Insights from Simultaneous Echo and Cath Gradients in Rheumatic Compared to Calcific Mitral Stenosis

Abstract

There are currently 2 major forms of mitral stenosis (MS), with rheumatic MS in decline and calcific MS on the rise. Calcific MS is associated with circumferential mitral annular calcification (MAC), compared to the leaflet tip stenosis seen in rheumatic MS.1Reddy Y.N.V. Murgo J.P. Nishimura R.A. Complexity of Defining Severe “Stenosis” From Mitral Annular Calcification.Circulation. 2019; 140: 523-525Crossref PubMed Scopus (24) Google Scholar MAC MS is additionally associated with a multicomorbid elderly patient profile where there is frequently superimposed left ventricular (LV) and left atrial (LA) noncompliance confounding interpretation of MS severity.2Reddy Y.N.V. Obokata M. Verbrugge F.H. et al.Atrial Dysfunction in Patients With Heart Failure With Preserved Ejection Fraction and Atrial Fibrillation.J Am Coll Cardiol. 2020; 76: 1051-1064Crossref PubMed Scopus (104) Google Scholar Doppler-derived mitral valve gradients were originally validated in rheumatic MS with high accuracy.3Nishimura R.A. Rihal C.S. Tajik A.J. et al.Accurate measurement of the transmitral gradient in patients with mitral stenosis: a simultaneous catheterization and Doppler echocardiographic study.J Am Coll Cardiol. 1994; 24: 152-158Crossref PubMed Scopus (116) Google Scholar The use of Doppler echocardiography to estimate MAC MS gradients has been largely extrapolated from the rheumatic MS literature without simultaneous echo-cath validation studies. We have observed significant discrepancies between the echo-estimated and cath-measured instantaneous mitral gradients in MAC MS, in contrast to rheumatic MS where the correlations are excellent (Figure 1). The figure demonstrates simultaneous echo-estimated instantaneous pressure gradients by Bernoulli compared with the directly measured LA-LV pressure gradient by catheterization in the 2 forms of MS. Note the excellent concordance in measured and estimated instantaneous pressure gradient in rheumatic MS in both the mean gradient and temporal profile of changes through diastole. In contrast, MAC MS is generally associated with a large LA v wave (and associated high mitral inflow E wave) reflective of functional LA noncompliance, but the early diastolic catheterization gradient tends to be higher than the early gradient estimated from Doppler. This is followed by a rapid y descent and equalization of LA-LV pressures in MAC MS, and notably this equalization is not demonstrated in the echo-estimated pressure gradients, which decline much more slowly (despite the known LV noncompliance frequently present in MAC patients) without demonstrable pressure equalization by echo. Given that echocardiography is currently critical to patient selection for MAC MS interventions, further study of the source of these echo-cath discrepancies would be of great interest. The rapid early diastolic filling from a large LA v wave may contribute inertial forces to the cath pressure gradient4Firstenberg M.S. Vandervoort P.M. Greenberg N.L. et al.Noninvasive estimation of transmitral pressure drop across the normal mitral valve in humans: importance of convective and inertial forces during left ventricular filling.J Am Coll Cardiol. 2000; 36: 1942-1949Crossref PubMed Scopus (62) Google Scholar that are ignored in the simplified Bernoulli equation for Doppler gradient estimation, thereby underestimating instantaneous echo gradients in early diastole. Proximal velocities may also be nonnegligible during mid diastole, potentially contributing to an overestimation of the instantaneous echo mitral gradient by the simplified Bernoulli equation in mid diastole and a tendency for the decline in instantaneous echo gradient to be slower than the changes in true pressure measured at cath. Since MS gradients vary substantially based on heart rate and preload, metrics based on the pattern of instantaneous gradient change on resting echo (such as the pressure half time) are commonly used to assess the severity of rheumatic MS. Although such patterns may provide qualitative insight into the degree of LV/LA noncompliance (with a short pressure half time) versus true stenosis (with a longer pressure half time), they should not be used to calculate a mitral valve area in MAC MS. The pressure half-time valve area calculation was validated in rheumatic MS with an empirical constant of 220 used to generate a valve area,5Stamm R.B. Martin R.P. Quantification of pressure gradients across stenotic valves by Doppler ultrasound.J Am Coll Cardiol. 1983; 2: 707-718Crossref PubMed Scopus (220) Google Scholar and given the LV-LA compliance abnormalities and incongruent instantaneous echo-cath pressure changes demonstrated in MAC MS, calculation of valve area with a rheumatic MS–derived constant is prone to error. Independent of valve area, the observed differences between instantaneous gradients in MAC compared to rheumatic MS may also have potential diagnostic value to identify subsets with greater obstruction where valve intervention may be appropriate, as well as those with more myocardial problems that may benefit more from medical therapy.