Eur J Cardiothorac Surg 2004;25:84-90
© 2004 Elsevier Science NL
Passive external cardiac constraint improves segmental left ventricular wall motion and reduces akinetic area in patients with non-ischemic dilated cardiomyopathy
Alexander Lembckea*,
Simon Dusheb,
Christian N.H. Enzweilera,
Christian Kloetersa,
Till H. Wiesea,
Kay-Geert A. Hermanna,
Bernd Hamma,
Wolfgang F. Konertzb
a Department of Radiology, Charité Medical School, Humboldt Universität zu Berlin, Berlin, Germany
b Department of Cardiovascular Surgery, Charité Medical School, Humboldt Universität zu Berlin, Schumannstrasse 20/21, 10098 Berlin, Germany
Received 23 June 2003;
received in revised form 25 September 2003;
accepted 28 September 2003.
* Corresponding author. Tel.: +49-30-450-527038; fax: +49-30-450-527905
e-mail: alexander.lembcke{at}gmx.de
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Abstract
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Objective: To verify changes in left ventricular (LV) volumes and regional myocardial wall motion after implantation of a textile cardiac support device (CSD) for passive external constraint in non-ischemic dilated cardiomyopathy. Methods: In nine male patients participating in a non-randomized clinical trial LV volumes were determined and the segmental LV wall motion was studied by contrast-enhanced electron-beam CT in a sectionwise manner at three ventricular levels (base, middle and apex of ventricle) before and 32±6 months after CSD implantation. In 16 myocardial segments ejection fraction and wall thickening were measured semiautomatically after drawing the myocardial contours. The wall motion score index was calculated based on semiquantitative visual grading in each segment. Results: The global LV volumes decreased significantly from 304.3±90.9 to 231.5±103.9 ml at end-diastole and from 239.7±83.7 to 164.0±97.7 at end-systole (P<0.05). Overall ejection fraction increased from 14.8±8.2 to 25.7±17.1% (P<0.05). A segment-by-segment analysis demonstrated a significant increase of regional ejection fraction in the basal myocardium as well as in the mid-inferior, mid-inferolateral, and mid-anterolateral myocardium. Overall wall thickening increased from 16.4±13.3 to 24.2±18.1% (P<0.05), but without significant differences in a segment-by-segment comparison. The mean wall motion score index improved from 2.70±0.26 to 2.20±0.71 (P<0.05), with an increased wall motion in eight (89%) patients. A section-by-section analysis demonstrated significantly improved wall motion in the inferior and lateral segments at each ventricular level. Postoperatively, the number of akinetic and markedly hypokinetic segments decreased significantly (P<0.05) from 56 (39%) to 26 (18%) and from 76 (53%) to 56 (37%), respectively. Conclusion: CSD implantation improves segmental wall motion, predominantly in the inferior and lateral myocardium, and reduces the number of akinetic and hypokinetic segments.
Key Words: Computed tomography (CT) • Electron beam • Congestive heart failure • Dilated cardiomyopathy • Heart-assist device • Mechanical circulatory support
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1. Introduction
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Congestive heart failure (CHF) with left ventricular (LV) dilatation, wall motion abnormality, and a reduced ejection fraction represents the common end point of a variety of cardiac diseases of different etiology. It is one of the most common diseases affecting more than 20 million people worldwide and the number of patients is increasing due to prevention of premature death by optimized medical therapy and aging of the population. Surgical management of advanced CHF thus represents the fastest-growing area of cardiovascular surgery [1]. Heart transplantation has become the treatment of choice for refractory end-stage heart failure but is limited by donor organ shortage and unsuitability of patients. Additionally, transplantation is complicated by graft rejection and vasculopathy as well as adverse long-term effects associated with chronic immunosuppression [2]. A new surgical option, the implantation of a textile cardiac support device (CorCap Cardiac Support Device; Acorn Cardiovascular Inc., St. Paul, MN) aimed at preventing or delaying the further progression of CHF and the need for transplantation, is currently undergoing initial clinical trials. The cardiac support device (CSD) is a biocompatible and bidirectionally compliant mesh graft that is wrapped around the ventricles and stitched in place to stabilize the heart and prevent further cardiac deterioration (Fig. 1)
. Preliminary results of the ongoing worldwide clinical trials suggest that this technique can be safely performed and that there is a tendency towards improvement in clinical symptoms and hemodynamic parameters [3–5].
