Guidelines for implantation of cardiac pacemakers and antiarrhythmia devices. A report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures. (Committee on Pacemaker Implantation)

Recognition and Management of Cardiac Arrhythmias: Part II. Ventricular Arrhythmias and Bradyarrhythmias

This review discusses the treatment of ventricular arrhythmias and bradyarrhythmias. Recent studies addressing the management of nonsustained ventricular arrhythmias in patients with congestive heart failure and those recovering from myocardial infarction are discussed. Determination of the origin of wide QRS complex tachycardia is usually possible at the bedside and the diagnostic criteria are provided. Therapy to prevent recurrent ventricular tachycardia or ventricular fibrillation is difficult and controversial. A widely accepted approach based on electrophysiologic testing and implantable defibrillators appears to be the most effective. Recognition and management of common bradyarrhythmias including the indications for pacemakers are discussed.

Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model

Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias.

Characterization and financial impact of implantable cardioverter-defibrillator patients without interventions 5 years after implantation

BACKGROUND

Implantable cardioverter defibrillators (ICD's) are increasingly used for primary and secondary prevention of sudden cardiac death. However, data on how many ICD patients indeed receive appropriate ICD therapy during long-term follow-up is scarce.

AIM

The aim of our study was to determine the number of patients without appropriate ICD therapy 5 years after ICD implantation, to identify predicting factors, to assess the occurrence of late first ICD therapy and to quantify the financial impact of ICD therapy in a real-world setting.

DESIGN

Prospective observational study.

METHODS

We prospectively enrolled 322 consecutive ICD patients. Baseline data were collected at implantation and patients were followed for a median of 7.3 years (IQR 5.8-9.2 years). Time to first appropriate ICD therapy (either antitachycardia pacing or cardioversion) was documented.

RESULTS

Five years after implantation, 139 patients (43%) had not received appropriate ICD therapy. In multivariable analysis, a primary prevention indication and negative electrophysiological studies prior to ICD implantation were independent predictors of freedom from ICD therapy. Of the patients without ICD therapy, 5 years after implantation, 25% had experienced inappropriate ICD shocks. Two hundred and seven devices (1.5 devices per patient) were needed for the 139 patients without ICD intervention within 5 years, accounting for € 31,784 per patient. During an additional follow-up of 3 years, 12% of the patients with unused ICD received a late first appropriate ICD therapy.

CONCLUSION

About half of the ICD patients receive appropriate ICD therapy within 5 years after implantation. Furthermore, there is a significant proportion of patients receiving late first shocks after five initially uneventful years.

Assessing the appropriateness of coronary revascularization: the University of Maryland Revascularization Appropriateness Score (RAS) and its comparison to RAND expert panel ratings and American College of Cardiology/American Heart Association guidelines with regard to assigned appropriateness rating and ability to predict outcome

BACKGROUND

Significant regional variation in procedural frequencies has led to the development of the RAND and American College of Cardiology/American Heart Association (ACC/AHA) guidelines; however, they may be difficult to apply in clinical practice. The University of Maryland Revascularization Appropriateness Score (RAS) was created to address the need for a simplified point scoring system.

HYPOTHESIS

The study was undertaken to compare revascularization appropriateness ratings yielded by the RAND Expert Panel Ratings, ACC/AHA guidelines, and the University of Maryland RAS.

METHODS

We applied these three revascularization appropriateness scoring systems to 153 catheterization laboratory patients with a variety of cardiac diagnoses and treatments. For each patient, appropriateness scores assigned by each of the three systems were compared with each other and with the actual treatment delivered. Concordance of care with appropriateness score was then correlated with outcome.

RESULTS

There were significant differences among all three scoring systems in their ratings and in the concordance of treatment with appropriateness rating. When treatment provided was concordant with RAND ratings, there was a lower occurrence of subsequent coronary artery bypass grafting (CABG), the composite end point of either CABG or percutaneous transluminal coronary angioplasty (PTCA), and the composite end point of death, myocardial infarction (MI), or revascularization. When treatment was concordant with the ACC/AHA guidelines, there was lower occurrence of all-cause mortality, PTCA, the composite end point of either CABG or PTCA, and the composite end point of death, MI, or revascularization. When treatment provided was concordant with the RAS, there was lower occurrence of cardiac death, all-cause death, CABG, the composite end point of either CABG or PTCA, and the composite end point of death, MI, or revascularization.

CONCLUSIONS

The RAS is a simple scoring system to assess revascularization appropriateness. When the RAND, ACC/AHA, and RAS systems are compared in a catheterization laboratory population, they rate the same patient differently and vary in their correlation of appropriateness rating with outcome.

Reasons for escalating pacemaker implants

Surveys of pacing practice have shown a steady increase in pacemaker implantation rates in the past 15 years, despite no major changes in United States guidelines for permanent pacing. There are no data to explain why this is occurring. In this study, records were extracted from the National Hospital Discharge Survey to investigate this. There were 3 major findings. First, age-adjusted implantation rates increased progressively over the study period from 370 per million in 1990 to 612 per million in 2002. Second, it was found that the escalating implantation rate is attributable to increasing implantation for isolated sinus node dysfunction (SND). Implantation for SND increased significantly over the study period (by 102%), whereas implantation for all other indications did not. The increasing implantation for SND is due primarily to the increasing prevalence of SND, with a lesser increase in implantation rate relative to prevalence rate. The third major finding of this study is that there has been a progressive relative and absolute increase in the dual-chamber implantation rate. In 2002, 82.8% of all initial pacemaker implantations were dual-chamber devices. Furthermore, the National Hospital Discharge Survey data indicate that the major randomized pacing trials seem to have had no impact on pacing practice in the United States. In conclusion, age-adjusted implantation rates increased progressively over the study period. This escalating implantation rate is primarily attributable to increasing implantation for SND.

