New insights into cardiac resynchronization therapy

Ventricular dyssynchrony plays a central role in the expression and progression of heart failure (HF). An independent risk factor for cardiac mortality, ventricular dyssynchrony is characterized by delay in left ventricular (LV) lateral wall contraction. This leads to decreased pumping efficiency, with resulting fluid retention and impaired exercise tolerance. Cardiac resynchronization therapy (CRT) attempts to improve cardiac efficiency by restoring the normal mechanical relationship between right and left ventricular contraction. Cardiac output increases with resynchronization, while ventricular filling pressure decreases without increasing cardiac oxygen consumption. Cardiac resynchronization therapy can also reverse LV dysfunction and reduce mitral regurgitation in patients with HF. Since 1999, the efficacy of implantable CRT devices has been evaluated in clinical trials enrolling more than 4,000 patients with heart disease. In the CARE-HF trial, CRT reduced the risk of death by 36% relative to standard pharmacologic therapy. Combining CRT with a defibrillator might produce an added benefit. In the COMPANION trial, all-cause mortality in patients randomized to a CRT-defibrillator combination was less than in patients receiving CRT therapy alone. Cardiac resynchronization therapy has also been found to decrease morbidity and improve functional status and quality of life. At the present time, the indications for CRT are limited and include symptomatic HF despite optimal medical therapy, prolonged QRS interval, and LVEF < or = 35%. However, indications for CRT are still evolving and may be expanded as further studies identify those most likely to benefit.

Multicenter experience with failed and recalled implantable cardioverter-defibrillator pulse generators

BACKGROUND

Despite the widespread and growing use of implantable cardioverter-defibrillators (ICDs), little information is available regarding their performance or the impact of advanced pacing functions on ICD reliability and longevity.

OBJECTIVES

The purpose of this study was to examine the performance of contemporary ICD pulse generators that failed or were replaced because of manufacturers recalls.

METHODS

ICD data were entered prospectively by nine participating centers. ICD pulse generator failure was defined as removal from service because the device was not functioning according to the manufacturer's specifications. A recalled ICD was a normally functioning pulse generator that was replaced as the result of a recall or advisory.

RESULTS

From 1998 to 2005, 1,220 ICDs failed and 135 were recalled and replaced. The average implant time of failed ICDs was 4.4 +/- 1.5 years and of recalled ICDs was 1.7 +/- 0.8 years. The average implant time of single- and dual-chamber ICDs with rate responsive or cardiac resynchronization (CRT-D) pacing capabilities was significantly shorter than the average implant time of single- or dual-chamber devices without these features (P <.001). ICDs that provided rate responsive or CRT-D pacing failed earlier because of battery depletion (P <.001) and were significantly more prone to unexpected electronic or housing failure (9% vs 5%, P = .008) and recalls (25% vs 1%, P <.0001). Major adverse events included death (n = 2), failure to convert ventricular tachyarrhythmias (n = 6), and inappropriate shocks (n = 11).

CONCLUSION

Based on our analysis of failed and recalled devices, the performance of contemporary ICDs has been adversely affected by premature battery depletion, electronic failure, and manufacturers' recalls. Additional studies are needed to precisely estimate ICD longevity and to determine the incidence of unexpected ICD failure.

Decrease in fluoroscopic cardiac silhouette excursion precedes hemodynamic compromise in intraprocedural tamponade

BACKGROUND

Acute pericardial tamponade is a life-threatening complication of invasive cardiovascular procedures. Survival depends on early recognition and treatment. A diagnostic test to detect pericardial fluid accumulation before a significant fall in blood pressure and without contamination of the sterile field would be valuable.

OBJECTIVE

We tested the hypothesis that fluoroscopic excursion of the cardiac silhouette decreases early in the course of acute pericardial tamponade and precedes hemodynamic compromise.

