ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices--summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/NASPE Committee to Update the 1998 Pacemaker Guidelines)

Permanent Pacemakers and Implantable Defibrillators

Pacemakers and cardioverter-defibrillators are implanted in patients with cardiovascular disease for an ever-increasing array of indications. Intensivists provide care frequently for patients who have these devices, and thus, they must be familiar with common problems and nuances that may contribute to critical illness. Close collaboration of the critical care physician and cardiologist/electrophysiologist assures that pacemakers and defibrillators are tuned to optimize the hemodynamic milieu of critically ill patients. Many recent advances in the sophistication of implanted devices are reviewed herein.

Microvolt T-wave alternans distinguishes between patients likely and patients not likely to benefit from implanted cardiac defibrillator therapy: a solution to the Multicenter Automatic Defibrillator Implantation Trial (MADIT) II conundrum

BACKGROUND

In 2003, the Centers for Medicaid and Medicare Services recommended QRS duration as a means to identify MADIT II-like patients suitable for implanted cardiac defibrillator (ICD) therapy. We compared the ability of microvolt T-wave alternans and QRS duration to identify groups at high and low risk of dying among heart failure patients who met MADIT II criteria for ICD prophylaxis.

METHODS AND RESULTS

Patients with MADIT II characteristics and sinus rhythm had a microvolt T-wave alternans exercise test and a 12-lead ECG. Our primary end point was 2-year all-cause mortality. Of 177 MADIT II-like patients, 32% had a QRS duration >120 ms, and 68% had an abnormal (positive or indeterminate) microvolt T-wave alternans test. During an average follow-up of 20+/-6 months, 20 patients died. We compared patients with an abnormal microvolt T-wave alternans test to those with a normal (negative) test, and patients with a QRS >120 ms with those with a QRS < or =120 ms; the hazard ratios for 2-year mortality were 4.8 (P=0.020) and 1.5 (P=0.367), respectively. The actuarial mortality rate was substantially lower among patients with a normal microvolt T-wave alternans test (3.8%; 95% confidence interval: 0, 9.0) than the mortality rate in patients with a narrow QRS (12.0%; 95% confidence interval: 5.6, 18.5). The corresponding false-negative rates are 3.5% and 10.2%, respectively.

CONCLUSIONS

Among MADIT II-like patients, a microvolt T-wave alternans test is better than QRS duration at identifying a high-risk group and also better at identifying a low-risk group unlikely to benefit from ICD therapy.

Drug-induced atrioventricular block: prognosis after discontinuation of the culprit drug

OBJECTIVES

The goal of this study was to determine how often atrioventricular (AV) block is really caused by medications.

BACKGROUND

Beta-blockers, verapamil, and diltiazem are considered a cause of AV block for which pacemaker implantation is not indicated. However, it is not known if such patients can expect a benign course after discontinuation of the culprit medication.

METHODS

Consecutive patients with II or III degree AV block not related to acute myocardial infarction, digitalis toxicity, or vasovagal syncope were studied. The level of AV block (AV-nodal or infranodal) was defined by electrocardiographic criteria. The cause and effect relation between AV block and drugs was defined according to the response to drug discontinuation.

RESULTS

Of 169 patients with AV block, 92 (54%) were receiving beta-blockers and/or verapamil or diltiazem. Patients receiving medications had similar clinical and electrocardiographic characteristics with patients who had AV block in the absence of drugs. Drug discontinuation was followed by resolution of AV block in 41% of cases, whereas spontaneous improvement of AV conduction occurred in 23% of patients who had AV block in the absence of drugs. However, 56% of the patients for whom drug discontinuation led to resolution of AV block had recurrence of AV block in the absence of therapy. Atrioventricular block that was "truly caused by drugs" was found in only 15% of patients who had II or III degree AV block during therapy with beta-blockers, verapamil, or diltiazem.

CONCLUSIONS

Atrioventricular block is commonly "related to drugs" but is rarely "caused by drugs."

