Overestimation of the severity of mitral regurgitation (MR) by the proximal isovelocity surface area (PISA) method has been reported. We sought to test whether angle correction (AC) of the constrained flow field is helpful to eliminate overestimation in patients with eccentric MR.
In a total of 33 patients with MR due to prolapse or flail mitral valve, both echocardiography and cardiac magnetic resonance image (CMR) were performed to calculate regurgitant volume (RV). In addition to RV by conventional PISA (RVPISA), convergence angle (α) was measured from 2-dimensional Doppler color flow maps and RV was corrected by multiplying by α/180 (RVAC). RV measured by CMR (RVCMR) was used as a gold standard, which was calculated by the difference between total stroke volume measured by planimetry of the short axis slices and aortic stroke volume by phase-contrast image.
The correlation between RVCMR and RV by echocardiography was modest [RVCMR vs. RVPISA (r = 0.712,
Conventional PISA method tends to provide falsely large RV in patients with eccentric MR and a simple geometric AC of the proximal constraint flow largely eliminates overestimation.
Quantitative assessment of the severity of mitral regurgitation (MR) is critical for both diagnosis of severe MR and clinical decision making of the optimal timing of surgical intervention.
Consecutive patients aged more than 18 years referred for echocardiographic examination at the Asan Medical Center were prospectively included if they showed eccentric MR from prolapsed or failed MV in echocardiography. Exclusion criteria included patients with pronounced multiple jets (≥ 2 large jets), MR from infective endocarditis, functional MR, presence of mitral stenosis or aortic valve disease of any severity, intracardiac shunt, poor echocardiographic window resulting in inadequate image quality, and atrial fibrillation or other arrhythmias that would lead to suboptimal analysis. This study was approved by the Institutional Review Board of Asan Medical Center (AMC 2013-0058), and all patients were required to provide written informed consent before participation.
Comprehensive 2D and Doppler echocardiographic examinations were performed in all patients. We followed the standards and techniques recommended by the American Society of Echocardiography.
CMR was performed using a 1.5 T CMR scanner (Magnetom Avanto, Siemens, Erlangen, Germany) with a phase array cardiac coil. A three-lead vector cardiogram was applied for retrospective electrocardiogram-gating scan. For evaluation of left ventricular (LV) stroke volume, cine images using steady state free precession technique was obtained in the short-axis and three long-axis (2-, 3-, 4-chamber) views of the LV. The short axis images covered from the LV apex to the mitral annular plane. Typical parameters of the cine image were 8-mm slice thickness (2-mm slice gap), 30 phases per R-R interval, repetition time of 43.2 ms, echo time of 1.5 ms, generalized autocalibrating partially parallel acquisitions acceleration factor of 2, a field of view of 273 × 340 mm2, and matrix of 224 × 180 pixels. For evaluation of aortic flow, breath-held, though-plane phase-contrast flow imaging was performed at the level of ascending aorta (2–4 cm above the aortic valve) with following scan parameters: repetition time, 39.2 ms; echo time, 2.6 ms; flip angle, 30°; number of average, 1; 30 phases per R-R interval; in-plane spatial resolution, 1.5 × 1.5 mm; slice thickness, 6.0 mm; and scan time, 10–15 sec. A maximum velocity started at 150 cm/sec and the maximum velocity was increased by 20 cm/sec if aliasing occurred. Blinded CMR measurements were performed by two experienced radiologists in consensus. Quantification of LV end-systolic and end-diastolic volumes was performed on the short-axis cine images after semi-automatic segmentation of the epicardial and endocardial borders. Papillary muscles were included with the LV chamber. LV stroke volume was obtained by subtracting LV end-systolic volume from LV end-diastolic volume. By tracing the borders of the aorta on flow image, aortic anterograde flow was measured. The RV using CMR (RVCMR) was calculated by the difference between LV stroke volume and antegrade aortic volumes (