METHODS

The pericardial space of seven pigs was accessed by a sub-xiphoid puncture. Tamponade was produced by intrapericardial saline infusion at 20-25 mL/minute until the pericardial pressure equalized with right ventricular end diastolic pressure or the systolic blood pressure reached 40 mmHg. Supine fluoroscopic images were obtained every 2 minutes in the left anterior oblique view with simultaneous echocardiography. The fluoroscopic heart silhouette was digitized, and the maximum excursion during the cardiac cycle was quantified by custom software. The qualitative excursion of the fluoroscopic heart silhouette on randomly selected video images was also graded by two independent observers who were blinded to the time course of the experiment and the hemodynamics.

RESULTS

During progressive pericardial fluid accumulation, the cardiac silhouette excursion quantified by the custom software (p < 0.001) and by video rating (p < 0.0001) was significantly reduced within 2 minutes. A statistically significant fall in blood pressure compared with baseline did not occur until 6 minutes (89 +/- 21 vs. 121 +/- 15 mmHg, p < 0.001). The interobserver agreement was very close, with a kappa statistic of 0.78. The reduction in cardiac silhouette excursion was apparent as soon as the effusion was detected by echocardiography.

CONCLUSION

Cardiac silhouette excursion becomes reduced early in the course of acute pericardial fluid accumulation. This fluoroscopic observation can be used to detect impending pericardial tamponade before hemodynamic collapse.

Anticoagulation: American College of Chest Physicians guidelines for the prevention and management of postoperative atrial fibrillation after cardiac surgery

Post-cardiac surgery atrial fibrillation (AF) places patients at risk for thromboembolism and stroke, while the surgery and cardiopulmonary bypass alter the multiple factors of coagulation and may increase the tendency to bleed. It is in the context of this complex clinical picture that the physician must make decisions regarding the risks and benefits of anticoagulation therapy to lower the risk for thromboembolism and stroke associated with postoperative AF. Physicians must also weigh the usually transient and self-limited duration of new-onset postoperative AF against the potential for postoperative bleeding if anticoagulation therapy is started. No randomized, controlled clinical trials are available that specifically address the problem of anticoagulation therapy for the postoperative AF. In that context, recommendations are based on the established therapy for nonsurgical situations modified by the potential risk of bleeding in the postoperative patient.

Pharmacologic Prophylaxis

New-onset atrial fibrillation (AF) occurs frequently in patients after cardiac surgery. The purpose of this study was to review the published trials and to provide clinical practice guidelines for pharmacologic prophylaxis against postoperative AF. Trials of pharmacologic prophylaxis against AF after heart surgery were identified by searching MEDLINE, the Cochrane Controlled Trials Register, and the bibliographies of published reports. Evidence grades and clinical recommendation scores were assigned to each prophylactic drug based on published evidence. Ninety-one trials were identified. The primary study design was a randomized, controlled trial of one drug vs placebo/usual care. Pharmacologic therapies that are reviewed include Vaughan-Williams class II agents (ie, beta-receptor antagonists) [29 trials; 2,901 patients], Vaughan-Williams class III agents (ie, sotalol and amiodarone) [18 trials; 2,978 patients], Vaughan-Williams class IV agents (ie, verapamil and diltiazem) [5 trials; 601 patients], and Vaughan-Williams class I agents (ie, quinidine and procainamide) [3 trials; 246 patients], as well as digitalis (10 trials; 1,401 patients), magnesium (14 trials; 1,853 patients), dexamethasone (1 trial; 216 patients), glucose-insulin-potassium (3 trials; 102 patients), insulin (1 trial; 501 patients), triiodothyronine (2 trials; 301 patients), and aniline (1 trial; 32 patients). A consistent finding in this review is that antiarrhythmic drugs with beta-adrenergic receptor-blocking effects (ie, class II beta-blockers, sotalol, and amiodarone) demonstrated successful prophylaxis. Furthermore, those therapies that did not inhibit beta-receptors generally failed to demonstrate a decreased incidence in postoperative AF. While sotalol and amiodarone have been shown in some studies to be effective, their safety and the incremental prophylactic advantage in comparison with beta-blockers has not been conclusively demonstrated. On the basis of evidence that has been reviewed and graded for quality, it is recommended that strong consideration should be given to the prophylactic administration of Vaughan-Williams class II beta-blocking drugs as a means of lowering the incidence of new-onset post-cardiac surgery AF.