Dying and defibrillation: a shocking experience

Palliative Care physicians are frequently involved in the care of patients with significant comorbidity and often have to take coexisting conditions into account when treating patients. An example of an area in which this is particularly relevant and will undoubtedly increase is presented with the case report of a patient with terminal metastatic lung carcinoma and an Implantable Cardioverter Defibrillator (ICD) in place. The role of the ICD in preventing the patient from dying comfortably is discussed, as are means of deactivating the device. We conclude that patients with ICDs and terminal disease should have the issue of deactivation addressed at the earliest possible opportunity as practical difficulties may arise in the emergency setting, especially in the nonhospital environment.

Echocardiographic evaluation of cardiac resynchronization therapy: ready for routine clinical use?

Cardiac resynchronization therapy (CRT) has been proposed as an alternative treatment in patients with severe, drug-refractory heart failure. The clinical results are promising, and improvement in symptoms, exercise capacity, and systolic left ventricular (LV) function have been demonstrated after CRT, accompanied by a reduction in hospitalization and a superior survival as compared with optimized medical therapy alone. However, 20% to 30% of patients do not respond to CRT. Currently, patients are selected mainly on electrocardiogram criteria (wide QRS complex, left bundle branch block configuration). In view of the 20% to 30% of nonresponders, additional selection criteria are needed. Echocardiography (and, in particular, tissue Doppler imaging) may allow further identification of potential responders to CRT, based on assessment of inter- and intraventricular dyssynchrony. In addition, echocardiography may allow optimal LV lead positioning and follow-up after CRT. In the current review, the different echocardiographic approaches to predict response to CRT are discussed. In addition, the use of echocardiography to guide LV lead positioning and follow-up after CRT are addressed.

Sudden cardiac death

Sudden cardiac death (SCD) due to ventricular tachyarrhythmias is a leading cause of death in the United States. This phenomenon is associated with coronary artery disease, valvular heart disease, nonischemic cardiomyopathies, congenital heart disease, primary electrical abnormalities, autonomic nervous system abnormalities, and other less common disorders. Evaluation and management of patients at risk for SCD (primary prevention) and of patients who have survived at least 1 episode of SCD (secondary prevention) have evolved in recent years because clinical trials have shown consistent benefit from implantation of cardioverter-defibrillators in appropriately selected patients. An evidence-based approach to primary and secondary prevention of SCD is presented.

Abnormal heart rate variability in a subject with second degree atrioventricular blocks during sleep

OBJECTIVE

We compare the profiles of heart rate variability (HRV) during sleep stages in 9 healthy controls and one subject with second degree atrioventricular blocks (AVB), investigating the role of sympathovagal balance in such pathology.

METHOD

Sleep and cardiac records were taken for one night in 9 male subjects from 21:00 to 07:00 h and for two nights in a male subject with AVB. Time and frequency domain indexes of HRV were calculated over 5 min-periods.

RESULTS

In one subject without any daytime heart disease, 253 and 318 AVB of type 2 (Mobitz 2) were observed during the two experimental nights, predominantly during rapid eye movement (REM) sleep and the surrounding sleep stage 2 in the second half of the night. In the 9 control subjects, absolute HRV indexes and low frequency (LF)/(LF+high frequency, HF) (where LF and HF are low frequency and high frequency power) were low during slow wave sleep, and significantly increased during REM sleep and the preceding sleep stage 2. In the subject with AVB, these HRV indexes were abnormally low during all sleep stages, with a predominant increase in parasympathetic activity as inferred from low LF/(LF+HF). During wake, however, LF/(LF+HF) normally increased, and the tachycardia observed with the arousal that terminates SWS was preserved in the subject with AVB.

CONCLUSION

These results suggest that in the subject with second degree atrioventricular blocks, sleep processes, particularly during REM sleep, create a specific neurological background that prevents an increase in sympathetic tone and triggers cardiac pauses.

