Mitral stenosis: evaluation with MR imaging after percutaneous balloon valvuloplasty

Cardiac magnetic resonance imaging for assessment of mitral stenosis before and after percutaneous balloon valvuloplasty in comparison to two- and three-dimensional echocardiography

BACKGROUND

The experience with cardiac magnetic resonance (CMR) in mitral stenosis (MS) is limited in contrast to mitral regurgitation.

PURPOSE

To compare CMR versus 2D and 3D transthoracic (TTE) and 3D transesophgeal (TEE) echocardiography in assessment of rheumatic MS before and after percutaneous balloon mitral valvuloplasty (PBMV).

MATERIAL AND METHODS

Twenty consecutive symptomatic patients with MS were evaluated prospectively and independently by CMR, TTE, and TEE pre-PBMV, and by CMR and TTE post-PBMV. Mitral valve area (MVA) was assessed by CMR planimetry, TTE and TEE planimetry, and pressure half time (PHT). Further assessment included trans-mitral velocity, mitral regurgitation (MR), and left atrial (LA) volume.

RESULTS

PBMV was successful in 18 patients and failed in two patients (one with MVA <1.5 cm², one developed severe MR). Pre-PBMV and MVA by CMR, 2D TTE, biplane, 3D TTE, 3D TEE, and PHT were 1.16, 1.16, 1.10, 1.02, 1.05, and 0.99 cm², respectively. Post-PBMV, a significant increase in MVA was observed (2.15, 2.06, 2.07, 2.04, and 2.03 cm², respectively). High agreement was observed between CMR and echocardiography before and after PBMV, except for PHT method. CMR significantly underestimated trans-mitral velocity and gradients compared to echocardiography (P<0.001). Before PBMV, mild MR was observed in 11, 12, and 19 patients by 2D TTE, 3D TTE, and CMR. After PBMV, MR was observed in all patients (19 mild, one severe) by all modalities. Echocardiography significantly underestimated LA volume compared to CMR (P<0.001). LA volume decreased significantly after PBMV (P<0.001).

CONCLUSION

CMR provides comprehensive assessment of several parameters in MS patients before and after intervention. Agreement with echocardiography is acceptable.

Tools for cardiovascular magnetic resonance imaging

In less than fifteen years, as a non-invasive imaging option, cardiovascular MR has grown from a being a mere curiosity to becoming a widely used clinical tool for evaluating cardiovascular disease. Cardiovascular magnetic resonance imaging (CMRI) is now routinely used to study myocardial structure, cardiac function, macro vascular blood flow, myocardial perfusion, and myocardial viability. For someone entering the field of cardiac MR, this rapid pace of development in the field of CMRI might make it difficult to identify a cohesive starting point. In this brief review, we have attempted to summarize the key cardiovascular imaging techniques that have found widespread clinical acceptance. In particular, we describe the essential cardiac and respiratory gating techniques that form the backbone of all cardiovascular imaging methods. It is followed by four sections that discuss: (I) the gradient echo techniques that are used to assess ventricular function; (II) black-blood turbo spin echo (SE) methods used for morphologic assessment of the heart; (III) phase-contrast based techniques for the assessment of blood flow; and (IV) CMR methods for the assessment of myocardial ischemia and viability. In each section, we briefly summarize technical considerations relevant to the clinical use of these techniques, followed by practical information for its clinical implementation. In each of those four areas, CMRI is considered either as the benchmark imaging modality against which the diagnostic performance of other imaging modalities are compared against, or provides a complementary capability to existing imaging techniques. We have deliberately avoided including cutting-edge CMR imaging techniques practiced at few academic centers, and restricted our discussion to methods that are widely used and are likely to be available in a clinical setting. Our hope is that this review would propel an interested reader toward more comprehensive reviews in the literature.

Mitral valve flow measured with cine MR velocity mapping in patients with ischemic heart disease: comparison with Doppler echocardiography

Diastolic function is an important element of overall left ventricular function. The pattern of flow across the mitral valve is commonly used as a measure of diastolic ventricular function. Magnetic resonance (MR) velocity mapping of blood flow across the mitral valve was compared with Doppler echocardiography. Nineteen patients with known coronary artery disease (mean age, 62 years; 11 with previous myocardial infarction) were studied. The mean value of peak early filling velocity (+/- standard deviation) was 60.1 cm/sec +/- 14.3 with the MR method and 59.4 cm/sec +/- 13.7 with echocardiography (P = .732). The mean difference between the two measurements (95% confidence interval) was -0.8 cm/sec (-5.2 cm/sec, +2.2 cm/sec). The mean value of early deceleration was 4.3 m/sec2 +/- 1.5 with the MR method and 4.0 m/sec2 +/- 1.5 with echocardiography (P = .073). The mean difference was -0.4 cm/sec2 (-0.92 cm/sec2, +0.05 cm/sec2). The mean value of peak atriosystolic velocity was 51 cm/sec +/- 14.6 with the MR method and 62 cm/sec +/- 17.2 with echocardiography (P = .002). The mean difference was -11 cm/sec (-18.1 cm/sec, -3.45 cm/sec). Peak atrial filling was consistently lower with the MR method than with echocardiography. Time-averaged measurements of ventricular filling with MR velocity mapping are an accurate measure of early diastolic filling but underestimate the velocity of atriosystolic filling.

Imaging of the human cardiovascular system using the rapid echo flow-rephased spin-echo technique

Using a flow-rephased spin-echo technique with a short echo time of TE = 9.7 msec, "white blood" multislice and single slice first echo images of the human heart were acquired using standard 1.5 T whole-body imagers. The technique almost completely eliminates phase shifts for flow with constant velocity and constant acceleration, so the investigations with healthy volunteers show images which are almost free of the artifacts often found in ECG-gated standard spin-echo imaging of the heart. T1-weighted images with good contrast between tissue and blood are achieved at any time during the whole heart cycle. The results obtained indicate that the technique might be helpful for imaging small vessels, vessels which contain slowly flowing blood, and vessels located in regions with static field inhomogeneities, for example, lung vessels.

Evaluation of mitral stenosis by cine magnetic resonance imaging

To evaluate the ability of cine magnetic resonance imaging (cine MRI) in the assessment of mitral stenosis (MS), we studied 20 patients (14 women and 6 men, mean age 60.6 +/- 8.5 years) with rheumatic mitral valve stenosis by using an 0.5 T magnet. Cine MRI showed several signs of MS. Mitral leaflet thickening, reduced diastolic opening, and abnormal valve motion toward the left ventricular outflow tract were all common features. MS was also characterized by an abnormal diastolic transmitral signal from blood. Both left atrial and left ventricular dimensions were similar to those obtained at two-dimensional echocardiography (2-DE) (r = 0.89 and r = 0.86, respectively; p less than 0.001). A significant relationship was also found between the maximum mitral leaflet separation measured by cine MRI in diastole and the mitral valve area as calculated using the pressure half-time method and continuous wave Doppler (r = 0.81; p less than 0.001). These data indicate the improved ability of MRI to detect and assess MS and also suggest that this technique may contribute to the noninvasive assessment of MS.