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J Thorac Cardiovasc Surg 2008;135:1247-1253
© 2008 The American Association for Thoracic Surgery
Surgery for Acquired Cardiovascular Disease |
a Department of Radiology, Division of Image Processing, Leiden University Medical Center, The Netherlands
b Department of Cardiothoracic Surgery, Leiden University Medical Center, The Netherlands
c Department of Cardiology, Leiden University Medical Center, The Netherlands
d Department of Radiology, Leiden University Medical Center, The Netherlands
Received for publication May 1, 2007; revisions received September 20, 2007; accepted for publication October 4, 2007. * Address for reprints: Jos J. M. Westenberg, PhD, Division of Image Processing, Department of Radiology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands. (Email: j.j.m.westenberg{at}lumc.nl).
| Abstract |
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Methods: Twenty-two selected patients (eligible to undergo magnetic resonance imaging) with mild to moderate heart failure (mean New York Heart Association class 2.2 ± 0.4), dilated cardiomyopathy (left ventricular ejection fraction 37% ± 5%, left ventricular end-diastolic volume 215 ± 34 mL), and severe mitral regurgitation (grade 3–4+) underwent restrictive mitral annuloplasty. Magnetic resonance imaging was performed 1 week before surgery and repeated after 3 to 4 years.
Results: There was no hospital mortality or major morbidity. Two patients died during follow-up (9%), and 2 patients could not undergo repeat magnetic resonance imaging because of comorbidity. New York Heart Association class improved from 2.2 ± 0.4 to 1.2 ± 0.4 (P < .05). Mitral regurgitation was minimal at late echocardiographic follow-up. There were significant decreases in indexed (to body surface area) left atrial end-systolic volume (from 84 ± 20 mL/m2 to 68 ± 12 mL/m2, P < .01), left ventricular end-systolic volume (from 42 ± 14 mL/m2 to 31 ± 12 mL/m2, P < .01), left ventricular end-diastolic volume (from 110 ± 18 mL/m2 to 80 ± 17 mL/m2, P < .01), and left ventricular mass (from 76 ± 21 g/m2 to 66 ± 12 g/m2, P = .03). Forward left ventricular ejection fraction improved from 37% ± 5% to 55% ± 10% (P < .01). Indexed left atrial end-diastolic volume did not show a significant decrease (from 48 ± 16 mL/m2 to 44 ± 10 mL/m2, P = .15).
Conclusion: Magnetic resonance imaging confirms sustained significant reverse left atrial and ventricular remodeling at late (3–4 years) follow-up in patients with nonischemic, dilated cardiomyopathy, and mild to moderate heart failure after restrictive mitral annuloplasty.
| Introduction |
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| Materials and Methods |
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Patients selected for this study had to be eligible to undergo repeat MRI examination. Therefore, in addition to general MRI exclusion criteria (ie, pacemakers/defibrillators, intracranial clips, pregnancy, claustrophobia), disease-related specific criteria were applied. These included the presence of (supra)ventricular arrhythmias or an existing indication for postoperative (biventricular) pacemaker/defibrillator implantation. To maintain uniformity of surgical intervention in this small patient group, additional valve surgery, including tricuspid valve repair, was another exclusion criterion. These factors inevitably limited the patient selection to those with relatively mild heart failure, a group of patients representing the better part of our heart failure program. None of the patients had pulmonary hypertension, and all patients had preserved right ventricular function. MRI was performed within 1 week before surgery and repeated 3 to 4 years later (43 ± 8 months). At follow-up, a routine transthoracic echocardiographic examination was performed.
Surgery
All surgical procedures were performed via a midline sternotomy under normothermic cardiopulmonary bypass with intermittent antegrade warm blood cardioplegia. The mitral valve was exposed through a vertical transseptal approach along the right border of the foramen ovale, leaving the roof of the left atrium untouched. Ring size (Carpentier-Edwards Physio ring, Edwards Lifesciences, Irving, Calif) was determined after careful measurement of the intercommissural distance and height of the anterior leaflet, and then downsizing by 2 ring sizes (ie, size 26 when measuring 30). All patients had intraoperative transesophageal echocardiographic assessment of valve function. Mitral valve repair was considered successful if there was no residual MR and a leaflet coaptation height of at least 8 mm at the A2-P2 level was achieved on intraoperative echocardiography.
Magnetic Resonance Imaging
MRI was performed using a 1.5 T MRI scanner (ACS-NT15 Gyroscan with the Powertrack 6000 gradient system; Philips Medical Systems, Best, The Netherlands). The body coil was used for transmission, and a 5-element phased-array synergy cardiac-coil was placed on the chest for signal reception. Standard 2- and 4-chamber long-axis series and a complete set of short-axis cine acquisitions were performed (conform standard cardiac MRI protocols5
using steady-state free precession6
) with the patient performing a breath hold in end expiration. Imaging parameters of the 2- and 4-chamber long-axis series and for the short-axis series were as follows: TE/TR = 1.52/3.0, flip angle = 50 degrees, field of view = 350 mm, scan matrix = 192 x 153, slice thickness = 8 mm, and gated cardiac triggering with retrospective reconstruction of 30 phases. For the short-axis series, 10 to 12 parallel oriented slices were acquired with a 2-mm slice gap, 1 slice during each breath hold. LVEDV and LV end-systolic volume (LVESV) (from short-axis MRI7
) and LAEDV and LAESV (from measuring biplane area-length in orthogonal long-axis 2- and 4-chamber views3
) were obtained by manual segmentation. Image analysis was performed blinded with respect to echocardiographic data.