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Fig. 1. Illustration of passive external cardiac constraint showing placement and attachment of the cardiac support device on the epicardial surface of both ventricles.
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Nevertheless, the data currently available are still incomplete. Since there is a lack of information on the effects of passive cardiac constraint on regional LV function it was the aim of this study to investigate prospectively the mid-term postoperative changes of regional LV wall motion and ejection fraction in patients with CHF caused by non-ischemic dilated cardiomyopathy.
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2. Material and methods
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2.1. Study population:
A total of nine male patients (mean age of 57.7±9.4 years, range 37–71 years) participating in a non-randomized clinical safety study received the CSD without other concomitant surgical procedures (such as mitral valve repair) and underwent electron-beam CT pre- and postoperatively.
Device implantation had previously been approved by the institutional review board and all patients gave written informed consent.
Non-ischemic dilated cardiomyopathy was the underlying disease in all nine cases. Dilatation of the cardiac chambers was associated with mitral regurgitation of echocardiographic grade I in six patients, grade II in one patient, and grade III in two patients and with tricuspid valve regurgitation of echocardiographic grade I in four patients and grade III in one patient. To exclude effects from additional factors, patients who underwent concomitant mitral valve repair were not included in this study since valve repair alone may have beneficial hemodynamic effects [6]. According to the classification of the New York Heart Association (NYHA) six patients had class III disease, three patients had class II disease but with a history of at least one NYHA class III episode. All patients were on intensive drug treatment (all nine patients were on angiotensin-converting enzyme inhibitors, diuretics and digoxin, seven patients were on additional beta-blocker therapy or received other cardiac medication) and in a stable condition. After implantation of the cardiac support device the preoperative drug regimen was continued in all patients without any postoperative changes. Dosages were not increased and no additional cardiac medication was given.
Candidate patients were excluded if they had undergone previous cardiac surgery, had an estimated survival prognosis of less than 1 year or had concomitant systemic disorder (significant pulmonary, hepatic, or renal dysfunction) as well as additional cardiovascular disease (obstructive, arrhythmic, or uncontrolled hypertension).
2.2. Surgical procedure
The CSD was implanted in a standardized fashion as described in detail elsewhere [3–5]. Briefly, after standard sternotomy and pericardiotomy the ventricles were measured in circumference and in length from apex to base to select a device of proper size. While the heart was beating on cardiopulmonary bypass, the CSD was then placed around the ventricles and anchored slightly above or below the atrioventricular groove. With the ventricles fully loaded, excess mesh was excised, the cut edges were approximated, and the mesh graft was secured to ensure a snug fit. The device was fitted in such a way as to achieve an immediate left ventricular size reduction of up to 10%, as assessed intraoperatively by transesophageal echocardiography. The pericardial sac was not closed after implantation of the CSD.
2.3. Evaluation by electron-beam CT
Contrast-enhanced electron-beam CT (Evolution scanner C-150 XP, GE Imatron, San Francisco, CA) was performed within 3 weeks preoperatively (baseline) and 32±6 months postoperatively (follow-up). Data were acquired at 625 mA and 130 kV with an acquisition time (=temporal resolution) of 50 ms, a slice thickness of 8 mm, and a matrix of 256x256.
An ECG-triggered, contrast-enhanced (using 90 ml of contrast material at a flow of 3 ml/s; iodine content 370 mg/ml; Ultravist, Schering, Berlin, Germany) cine study was performed along the approximated short heart axis, consisting of a total of 156 scans acquired during a single breathhold period in 12 slices each with 13 scans per cardiac cycle and covering the left ventricle from apex to base.
All measurements of LV volumes, ejection fraction, and wall thickening were done using the manufacturer's implemented software after visual identification and manual drawing of the endocardial and epicardial contours of the left ventricle on the images. Using the implemented software, the left ventricle was divided into 36 subsegments (12 basal, 12 midventricular, and 12 apical subsegments; Fig. 2)
, which were then assigned to the 16 segments (six basal, six midventricular, and four apical segments) distinguished in the American Heart Association classification [7]. This segmentation served as the basis for computer-assisted calculation of regional ejection fraction and wall thickening.