Arrhythmic complications of acute coronary syndromes

Cardiac arrhythmias routinely manifest during or following an acute coronary syndrome (ACS). Although the incidence of arrhythmia is directly related to the type of ACS the patient is experiencing, the clinician needs to be cautious with all patients in these categories. As an example, nearly 90% of patients who experience acute myocardial infarction (AMI) develop some cardiac rhythm abnormality and 25% have a cardiac conduction disturbance within 24 hours of infarct onset. In this patient population, the incidence of serious arrhythmias, such as ventricular fibrillation (4.5%) ,is greatest in the first hour of an AMI and declines rapidly thereafter. This article addresses the identification and treatment of arrhythmias and conduction disturbances that complicate the course of patients who have ACS, particularly AMI and thrombolysis. Emphasis is placed on mechanisms and therapeutic strategies.

Serial antiarrhythmic therapy: role of amiodarone in prevention of atrial fibrillation recurrence--a lesson from the HOT CAFE Polish Study

Antiarrhythmic drug prophylaxis is known to improve long-term success of electrical cardioversion (CV) in persistent atrial fibrillation (AF). This prospective study evaluates the efficacy of sequential antiarrhythmic drug therapy in sinus rhythm (SR) maintenance after successful elective CV in patients with persistent nonvalvular AF.

MATERIALS AND METHODS

One hundred and twenty-eight patients (61+/-8 years old) with persistent AF underwent CV. Mean AF duration preceding CV was 268+/-99 days. Following SR restoration, patients were treated sequentially with either of the following antiarrhythmic drugs: propafenone, sotalol or disopyramide. Where arrhythmia recurred, patients received another CV and a new drug from the range defined above. Where such treatment failed, patients were loaded with 14.0- to 16.0-gram doses of amiodarone and a third CV was performed. If the first CV failed to restore SR, patients received a loading dose of amiodarone followed by another CV. When successful, amiodarone was administered on continuous basis.

RESULTS

The first CV proved successful in 55.5% of patients. During 1-year of follow-up, 31 patients (43.7%) presented with SR were treated with one antiarrhythmic agent (median does not exist). Application of the second drug proved to be effective in 6 patients (15.0%; median 13 days). Amiodarone was administered as the third antiarrhythmic agent to patients who had AF recurrence on the first two antiarrhythmic agents (propafenone, sotalol or disopyramide). It proved to be effective in 18 patients (52.9%; median does not exist) remaining free from AF for a period of 1 year as of commencement of the sequential antiarrhythmic therapy. Fifty-seven patients, in whom the first CV was ineffective, received amiodarone. During the loading period, SR was restored in 7 patients (12.3%). The remaining 50 patients underwent repeated CV, with SR restored in 37 (74.0%) of them. Long-term amiodarone treatment maintained SR in 30 (68.2%) patients during the follow-up period. Amiodarone helped to maintain SR in a total of 56.5% of patients.

CONCLUSIONS

Amiodarone seems to be the drug most effectively restoring and maintaining SR in patients with persistent AF resistant to CV and standard antiarrhythmic drug prophylaxis.

Rate control vs rhythm control in patients with nonvalvular persistent atrial fibrillation: the results of the Polish How to Treat Chronic Atrial Fibrillation (HOT CAFE) Study

STUDY OBJECTIVES

The relative risks and benefits of strategies of rate control vs rhythm control in patients with atrial fibrillation (AF) remain to be fully explored.

DESIGN

The How to Treat Chronic Atrial Fibrillation (HOT CAFE) Polish trial was designed to evaluate in a randomized, multicenter, and prospective manner the feasibility and long-term outcomes of rate control vs rhythm control strategies in patients with persistent AF.

PATIENTS

Our study population comprised 205 patients (134 men and 71 women; mean [+/- SD] age, 60.8 +/- 11.2 years) with a mean AF duration of 273.7 +/- 112.4 days. The mean observation period was 1.7 +/- 0.4 years. One hundred one patients were randomly assigned to the rate control group and received rate-slowing therapy guided by repeated 24-h Holter monitoring. Direct current cardioversion and atrioventricular junctional ablation with pacemaker placement were alternative nonpharmacologic strategies for patients with tachycardia that was resistant to medical therapy. One hundred four patients were randomized to sinus rhythm restoration and maintenance using serial cardioversion supported by a predefined stepwise antiarrhythmic drug regimen (ie, disopyramide, propafenone, sotalol, and amiodarone). In both groups, thromboembolic prophylaxis followed current guidelines.

MEASUREMENTS AND RESULTS

At the end of follow-up, 63.5% of patients in the rhythm control arm remained in sinus rhythm. No significant differences in the composite end point (ie, all-cause mortality, number of thromboembolic events, or major bleeding) were found between the rate control group and the rhythm control group (odds ratio, 1.98; 95% confidence interval, 0.28 to 22.3; p > 0.71). The incidence of hospital admissions was much lower in the rate control arm (12% vs 74%, respectively; p < 0.001). New York Heart Association functional class improved in both study groups, while mean exercise tolerance, as measured by the maximal treadmill workload, improved only in the rhythm control group (5.2 +/- 5.1 vs 7.6 +/- 3.3 metabolic equivalents, respectively; p < 0.001). The rhythm control strategy led to an increased mean left ventricular fractional shortening (29 +/- 7% vs 31 +/- 7%, respectively; p < 0.01). One episode of pulmonary embolism occurred in the rate control group despite oral anticoagulation therapy, while three patients in the rhythm control arm of the study experienced ischemic strokes (not significant).

