Methods

A retrospective analysis was performed on 81 consecutive patients affected by FMR submitted to percutaneous MVR with the MitraClip device form October 2008 to December 2012. Clinical, echocardiographic, operative, and outcome data were collected prospectively in a specifically designed database. Patients were selected for the procedure if they had moderate-to-severe (3+) or severe (4+) MR as graded according to the recommendations of the American Society of Echocardiography, and if they met class I or IIa indications for mitral valve surgery as recommended by the 2006 American College of Cardiology/American Heart Association guidelines for management of patients with valvular heart disease. MR was defined functional if resulting from either a regional or global left ventricular remodeling and/or dysfunction in the presence of an anatomically normal valve apparatus. MitraClip therapy suitability was decided by an interdisciplinary heart team.

All procedures were performed by an experienced operator (FM). The procedure was performed under general anesthesia using 3-dimensional transesophageal echocardiography and fluoroscopy guidance. The MitraClip device was advanced after an echo-guided transseptal catheterization to the left atrium and across the mitral valve to the left ventricle. The leaflets were grasped and the arms of the clip were closed. The reduction of MR severity was assessed by color Doppler echocardiography in a semiquantitative manner, added to the assessment of the width of the vena contracta. More than 1 clip was placed if further reduction of MR was needed. All patients were transferred to the intensive care unit (ICU) after the procedure.

Transthoracic echocardiographic data collected before the procedure, in the early postoperative period (within 12 hours from the procedure, while the patients were in the ICU), and before the hospital discharge were analyzed. All examinations were performed by experienced investigators (GM and SA) using commercially available ultrasound systems (E9; GE Vingmed, Horten, Norway and iE33; Philips Medical Systems, Andover, Massachusetts). Off-line analyses of examinations were conducted by an independent expert investigator, who was not involved in MitraClip implantation procedure (MK). Chamber quantifications and Doppler measurements were performed according to the criteria of the American Society of Echocardiography. From the apical 4- and 2-chamber views, left ventricular end-diastolic and end-systolic volumes and left ventricular ejection fraction (LVEF) were calculated by the biplane method of discs. Right ventricular (RV) function was studied through multiple parameters (tricuspid annular plane systolic excursion, tissue Doppler systolic velocity of tricuspid annulus, and RV fractional area change) according the recent recommendations of the American Society of Echocardiography. RV dysfunction was defined in presence of at least one of the following criteria: tricuspid annular plane systolic excursion <16 mm, tissue Doppler systolic velocity of tricuspid annulus <10 cm/s, and fractional area change <35%. Pulmonary artery systolic pressure was estimated from tricuspid regurgitation velocity and right atrial pressure. Left ventricular end-systolic wall stress (LVESS) was calculated by the method of Reichek et al : LVESS (dynes/cm ² ) = 0.334·(SBP)·(ESD)·PWs ⁻¹ ·[1 + (PWs/ESD) ⁻¹ ], where SBP is systolic blood pressure (mm Hg), ESD is end-systolic diameter, and PWs is left ventricular posterior wall thickness at end-systole.

All patients undergoing MitraClip procedure were included consecutively in the study. Patients without significant reduction of MR (postprocedural MR >2+) were excluded from the analysis, because persistence of significant mitral leakage would not have changed left ventricular afterload condition after MitraClip implantation. Also, patients requiring emergent open mitral repair or replacement were excluded. Only patients with available echocardiographic assessment of left ventricular function in the ICU were included.

Patients were assigned to 2 groups according to the occurrence of the afterload mismatch: patients with afterload mismatch (AM+) and patients without afterload mismatch (AM−). Afterload mismatch was defined as an acute reduction of LVEF after MVR procedure compared with baseline. The acute change of the LVEF after MVR procedure was calculated as (early postoperative LVEF − preoperative LVEF)/preoperative LVEF. We considered significant an acute reduction of 28% compared with baseline. This value represents the median value of the LVEF reduction and was considered as the threshold to define the occurrence of afterload mismatch. Baseline preoperative demographics and clinical and echocardiographic data were compared between the 2 groups.

The following adverse event rates occurring in the early postoperative period were collected: new-onset RV dysfunction, pulmonary hypertension (defined as systolic pulmonary pressure >50 mm Hg or persistence of pulmonary hypertension), need for inotropes (defined as need of either dopamine, dobutamine, or epinephrine at any dose), new-onset renal failure (defined as R-RIFLE [Risk of renal dysfunction, Injury to the kidney, Failure of kidney function, Loss of kidney function and End-stage kidney disease] ), and prolonged length of stay in the ICU (defined as a stay of >24 hours). The effect of afterload mismatch on long-term mortality was evaluated. The mean follow-up period was 14.6 ± 11 months (range 6 to 48.3). All included patients had at least 6-month follow-up at the time of the analysis; 76.7% of patients completed 1-year follow-up period. Clinical and echocardiographic follow-up visits were performed at our clinic in 89.4% of patients, the remaining with telephonic interview and questionnaire.

Statistical analysis was conducted using the JMP 8.0 software (SAS Institute Inc., Cary, North Carolina). Continuous variables are presented as mean ± SD or as median (interquartile range, Q1 to Q3), and categorical variables are expressed as percentage. Univariate comparisons were performed with Student unpaired or paired t test for continuous normally distributed data, which were tested by the Shapiro-Wilk normality test. Mann-Whitney rank sum test was used for comparisons of nonparametric continuous data and the chi-square test for categorical data. Survival was assessed using the Kaplan-Meier method and the log-rank method was used for comparison. A p value of ≤0.05 was considered statistically significant, and all reported p values are 2-sided. Univariate analysis of predictors for events was performed with nominal logistic regression.

