Dual-chamber pacing for cardiomyopathies: a 1996 clinical perspective

Pacing for drug-refractory or drug-intolerant hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a genetic disease with an autosomal-dominant inheritance for which negative inotropes are the most widely used initial therapies. Observational studies and small randomised trials have suggested symptomatic and functional benefits using pacing and several theories have been put forward to explain why. Pacing, although not the primary treatment for HCM, could be beneficial to patients with relative or absolute contraindications to surgery or alcohol ablation. Several randomised controlled trials comparing pacing to other therapeutic modalities have been conducted but no Cochrane-style systematic review has been done.

OBJECTIVES

To assess the effects of pacing in drug-refractory or drug-intolerant hypertrophic cardiomyopathy patients.

SEARCH METHODS

We searched the following on the 14/4/2010: CENTRAL (The Cochrane Library 2010, Issue 1), MEDLINE OVID (from 1950 onwards ), EMBASE OVID (from 1980 onwards ), Web of Science with Conference Proceedings (from 1970 onwards). No language restrictions were applied.

SELECTION CRITERIA

Randomised controlled trials of either parallel or crossover design that assess the beneficial and harmful effects of pacing for hypertrophic cardiomyopathy were included. When crossover studies were identified, we considered data only from the first phase.

DATA COLLECTION AND ANALYSIS

Data from included studies were extracted onto a pre-formed data extraction paper by two authors independently. Data was then entered into Review Manager 5.1 for analysis. Risk of bias was assessed using the guidance provided in the Cochrane Handbook. For dichotomous data, relative risk was calculated; and for continuous data, the mean differences were calculated. Where appropriate data were available, meta-analysis was performed. Where meta-analysis was not possible, a narrative synthesis was written. A QUROUM flow chart was provided to show the flow of papers.

MAIN RESULTS

Five studies (reported in 10 papers) were identified. However, three of the five studies provided un-usable data. Thus the data from only two studies (reported in seven papers) with 105 participants were included for this review. There was insufficient data to compare results on all-cause mortality, cost effectiveness, exercise capacity, Quality of life and Peak O2 consumption.When comparing active pacing versus placebo pacing on exercise capacity, one study showed that exercise time decreased from (13.1 ± 4.4) minutes to (12.6 ± 4.3) minutes in the placebo group and increased from (12.1 ± 5.6) minutes to (12.9 ± 4.2) minutes in the treatment group (MD 0.30; 95% CI -1.54 to 2.14). Statistically significant data from the same study showed that left ventricular outflow tract obstruction decreased from (71 ± 32) mm Hg to (52 ± 34) mm Hg in the placebo group and from (70 ± 24) mm Hg to (33 ± 27) mm Hg in the active pacing group (MD -19.00; 95% CI -32.29 to -5.71). This study was also able to show that New York Heart Association (NYHA) functional class decreased from (2.5 ± 0.5) to (2.2 ± 0.6) in the inactive pacing group and decreased from (2.6 ± 0.5) to (1.7 ± 0.7) in the placebo group (MD -0.50; 95% CI -0.78 to -0.22).When comparing active pacing versus trancoronary ablation of septal hypertrophy (TASH), data from one study showed that NYHA functional class decreased from (3.2 ± 0.7) to (1.5 ± 0.5) in the TASH group and decreased from (3.0 ± 0.1) to (1.9 ± 0.6) in the pacemaker group. This study also showed that LV wall thickness remained unchanged in the active pacing group compared to reduction from (22 ± 4) mm to (17 ± 3) mm in the TASH group (MD 0.60; 95% CI -5.65 to 6.85) and that LV outflow tract obstruction decreased from (80 ± 35.5) mm Hg in the TASH group to (49.3 ± 37.7) mm Hg in the pacemaker group.

AUTHORS' CONCLUSIONS

Trials published to date lack information on clinically relevant end-points. Existing data is derived from small trials at high risk of bias, which concentrate on physiological measures. Their results are inconclusive. Further large and high quality trials with more appropriate outcomes are warranted.