CONCLUSIONS

The Polish HOT CAFE study revealed no significant differences in major end points between the rate control group and the rhythm control group.

Trends in hospital treatment of ventricular arrhythmias among Medicare beneficiaries, 1985 to 1995

BACKGROUND

Treatment options for patients with ventricular arrhythmias have undergone major changes in the last 2 decades. Trends in use of invasive procedures, clinical outcomes, and expenditures have not been well documented.

METHODS

We used administrative databases of Medicare beneficiaries from 1985 to 1995 to identify patients hospitalized with ventricular arrhythmias. We created a longitudinal patient profile by linking the index admission with all earlier and subsequent admissions and with death records.

RESULTS

Approximately 85,000 patients aged > or =65 years went to hospitals in the United States with ventricular arrhythmias each year, and about 20,000 lived to admission. From 1987 to 1995, the use of electrophysiology studies and implantable cardioverter defibrillators in patients who were hospitalized grew substantially, from 3% to 22% and from 1% to 13%, respectively. Hospital expenditures rose 8% per year, primarily because of the increased use of invasive procedures. Survival improved, particularly in the medium term, with 1-year survival rates increasing between 1987 and 1994 from 52.9% to 58.3%, or half a percentage point each year.

CONCLUSION

Survival of patients who sustain a ventricular arrhythmia is poor, but improving. For patients who are admitted, more intensive treatment has been accompanied by increased hospital expenditures.

Implantable cardioverter defibrillator implantation rates in the Olmsted County, Minnesota, population: 1989-1999

Although the efficacy of implantable cardioverter defibrillators (ICDs) has been demonstrated in randomized clinical trials, implantation and survival rates have not been reported for a defined population. We performed a retrospective cohort analysis of Olmsted County, Minnesota residents (n = 70) who received their first ICD between 1 January 1989 and 31 December 1999. The ICD implantation rate increased from approximately 2.5/100,000 (95% confidence interval [CI], 0.9-4.1) in the first 4 years to 11.5/100,000 (95% CI, 6.7-16.2) in the last 2 years. Twenty-three patients (33%) received an appropriate ICD shock during the observation period. Based on these data, ICDs are estimated to reduce total mortality rates in this population by 0.3%. We conclude that, in patients drawn from a community setting with AHA/ACC class I indications for ICD implantation, implantation of ICDs appears to be highly efficacious in aborting potentially fatal events.

2:1 Atrioventricular block: order from chaos

2:1 AV block can occur in either the AV node or the His-Purkinje system and cannot be classified into type I or type II second-degree AV block because there is only one PR interval to examine before the blocked P wave. It is inappropriate to use terms such as 2:1 or 3:1 type I or type II AV block because this characterization violates the accepted traditional definitions of type I and type II block based on electrocardiographic patterns and not on the anatomical site of block. Type I and type II second-degree AV block can progress to 2:1 AV block, and 2:1 AV block can regress to type I or type II block. Consequently, the site of the lesion in 2:1 block can often be determined by seeking the company 2:1 AV block keeps. An association with type I block and a narrow QRS complex almost always reflects AV nodal block but type I block with a wide QRS complex occurs more commonly in the His-Purkinje system than the AV node. Type II block, if correctly defined, is always infranodal. Outside of acute myocardial infarction, sustained 2:1 and 3:1 AV block with a wide QRS complex occurs in the His-Purkinje system in 80% of cases and 20% in the AV node. Administration of atropine in patients with His-Purkinje disease may increase the degree of AV block.

Programming of sensor driven pacemakers

The chronotropic response is the most important means by which cardiac output is increased and oxygen delivery is maintained in response to increased oxygen consumption during exercise or stress. When the chronotropic response is suboptimal or absent, exercise intolerance results. This condition, called chronotropic incompetence can be treated effectively with a sensor-driven rate-responsive pacemaker. The effectiveness of this therapy assumes that the pacemaker is programmed appropriately. This article focuses on the programming of sensor-driven pacemakers and provides additional suggestions for follow-up testing to ensure maximal benefit from these devices.

Electrophysiologic parameters to predict clinical recurrence of ventricular tachycardia in patients under electrophysiologic study-guided effective pharmacological therapy

Although an electrophysiologic study (EPS) is the most reliable method for selecting the treatment for a patient with sustained ventricular tachycardia (VT), VT recurrence may occur even during EPS-guided effective therapy. Electrophysiologic parameters were compared between patients with and without arrhythmic events under EPS-guided effective therapy to identify the predictive parameters of VT recurrence during the clinical course. The study population consisted of 77 consecutive patients with sustained VT who were receiving long-term pharmacological therapy that was demonstrated to be effective by the EPS assessment. The VT induction protocol employed 1-3 extrastimuli and rapid ventricular pacing at 2 right ventricular sites and 1 left ventricular site, and isoproterenol was infused when VT was not induced. To determine the 'effective' antiarrhythmic drug, all sustained ventricular arrhythmias had to be prevented during the whole induction protocol, but repetitive ventricular responses (RVR) were allowed to remain for up to 5 beats when they were in the same QRS configurations as the clinical VT and up to 12 beats when they were in polymorphic QRS configurations. The effective refractory periods (ERPs) at the 3 ventricular pacing sites and their difference (i.e., ERP-dispersion) and the maximum number of RVR beats were evaluated in an EPS during the control state and at the time of drug assessment. In the comparison of patients with and without VT recurrence, there was no significant difference in clinical characteristics or ERPs, but the deltaERP-dispersion (i.e., the increase in ERP-dispersion caused by the antiarrhythmic drug) and the maximum number of RVRs were significantly smaller in the group of patients without VT recurrence (deltaERP-dis, -3+/-8 vs. 6+/-12, p = 0.0027; maxRVR, 3+/-3 vs. 5+/-4, p = 0.0160). The VT recurrence rate was significantly lower in the patients with deltaERP-dis < or =0 or maxRVR<6 in comparison with the others (p = 0.01 14 and p = 0.0360). Patients with VT recurrence showed greater deltaERP-disp and a longer duration of RVRs at the time of drug assessment in comparison with the patients without VT recurrence. The prognosis of patients under EPS-guided therapy may be improved by the use of stricter criteria for drug assessment in the EPS, although this may decrease the number of drug responders determined in the EPS.

