the cases. During a follow up of 6.8 (4.9) years, sudden death occurred in 24% of the patients, 7% of whom had anoxic brain damage. Autosomal dominant inheritance was seen in 8% of the patients' families. beta Blockers completely controlled CPVT in only 31% of cases. Calcium antagonists partially suppressed CPVT in autosomal dominant cases.

CONCLUSIONS

CPVT may arise in certain distinct areas but the prognosis is poor. The onset of CPVT may be an indication for an implanted cardioverter-defibrillator.

Detection and management of an implantable cardioverter defibrillator lead failure: incidence and clinical implications

OBJECTIVES

This study evaluated the long-term reliability of an implantable cardioverter defibrillator (ICD) lead to determine the incidence, clinical presentation, and management of lead failure.

BACKGROUND

Despite recent advances in ICD technology, the long-term reliability of ICD leads remains a significant problem.

METHODS

Concern about long-term reliability of coaxial polyurethane ICD leads caused us to systematically study all patients implanted with Medtronic (Minneapolis, Minnesota) 6936 lead at our institution. We performed follow-up of 74 patients with 76 ICD leads that were implanted from February 28, 1995 to September 8, 1997. Thirty-seven patients underwent routine clinical ICD follow-up testing and ventricular fibrillation induction to determine the status of their ICD lead after a mean follow-up of 68.6 +/- 8.2 months.

RESULTS

The lead survival analysis shows a cumulative failure probability of 37% (confidence interval, 24% to 54%) at 68.6 months. Six patients demonstrated a previously undescribed mode of ICD lead failure: prolonged oversensing immediately after shock therapy. The use of short interval counters to monitor nonphysiologic R-R intervals and the measurement of ring-to-coil impedance detected early lead failures in five patients.

CONCLUSIONS

This analysis shows: 1) problems with ICD leads may not become apparent until late during follow-up and may become a significant late problem, 2) a "signature" mode of lead failure for the 6936 consisting of oversensing of electrical noise following shocks, 3) early detection of lead failure with a short interval counter algorithm or measurement of ring-to-coil impedance may be clinically useful.

[Inpatient cardiac defibrillation: efficacy of bipolar sinusoidal impulse]

Efficacy of external defibrillation of the heart with low energy (</=65-195 J) bipolar quasi sinusoidal discharges was studied in 76 patients with induced, primary (overall 70 episodes), and secondary (88 episodes) ventricular fibrillation (VF) and hemodynamically unstable ventricular tachycardia (VT) with or without acute myocardial infarction. Maximal effective discharge energy used for termination of induced and primary VF or VT was 90 J in 10 of 66 patients (15%) ). Meanwhile discharge energy 165-193 J was required for termination of secondary VF in 6 of 34 patients (18%). Overall efficacy of cardiac defibrillation with discharge energies </=115 and </=193 J was 92 and 100%, respectively. Success of resuscitation in patients with prolonged (2-28 min) primary and secondary VF was 82 and 68%, respectively. VF duration before first discharge (0,5-8 min) did not affect significantly magnitude of effective energy in interval between 90 and 193 J. However lower energy discharges were less effective when duration of fibrillation exceeded 30 sec.

Biventricular implantable cardioverter defibrillator and inappropriate shocks

A 53-year-old man with nonischemic cardiomyopathy underwent implantation of a biventricular implantable cardioverter defibrillator (ICD) for symptomatic ventricular tachycardia. He received five shocks while attempting to exercise, 48 hours after implantation. Interrogation of the device revealed double counting of ventricular sensed events by the left and right ventricular leads. Shortening the AV delay and AV nodal blockade (beta-blocker) to promote ventricular pacing failed to prevent additional inappropriate ICD discharges. After detailed consideration of all options including AV nodal ablation, we chose to disconnect the left ventricular lead pending availability of newer devices with sensing functions limited to the right ventricular lead. Since then, the patient has not experienced any additional inappropriate discharges.

Transvenous defibrillation leads: high incidence of failure during long-term follow-up

INTRODUCTION

Patients with implantable cardioverter defibrillators (ICD) critically depend on correct functioning of their system. The aim of this study was to determine the incidence and clinical presentation of transvenous ICD lead failures during long-term follow-up.