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Fig. 2. Fifty-six year-old patient with dilated cardiomyopathy. Status before (top) and 36 months after (bottom) implantation of the CSD. Manually traced endo- and epicardial contours for calculation of the center of the ventricle and subsequent division into 12 segments by the implemented standard software. The postoperative decrease in end-diastolic and end-systolic ventricular size as well as the postoperative increase in end-systolic wall thickness are already obvious on mere visual inspection.
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Furthermore, wall motion of all myocardial segments was assessed visually on the workstation in the cine mode by an experienced radiologist and graded semiquantatively according to the following scale: normal=1, mildly hypokinetic=2, markedly hypokinetic=2.5, akinetic=3, dyskinetic=4. The sum of segmental scores divided by the number of segments yielded the wall motion score index.
Finally, curves of global LV volume versus time were reconstructed throughout the cardiac cycle, as described previously [8]. The volume–time curves were used to calculate the following parameters of diastolic function, as defined by others [8]: early diastolic peak filling rate (PFR), early diastolic peak filling rate relative to the end-diastolic volume and to the stroke volume (PFR/EDV and PFR/SV), time to early diastolic peak filling (TPF), and early diastolic filling fraction (FF).
2.4. Data analysis and statistical methods
Data are presented as mean±standard deviation. The two-tailed Wilcoxon test for paired samples was used for comparison of the mean values between different myocardial regions and between pre- and postoperative mean values. Differences between the pre- and postoperative number of hypokinetic and akinetic segments were assessed for significance using the marginal homogeneity test. A P-value of less then 0.05 was considered significant.
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3. Results
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All patients enrolled in this study recovered smoothly from surgery, had no intraoperative complications, and tolerated the implant well without early or late episodes of device-related adverse events, renewed cardiac decompensation or ventricular arrhythmias. In the immediate postoperative period all patients were monitored in the intensive care unit and received intravenous inotropic support for a mean of 48.6±46.2 h. Three patients developed atrial fibrillation immediately postoperatively, which was successfully treated by cardioversion in all three cases. None of the patients required additional mechanical circulatory support or implantation of a pacemaker or defibrillator in the early postoperative period or further course.
In all patients electron-beam CT examinations yielded adequate data for evaluation with regular ECG triggering of data acquisition and sufficient opacification of the cardiac cavities.
CSD implantation improved clinical, morphometrical, and functional parameters. NYHA class improved significantly from 2.7±0.5 to 2.1±0.8 (all patients improved by at least one NYHA class: two patients from class III to I, four patients from class III to II, and three patients from class II to I; P<0.05). LV volume decreased from 304.3±90.9 ml to 231.5±103.9 ml during end-diastole and from 239.7±83.7 ml to 164.0±97.7 ml during end-systole (P<0.05 each). The severity of concomitant mitral insufficiency improved significantly (P<0.05), from grade III to I, from grade III to II, and from grade II to I in one patient each and from grade I to 0 in two patients. It remained unchanged in four patients with grade I. The severity of concomitant tricuspid insufficiency improved from grade III to II and from grade I to 0 in one patient each and remained unchanged in the other patients with grades I and 0.
Quantitative measurement of the ejection fraction and wall thickening as well as semiquantitative assessment of wall motion demonstrated a tendency towards improvement for all myocardial regions (Tables 1–3). For the sum of all segments mean ejection fraction increased from 14.8±8.2 to 25.7±17.1% and mean wall thickening increased from 16.4±13.3 to 24.2±18.1% (P<0.05 each). Section-by-section analysis also showed a significant increase at each ventricular level for ejection fraction (basal from 12.2±3.8 to 23.0±11.9%, midventricular from 13.8±6.3 to 26.5±16.0%, and apical from 19.6±8.4 to 30.3±19.4%, P<0.05 each; Fig. 3)
as well as for wall thickening (basal from 13.4±3.4 to 23.4±11.0%, midventricular from 19.8±9.0 to 26.4±16.1% and apical from 16.1±11.0 to 21.4±14.3%, P<0.05 each, Fig. 4)
. However, segment-by-segment analysis demonstrated a significant increase in ejection fraction for the basal, inferior, and lateral myocardial region only (Table 1), whereas for wall thickening no significant differences were found among myocardial segments (Table 2).
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Fig. 3. Mean ejection fraction and standard deviation determined at the three ventricular levels (basal, midventricular, apical) before and after CSD implantation. A significant postoperative increase in the ejection fraction is demonstrated at each of the three levels (Wilcoxon test for paired samples).