Cardiac pacemakers and implantable defibrillators in terminal care

The use of cardiac pacemakers and arrhythmia control devices is increasingly common. The presence of a previously placed pacemaker or implantable cardioverter-defibrillator (ICD) in a terminally ill patient may result in medical and ethical issues for the patient, family, and healthcare provider. Two cases are presented to illustrate the complex issues that may arise in the terminally ill with a pacemaker or an ICD. Based on these cases and a review of published data, it is likely that the disabling of a previously placed pacemaker will neither hasten nor prolong the natural history of the underlying illness in most instances. There are uncommon but potentially severe adverse effects of disabling the pacemaker; therefore, pacemakers should generally be left intact in terminally ill patients. It is more difficult to generalize as to whether deactivation of an ICD is appropriate; in this case death may be hastened and the decision concerning an ICD will depend on the specific clinical scenario. Patient and family education regarding palliative care treatment goals and the function of pacemakers and other implanted arrhythmia control devices can help to alleviate anxiety surrounding the impact of this technology at the end of life.

Rate adaptive atrial pacing in the bradycardia tachycardia syndrome

In 42 patients (26 men, 16 women; mean age 69 +/- 10 years), who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome, chronotropic response and AV conduction with rapid atrial pacing during exercise were studied. Patients were included if they had no second- or third-degree AV block, no complete bundle branch or bifascicular block, and a PQ interval < or = 240 ms during sinus rhythm at rest. The interval between the atrial spike and the following Q wave (SQ) was measured in the supine position at rest with an AAI pacing rate of 5 beats/min above the sinus rate (SQ-R + 5), and at the end of exercise with 110 beats/min (SQ-E110). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol with the pacemakers being programmed to AAI with a fixed rate of 60 beats/min. Chronotropic incompetence was defined as peak exercise heart rate: (1) < 100 beats/min; (2) < 75% of the maximum predicted heart rate; or (3) the heart rate at half the maximum workload < 60 + 2 beats/min per mL O2/kg per minute (calculated O2 consumption). During exercise, one patient developed atrial fibrillation. Chronotropic incompetence was present in 71% (29/41) of the patients according to definition 2, and in 76% (31/41) according to definition 1 or 3. Ten out of 41 patients (24%) exhibited a second-degree AV block with atrial pacing at 110 beats/min at the end of exercise. Only 9 out of the remaining 31 patients (29%) showed a physiological adaptation of the SQ-E110, and 21 patients (68%) exhibited a paradoxical increase of the SQ interval with rapid atrial pacing at the end of exercise as compared to the SQ-R + 5. These observations indicate that the pacing system to be used in most patients paced and medicated for the bradycardia tachycardia syndrome should be dual chamber, and the option of rate adaptation should be considered.

Final-year-of life pacemaker recipients

BACKGROUND

Older persons who have initial cardiac pacemakers implanted during their final year of life have not been characterized as a group, which makes it difficult to evaluate the suitability of some of their health services utilizations.

OBJECTIVE

To help determine how prudently pacemakers are used in this group, we assessed its pacemaker candidates from the perspective of health and ability to perform physical activities of daily living.

DESIGN

A retrospective, population-based, cross-sectional study.

SETTING

The 1993 National Mortality Followback Survey.

PARTICIPANTS

An estimated 1,647,955 persons aged 65 years or older who died in the US in 1993.

MEASUREMENTS

Demographic and cause-of-death frequencies obtained by analyzing age, sex, race, and underlying cause-of-death variables in the survey. For persons who had initial pacemakers implanted during their last year of life, we determined the percent of persons, within 10-year age groups, who had no difficulty at any time during their final year of life performing 11 specific physical activities of daily living (e.g., climbing stairs, preparing meals, bathing). These data were obtained from negative responses to questions that asked if the decedents, at any time during their last year of life, had difficulty performing the specific activities.

RESULTS

Of the estimated 78,941 persons aged 65 years or older with a pacemaker who died in the US in 1993, 14,158 (18%) had their first pacemaker implanted during their last year of life. Estimated median survival of the final-year-of-life recipients of pacemakers after pacemaker implantation was 5 months. Compared with the general older population that died in 1993, the final-year-of-life recipients of pacemakers group had higher percentages of persons who died of acute disorders (49% vs 19%) and who lived alone in a private home (47% vs 20%), and a lower percentage of persons with Alzheimer's disease (1% vs 7%). The age-stratified means of the percentages of final-year-of-life recipients of pacemakers who had no difficulty performing each physical activity of daily living were all greater than 50.

