Cardiac resynchronization in chronic heart failure.

BACKGROUND: Previous studies have suggested that cardiac resynchronization achieved through atrial-synchronized biventricular pacing produces clinical benefits in patients with heart failure who have an intraventricular conduction delay. We conducted a double-blind trial to evaluate this therapeutic approach. METHODS: Four hundred fifty-three patients with moderate-to-severe symptoms of heart failure associated with an ejection fraction of 35 percent or less and a QRS interval of 130 msec or more were randomly assigned to a cardiac-resynchronization group (228 patients) or to a control group (225 patients) for six months, while conventional therapy for heart failure was maintained. The primary end points were the New York Heart Association functional class, quality of life, and the distance walked in six minutes. RESULTS: As compared with the control group, patients assigned to cardiac resynchronization experienced an improvement in the distance walked in six minutes (+39 vs. +10 m, P=0.005), functional class (P<0.001), quality of life (-18.0 vs. -9.0 points, P= 0.001), time on the treadmill during exercise testing (+81 vs. +19 sec, P=0.001), and ejection fraction (+4.6 percent vs. -0.2 percent, P<0.001). In addition, fewer patients in the group assigned to cardiac resynchronization than control patients required hospitalization (8 percent vs. 15 percent) or intravenous medications (7 percent vs. 15 percent) for the treatment of heart failure (P<0.05 for both comparisons). Implantation of the device was unsuccessful in 8 percent of patients and was complicated by refractory hypotension, bradycardia, or asystole in four patients (two of whom died) and by perforation of the coronary sinus requiring pericardiocentesis in two others. CONCLUSIONS: Cardiac resynchronization results in significant clinical improvement in patients who have moderate-to-severe heart failure and an intraventricular conduction delay.

Cardiac resynchronization therapy and other new approaches for the treatment of heart failure in the elderly.

Approximately 15% to 20% of patients with systolic heart failure have a QRS duration greater than 120 ms, which is most commonly seen as left bundle-branch block (LBBB). In LBBB, the left ventricle is activated through the septum from the right ventricle, resulting in a significant delay between the onset of right (RV) and left ventricular (LV) contraction. In patients with LV dysfunction, ventricular dyssynchrony caused by LBBB places the already failing left ventricle at an additional mechanical disadvantage. Ventricular dyssynchrony appears to have a deleterious impact on the natural history of heart failure, as a wide QRS complex has been associated with increased mortality in patients experiencing heart failure. On the basis of these observations, investigators hypothesized that patients with LV dysfunction and delayed ventricular conduction would benefit from pacing at sites that achieve a more favorable contraction pattern, and correct interatrial and/or interventricular conduction delays to maintain optimal atrial-ventricular (AV) synchrony. Multiple clinical trials of cardiac resynchronization therapy have demonstrated that it is safe and effective, with patients achieving significant improvement in both clinical symptoms as well as multiple measures of functional status and exercise capacity. Moreover, it has reduced measures of morbidity and mortality in several studies. Thus, cardiac resynchronization therapy should be routinely offered to eligible patients experiencing heart failure.

Effect of cardiac resynchronization therapy on left ventricular size and function in chronic heart failure.

BACKGROUND: Cardiac resynchronization therapy (CRT) has recently emerged as an effective treatment for patients with moderate to severe systolic heart failure and ventricular dyssynchrony. The purpose of the present study was to determine whether improvements in left ventricular (LV) size and function were associated with CRT. METHODS AND RESULTS: Doppler echocardiograms were obtained at baseline and at 3 and 6 months after therapy in 323 patients enrolled in the Multicenter InSync Randomized Clinical Evaluation (MIRACLE) trial. Of these, 172 patients were randomized to CRT on and 151 patients to CRT off. Measurements were made of LV end-diastolic and end-systolic volumes, ejection fraction, LV mass, severity of mitral regurgitation (MR), peak transmitral velocities during early (E-wave) and late (A-wave) diastolic filling, and the myocardial performance index. At 6 months, CRT was associated with reduced end-diastolic and end-systolic volumes (both P<0.001), reduced LV mass (P<0.01), increased ejection fraction (P<0.001), reduced MR (P<0.001), and improved myocardial performance index (P<0.001) compared with control. beta-Blocker treatment status did not influence the effect of CRT. Improvements with CRT were greater in patients with a nonischemic versus ischemic cause of heart failure. CONCLUSIONS: CRT in patients with moderate-to-severe heart failure who were treated with optimal medical therapy is associated with reverse LV remodeling, improved systolic and diastolic function, and decreased MR. LV remodeling likely contributes to the symptomatic benefits of CRT and may herald improved longer-term survival.

Pharmacologic therapies for atrial fibrillation.