Long-term effects of dual-chamber pacing with periodic echocardiographic evaluation of optimal atrioventricular delay in patients with hypertrophic cardiomyopathy >50 years of age

Various treatment modalities have been introduced to reduce the subaortic pressure gradient in patients with obstructive hypertrophic cardiomyopathy, including pacemaker insertion. Complete ventricular capture during pacing is essential and requires optimization of the atrioventricular interval (AVI). In this study, a protocol using echocardiographic examination assessing the changes in the left ventricular outflow tract (LVOT) gradient in different AVIs, pacing rates, and pacing modes was used for optimal pacemaker programming. Twenty-five patients with obstructive hypertrophic cardiomyopathy were implanted with DDD pacemakers and evaluated prospectively. The LVOT gradient was measured during periodic evaluations every 3 to 6 months. Gradient measurements were done with 5 different AVIs and 3 different rate combinations. After each evaluation, the optimal AVI, pacing rate, and mode were set on the basis of the minimal LVOT gradient not associated with systolic arterial cuff pressure reduction. Follow-up ranged from 18 to 126 months. Peak LVOT gradient immediately decreased in 92% of patients. During follow-up, the optimal AVI was prolonged in most patients. Sixty-four percent of patients showed a clear relation between pacemaker modifications and gradient reduction. In 75% of these patients, optimal gradient reduction required repeated AVI and pacing rate programming on the basis of echocardiographic evaluation. Symptoms decreased in 92% of patients, and New York Heart Association class improved significantly (3.1+/-0.7 vs 1.3+/-0.4, p<0.001) during follow-up. The symptomatic reduction was positively correlated with the LVOT gradient reduction. In conclusion, DDD pacing is effective in reducing the LVOT gradient and improving functional capacity in adult patients with hypertrophic cardiomyopathy. Pacemaker programming with the periodic echocardiographic evaluation of the optimal AVI, pacing rate, and mode is imperative for optimal results.

Difference in mechanical atrioventricular delay between atrial sensing and atrial pacing modes in patients with hypertrophic and dilated cardiomyopathy: an electrical hemodynamic catheterization study

For optimal pacemaker programming in patients with cardiomyopathy, it is important to understand the relationship between the programmed right atrial and ventricular delay and the mechanical contraction delay of the left atrium and left ventricle.

METHODS

We analyzed data from 34 patients with dilated cardiomyopathy (14) or hypertrophic obstructive cardiomyopathy (20) who had dual-chamber P-synchronous pacing (VDD) and atrioventricular sequential pacing (DVI) during hemodynamic catheterization. Using multiple atrioventricular intervals during VDD and DVI pacing, the relationship of the programmed right atrial-right ventricular interval to the mechanical left atrial-left ventricular delay (assessed by high-fidelity pressures) was determined.

RESULTS

We found that the optimal mechanical left atrial-left ventricular delay was 120 ms, which required a programmed right atrial-right ventricular interval of 160 ms during DVI pacing. Also, the mean difference in right atrial-right ventricular pacing interval between VDD and DVI modes was 54 +/- 28 ms (range, 10-120 ms) in the hypertrophic obstructive cardiomyopathy group and 64 +/- 38 ms (range, 20-150 ms) in the dilated cardiomyopathy group.

CONCLUSIONS

We concluded that the optimal right atrial-right ventricular interval during DVI pacing was 160 ms and that, to achieve the same mechanical left atrial-left ventricular delay, the programmed right atrial-right ventricular interval during VDD pacing was approximately 50 ms to 60 ms shorter than during DVI pacing. However, the difference of electrical atrioventricular pacing interval in VDD and DVI may vary widely from patient to patient.

Cardiac pacing. A review

Pacing is a field of rapid clinical progress and technologic advances. Clinical progress in the 1990s included the refinement of indications for pacing as well as the use of pacemakers for new, nonbradycardiac indications, such as the treatment of cardiomyopathies and CHF and the prevention of atrial fibrillation. Important published data and studies in progress are shedding new light on issues of pacing mode selection, and they may influence future practice significantly. Important technologic advances include development of new rate-adaptive sensors and sensor combinations and the evolution of pacemakers into sophisticated diagnostic devices with the capability to store data and ECGs. Automatic algorithms monitor the patient for appropriate capture, sensing, battery status, and lead impedance, providing better patient safety and pacemaker longevity.