CONCLUSION

Our results suggest that older persons who had initial pacemakers implanted during their final year of life and who died in 1993 were not terminally ill, inactive pacemaker candidates, in general, but relatively independent, physically functional candidates who frequently died abruptly. The physical, mental, and life expectancy factors recommended for consideration by expert guidelines for the implantation of cardiac pacemakers were generally applied to persons in this subgroup.

The current status of single lead dual chamber sensing and pacing

The use of single lead, atrial synchronous ventricular (VDD) pacing in patients with high grade atrioventricular (AV) block and normal sinus node function is an acceptable alternative to dual chamber (DDD) pacing. Implantation and follow up procedures are simplified, and cost is usually reduced by more than the cost of an additional atrial lead. With the use of either diagonally arranged dipole or closely spaced ring electrodes, reliable atrial sensing can be achieved using differential atrial amplifier and high atrial sensitivity. Also oversensing is infrequently observed using provocation tests and dynamic recordings, clinical undersensing is unusual and minimized by programming to the highest atrial sensitivity. However, as atrial pacing is not possible, loss of AV synchrony and rate response may occur for unrecognized or progressive sinus node disease and lower rate limit. The development of single lead dual chamber pacing system may overcome this limitation. Recent studies have demonstrated that atrial pacing can be effective either with the use of a special pacing lead configuration or via floating atrial electrode with a novel stimulation method. Overlapping Biphasic Impulse (OLBI) can reduce atrial pacing threshold. Early clinical experience suggested that this new pacing method can provide effective and reliable atrial pacing with a relatively low incidence of diaphragmatic pacing. Thus the problem of atrial sensing is solved with a single pass lead but further long term evaluation is required to assess the efficacy and feasibility of new instrumentation for single lead dual chamber pacing.

Arrhythmias associated with acute myocardial infarction and thrombolysis

Ninety percent of patients with acute myocardial infarction have some cardiac rhythm abnormality, and approximately twenty-five percent have cardiac conduction disturbance within 24 hours following infarct onset. Almost any rhythm disturbance can be associated with acute myocardial infarction, including bradyarrhythmias, supraventricular tachyarrhythmias, ventricular arrhythmias, and atrioventricular block. With the advent of thrombolytic therapy, it was found that some rhythm disturbances in patients with acute myocardial infarction may be related to successful coronary artery reperfusion. This article addresses the role and treatment of arrhythmias and conduction disturbances that complicate the course of patients with acute infarction and thrombolysis.

Permanent cardiac pacing

Implantation of a permanent pacemaker is the most commonly performed surgical operation involving the heart. The modern cardiac pacemaker is a complex device that can sense and pace in both the atrium and ventricle. It also modulates the pacing rate based on sensed physiologic parameters. This article reviews the fundamental principles of pacemaker technology and provides the emergency physician with approaches to common pacemaker problems.

Quality of life and clinical outcomes in elderly patients treated with ventricular pacing as compared with dual-chamber pacing. Pacemaker Selection in the Elderly Investigators

BACKGROUND

Standard clinical practice permits the use of either single-chamber ventricular pacemakers or dual-chamber pacemakers for most patients who require cardiac pacing. Ventricular pacemakers are less expensive, but dual-chamber pacemakers are believed to be more physiologic. However, it is not known whether either type of pacemaker results in superior clinical outcomes.

METHODS

The Pacemaker Selection in the Elderly study was a 30-month, single-blind, randomized, controlled comparison of ventricular pacing and dual-chamber pacing in 407 patients 65 years of age or older in 29 centers. Patients received a dual-chamber pacemaker that had been randomly programmed to either ventricular pacing or dual-chamber pacing. The primary end point was health-related quality of life as measured by the 36-item Medical Outcomes Study Short-Form General Health Survey.

RESULT

The average age of the patients was 76 years (range, 65 to 96), and 60 percent were men. Quality of life improved significantly after pacemaker implantation (P<0.001), but there were no differences between the two pacing modes in either the quality of life or prespecified clinical outcomes (including cardiovascular events or death). However, 53 patients assigned to ventricular pacing (26 percent) were crossed over to dual-chamber pacing because of symptoms related to the pacemaker syndrome. Patients with sinus-node dysfunction, but not those with atrioventricular block, had moderately better quality of life and cardiovascular functional status with dual-chamber pacing than with ventricular pacing. Trends of borderline statistical significance in clinical end points favoring dual-chamber pacing were observed in patients with sinus-node dysfunction, but not in those with atrioventricular block.

CONCLUSION

The implantation of a permanent pacemaker improves health-related quality of life. However, the quality-of-life benefits associated with dual-chamber pacing as compared with ventricular pacing are observed principally in the subgroup of patients with sinus-node dysfunction.

Ventricular pacemaker upgrade: experience, complications and recommendations

OBJECTIVE

To assess outcomes of pacemaker upgrade from single chamber ventricular to dual chamber.

DESIGN

Retrospective analysis of patients undergoing the procedure.

SETTING

Specialist cardiothoracic unit.

PATIENTS

44 patients (15 female, 29 male), mean (SD) age at upgrade 68.2 (12.9) years.

INTERVENTIONS

Upgrade of single chamber ventricular to dual chamber pacemaker.

MAIN OUTCOME MEASURES

Procedure duration and complications.

RESULTS

Principal indications for upgrade were pacemaker syndrome (17), "opportunistic"--that is, at elective generator replacement (8), heart failure (7), non-specific breathlessness/fatigue (7), and neurally mediated syncope (3). Mean (SD) upgrade procedure duration (82.9 (32.6) minutes) significantly exceeded mean VVI implantation duration (42.9 (13.3) minutes) and mean DDD implantation duration (56.6 (22.7) minutes) (both p < 0.01). Complications included pneumothorax (1), ventricular arrhythmia requiring cardioversion (2), protracted procedure (10), atrial lead repositioning within six weeks (8), haematoma evacuation (1), superficial infection (1), and admission to hospital with chest pain (1); 20 patients (45%) suffered one or more complications including four of the eight who underwent opportunistic upgrade.