Categorical variables are presented as numbers and percentages, and were compared using Chi square and Fisher's exact test. Continuous variables are expressed as mean ± standard deviation, and were compared using Student's t-test. We used the Fisher's Z transformation to assess the significance of the difference between the two correlation coefficients found in two independent samples. To test the intra- and inter-observer reproducibility of convergence angle, the intraclass correlation coefficient (ICC) was used. The kappa statistic was used to assess agreement in categorizing MR severity. MR severity was classified using calculated RV: mild MR (RV < 30 mL), moderate MR (RV of 30–59 mL), and severe MR (RV ≥ 60 mL). All reported
A total of 33 patients (mean age 52 ± 9 years) with MR due to prolapse or flail MV was included. Baseline characteristics of the patients are summarized in
The mean RVs obtained by conventional PISA, PISA with AC, and CMR were 96 ± 53 mL, 54 ± 27 mL, and 48 ± 31 mL, respectively. A quantitative comparison of RV by echocardiography and CMR is shown in
In this study, we have confirmed only a modest agreement between echocardiography and CMR in the assessment of MR severity. Of 25 patients with a diagnosis of severe MR by the conventional PISA method, 14 (56%) had non-severe MR by CMR, suggesting substantial discordance. The discordance or overestimation by the conventional PISA method can be effectively eliminated by simple geographic correction of the proximal flow field and AC should be routinely done in patients with characteristic eccentric MR.
This is not the first to report overestimation of MR severity by the conventional PISA method in the evaluation of MR severity resulting in varying degrees of discordance between CMR and echocardiography.
Recently, 3D echocardiography has been proposed as an advanced technology to overcome the inherent limitations of 2D PISA technique including geometric assumption of the proximal flow convergence region.
There were several limitations in this study. First, this study is based on a single-center clinical experience including a relatively small number of patients. Moreover, we selectively included patients with prolapse or flail MV characterized by eccentric MR. Thus, the frequency of overestimation or discordant rate cannot be generalized to all patients with different etiologies. However, we believe this selective enrollment can also be an advantage of our study, as prolapse or flail MV is the most common cause of primary MR requiring the MV surgery. The previous studies included MR patients with different etiologies including both primary and functional MR
Echocardiography is a cost-effective, readily available and well-established investigative tool for assessment of MR severity and the PISA method remains a main method for MR quantification. Along with an understanding of the inherent limitations of the 2D PISA method, a simple geometric correction of the proximal flow field, the AC, can eliminate the overestimation of RV and prevent discordant grading, especially in patients with prolapse or flail MV characterized by eccentric MR.
This study was supported by a research fund from Korean Society of Echocardiography.
Variables | Values |
---|---|
Demographic | |
Age, years | 52 ± 9 |
Male gender, n (%) | 27 (82) |
Body surface area, m2 | 1.73 ± 0.18 |
Underlying medical illness | |
Hypertension, n (%) | 13 (39) |
Diabetes mellitus, n (%) | 2 (6) |
Echocardiographic variables | |
LV end-systolic dimension, mm | 34 ± 4 |
LV end-diastolic dimension, mm | 54 ± 5 |
LV end-systolic volume, mL | 53 ± 22 |
LV end-diastolic volume, mL | 167 ± 39 |
LV ejection fraction, % | 69 ± 7 |
PISA radius, cm | 1.1 ± 0.3 (0.8–1.2) |
PISA angle, ° | 102 ± 10 (95–111) |
LV: left ventricular, PISA: proximal isovelocity surface area
PISA | CMR | PISAAC | CMR | ||||||
---|---|---|---|---|---|---|---|---|---|
Mild | Moderate | Severe | Total | Mild | Moderate | Severe | Total | ||
Mild | 0 | 2 | 0 | 2 | Mild | 4 | 3 | 0 | 7 |
Moderate | 4 | 2 | 0 | 6 | Moderate | 8 | 5 | 3 | 16 |
Severe | 8 | 6 | 11 | 25 | Severe | 0 | 2 | 8 | 10 |
Total | 12 | 10 | 11 | 33 | Total | 12 | 10 | 11 | 33 |
MR: mitral regurgitation, CMR: cardiac magnetic resonance image, PISA: proximal isovelocity surface area, AC: angle correction