The study protocol was performed in accordance with the institutional ethics committee, and all patients gave informed written consent for the procedures. The need for consent to participate in this research study was waived in view of its observational and anonymous nature.

Results

Complete clinical and echocardiographic baseline and follow-up data were available in 78 patients. Three patients with postprocedural MR ≥3 and 2 patients requiring emergent open mitral surgery were excluded from the analysis. The mean age was 69 ± 9 years; 61 patients (84%) were male. The clinical characteristics of the study population are listed in Table 1 .

Echocardiographic characteristics of the population are listed in Table 2 . All patients had moderate-to-severe or severe MR. Most patients presented with severe left ventricular dilatation, with increased end-diastolic diameter and ESD, associated with a significant reduction of LVEF (mean 27 ± 9%, range 12 to 52) and pulmonary hypertension (mean 50 ± 15 mm Hg, range 25 to 82); 40 patients (55%) had RV dysfunction.

At least 1 MitraClip was successfully implanted in all patients. MitraClip therapy reduced the severity of MR in all patients, with at least a decrease of 2 degrees. Residual MR was absent or trivial in 16 patients (22%), mild in 37 (51%), and moderate in 20 (27%). Most patients (53 patients, 73%) needed implantation of >1 clip (in 4 patients (5%), 3 clips were implanted). No patient suffered from postprocedural mitral stenosis, defined as mean transmitral gradient >5 mm Hg or planimetric mitral valve area <2.5 cm ² . Blood pressure, heart rate, and rhythm are provided in Table 3 .

Afterload mismatch was observed in 19 patients (26%) in the early postoperative period (AM+ group). Such patients experienced a significant acute reduction of the LVEF, consistent with the study definition of the afterload mismatch: at baseline, mean LVEF was 27% in both AM+ and AM− groups, whereas in the postprocedural evaluation it was 18% in AM+ versus 29% in AM− group (p = 0.0001).

Preoperative clinical characteristics were not significantly different between groups ( Table 1 ). Univariate comparison of the echocardiographic preoperative variables from the group AM+ and the group AM− revealed that end-diastolic diameter and ESD were both significantly larger in the AM+ group. However preoperative LVEF was not significantly different between the 2 groups. Preoperative RV dysfunction was more frequent in the AM+ group, but the difference did not reach statistical significant. No difference in preoperative systolic pulmonary artery pressure was observed between the groups. Preoperative systolic blood pressure was significantly lower in AM+ group. Incidence of afterload mismatch was not influenced by procedural success.

The postprocedural outcomes are listed in Table 4 . AM+ patients experienced an increased incidence of RV dysfunction and pulmonary hypertension. However, RV dysfunction and pulmonary hypertension significantly improved after MitraClip implantation in the overall population (RV failure 55% vs 41%, p = 0.029 and systolic pulmonary artery pressure 50 ± 15 vs 42 ± 10, p = 0.0003, respectively). No difference in acute renal failure was recorded. There was no difference in the use of inotropes in the 2 groups. The length of stay in the ICU was similar in both groups; also, the total hospital stay did not significantly differ. No difference in baseline LVESS values between the 2 groups was found. In the group AM+, a significant increase of postoperative LVESS compared with baseline LVESS values was found (p<0.001), whereas no changes in AM− group were observed (p = 0.31). Moreover, postoperative LVESS values were significant higher in AM+ than AM− group (p = 0.0068).

Table 4

Postprocedural echocardiographic data and outcomes

Variable	Overall Population (n = 73)	Afterload Mismatch		p Value
		Yes (n = 19)	No (n = 54)
MR, grade	1.1 ± 0.9	1.3 ± 0.8	1.0 ± 0.9	0.28
End-diastolic diameter (mm)	64 ± 9	68 ± 9	62 ± 8	0.0108 ∗
ESD (mm)	52.6 ± 8.3	60.7 ± 7.4	49.7 ± 6.6	<0.0001 ∗
End-systolic left ventricular posterior wall (mm)	11.3 ± 2.4	11.4 ± 2.7	11.2 ± 2.3	0.39
LVESS (dynes/cm 2 )	236.1 ± 56.5	263.3 ± 60.5	226.5 ± 52.4	0.0068 ∗
LVEF (%)	25 ± 10	17 ± 7	29 ± 10	<0.0001 ∗
LVEF ≤25%	43 (59)	18 (95)	25 (46)	0.0002 ∗
Systolic pulmonary artery pressure (mm Hg)	42 ± 10	49 ± 10	40 ± 10	0.0009 ∗
Systolic blood pressure (mm Hg)	120.9 ± 16.2	120.3 ± 15.6	121.2 ± 16.5	0.41
RV dysfunction	30 (41)	13 (68)	17 (31)	0.0049 ∗
Use of inotropes	61 (84)	16 (84)	45 (83)	0.92
Length of stay in ICU (h)	23.3 (18.6–48.8)	22.4 (18.9–43.9)	23.7 (18.3–53.3)	0.92
Length of stay in ICU >1 day	23 (36)	5 (29)	18 (39)	0.47
Hospital stay (days)	9.1 (2.13–117)	5.9 (2.9–16)	10.2 (2.13–117)	0.19
Renal failure	17 (25)	3 (16)	14 (28)	0.29
Predischarge LVEF (%)	32 ± 11	31 ± 9	33 ± 11	0.65

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