Cardiac resynchronization by pacing: an electrical treatment of heart failure

Various modalities of cardiac pacing have been proposed in the past to improve hemodynamics, either directly or indirectly. Some of these are conventional ways of cardiac stimulation, others such as biventricular or left ventricular pacing, represent dedicated pacing techniques. Left ventricular and biventricular pacing are successfully applied in those patients with congestive heart failure who have conduction disturbances (i.e. left bundle branch block) as they correct the ensuing intra- and interventricular dyssynchrony. This is the reason why these pacing modalities are described as cardiac resynchronization therapy. According to the results of a series of studies, the cardiac resynchronization therapy seems to have a favourable clinical impact in terms of quality of life, morbidity and hospitalization rate. On-going and future studies should assess the impact of resynchronization therapy on overall mortality and its cost-effectiveness profile in specific subgroups of patients. Other open issues regard (i) the convenience of using biventricular pacing as a pacing-alone therapy or in combination with ventricular defibrillation capability, especially for potential candidates to heart transplantation, and (ii) the ways to identify properly the responders to resynchronization therapy.

Recent advances in pacemaker and implantable defibrillator therapy for young patients

PURPOSE OF REVIEW

This review is intended to highlight major clinical advances over the past year related to (1). biventricular pacing as a treatment for dilated myopathy, (2). growing clinical experience with implantable cardioverter defibrillators in pediatrics, (3). technical advances in standard antibradycardia pacing, and (4). an appraisal of the newly updated ACC/AHA/NASPE guidelines for device implant in children and adolescents.

RECENT FINDINGS

Complex rhythm devices are being used more frequently in children. Biventricular pacing to improve ventricular contractility is a rapidly evolving technology that has now been applied to children and young adults with intraventricular conduction delay, such as bundle branch block after cardiac surgery. Implantable defibrillators are also being used for an expanding list of conditions, although lead dysfunction is seen as a fairly common complication in active young patients. Guidelines for device implantation have been developed, but the weight of evidence remains somewhat limited by the paucity of pediatric data in this field.

SUMMARY

Thanks to refinements in lead design and generator technology, coupled with rapidly expanding clinical indications, pacemakers and implantable defibrillators have become increasingly important components of cardiac therapy for young patients. Expanded multicenter clinical studies will be needed to develop more objective guidelines for use of this advanced technology.

Current status of cardiac resynchronization therapy

PURPOSE OF REVIEW

Cardiac resynchronization therapy with biventricular pacing has rapidly emerged as an indispensable treatment option in patients with moderate-to-advanced heart failure and left bundle branch block. New findings on the pathophysiology of cardiac resynchronization therapy and its clinical effects are reviewed.

RECENT FINDINGS

Several randomized trials have evaluated the effects of cardiac resynchronization therapy on cardiac haemodynamics and clinical parameters in selected heart failure patients with left bundle branch block. The effects of cardiac resynchronization therapy on mechanical synchrony have been evaluated by different imaging modalities, such as echocardiography and radionuclide angiography. Cardiac resynchronization therapy leads to improved haemodynamics at a diminished energy cost, and improves functional mitral regurgitation. This haemodynamic improvement is associated with a significantly better quality of life, improved exercise capacity, and less frequent hospitalization. Recent preliminary data suggest a positive effect on cardiac mortality. However, approximately a third of implanted patients do not benefit from cardiac resynchronization therapy, and therefore additional criteria for the identification of mechanical dyssynchrony are needed to identify those patients who will respond before implantation.

SUMMARY

Many randomized trials have confirmed the benefits of cardiac resynchronization therapy in selected heart failure patients. The successful resynchronization of the ventricular activation-contraction sequence is the major determinant of acute haemodynamic and long-term clinical improvement. The diagnostic sensitivity and specificity of the non-invasive identification of mechanical dyssynchrony may be improved by echocardiography, but further research is needed to identify the optimal strategy for patient identification.

Potential Candidates for Cardiac Resynchronization Therapy in Japanese Patients With Idiopathic Dilated Cardiomyopathy-A Niigata Multicenter Study of DCM-

BACKGROUND

The purpose of this study was to assess the candidates suitable for cardiac resynchronization therapy (CRT) and to examine the significance of the QRS duration in Japanese patients with idiopathic dilated cardiomyopathy (DCM).