CONCLUSIONS

Pacemaker upgrade takes longer and has a higher complication rate than either single or dual chamber pacemaker implantation. This suggests that the procedure should be performed by an experienced operator, and should be undertaken only if a firm indication exists. Patients with atrial activity should not be offered single chamber ventricular systems in the belief that the unit can be upgraded later if necessary at minimal risk.

High failure rate for an epicardial implantable cardioverter-defibrillator lead: implications for long-term follow-up of patients with an implantable cardioverter-defibrillator

OBJECTIVES

The purpose of this study was to determine the risk of epicardial lead failure during long-term follow-up and its mode of presentation.

BACKGROUND

Despite the high prevalence of epicardial lead-based implantable cardioverter-defibrillators, their long-term performance is unknown, and appropriate follow-up has not been established.

METHODS

The study group comprised all patients in whom an epicardial lead system was implanted at the Mayo Clinic between October 31, 1984 and November 3, 1994. The number of lead fractures and leads with fluid within the insulation and the mode of presentation were determined retrospectively by review of patient visits, radiographs of lead systems and data derived from formal lead testing.

RESULTS

At 4 years, the survival rate free of lead malfunction, using formal lead testing, for 160 Medtronic epicardial patches (models 6897 and 6921) was 72% compared with 92.5% for the 179 Cardiac Pacemaker, Inc. (CPI) patches (models 0040 and 0041) (p = 0.01). In addition, five Medtronic patches in three patients had fluid within the lead insulation but no obvious fracture. No CPI patches had fluid identified within the leads. Of 330 Medtronic epicardial pace/sense leads (model 6917), the 4-year survival rate free of lead malfunction as assessed by lead testing was 96%. In all, 19 presentations of lead malfunction were found in 17 patients (2 patients had more than one lead fracture at different times). In 11 (58%) of these presentations, the patients were asymptomatic despite the presence of obvious lead fracture.

CONCLUSIONS

Epicardial lead malfunction is common on long-term follow-up, and some leads have a failure rate of 28% at 4 years. Many patients with fractured leads remain asymptomatic, despite involvement of multiple leads in some cases. Therefore, consideration should be given to regular periodic lead testing in addition to routine X-ray examination, as asymptomatic lead malfunction can present with normal chest X-ray findings.

Cost savings with nonthoracotomy implantable cardioverter-defibrillators

We analyzed hospital and physician charges for 99 consecutive patients who underwent implantable cardioverter-defibrillator (ICD) implantation at our institution. Eighteen patients received an epicardial lead system and 81 were scheduled to receive a nonthoracotomy lead system, the generator being implanted either abdominally (n = 62) or pectorally (n = 19). The epicardial group had a significantly longer convalescent stay (11.6 +/- 2.5 days; mean +/- SEM) than the abdominal nonthoracotomy group, analyzed by intention to treat (4.6 +/- 0.5 days) or by treatment received (3.8 +/- 0.2 days; p <0.0001). Postoperative stay for the pectoral group was shorter still (2.9 +/- 0.4 days; p <0.033). Total charges for the epicardial group were $99,081 +/- $25,094, significantly higher than those for any of the nonthoracotomy groups (p <0.017). Total charges for the pectoral group were $44,128 +/- $2,465, significantly less than those for the abdominal nonthoracotomy group, analyzed by intention to treat ($59,961 +/- $1,369; p <0.05) or by treatment received ($56,679 +/- $635; p <0.05). Cost reductions in the nonthoracotomy groups were primarily due to decreased in-hospital convalescence period, lower surgeon and anesthesiologist fees, and lower procedure-day hospital charges in the pectoral group. The use of ICDs with nonthoracotomy leads can result in significantly shorter in-hospital convalescence and a reduction in total implant-related charges of 40% to 55%. The use of pectorally implanted ICDs results in further reduction in hospital stay and further cost reduction of 22% to 26%. The trend toward shorter convalescent stay without postimplant testing is likely to reduce further the overall costs of ICD implantation.

Use of automatic mode change between DDD and AAI to facilitate native atrioventricular conduction in patients with sick sinus syndrome or transient atrioventricular block

The benefits of the automatic DDD (DDD/AMC) mode in the Chorus II pacemaker (Chorus 6234; Ela Medical Inc.), which automatically switches the modes between DDD and AAI to respect spontaneous AV conduction as much as possible in AAI while preserving safety pacing in DDD during paroxysmal AV block (AVB) only, remain unproven. This study examined the functions of the DDD/AMC mode in 12 patients with sick sinus syndrome (SSS; n = 10) or paroxysmal complete AVB (n = 2). A short-term (24 hours) comparative study between simple DDD mode and the DDD/AMC mode was performed in 8 of the 12 patients, and a medium-term (55.2 +/- 54.6 days) follow-up of the DDD/AMC mode was completed in all 12 patients. A comparative pair of 24-hour surface Holter ECGs was obtained in 6 of the 8 patients in the short-term study. Telemetry and built-in Holter histograms were collected in the outpatient clinic in all 12 patients. Although the percentage atrial pacing of the telemetry increased from 59.2 +/- 35.4 in DDD to 70.4 +/- 31.8 in DDD/AMC (P < 0.009; n = 8), the percentage ventricular pacing decreased from 64.6 +/- 37.7 in DDD to 36.2 +/- 43.1 in DDD/AMC (P < 0.027) in the short-term study. In particular, the reduction of percentage ventricular pacing to < 10% was observed in four patients with SSS not associated with > or = first-degree (1 degree) AVB on preoperative ECGs. Between the two modes a significant difference in arrhythmic events was not observed by the 24-hour surface Holter ECGS taken from the six patients in the short-term study. AAI-DDD switching associated with automatic modulation of AV delay and AV hysteresis occurred in all patients in the medium-term study. From the medium-term study, the total AV delay (AV delay plus AV hysteresis) exceeded 300 ms in 6 of the 12 patients in DDD/AMC, and usually became longest during nighttime. From the short- or medium-term study in the 12 patients, two patients preferred the DDD/AMC mode while one preferred the DDD mode. These results suggest that the DDD/AMC mode is useful, at least in SSS patients without > or = 1 degree AVB, by reducing the percentage ventricular pacing.