METHODS AND RESULTS

The study group consisted of 261 consecutive patients who received Medtronic right ventricular polyurethane transvenous leads (models 6884, 6966, 6936) between 1990 and 1998 as part of an abdominal (n = 70) or pectoral (n = 191) ICD system. During mean follow-up of 4.0 +/- 2.6 years, 31 patients (12%) developed a lead-related sensing failure with oversensing of artifacts. All failures except two were compatible with an insulation defect and occurred late after ICD placement (6.0 +/- 1.8 years after implant). Lead survival decreased from 98% at 4-year follow-up to only 62% at 8-year follow-up. Lead survival was not related to patient age, sex, venous lead implantation route, or device implantation site. In 26 (87%) of 31 patients, a sensing defect resulted in inappropriate detection of ventricular fibrillation and subsequent delivery of 3 +/- 3 (range 1-11) inappropriate shocks in 19 (61%) of 31 patients. Device interrogation showed artifacts classified as nonsustained ventricular tachycardia in 21 patients, 40 +/- 43 days before clinically relevant failure of the system. One patient with a subclavian crush syndrome required resuscitation because of undersensing of true ventricular fibrillation.

CONCLUSION

Transvenous polyurethane ICD leads showed a high rate of lead insulation failure late after implantation with frequent inappropriate shock deliveries. Close follow-up is mandatory in patients with these leads. Automated device control features with patient alert function integrated into new devices may contribute to early detection of lead failure.

Evaluation of a dual chamber implantable cardioverter defibrillator for the treatment of atrial and ventricular arrhythmias

Eighty-nine patients with a documented history of atrial tachyarrhythmias or fibrillation (AF) received a cardioverter defibrillator designed to selectively differentiate and treat atrial and ventricular arrhythmias. Twenty-two patients received a coronary sinus lead and, therefore, could use a separate shock vector for selective treatment of atrial tachyarrhythmias/AF. The device is designed to treat tachyarrhythmias with antitachycardia pacing (ATP) and/or shock therapy using an atrial and/or a ventricular shock vector. Patients underwent induction and shock termination of atrial or dual tachyarrhythmias (AF/VF) to verify proper device function and to measure the arrhythmia detection time with enhancements and preventive algorithms programmed On and Off, respectively. Detection time for 329 VF inductions was 2.41 +/- 0.64 seconds with enhancements On and 2.29 +/- 0.47 with enhancements Off (NS). At implant or predischarge, 283 AF and/or AF/VF (121 atrial and 162 atrial/ventricular fibrillation) were induced. Shock conversion efficacy was 89.8% with AF conversion energies ranging from 0.9 to 27 J. Thirteen of the 23 patients had atrial shock conversions using the separate shock vector with an average conversion energy of 1.9 +/- 1.4 J. (range 0.5-5 J). During follow-up the efficacy of ATP on atrial tachyarrhythmias was 59% and the efficacy of delivered shocks on AF was 85%. This new dual chamber cardioverter defibrillator appropriately detected and classified atrial arrhythmias, and shock therapy for AF was highly effective. The detection algorithm differentiated atrial tachyarrhythmia/AF and did not delay VF detection. The separate shock vector converted induced AF with energies ranging from 0.6 to 5 J.

Moricizine induced increase in pacing threshold

A 72-year-old woman who was experiencing incessant ventricular tachycardia and recurrent automatic implantable cardioverter defibrillator (AICD) firing despite amiodarone therapy was referred to the Cleveland Clinic Foundation. Myocardial ischemia and infarction were ruled out by standard means. Several antiarrhythmic medications were tried previously without success. Moricizine, 200 mg three times daily, was initiated and controlled the ventricular tachycardia. However, after the dose of moricizine was titrated upward, the patient became symptomatically bradycardic and the ECG exhibited 2:1 block of her paced rhythm and an increased ventricular pacing threshold.

T wave alternans for ventricular arrhythmia risk stratification

Sudden cardiac death remains one of the leading causes of death in western societies. Accordingly, the ability to identify patients at high risk of sudden cardiac death is important so that appropriate treatments can be used efficiently. Recently, T wave alternans (TWA) has emerged as a promising new test for such risk stratification. TWA is a heart rate-dependent measure of arrhythmia vulnerability, with maximal predictive accuracy at sustained, regular heart rates of 100 to 120 bpm. In the clinical setting, these conditions may be achieved by either exercise or atrial pacing. TWA has been shown to predict inducibility of ventricular tachycardia with programmed stimulation and also spontaneous arrhythmic events. TWA has been successfully applied to diverse populations, including patients with coronary artery disease, nonischemic cardiomyopathy, congestive heart failure, and implantable defibrillators. Despite these encouraging results, the role of TWA to guide clinical therapy still needs to be elucidated better.