Use of implantable pacemakers and implantable defibrillators in hypertrophic cardiomyopathy

Recent data have emerged to help guide the use of implantable pacemakers and implantable defibrillators in patients who have hypertrophic cardiomyopathy (HCM). Controlled studies of the use of dual chamber pacemakers to treat outflow tract obstruction in HCM have shown little benefit, and have raised the possibility that earlier favorable reports were demonstrating an element of placebo effect. In particular, there is no recent support for earlier claims of regression of ventricular hypertrophy from chronic dual chamber pacing. Several reports have added to our understanding of the risk factors for sudden death in HCM. A normal blood pressure response to exercise appears to identify a subset of patients at low risk for sudden death. In a recent study of a large number of HCM patients, the risk of sudden death was found to be directly proportional to the extent of left ventricular hypertrophy. There is accumulating evidence that the implantable defibrillator is highly effective in terminating malignant ventricular arrhythmias in HCM patients, and HCM patients thought to be at significant risk for sudden death should be offered defibrillator implantation.

Anesthesia for Pacemaker Insertion

In recent years, the nature of pacemaker implantation in the United States has changed dramatically, as ad vances continue in the technology of pacemakers and the techniques for insertion. Changes have also allowed for the expansion of indications for pacing to include cases in which it can serve as a therapeutic modality to alter hemodynamic states. Where once surgeons were primarily responsible for the procedure, the task now falls under the services of cardiologists. Insertions are commonly performed on an outpatient basis in the cardiac catherization suite. Local anesthesia is sufficient and, therefore, limits the need for anesthesiologists during pacemaker insertion. However, complicated, high-risk patients are now presented for pacemaker insertion. Furthermore, the 1998 American College of Cardiology/American Heart Association (ACC/AHA) guidelines include hypertrophic obstructive cardiomy opathy, dilated cardiomyopathy, and pacing after car diac transplantation as 3 new indications of particular interest. It is these conditions that enlist the expertise of anesthesiologists for monitoring, administering of anal gesics and sedatives, and resuscitation because of complications. This article provides a comprehensive description of common implantation procedures and the anesthesia used for pacemaker insertion. The focus is on the new 1998 ACC/AHA indications as well as general complications that invariably arise even during routine insertion. It is these areas that are of particular interest to anesthesiology as technology, technique, and indications for pacemaker insertion continue to evolve.

Ventricular pacing with premature excitation for treatment of hypertensive-cardiac hypertrophy with cavity-obliteration

BACKGROUND

Hypertensive left ventricular hypertrophy with supranormal systolic ejection and distal cavity obliteration (HHCO) can result in debilitating exertional fatigue and dyspnea. Dual-chamber pacing with ventricular preactivation generates discoordinate contraction, which can limit cavity obliteration and thereby increase potential ejection reserve. Accordingly, we hypothesized that pacing may improve exercise tolerance long-term in this syndrome.

METHODS AND RESULTS

Dual-chamber pacemakers were implanted in 9 patients with exertional dyspnea caused by HHCO. Intrinsic atrial rate was sensed, and ventricular preactivation was achieved by shortening the atrial-ventricular delay. Pacing was on or off for successive 3-month periods (randomized, double-blind, crossover design), followed by 6 additional pacing-on months. Metabolic exercise testing, quality-of-life assessment, and rest and dobutamine-stress echocardiographic/Doppler data were obtained. After 3 months of pacing-on, exercise duration rose from 324+/-133 to 588+/-238 s (mean+/-SD; P=0.001, with 7 of 9 patients improving >/=30%), and maximal oxygen consumption increased from 13.6+/-2.9 to 16.7+/-3.3 mL of O(2). min(-1). kg(-1) (P<0.02). Both parameters were little changed from baseline during the pacing-off period. Improved exercise capacity persisted at 1-year follow-up. Clinical symptoms and activities of daily living improved during the pacing-on period and stayed improved at 1 year, but they were little changed during the pacing-off period. Despite similar basal values, stroke volume (P<0.001) and cardiac output (P<0.02) increased with dobutamine stimulation 2 to 3 times more after 1 year of follow-up as compared with baseline.

CONCLUSIONS

Long-term dual-chamber pacing can improve exercise capacity, cardiac reserve, clinical symptoms, and activities of daily living in patients with HHCO. This therapy may provide a novel alternative for patients in whom traditional pharmacological treatment proves inadequate.