Drugs or implantable cardioverter-defibrillators in patients with poor left ventricular function?

Poor left ventricular function is a predictor of sudden death. Both antiarrhythmic drugs and implantable cardioverter-defibrillators (ICDs) promise to reduce the sudden death rate in these patients and consequently improve survival. In patients without spontaneous ventricular tachyarrhythmias, only beta-blocking agents and amiodarone have been shown to reduce sudden death and improve survival in some studies, whereas class I antiarrhythmic drugs increased mortality. For patients with documented ventricular tachyarrhythmias, protection against sudden death by serially tested class I antiarrhythmic drugs is at best moderate. There is some evidence suggesting that therapy with class III antiarrhythmic drugs, either amiodarone or dl-sotalol, may reduce sudden death rates and improve overall mortality in comparison to therapy with class I antiarrhythmic drugs. ICDs have been shown to prevent sudden death reliably. In published patient cohorts in which only patients who were not inducible off antiarrhythmic drugs or still inducible on antiarrhythmic drugs received an ICD, the ICD seemed to improve overall survival in comparison to class I antiarrhythmic drugs. A small prospective randomized study that compared a conventional therapy strategy to primary ICD implantations showed an improved outcome with ICDs as therapy of first choice. However, these studies included many patients treated with class I antiarrhythmic drugs considered to be less effective. In matched control studies comparing the ICD to amiodarone or dl-sotalol, less sudden deaths and an improved overall survival could be shown for the ICD in general without stratification for left ventricular function. Thus, in patients with hemodynamically nontolerated ventricular tachyarrhythmias, the ICD seems to improve survival in comparison to class I antiarrhythmic drugs, dl-sotalol, or amiodarone. However, in patients with poor left ventricular function, therapy with ICDs seems to be less cost-effective than in patients with preserved left ventricular function. In patients with very poor left ventricular function who are evaluated for cardiac transplantation, the ICD seems to change only the mode of death from sudden to a nonsudden cardiac death if transplantation cannot be performed soon.

Cardiac electrophysiology: a cost-effective approach

Clinical cardiac electrophysiology is a relatively new discipline, heavily dependent upon new technology that is often expensive. In cardiac pacing, no effective alternative to permanent pacing usually exists for patients with Class I indications, so cost-reduction strategies involve appropriate selection and utilization of hardware and facilities. Cost-effective utilization of radiofrequency ablation and implantable cardioverter-defibrillators requires that these techniques be compared with alternative therapies, usually antiarrhythmic drugs. Both ablation and defibrillator implantation can be shown to be cost effective in selected populations, but a cost-conscious approach to procedures and patient selection can make them cost effective in a broad range of patients.

Effectiveness and limitations of the fallback I algorithm for transient supraventricular tachyarrhythmias in DDD pacing

To examine the function of the fallback I algorithm (Chorus I, Ela Medical Inc., Montrouge, France), which automatically changes the DDD mode to VDI during transient supraventricular tachyarrhythmias to prevent high-rate tracking of the venticule, a total of 45 patients who were preoperatively diagnosed with sick-sinus syndrome (SSS) (Group 1; n = 19) or with advanced or complete atrioventricular block (AVB) (Group 2; n = 26) were followed up and analyzed. Mean follow-up times (mean +/- SD) were 22.4 +/- 9.7 and 12.4 +/- 10.9 months, respectively. Each of the groups was further divided into subgroups according to the preoperative existence of of paroxysmal atrial fibrillation (PAF) or paroxysmal supraventricular tachyarrhythmia (PSVT). During follow-up, the fallback started through a given cycle of ventricular pacing at a upper-rate limit (URL) to avoid a continuous high-rate tracking during the arrhythmias specifically in the patients with PSVT (0/4) (p = 0.0004). The fallback, however, sometimes started in the patients who had AVB not associated with either PAF or PSVT (4/21) during normal exercise because the fallback algorithm did not distinguish a normal P wave from the abnormal atrial waves. To further clarify the behavior of the fallback, a treadmill test was conducted in 25 of the 45 patients. The fallback start was observed in 12 of the 17 patients with AVB (Group 2). In such patients, the use of a long fallback delay and/or a high URL setting prevented the fallback starts during normal exercise. These results suggest that, in DDD pacing, the algorithm in Chorus I is useful in patients with SSS or AVB to avoid highrate tracking of the ventricle during transient supraventricular tachyarrhythmias, but special care must be taken to avoid the fallback starts during the normal exercise in AVB patients.