Pharmacologic Control of Ventricular Rate

While there is a deficiency in the number of randomized control studies dealing with the pharmacologic control of the ventricular response to atrial fibrillation (AF) or atrial flutter (AFL) after cardiac surgery, evidence-based recommendations are presented from those studies that are available. Because of the hyperadrenergic state after surgery, beta-blockers are recommended as the first line of therapy for patients with AF or AFL who do not require urgent cardioversion. Calcium channel blockers are recommended as second-line therapeutic agents. Digoxin has little efficacy because of the heightened adrenergic tone that is present postoperatively. Agents that are proarrhythmic, such as dofetilide, or agents that are contraindicated in patients with coronary artery disease, such as flecainide and propafenone, are not recommended.

The Role of Cardiac Pacing

New-onset atrial fibrillation (AF) occurs frequently after cardiac surgery. The utility of prophylactic atrial pacing to prevent AF following cardiac surgery has been investigated in a number of trials, but clinical guidelines for its use are lacking. Trials of prophylactic atrial pacing to prevent AF following cardiac surgery were identified by searching PubMed, the Cochrane database, selected medical journals, and references in selected articles. Nine randomized controlled trials were identified that addressed prophylactic atrial pacing after cardiac surgery to prevent AF. Prophylactic right atrial pacing and prophylactic left atrial pacing have yielded inconclusive results. Prophylactic biatrial pacing (BAP) reduced the incidence of AF significantly in four studies, reduced it nonsignificantly in one study, and had no effect in one study. On the basis of the literature that was reviewed and graded for quality, it was concluded that prophylactic atrial pacing to prevent AF after cardiac surgery is safe. We recommend that BAP be considered, particularly in patients who are at high risk for the development of postoperative AF.

Future Directions

The recommendations put forth in these guidelines for the management and prevention of atrial fibrillation (AF) after cardiac surgery are based on information available at the time of the final literature review. As a result, they will become dated as new information and results from new trials becomes available. The maintenance of clinical practice guidelines is an evolving process requiring the alteration of recommendations over time, based on new studies and new results. The current set of guidelines attempts not only to identify new therapeutic options for AF after cardiac surgery but also to develop a strategy to indicate how and when to update the guidelines themselves.

A comparison of the AVID and DAVID trials of implantable defibrillators

We compared 2 studies of implantable cardiac defibrillators (ICDs) to determine the effects of device mode on outcomes. The Antiarrhythmics Versus Implantable Defibrillators (AVID) trial (1993 to 1997) demonstrated improved survival with the ICD compared with antiarrhythmic drug therapy. The Dual-chamber And VVI Implantable Defibrillator (DAVID) trial (2000 to 2002) showed that VVI pacing at 40 beats/min in patients with ICDs reduced the combined end point of death and hospitalization for congestive heart failure compared with DDDR pacing at 70 beats/min. Patients in the AVID trial (631 of 1,016) and the DAVID trial (221 of 506) meeting common inclusion and all exclusion criteria were studied. The major end points were the time to death, and the composite end point of time to death or hospitalization for congestive heart failure. Patients in the AVID and DAVID trials were similar, but more AVID patients had coronary artery disease (p = 0.04), history of myocardial infarction (p = 0.005), and previous ventricular arrhythmias (p = 0.03). DAVID patients underwent more previous revascularization procedures (coronary artery bypass surgery, p = 0.03; percutaneous coronary intervention, p = 0.001), and were more often taking beta-blocking drugs at hospital discharge (p <0.001). The backup VVI ICD groups in both studies had similar outcomes (p = 0.4), even when corrected for the previous demographic differences. The time-to- composite end point was similar in AVID patients treated with antiarrhythmic drugs and DAVID patients treated with DDDR ICDs (p = 0.6). Despite improved pharmacologic therapy and revascularization, outcomes have not improved with backup VVI pacing ICDs. If DDDR ICDs had been used in the AVID trial, benefit from ICDs for patients with serious ventricular arrhythmias could have been missed.