Pharmacologic therapy for atrial fibrillation may be used for acute cardioversion or ventricular rate control or for long-term therapy to maintain sinus rhythm or control ventricular rates in atrial fibrillation. Therapies must be tailored to elderly patients, with particular attention to structural heart disease, bradycardia, hypotension, and other comorbidities, including renal or hepatic insufficiency. Such considerations may dictate the use or avoidance of certain agents. Other important considerations for elderly patients include challenges associated with anticoagulation and maintaining therapeutic international normalized levels without risk of bleeding. When considering pharmacologic agents for elderly patients, it is also valuable to take into account socioeconomic issues, such as access to medications, adherence to complicated dosing schedules, and availability of appropriate clinical follow-up to assess therapeutic efficacy and adverse reactions to various agents. A carefully constructed therapeutic regimen can provide effective symptom control and atrial fibrillation management for elderly patients.

Cardiac Resynchronization Therapy for Heart Failure.

Cardiac resynchronization therapy has been established as important adjuvant therapy in the treatment of severe heart failure. As lead delivery systems have improved and the number of experienced implanters has increased, more patients have access to transvenous left ventricular lead implantation, outside of clinical trials at large medical centers. Ongoing research continues to perfect implantation techniques to optimize patient outcomes, as well as develop hardware and software technology used in implanted devices. Resynchronization therapy typically results in a decreased burden of emergency room visits and hospitalizations for decompensated heart failure. In addition, diagnostic tools available in resynchronization devices allow clinicians to not only predict heart failure decompensation and adjust medical therapies accordingly, but they also allow for the diagnosis of asymptomatic arrhythmias that may predict adverse outcomes, as well as allow for the diagnosis of symptomatic arrhythmias without the need for additional costly workup. This suggests that in the long term, biventricular device implantation may actually provide cost savings to the health care system. On a macroeconomic scale, there are significant concerns about the cost burden to society of increased implantation of resynchronization therapy devices, along the same lines as concerns raised regarding the expanding indications for implantable cardioverter-defibrillator implantation. As future research broadens indications for implanting implantable cardioverter-defibrillators, as well as resynchronization systems, we may see cardiac resynchronization therapy become a secondary prevention tool yielding long-term patient benefits by postponing or preventing a decline in heart failure status.

Overview of the management of atrial fibrillation: what is the current state of the art?

Management of Atrial Fibrillation. There are three fundamental approaches to the management of atrial fibrillation (AF): rate control, rhythm control, and anticoagulation. Selecting a course of treatment requires a thorough knowledge of these therapeutic alternatives. This article explores treatment options, including the relative benefits of rate control versus rhythm control, which are complicated by the lack of highly effective and safe antiarrhythmic drugs. Anticoagulation is also an important issue in AF management, and warfarin effectively reduces the incidence of thromboembolic events in AF patients. The use of warfarin, however, presents its own complications. We conclude that individualization of therapy is paramount when treating AF.

Elevations in ventricular pacing threshold with the use of the Y adaptor: implications for biventricular pacing.

Cardiac resynchronization therapy (CRT) is a new and promising therapeutic option for patients with severe heart failure and intraventricular conduction delay. Patients who are candidates for CRT and have a previously implanted device may utilize a "Y" IS 1 connector to accommodate the coronary sinus lead. This modification has the potential to alter biventricular pacing thresholds. During an 18 month period, successful biventricular pacemaker implantation was performed in 72 patients (age: 67 +/- 11 years, left ventricular ejection fraction: 20.5 +/- 5.6%). All of these patients had severe symptomatic congestive heart failure (NYHA Class III and IV). In 20 patients a special "Y" adaptor that bifurcates the ventricular IS 1 bipolar output to two bipolar outputs or one unipolar and one bipolar output was utilized. During initial implantation, LV thresholds obtained in a unipolar configuration prior to connecting to the "Y" adaptor were significantly lower than thresholds obtained after connecting to the "Y" adaptor (1.7 +/- 1.11 V at 0.5 ms pulse width versus 2.8 +/- 1.5 V at 0.5 ms pulse width [P = 0.01]). Two patients (10%) required left ventricular lead revisions due to unacceptably high left ventricular thresholds during device follow-up. The difference in measured left ventricular thresholds between the two configurations is best explained by a resistive element that is added to the circuit when performing threshold measurement of the LV lead through the "Y" adaptor (combined tip to RV ring configuration) versus measurement of the LV lead in a unipolar configuration. This resistive element represents multiple factors including anode surface area, resistive polarization at the tissue-electrode interface, and transmyocardial resistance. LV thresholds should be measured in an LV tip to RV ring configuration or ideally in a combined tip (LV and RV) to shared ring configuration in order to accurately assess LV thresholds. This observation has significant clinical implications as loss of capture may occur as a result of improper measurement of left ventricular thresholds at the time of implantation.