Cardiac pacemakers in pediatric heart transplant recipients: incidence, indications, and associated factors. Pediatric Heart Transplant Group-Loma Linda

This study was undertaken to assess the incidence, indications, and predisposing factors for pacemaker placement in a pediatric heart transplant population. From November 1985 to May 1994, 246 pediatric patients have undergone cardiac transplantation at Loma Linda University Medical Center. Seven (2.8%) have received pacemaker placement with an 8-50 month follow-up period. Median age at transplant was 462 days (0 days to 2.5 years). The median time to pacemaker placement was 190 days (18-1,672 days) after transplantation. Indications were sick sinus syndrome (SSS) in 5 and heart block in 2 patients (1 during acute rejection). Three patients with SSS underwent electrophysiology studies (EPS); 1 was normal and 2 showed sinus node dysfunction. The mode of pacing was VVIR in 6 patients and VVI in 1 patient. All 6 survivors are doing well and 5 patients' pacemakers still provide support. These 7 patients were compared with 185 pediatric patients (0 days to 12-years-old) transplanted during 1985 through 1993 who survived at least 6 months after transplantation. There was no correlation between the receipt of a pacemaker and graft cold ischemic time, rejection history, donor age, or recipient age at transplantation. The 5 patients with SSS had significantly lower average heart rates in the first month after transplantation (108 +/- 16 vs 130 +/- 12; P = 0.0002). The need for permanent pacemakers in this population is uncommon. Pacemakers, however, can be safely performed when necessary with excellent clinical results.

Single lead atrial synchronous ventricular pacing: a dream come true

Single lead, atrial synchronous pacing systems were developed in the late 1970s. Clinical experience has demonstrated the need to position the "floating" atrial electrode in the mid-to-high right atrium and the need for a specially designed pulse generator (with very high atrial sensitivity) to provide a high quality and amplitude atrial electrogram for consistent sensing. A 12-year experience with different electrode configurations, from the first unipolar designed in 1980 to the most recent atrial bipolar electrodes, has confirmed the validity of the original concept and the long-term reliability of the single lead atrial synchronous pacing system, which can reliably produce long-term atrial sensing and ventricular stimulation in the presence of normal sinoatrial function.

Consistent subcutaneous prepectoral implantation of a new implantable cardioverter defibrillator

OBJECTIVE

To describe the use of a new implantable cardioverter defibrillator (ICD) that can be placed in the prepectoral region rather than implanted in the abdominal wall.

DESIGN

We report the experience of placement of this new ICD in the prepectoral region in 13 patients from Sept. 28, 1993, through Jan. 10, 1994, at the Mayo Clinic.

MATERIAL AND METHODS

Thirteen consecutive patients offered this new ICD underwent placement of transvenous defibrillation leads, and the pulse generator was placed in a pocket formed in the subcutaneous, prepectoral space. Testing ensured a defibrillation threshold of 24 J or less.

RESULTS

In all 13 patients, the pulse generator could be placed in the subcutaneous, prepectoral space. In all except one patient, acceptable defibrillation thresholds were achieved by using lead systems placed totally transvenously. Only one patient required placement of a subcutaneous patch. All but two patients were dismissed from the hospital within 3 days after the ICD implantation.

CONCLUSION

Consistent subcutaneous, prepectoral placement of this new ICD pulse generator is possible. Because the entire procedure can be performed in the pacemaker implantation room, the potential exists for decreasing the duration of the hospitalization and associated costs.

Permanent cardiac pacemakers in the elderly

OBJECTIVE

To review (1) Changes in cardiac impulse generation, conduction, and ventricular filling in normal aging and disease; (2) Pacemaker technology and nomenclature; (3) Expert guidelines about pacemaker use; (4) Studies of pacemaker effectiveness and utilization.

DESIGN

Articles were identified through a Medline search, review of articles' bibliographies, and contact with pacemaker manufacturer representatives for information on device features and costs. These articles were reviewed, and the relevant data are presented.

RESULTS

Abnormalities in impulse generation and conduction are common in the elderly. Pacemaker use is higher in the elderly than in other population groups. Hemodynamic changes associated with aging include an increased contribution of atrial contraction to ventricular filling. Pacemakers, which maintain the synchrony between the atria and ventricles, may be particularly advantageous in the elderly for this reason. Rate-responsive ventricular pacemakers improve the quality of life compared with fixed rate devices in some patients over the age of 75. Dual-chamber, sequential pacemakers are more likely to reduce symptoms of pacemaker syndrome than ventricular pacemakers and probably also prolong survival and reduce risk of atrial fibrillation in certain groups of patients. However, dual chamber devices are more expensive and require more frequent follow-up. Pacemaker utilization can vary widely by region. Decisions about pacemakers require explicit tradeoffs between risk and quality of life on one hand and cost on the other. In many clinical situations, there is controversy as to whether pacemakers should be used.

CONCLUSIONS

Pacemakers provide definite benefits to some patients, whereas in others, the likelihood of benefit is uncertain. More sophisticated devices may provide some additional benefit, but they are more costly. Further data is still required to define precisely which groups of patients substantially benefit from complex and expensive pacing modalities compared with simpler ones.

Interventional electrophysiology--state-of-the-art 1993

The field of clinical electrophysiology has broadened significantly in the last several years, spawning a new discipline known as Interventional or Therapeutic Electrophysiology. In the United States, Electrophysiology has its own training path and accreditation requirements. One of the reasons for the growth of interest in electrophysiology is the exciting introduction of nonpharmacologic methods of arrhythmia therapy, including curative radiofrequency catheter ablation and implanted devices for antitachycardia pacing/defibrillation. The arrhythmia specialist now has at his/her disposal a wide range of options for patients with symptomatic or life-threatening cardiac arrhythmias.