Tachycardia-induced cardiomyopathy

Systolic dysfunction associated with chronic tachyarrhythmias, known as tachycardia-induced cardiomyopathy, is a reversible form of heart failure characterized by left ventricular dilatation that is usually reversible once the tachyarrhythmia is controlled. Its development is related to both atrial and ventricular arrhythmias. The diagnosis is usually made following observation of a marked improvement in systolic function after normalization of heart rate. Clinicians should be aware that patients with unexplained systolic dysfunction may have tachycardia-induced cardiomyopathy, and that controlling the arrhythmia may result in improvement and even complete normalization of systolic function.

Quality of life and psychological impact of implantable cardioverter defibrillators: focus on randomized controlled trial data

The defibrillator has been shown to reduce mortality in a number of patient groups with cardiac disease. Given the number of individuals with defibrillators it is important to understand the influence of these devices quality of life. Advances have led to smaller devices, less-invasive implantation, and more refined arrhythmia management. The potential impact of the defibrillator on quality of life continues to evolve with these advances. This review discusses the impact of the defibrillator on psychological well-being and quality of life, particularly the results of recent large randomized trials. Observational studies evaluating the relationship between defibrillator implantation and quality of life have not shown consistent results, but recent data from randomized trials provide important insights. Among patients who have survived life-threatening arrhythmias the defibrillator is associated with similar or perhaps superior quality of life versus antiarrhythmic drug therapy. However, patients who experience shocks have poorer quality of life versus those who do not. The reduction in quality of life with multiple shocks is of similar magnitude to serious side effects from antiarrhythmic drugs. While patients with defibrillators are at risk for poor quality of life. The advantages and disadvantages of defibrillator therapy versus amiodarone or usual medical care should be discussed with patients in whom a defibrillator is recommended. Those undergoing defibrillator implantation should be advised that adverse events and/or multiple shocks occur in a minority of patients, but may lead to reduced quality of life and it is vital that support resources be made available for these individuals.

Dual-chamber pacing or ventricular backup pacing in patients with an implantable defibrillator: the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial

CONTEXT

Implantable cardioverter defibrillator (ICD) therapy with backup ventricular pacing increases survival in patients with life-threatening ventricular arrhythmias. Most currently implanted ICD devices provide dual-chamber pacing therapy. The most common comorbid cause for mortality in this population is congestive heart failure.

OBJECTIVE

To determine the efficacy of dual-chamber pacing compared with backup ventricular pacing in patients with standard indications for ICD implantation but without indications for antibradycardia pacing.

DESIGN

The Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial, a single-blind, parallel-group, randomized clinical trial.

SETTING AND PARTICIPANTS

A total of 506 patients with indications for ICD therapy were enrolled between October 2000 and September 2002 at 37 US centers. All patients had a left ventricular ejection fraction (LVEF) of 40% or less, no indication for antibradycardia pacemaker therapy, and no persistent atrial arrhythmias.

INTERVENTIONS

All patients had an ICD with dual-chamber, rate-responsive pacing capability implanted. Patients were randomly assigned to have the ICDs programmed to ventricular backup pacing at 40/min (VVI-40; n = 256) or dual-chamber rate-responsive pacing at 70/min (DDDR-70; n = 250). Maximal tolerated medical therapy for left ventricular dysfunction, including angiotensin-converting enzyme inhibitors and beta-blockers, was prescribed to all patients.

MAIN OUTCOME MEASURE

Composite end point of time to death or first hospitalization for congestive heart failure.

RESULTS

One-year survival free of the composite end point was 83.9% for patients treated with VVI-40 compared with 73.3% for patients treated with DDDR-70 (relative hazard, 1.61; 95% confidence interval [CI], 1.06-2.44). The components of the composite end point, mortality of 6.5% for VVI-40 vs 10.1% for DDDR-70 (relative hazard, 1.61; 95% CI, 0.84-3.09) and hospitalization for congestive heart failure of 13.3% for VVI-40 vs 22.6% for DDDR-70 (relative hazard, 1.54; 95% CI, 0.97-2.46), also trended in favor of VVI-40 programming.

CONCLUSION

For patients with standard indications for ICD therapy, no indication for cardiac pacing, and an LVEF of 40% or less, dual-chamber pacing offers no clinical advantage over ventricular backup pacing and may be detrimental by increasing the combined end point of death or hospitalization for heart failure.