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Fig. 4. Mean wall thickening and standard deviation at the three ventricular levels (basal, midventricular, apical) before and after CSD implantation. A significant postoperative increase in wall thickening is demonstrated at each of the three levels (Wilcoxon test for paired samples).
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In addition, in our study group of patients with non-ischemic cardiomyopathy we observed a gradual decrease in regional ejection fraction from apex to base. The difference in regional ejection fraction between the basal section and the apical section was statistically significant and was seen both preoperatively and postoperatively (P<0.05 each).
The wall motion score index improved in eight patients and remained unchanged in only one patient. The mean wall motion score index changed from 2.70±0.26 to 2.20±0.71 (P<0.05). Section-by-section analysis showed significantly improved wall motion at each ventricular level (basal from 2.69±0.31 to 2.16±0.67%, midventricular from 2.73±0.27 to 2.26±0.75%, and apical from 2.78±2.2 to 2.19±0.72%; P<0.05 each), whereas segment-by-segment analysis showed significantly improved wall motion in the inferior and lateral region only (Table 3).
The proportion of akinetic and markedly hypokinetic segments significantly decreased from 39% preoperatively to 18% postoperatively and from 53% to 37%, respectively. Of a total of 144 segments, 56 were akinetic and 76 markedly hypokinetic preoperatively compared with 26 akinetic and 53 markedly hypokinetic segments postoperatively (Fig. 5)
. This decrease was associated with a significant increase in normokinetic segments from zero preoperatively to 32 (22%) postoperatively.
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Fig. 5. Semiquantitative assessment of wall motion (Scale: normal=1, mildly hypokinetic=2, markedly hypokinetic=2.5, akinetic=3, dyskinetic=4) in all 16 segments in the nine study patients before (top) and after (bottom) CSD implantation. There is a significant postoperative decrease in the number of akinetic and markedly hypokinetic segments while the number of normokinetic segments significantly increases (marginal homogeneity test).
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A postoperative decrease of EDV from 304.3±90.9 ml to 231.5±103.9 ml was accompanied by a corresponding increase of PFR/EDV from 1.0±0.2/s preoperatively to 1.3±0.6/s postoperatively (P<0.05). However, most parameters of early diastolic filling were nearly unchanged after surgery: PFR: 374.4±134.1 ml/s preoperatively vs. 359.4±124.1 ml/s postoperatively, PFR/SV 5.7±1.8/s preoperatively vs. 5.3±1.8/s postoperatively, TPF 135.7±83.5 ms preoperatively vs. 134.6±62.4 ms postoperatively and FF 41.8±15.3% preoperatively vs. 48.2±9.5% postoperatively (P>0.05 each).
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4. Discussion
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Heterogeneous abnormal regional LV function is a characteristic of idiopathic dilated cardiomyopathy. This dysfunction is attributed to various local factors rather than systemic causes. The factors discussed as underlying mechanisms comprise heterogeneous regional myocyte loss and reactive myocyte hypertrophy [9], inhomogeneous regional perfusion and autonomic innervation [10–12] as well as heterogeneity in oxidative metabolism [13] but above all regional differences in ventricular geometry and wall stress [14,15]. Enlargement and spherical deformation of the left ventricle with a concomitant increase in wall stress are the key factors in the pathogenesis of dilated cardiomyopathy [3]. This is the rationale for passive external containment by mesh graft implantation, which aims at counteracting progressive left ventricular dilatation and deformation and has evolved from dynamic cardiomyoplasty, in which a latissimus dorsi muscle flap is wrapped around the dilated heart and stimulated electrically [16]. Dynamic cardiomyoplasty increases both global ejection fraction and segmental myocardial contractility of the left ventricle but patient selection criteria and concerns about long-term muscle flap characteristics have limited its application. Furthermore, dynamic cardiomyoplasty did not reduce the incidence of arrhythmias and sudden death [17]. Dynamic cardiomyoplasty was originally based on two ideas: first, active support of systolic function and, second, passive stabilization by the additional muscle flap. However, long-term follow-up studies have demonstrated that patients with CHF do not seem to benefit from active muscle stimulation but from passive mechanical reinforcement alone, the so-called girdling effect [18,19].