Fixed left ventricular outflow tract obstruction in presumed hypertrophic obstructive cardiomyopathy: implications for therapy

BACKGROUND

A subset of patients presenting with a presumed diagnosis of hypertrophic obstructive cardiomyopathy (HOCM) have a fixed left ventricular outflow tract (LVOT) obstruction. Recognition of this pathophysiologic abnormality is important in choosing therapy.

METHODS

Of patients referred for treatment of HOCM, 4 had fixed LVOT obstruction. Clinical and echocardiographic data and surgical findings were reviewed.

RESULTS

In the 4 patients with clinical features consistent with HOCM or HOCM-like conditions, echocardiography showed fixed LVOT obstruction with an early-peaking LVOT Doppler signal or absence of severe systolic anterior motion of the mitral valve. The causes of fixed obstruction included accessory mitral tissue with associated fibrous ring (1 patient), fixed subaortic tunnel stenosis (2 patients), and a discreet subaortic ridge (1 patient). After surgical relief of the fixed LVOT obstruction, all patients had relief of the ventricular outflow tract gradient.

CONCLUSIONS

Not all patients with a presumed diagnosis of HOCM have isolated dynamic LVOT obstruction but may have isolated or additional fixed obstruction. Careful two-dimensional and Doppler echocardiography are needed to identify this subset of patients who are best treated surgically.

Hypertrophic and restrictive cardiomyopathies in the elderly

Congestive heart failure (CHF) increases with age, but most CHF in the elderly is due to diastolic dysfunction with preserved systolic function. The etiology, pathophysiology, diagnosis, natural history, and treatment of hypertrophic and restrictive cardiomyopathies in the elderly are discussed as a paradigm for CHF with normal systolic function. Hypertrophic obstructive and hypertensive hypertrophic cardiomyopathies are compared and contrasted. As an example of a restrictive cardiomyopathy, the various types of amyloidosis and their clinical import in older patients are covered.

Hypertrophic cardiomyopathy: presentation and pathophysiology

HCM is a heterogeneous disease with various clinical presentations. Recent advances in understanding the genetic abnormalities responsible for ventricular hypertrophy promise to improve our ability to diagnose this condition and to identify subgroups who are at the highest risk of cardiovascular mortality. Numerous difficulties remain in treating patients with HCM, including obtaining relief of symptoms and preventing SCD, but several new treatment options are currently being evaluated. In the future, randomized trials comparing the major treatment options (eg, pharmacologic therapy, myotomy/myectomy, mitral valve replacement, pacemaker implantation, and nonsurgical septal reduction) will be needed to provide guidance concerning the optimal treatment of patients with HCM.

Newer clinical applications of pacing

For many years, the indications for permanent cardiac pacing consisted primarily of AV block and sinus node dysfunction. In recent years, the indications for pacing have expanded considerably. This article details recent advances in the application of permanent pacing and the use of permanent pacing for patients with hypertrophic cardiomyopathy, dilated cardiomyopathy, prevention of atrial fibrillation, and pacing in the long QT syndrome. Pacing is now an accepted therapeutic modality in hypertrophic cardiomyopathy and has rapidly gained acceptance in the United States, although there are still many unknowns about selection of patients and long-term benefits. Even less is known about pacing for dilated cardiomyopathy. Certain patients do respond with definite subjective improvement and improved quality of life, although there are no data to date to suggest improved longevity. Pacing for long QT syndrome is now a well-accepted indication for this relatively small subset of patients. Pacing for the prevention of atrial fibrillation is still in the very early stages of development. Multiple methods have been tried with the current method of choice being dual site atrial pacing. However, it is too early to predict the long-term success of this modality.

Recipient selection and management before cardiac transplantation

Cardiac transplantation is a proven, effective therapy for selected patients with end-stage congestive heart failure. Recipient selection is performed by a multidisciplinary team consisting of transplant physicians and surgeons. Clinicians responsible for patient assessment must establish the severity of cardiac dysfunction, formulate a prognosis, and stratify patients according to risk for mortality. Patients whose survival and quality of life are most limited without cardiac transplantation are candidates for therapy. The scarcity of organ donors makes careful screening of potential recipients necessary to identify those individuals most likely to obtain a long-term benefit. Recipient selection criteria and management strategies are evolving because of extended waiting times and high mortality caused by the lack of sufficient numbers of donors. Alternative therapies should be applied wherever possible.