Passive external cardiac constraint improves segmental left ventricular wall motion and reduces akinetic area in patients with non-ischemic dilated cardiomyopathy

Diastolic ventricular support with cardiac support devices: an alternative approach to prevent adverse ventricular remodeling

Heart failure is a global epidemic with limited therapy. Abnormal left ventricular wall stress in the diseased myocardium results in a biochemical positive feedback loop that results in global ventricular remodeling and further deterioration of myocardial function. Mechanical myocardial restraints such as the Acorn CorCap and Paracor HeartNet ventricular restraints have attempted to minimize diastolic ventricular wall stress and limit adverse ventricular remodeling. Unfortunately, these therapies have not yielded viable clinical therapies for heart failure. Cellular and novel biopolymer-based therapies aimed at stabilizing pathologic myocardium hold promise for translation to clinical therapy in the future.

Successful Implantation of a Left Ventricular Assist Device After Treatment With the Paracor HeartNet

The Paracor HeartNet, a ventricular constraint device for the treatment of heart failure (HF), is implanted through a left lateral thoracotomy. It envelopes the heart like a mesh "bag." This method of application raises the question of whether adhesions with the pericardium allow the safe implantation of a left ventricular assist device (LVAD) if HF worsens. A male patient who had undergone implantation of the Paracor HeartNet 42 months earlier presented with advanced HF for cardiac transplantation. The patient's condition deteriorated, and because no suitable organ for transplantation was available, implantation of an LVAD became necessary. Surgery was performed via a median sternotomy without complications. No severe adhesions were found. This is the first report on "how to do" LVAD implantation after Paracor HeartNet implantation with images and information about cutting the constraint. Because the Paracor HeartNet is "wrapped" around the heart, concerns persist that severe adhesions with the pericardium might occur. In this case, LVAD implantation after therapy with the Paracor HeartNet was without complications, and the expected massive adhesions were absent.

Sustained Benefits of the CorCap Cardiac Support Device on Left Ventricular Remodeling: Three Year Follow-up Results From the Acorn Clinical Trial

BACKGROUND

The objective of this study was to assess the long-term effects of the CorCap Cardiac Support Device (CSD; Acorn Cardiovascular, Inc, St. Paul, MN) on left ventricular (LV) structure and function in patients with heart failure. Cardiac support devices, which reduce LV wall stress, have been shown to promote reverse remodeling in three different experimental models of heart failure. However, long-term effects in patients with heart failure have not been reported.

METHODS

We enrolled 300 patients with heart failure in the Acorn Randomized Trial, as previously reported (Ann Thorac Surg 2007;84:1226-35). Echocardiograms were obtained every six months until the last patient was followed for one year, and then annually thereafter. Standard measurements of LV volumes, ejection fraction, and sphericity index were made by a Core laboratory at the Mayo Clinic who were blinded to treatment assignment.

RESULTS

Patients treated with the CorCap Cardiac Support Device had significant reductions in LV end diastolic volume (average difference 18.8 mL; p = 0.005) and LV end systolic volume (average difference 15.6 mL; p = 0.013) compared with the control group. Sphericity index was significantly increased in the treatment group (average difference 0.045 units; p = 0.018). These changes were maintained over three years of follow-up. The improvements in LV size and shape were observed when the CorCap was implanted concomitantly with mitral value surgery or by itself.

CONCLUSIONS

These results demonstrate that the CorCap Cardiac Support Device has a long-term beneficial impact on LV size and shape in patients with heart failure.

Effect of passive cardiac containment on ventricular synchrony and cardiac function in awake dogs

OBJECTIVE

Passive restraint of the left ventricle (LV) has been shown to have beneficial effects on acute hemodynamics and reverse remodeling in both animal and human models. The goals of this study were to test whether a left ventricular support device (LVSD) improves LV synchrony and/or affects cardiac performance.

METHODS

Ten dogs were chronically instrumented to measure hemodynamics and LV volume (sonomicrometry). Congestive heart failure (CHF) was induced by repeated intracoronary microembolization via a chronically implanted coronary catheter. The LVSD was implanted after establishment of CHF in five animals, and five animals were observed as controls. All animals were then observed for 8 weeks. A mathematical model to measure LV synchrony was used to evaluate LV motion over time.

RESULTS

Mean arterial pressure and LV pressures was significantly increased after LVSD therapy, and LV pressure-volume relationships were shifted leftwards, although no change was seen in ejection fraction, end-systolic elastance, or LV dP/dt versus control. There was no significant change in diastolic function in LVSD animals compared with control animals. End-diastolic volumes were reduced by 15% after 8 weeks with LVSD treatment, versus an increase of 8% in control animals (p<0.05). Synchrony was significantly improved with LVSD therapy compared with control (9% vs 76% of baseline) in 1 of 11 ventricular dimension axes (Anterior-Apex).