In addition to constraining cardiac enlargement, the girdling effect is assumed to also reduce regional ventricular wall stress and myocardial work seems to be more efficient due to a shift of the pressure–volume relation to the left, reduced oxygen consumption, and improved adrenergic response [20]. Several studies using animal models of dilated cardiomyopathy have demonstrated beneficial effects of passive cardiac containment on myocardial structure and function [20–22], and structural, functional, and biochemical findings at the cellular level indicate that the girdling effect causes a downregulation of abnormally increased local neuroendocrine activity as well as a reduction of maladaptive regional gene expression [23,24].
The results obtained by electron-beam CT presented here confirm initial clinical experience with CSD implantation in humans. This experience suggests not only that the CSD can be implanted safely and without complications but also that patients have a significant improvement of clinical symptoms (according to NYHA classification) and an increase in global left ventricular ejection fraction with a concomitant decrease in ventricular size [3–5].
In our study group of patients with non-ischemic cardiomyopathy we observed a tendency to a more pronounced reduction in segmental ejection fraction in basal segments compared to apical segments. This regional difference was seen both preoperatively and postoperatively. Earlier studies have already demonstrated a direct correlation between regional ejection fraction and regional wall stress with wall stress being greater in basal segments than in apical segments [14,15]. This difference has been attributed to the different ratio of the diameter of the spherical ventricle to wall thickness or different degrees of increased wall stress at the different scanning levels.
However, it is still unclear whether the improved regional function is attributable to the global reduction of ventricular size alone or whether a direct local mechanical effect of the mesh graft also plays a role. The results of the present study at least indicate that a significant recovery of wall motion was most obvious in the area of the free ventricular wall while a clear-cut beneficial effect was not seen for the area of the ventricular septum, which, unlike the other myocardial areas, is not in direct contact with the mesh graft.
Positive effects on regional wall motion by the CSD have recently also been described in an animal model of acute myocardial infarction [25]. In this study, CSD implantation resulted in a decreased akinetic area and increased ventricular wall thickness compared to an untreated control group. It was hypothesized that passive cardiac containment reduces wall stress by stabilizing chamber size and increasing wall thickness. This mechanism is assumed to inhibit the migration of the akinetic border zone into the infarct and to improve contractility of this myocardial region. A similar mechanism may also lead to a more or less pronounced functional improvement of preoperatively akinetic areas in the patients with primary dilated cardiomyopathy investigated here since such improvement was seen in nearly 50% of akinetic segments following CSD implantation.
Finally, it should be emphasized that our study provides no evidence for the assumption that diastolic function of the left ventricle is compromised by the CSD. In particular, none of the parameters of early diastolic filling indicated an impairment of left ventricular diastolic function after surgery in our patients.
In summary, assessment of regional wall motion by electron-beam CT supplements other diagnostic procedures by providing important additional information on LV function before and after CSD implantation. The results presented here corroborate first reports in the literature on the potential of the CSD to improve heart failure. However, further investigations and long-term results of the ongoing worldwide clinical trials are needed for definitively assessing the benefits of this alternative surgical approach.
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5. Limitations
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The investigation was undertaken in the context of an initial non-randomized feasibility and clinical safety study limited by the investigation of a selected, relatively small sample size of heart failure patients and the lack of a control group with alternative management for comparison. Moreover, our study does not provide any reliable data on the long-term survival of patients having received the textile CSD with regard to the incidence of sudden death due to acute cardiac failure or ventricular arrhythmia. In addition, the method's systematic and random errors have to be taken into account. Particularly, manual tracing of the endo- and epicardial borders crucially relies on the examiner's experience and expertise and may be prone to bias. However, sectional imaging modalities such as electron-beam CT do not use simplified geometric models, which may reflect LV geometry only inadequately, and are therefore relatively precise in determining LV size and shape. Furthermore, data acquisition by electron-beam CT is not limited by the accessibility of individual patients and not contraindicated in patients with metal implants.
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Acknowledgments
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This study was supported in part by a research grant from Acorn Cardiovascular Inc. St. Paul, MN, USA. The authors would like to thank Holger Hotz, MD, Department of Cardiovascular Surgery, Charité for assistance in performing the surgical procedure, Christian Schmidt, GE Imatron Inc. for technical support and assistance in acquiring the data as well as Bettina Herwig for translation of the manuscript.
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Top
Abstract
1. Introduction