METHODS AND RESULTS

The study population consisted of 357 patients. The selection criteria for candidates suitable for CRT were QRS duration =130 ms, left ventricular ejection fraction (LVEF) =35% and New York Heart Association (NYHA) functional class III or IV by ACC/AHA/NASPE 2002 guidelines. We divided the study population into 2 groups: group A with a QRS duration <130 ms, and group B with a QRS duration =130 ms. In 25 of the 375 patients (7.0%), all the criteria were fulfilled. Group B had a significantly larger left ventricular diameter end-diastole and end-systole than group A (P<0.0001). Group B had a lower LVEF (P<0.0001). There was a fair inverse correlation (r=-0.58, P<0.0001) between the length of the QRS duration and LVEF.

CONCLUSION

Approximately 7% of the Japanese patients with DCM are CRT candidates. In the present study, we found that prolonged QRS duration was associated with poor systolic function.

Translation of clinical trials into clinical practice: use of results in formulating guidelines

The "evidence base" for arrhythmology is enormous and highly variable in quality and relevance. Every day, more information becomes available from basic science, bedside research, randomized trials, structured registries, and clinical experience. It has become critically important to develop methods for collating and synthesizing all of these strands of evidence into a useful and applicable format. The guideline is an increasingly valuable tool for this purpose. Guidelines are constructed in a formal and approved manner such that the evidence is graded and combined to produce appropriately classified practical recommendations. Arrhythmology guidelines now must be funded, implemented, value tested, and regularly revised.

Cardioverter-defibrillators after MADIT-II: the balance between weight of evidence and treatment costs

The possibility of using implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden death in selected high-risk patients has prompted a series of prospective controlled studies. Recently, the MADIT II study highlighted the possibility of effective primary prevention of sudden death in patients with coronary artery disease selected by straightforward clinical data and without expensive screening (electrophysiological study). For patients with previous myocardial infarction and low left ventricular ejection fraction (</=30%), ICD implantation may reduce mortality risk by approximately 31% in the following 2 years. Implementation of this therapeutic strategy threatens to impact on public health-care spending. Possible cost-limiting mechanisms include price cuts because of increasing usage (market forces); identification of subgroups at higher risk of sudden death and use of cheaper devices with limited diagnostic and therapeutic options. Further long-term evaluation of the cost-effectiveness and cost-utility of ICDs should identify subgroups of patients for whom implantation is affordable despite current economic constraints. For heart failure patients, randomized controlled trials are currently evaluating the effects on overall survival of both conventional ICDs and devices with biventricular pacing capabilities. In this perspective, data from the COMPANION trial are expected to stimulate the use of devices with defibrillation back-up in candidates for biventricular pacing.

Expression and function of a biological pacemaker in canine heart

BACKGROUND

We hypothesized that localized overexpression of the hyperpolarization-activated, cyclic nucleotide-gated (HCN2) pacemaker current isoform in canine left atrium (LA) would constitute a novel biological pacemaker.

METHODS AND RESULTS

Adenoviral constructs of mouse HCN2 and green fluorescent protein (GFP) or GFP alone were injected into LA, terminal studies performed 3 to 4 days later, hearts removed, and myocytes examined for native and expressed pacemaker current (I(f)). Spontaneous LA rhythms occurred after vagal stimulation-induced sinus arrest in 4 of 4 HCN2+GFP dogs and 0 of 3 GFP dogs (P<0.05). Native I(f) in nonexpressed atrial myocytes was 7+/-4 pA at -130 mV (n=5), whereas HCN2+GFP LA had expressed pacemaker current (I(HCN2)) of 3823+/-713 pA at -125 mV (n=10) and 768+/-365 pA at -85 mV.

CONCLUSIONS

HCN2 overexpression provides an I(f)-based pacemaker sufficient to drive the heart when injected into a localized region of atrium, offering a promising gene therapy for pacemaker disease.