Clinical Assessment and Management of Patients With Implanted Cardioverter-Defibrillators Presenting to Nonelectrophysiologists

All physicians increasingly will encounter patients who have implanted cardioverter-defibrillators (ICDs) for protection from ventricular arrhythmias. This advisory provides a concise summary relevant to the assessment and management of patients with ICDs, including those who present to primary care or emergency department physicians with symptoms suggesting arrhythmia or ICD malfunction and those who require cardiac or surgical procedures.

Prophylactic implantable cardioverter-defibrillator therapy in patients with left ventricular systolic dysfunction

Strategies to decrease sudden cardiac death in patients with left ventricular systolic dysfunction are evolving. Recent clinical trials have evaluated the role of prophylactic implantable cardioverter-defibrillators (ICDs) in patients with and without additional risk stratifiers. We pooled studies comparing treatment with and without ICDs from published data and presented abstracts, irrespective of QRS duration and etiology of systolic dysfunction. On the basis of the available clinical trials, implantation of an ICD for primary prevention of death provides a 7.9% absolute mortality reduction (p = 0.003) in patients with left ventricular (LV) systolic dysfunction who were receiving optimized medical therapy. This finding was not sensitive to the exclusion of any individual trial. The ICD is an effective primary preventative measure in patients who are at risk for death; however, the application of this therapy needs to be individualized for the patient, similar to drug therapies in LV systolic dysfunction. In health care settings without unlimited resources, optimal use of this therapy will require better risk stratification methods or lowering of the initial device cost.

Alternative endpoints for mortality in studies of patients with atrial fibrillation: The AFFIRM study experience

OBJECTIVES

The purpose of this study was to examine possible alternatives for death, particularly hospitalization for cardiovascular reasons (CV hospitalization), as an endpoint in studies of atrial fibrillation (AF) using the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) database.

BACKGROUND

AF is associated with increased mortality, but large numbers of patients are needed to demonstrate even a moderate effect of a therapy on mortality.

METHODS

AFFIRM studied 4,060 patients with AF, randomized to either rate-control or rhythm-control strategy with death as the primary endpoint.

RESULTS

Only CV hospitalization occurred more frequently than death. Like death, CV hospitalization was more frequent in the rhythm-control arm (46% vs 36%, P < .001) overall but not in a cohort that attempted to exclude those CV hospitalizations possibly related to treatment strategy (e.g., cardioversion, 24% vs 27%). In either model there was no interaction of CV hospitalization (analyzed as a time-dependent covariate) with treatment arm (P = .18 and P = .21, respectively). CV hospitalization was highly predictive of death in both treatment arms (P < .001) in either model, but after this event, there was no difference in time to death. A composite endpoint of CV hospitalization combined with death might increase power and reduce the size of trials of therapy for AF in such patients.

CONCLUSIONS

In patients with AF such as those in the AFFIRM study, CV hospitalization has many attributes of a surrogate for mortality. More research on CV hospitalization, alone or as part of a composite endpoint, is warranted.

Highlights of Heart Rhythm 2004, the Annual Scientific Sessions of the Heart Rhythm Society: May 19 to 22, 2004, in San Francisco, California

Heart Rhythm 2004, the 25th Annual Scientific Sessions of the Heart Rhythm Society (formerly the North American Society of Pacing and Electrophysiology), met in San Francisco in May 2004. The meeting is the world's premier forum for the presentation of research and the exchange of state-of-the-art information in cardiac electrophysiology and pacing. Major new research findings were presented on the value of implantable cardioverter-defibrillator therapy, noninvasive methods for risk stratification, treatment of vasovagal syncope, radiofrequency ablation for atrial fibrillation, resynchronization therapy for heart failure, and new insights from basic science into the mechanisms of cardiac arrhythmias.