In the presence of significant MR, LVEF does not represent the true forward blood flow (through the aortic valve) because a substantial part of the blood volume leaks back into the left atrium. To correct for this effect, we have recently used the "forward LVEF," which was derived by calculating the ratio of the forward stroke volume and the EDV.3
The forward stroke volume was obtained from aortic flow measurements derived from velocity-encoded MRI.8
QMass and QFlow software (Medis, Leiden, The Netherlands) were used for image analysis. MRI examination was repeated at 3 to 4 years follow-up, and similar parameters were assessed. Significant reverse remodeling was defined as a volume reduction exceeding 15%. An increase in forward LVEF of 5% or more and a decrease in LV mass 10 g or more were considered significant.3
The medical ethics committee of our institute approved all examinations. All patients gave informed consent.
Statistical Analysis
Continuous data were expressed as mean ± standard deviation and compared using the Student t test for paired data.
| Results |
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During follow-up, 2 patients (9%) died of refractory heart failure before repeat MRI. In 2 additional patients, follow-up MRI could not be performed because of comorbidity (Alzheimer's disease and amyotrophic lateral sclerosis). There were no cases of endocarditis or thromboembolic events.
At late follow-up (43 ± 8 months) NYHA class was 1.2 ± 0.4 (P < .05 vs baseline), and transthoracic echocardiography showed minimal MR (mean grade 0.6 ± 0.5), with a mean leaflet coaptation length of 8 ± 3 mm, without mitral stenosis.
Reverse Remodeling on Magnetic Resonance Imaging
Figure 1 shows the LA and LV reverse remodeling assessed by MRI. The MRI results are summarized in
Table 1. Although LAEDVi (i indicating indexation to body surface area) did not decrease significantly (predefined by a volume reduction
15%) (from 48 ± 16 mL/m2 to 44 ± 10 mL/m2, P = .15), significant LA reverse remodeling for EDV occurred in 56% of the patients. Individual data are presented in
Figure 2, A. LAESVi decreased significantly from 84 ± 20 mL/m2 to 68 ± 12 mL/m2 (P < .01), with significant LA reverse remodeling for ESV occurring in 67% of patients (Figure 2, B).
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5% in forward LVEF); individual results are shown in
10 g) from 76 ± 21 g/m2 to 66 ± 12 g/m2 (P = .03). In addition, 83% of the patients showed a significant decrease in LV mass (Figure 4, B).
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| Discussion |
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However, the use of MRI for follow-up purposes is still limited by technical factors, and, as explained before, the patient group presented here represents the better part of our heart failure program. Currently, all patients with heart failure undergo MRI before surgery, but only those not requiring implantation of an epicardial LV lead or a pacemaker/defibrillator and those without (supra)ventricular arrhythmias are eligible to undergo follow-up MRI. These contraindications currently hamper widespread use of MRI in patients with heart failure. It is expected that these technical limitations of MRI will be overcome in the near future, which will greatly increase the possibilities of follow-up imaging in patients with heart failure.
In the current study, the beneficial effects of restrictive mitral annuloplasty in a selected group of patients with mild to moderate heart failure was shown. Currently, not much information on the effects of restrictive mitral annuloplasty in this patient category is available. Acker et al10
recently reported initial results from the Acorn trial. In this study, a subgroup of patients with mild heart failure (NYHA class II and relatively preserved LVEF and functional MR) underwent isolated mitral valve surgery, similar to the patients in the current study. The outcome of this subset of patients was not reported separately, making direct comparison with the current findings impossible.
Another conclusion that can be drawn from the present study is that treatment of functional MR in nonischemic dilated cardiomyopathy by restrictive annuloplasty alone eliminates MR and leads to LA and LV reverse remodeling in the majority of this selected patient population. It has been questioned whether LV reverse remodeling is maintained over longer follow-up periods. Our current results confirm that LV reverse remodeling is indeed present at long-term follow-up. These favorable results may be related to the fact that only patients with milder heart failure were included (mean NYHA class 2.2 ± 0.4 and mean forward LVEF 37% ± 5%), reflecting the less ill patients in our heart failure program. In addition, only patients with preserved right ventricular function and without pulmonary hypertension or significant tricuspid regurgitation were selected. For reference, in our institution patients with more advanced stages of heart failure undergo tricuspid annuloplasty when significant tricuspid regurgitation or severe annular dilatation (annular diameter
40 mm) is present. When LV end-diastolic diameter exceeds 65 mm, an external cardiac constraint device (CorCap cardiac support device; Acorn Cardiovascular, St Paul, Minn) is also applied. These patients have a 6% operative mortality, and long-term results are currently being evaluated. When LV end-diastolic dimension exceeds 80 mm, surgical LV restoration is considered as described by Isomura et al.11
The current results strengthen the hypothesis that grades 3 to 4+ functional MR can be successfully treated by restrictive mitral annuloplasty in patients with LV dilatation but relatively mild heart failure (NYHA class II to III). On a patient basis, 89% and 72% of patients exhibited a significant reduction in LV volumes. These observations are clinically relevant because LV function and volumes have been demonstrated to be important predictors of long-term outcome in patients with LV dysfunction.12,13
Also, LA dimensions have been shown to provide prognostic information.14,15
In the present study, LA volume in end systole showed a significant decrease, although LA volume in end diastole did not exhibit a decrease in the entire study population.
On the basis of the reverse remodeling observed in the current study, one could speculate that the point of no return (irreversible LV dilatation) was not yet reached in this patient category, suggesting that mitral valve surgery may be considered at an earlier stage in patients with nonischemic dilated cardiomyopathy. Further prospective studies are needed to confirm the benefit of early surgical intervention in patients with mild heart failure.
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| Footnotes |
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| References |
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