CONCLUSIONS

LVSD therapy provided only minimal improvement in ventricular synchrony and partially improved hemodynamics. Further study into mechanisms of benefit are warranted.

Assessment of left ventricular wall motion using 16-channel multislice computed tomography: comparison with left ventriculography

PURPOSE

Using the raw data from coronary computed tomography (CT) angiography, multislice CT (MSCT) can be used to evaluate cardiac function. However, the accuracy of left ventricular (LV) wall motion assessment by MSCT has not been thoroughly investigated. We investigated whether 16-channel MSCT could accurately assess LV wall motion by comparing its results with those of conventional biplane left ventriculography (LVG).

MATERIALS AND METHODS

The study included 20 patients with various kinds of heart disease. All patients underwent both contrast-enhanced MSCT and biplane LVG. Using a retrospective electrocardiography-gating technique, 10 phases over one cardiac cycle were extracted. The left ventricle was divided into seven segments according to the American Heart Association classification. Wall motion was scored as follows: 1, normal; 2, mild to moderate hypokinesis; 3, severe hypokinesis; 4, akinesis; 5, dyskinesis; and 6, aneurysm. The scores obtained by MSCT were compared with those obtained by LVG. The wall motion scores were analyzed using the chi-squared independence test (6 x 6 contingency table).

RESULTS

Wall motion could be assessed in all segments of the 20 patients using interactive multiplanar animation. Among a total of 140 segments in 20 patients, scores in 118 were concordant between MSCT and LVG (118/140, 84.3%).

CONCLUSION

The 16-MSCT can accurately assess LV wall motion.

Synergy of MDCT and Cine MRI for the Evaluation of Cardiac Motility

OBJECTIVE

The objective of our study was to validate the feasibility of the synergistic use of cardiac MR and CT data sets for ventricular motility analysis and to correlate measurement variability with underlying heart rate.

SUBJECTS AND METHODS

Twenty patients underwent concurrent ECG-gated MDCT and MRI for evaluation of ventricular motility, expressed as ventricular wall thickening and motion. Initially, individual measurement repetition series were analyzed by determining intraobserver variability and detecting intraobserver bias related to heart rates. Subsequently, absolute measurement differences of CT or MR data were statistically evaluated. Finally, absolute measurement differences were correlated with underlying heart rates by curve estimation regression.

RESULTS

Analysis of measurement reproducibility proved that data variability was dependent on only the anatomic localization of the analyzed ventricular segment, not on the imaging technique used or underlying heart rate, in normofrequent patients. Comparing MR and CT image data sets, no statistically significant differences were identified when ventricular motility was evaluated based on data sets of either imaging technique in normofrequent patients. Tachycardic frequencies, above 100 beats per minute, led to exponential error propagation due to insufficient temporal resolution of the current CT technology.

CONCLUSION

This study proved that cardiac motility assessment based on ECG-gated CT and MR data sets resulted in comparable ventricular function results for normofrequent patients; however, the high spatial resolution of cardiac MDCT cannot compensate for the lack of temporal resolution in patients with tachycardia, thus emphasizing the necessity of reporting ventricular motility analysis results in combination with heart rate to allow consideration of this possible cause for measurement variation.

Internal defibrillation with minimal skeletal muscle activation: A new paradigm toward painless defibrillation

BACKGROUND

Shock-induced pain produces substantial morbidity in recipients of implantable cardioverter-defibrillators (ICDs). This pain likely derives from activation of skeletal muscle and associated nerves in the chest and abdomen. In an effort to develop a painless defibrillation system, we designed an electrode arrangement that incorporates a conductive sock placed around the heart to confine the electric shock field to cardiac tissue.

OBJECTIVES

The purpose of this study was to test whether cardiac defibrillation could be achieved without skeletal muscle activation using a novel electrode system.

METHODS

Eight adult mongrel dogs were studied. Force of skeletal muscle contraction was measured by strain gauges attached to the forelimbs during delivery of internal shocks ranging in energy from 0.1 to 31 J. Biphasic shocks were delivered (1) between a right ventricular coil and a subcutaneous dummy can (standard configuration), and (2) between a left ventricular coil and an epicardial electrode sock. Internal and external defibrillation thresholds (DFTs) were determined for each electrode configuration.

RESULTS

Shock-induced muscle contraction force was significantly lower using the sock electrode than with standard ICD electrodes at every shock energy level tested (P < .0001). Internal DFT was similar between electrode configurations (sock electrode: 8.6 +/- 4.2 J; standard: 11.0 +/- 6.3 J, P = .4), but muscle contraction force at DFT was greatly reduced with the new electrode system (1.8 +/- 2.0 kg vs 10.6 +/- 2.1 kg, P < .0001). The sock electrode rendered external defibrillation impossible, however, even at 360 J.

CONCLUSION

Skeletal muscle activation induced by ICD shocks can be greatly reduced using an electrode system that confines the electric shock field to the heart. Refinement of this strategy may allow for delivery of painless shocks by ICDs. Further development is needed to overcome implant complexity and the higher external DFT with this type of electrode system.

