Assessment of cardiac remodeling in asymptomatic mitral regurgitation for surgery timing: a comparative study of echocardiography and magnetic resonance imaging

Forty-six patients who had been under medical follow-up for moderate to severe MR in our outpatient clinic were evaluated by transthoracic echocardiography. Patients were excluded if they had MR due to ischemic heart disease and if they had an LV EF < 60% by echocardiography. Associated valve diseases such as mitral stenosis, aortic or tricuspid valve disease and arrhythmia (including sinus tachycardia) were also accepted as exclusion criteria. After these exclusion criteria, remaining 38 patients were assessed with respect to New York Heart Association (NYHA) functional class. Asymptomatic MR was defined as having functional capacity of class I or I-II according to patient's history (NYHA Class ≤I-II) and physical examination. Finally, 21 patients with asymptomatic MR were included to the study analysis. These 21 patients underwent transthoracic echocardiography and MRI for further cardiac evaluation. Before MRI was performed, all patients were reevaluated for their NYHA functional Class and physical examination findings like hypertension, tachycardia, crepitan ralles and edema; to minimize the hemodynamic dependent differences. Study protocol was approved by the local ethics committee and written informed consent was obtained from all participants.

All patients were evaluated by Sonos 7500 ultrasound machine (Philips) equipped with 2.5 MHz transducer. Two-dimensional and Doppler flow parameters were measured according to American Society of Echocardiography recommendations [8]. LA volume was calculated using the area-length technique [9, 10] from 4-chamber and 2-chamber views. LV diameters, volumes, and EFs were measured as recommended [11]. All images were analyzed on two occasions by two independent cardiologists; inter-observer correlation (rho) for maximum LVEF was 0.95 (p < 0.001) and for LA volume was 0.94 (p < 0.001).

The etiology of MR was determined according to subvalvular apparate and mitral valve morphology. The proximal isovelocity surface area was determined by measuring proximal-flow convergence [12]. Patient with an EROA >0.4 cm² was accepted as having severe MR, and >0.2 cm² as moderate MR [13]. Standard LV diastolic inflow was obtained in apical 4-chamber view by placing the sample volume at the valve tips level. Peak early inflow velocity (E) (m/s), peak atrial inflow velocity (A) (m/s), and their ratio were determined. Pulmonary vein (PV) flow velocities were obtained by positioning the sample volume into the right upper PV approximately 1 cm above its entry into the LA. Peak systolic (S) and peak diastolic (D) PV flow velocities were measured and S/D ratio was calculated. PV flow reversal duration and the velocity during atrial contraction were determined [14].

All MRI studies were acquired with a 1.5-T MRI scanner (Siemens Magnetom, Shymphony, Erlangen) and evaluated in ARGUS cardiac software (Siemens). For the evaluation of cardiac functions; images were acquired in standard planes, which were positioned either parallel to (horizontal and vertical long-axis planes) or perpendicular to the long axis of the heart (short-axis planes) [15]. We evaluated MR with standard cardiac planes obtained with ECG triggering cine gradient echo (GRE) sequences (FLASH, TrueFISP). Phase images were obtained by mitral FLASH technique. LV was scanned by consecutive sections at four chambers, long-axis, and short-axis by cine MRI. LA volumes, LA EFs, and LV EFs were measured with ARGUS software from the acquired images. LA EFs were calculated in 20 patients by MRI with the following formula: (LA end-diastolic volume-LA end-systolic volume)/LA end-diastolic volume. Axial and coronal planes were scanned at 6 mm sections by ECG-gated TrueFISP sequence to identify anatomic structure of PVs because of the connection and size variations. After determining PV connections at these images, all PVs [right upper PV, right lower PV, left upper PV, left lower PV] were displayed separately by breathold ECG-gated TrueFISP sequence with 5 mm section thickness (Figure 1). Because of breath disparities; when these sections did not pass through PVs properly, we used gap function (shifting the sections forwards and backwards only as thick as the interslice gap) to observe better images of PVs. When crosswise right upper-left lower PVs or left upper-right lower PVs were displayed at the same plane; if we considered the image was adequate, we didn't obtain additional images. To standardize these measurements, an imaginary circle that completed LA wall was drawn and right upper PVs were measured from the tangential of this circle (Figure 2). These measurements were repeated at the end of both systole and diastole. Right upper PV indices were calculated in 19 patients with the following formula: (Right upper PV diastolic diameter- Right upper PV systolic diameter)/Right upper PV diastolic diameter as a sign of atrial compliance. Right and LV volumes were assessed by ECG-triggered cine sequence and breathhold technique. The contours were drawn manually. The relationship between the severity of MR and PV index was assessed. LA EFs were also evaluated in patients with both depressed and normal LV EFs. Variability between the measurements of MRI was evaluated in 12 randomly selected subjects twice by the same observer and by two independent observers for interobserver and intraobserver variabilities. The measurements by two independent observers and by the same observer at different times did not differ in statistically significant terms (p > 0.05).

Statistical analysis was performed with SPSS 13.0 software. All values were expressed as mean ± standard deviation. Association between PV indices and echocardiographic parameters were evaluated with Pearson and Spearman correlation analysis. P value less than 0.05 was considered as statistically significant. Independent sample t test was performed to compare means of variables of groups to determine the statistical significance of difference. The relationship between echocardiograhic measurements and MRI measurements was analyzed by linear regression and Bland Altman analysis (Figure 3).