Assessment of Mitral Valve Regurgitation at Electron-Beam CT: Comparison with Doppler Echocardiography

PURPOSE

To prospectively compare mitral valve regurgitation fractions calculated at electron-beam computed tomography (CT) (Doppler echocardiography as reference standard) and to evaluate accuracy of electron-beam CT volume and flow measurements compared with magnetic resonance (MR) imaging results.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Volume and flow measurements were performed at electron-beam CT in 219 patients (197 men, 22 women; mean age, 61.5 years +/- 10.4 [standard deviation]), of whom 157 had known isolated mitral valve regurgitation. Regurgitation volume was calculated as the difference between left ventricular total and forward stroke volumes. Regurgitation fractions were compared with corresponding echocardiographic grades (grades 0-IV) by using Spearman rank correlation and a weighted kappa test. In 22 patients, CT volume and flow measurements were compared with MR results by using intraclass correlation.

RESULTS

Regurgitation fractions at CT correlated well with echocardiographic grading (rank correlation coefficient, r(S) = 0.82; P < .05). Mean regurgitation fractions for echocardiographic grades 0, I, II, III, and IV were 3.1% +/- 6.2, 12.7% +/- 9.9, 25.3% +/- 12.3, 40.4% +/- 11.5, and 55.9% +/- 13.7, respectively. The most suitable thresholds for differentiating echocardiographic grades were calculated regurgitation fractions of 6%, 20%, 30%, and 44%; with these thresholds, individual echocardiographic grades were differentiated (grades 0 vs I-IV, 0-I vs II-IV, 0-II vs III-IV, and 0-III vs IV, respectively) with sensitivities of 89%, 87%, 86%, and 93% and specificities of 81%, 87%, 92%, and 91%, respectively. There was perfect agreement in classification of mitral valve insufficiency between electron-beam CT and echocardiography in 134 (61%) patients and a mismatch by one grade in 72 (33%) and by two grades in 13 (6%) (kappa = 0.84). Intraclass correlation coefficients between CT and MR imaging for total and forward stroke volumes and regurgitation volume and fraction were 0.88, 0.79, 0.93, and 0.89, respectively.

CONCLUSION

Electron-beam CT provides quantitative information on severity of mitral valve regurgitation, but semiquantitative classification of regurgitation showed mismatch between electron-beam CT and Doppler echocardiography by at least one grade in more than one-third of all patients.

Worldwide clinical experience with the CorCap Cardiac Support Device

It has been hypothesized that the mechanical burden associated with LV remodeling leads to increased myocardial wall stress and adverse remodeling, all of which serve to further impair cardiac performance and contribute to disease progression. The CorCap Cardiac Support Device (CSD) (Acorn Cardiovascular, Inc., St. Paul, Minnesota) is a mesh-like device that is surgically implanted around the heart. The device is designed to provide circumferential myocardial wall support, and reduce wall stress and myocyte stretch. Clinical experience with CorCap CSD implants in patients with heart failure can be divided into 3 phases: (1) initial safety studies, (2) randomized controlled trials, and (3) limited marketed release. Initial safety studies were undertaken in 48 patients recruited between April 1999 and April of 2001. In 11 patients with complete follow-up, it was noted that LV size, as measured by LV end-diastolic dimension, significantly decreased as early as 3 months postimplant, with an even greater reduction at 6 months. Most importantly, this benefit was sustained, so that the LV end-diastolic dimension stayed smaller at 1, 2, and 3 years of follow-up. There was also an improvement in LV function, as manifested by changes in LV ejection fraction. Ejection fraction was significantly increased by 3 months and appeared to reach a peak improvement by 6 months. This benefit was likewise maintained at 1, 2, and 3 years postsurgery. Hemodynamic data did not show any evidence of constrictive physiology. These preliminary safety studies had shown that the CorCap CSD could be implanted safely and without excess operative morbidity or mortality. The primary objective of the Acorn Randomized Clinical Trial is to assess the efficacy and safety of the CorCap CSD in patients with advanced heart failure despite optimal medical therapy. A randomized trial with 2 arms (mitral valve surgery randomized to CSD and cardiomyopathy randomized to medical therapy alone or with CSD) enrolled 300 patients. The primary endpoint of the trial is a change in clinical status from baseline to the end of the efficacy phase as determined by a clinical composite score. The Acorn CorCap CSD received CE mark approval in Europe in 2001 and has been available to a small number of centers in a Limited Market Release Surveillance Study (LMRSS).

Device therapy for the management of advanced heart failure

Rapid advances have been made over the last decade in the nonpharmacological treatment of patients with advanced heart failure. This article reviews the current application of device therapy including cardiac resynchronization, defibrillators, cardiac restraint devices and mechanical ventricular support in patients with advanced heart failure.