Madhavi Kadiyala

Feature Tracking: a novel method to analyze myocardial strain: Results from the CMR strain study in healthy volunteers

Objective We sought to determine normal gender-specific strain values in healthy subjects using Feature Tracking (FT-MRI).

CTA Detection of Left Atrial Stasis and Thrombus in Patients with Atrial Fibrillation.

We investigated computed tomography (CT) angiography (CTA) in assessment of left atrial appendage (LAA) stasis and thrombus in preprocedural evaluation for atrial fibrillation (AF) ablation in a large community cohort.

Afterload excess and myocardial performance.

Background Systolic circumferential and longitudinal strain(CSt%, LSt %) are widely used to assess myocardial performance, but their afterload dependence has not been well characterized. Using geometric estimates of left ventricular (LV) circumferential and meridional wall stress(CWS, MWS) as indices of afterload at the myocardial level, we compared LV CSt and LSt to estimates of CWS and MWS in normals (NL, n= 39, 46% female, age 54.6+/-14.6 yrs) and patients with dilated cardiomyopathy (DCM, n= 35, 23% female, age 50.8+/-15.0 yrs, EF 27.2+/-10.8%). Methods

Physiologic assessment of CMR strain: afterload and contractility

Background All indices of systolic myocardial performance, including CMR strain, reflect the interplay between contractile state and loading conditions. However, CMR strains have been used largely in descriptive fashion, without consideration of physiologic determinants. We have previously demonstrated the role of increased afterload as a determinant of CMR strain using feature tracking (FT) in dilated cardiomyopathy as compared to normals, as well as the utility of an afterload index based on 3D volumetric geometric determinants (PV/M) compared to wall stress (WS) calculation. We have also shown the potential value of ratios of strain to afterload (S/A) as simple, practical contractility indices and that low dose dobutamine (Dob) can increase contractility, increasing both strain and strain rate without detectable change in blood pressure (BP) or heart rate (HR). However the relative sensitivity of CMR strain, S/A indices and strain rate to changes in contractile state and the performance of these indices with various CMR strain methods are unknown.

ASSESSMENT OF LEFT ATRIAL VOLUMES BY 3D CT ANGIOGRAPHY AND 2D ECHOCARDIOGRAPHY IN PATIENTS UNDERGOING ATRIAL FIBRILLATION ABLATION

In patients with atrial fibrillation (AF), left atrial size is associated with ablation outcomes and recurrence of AF. CT angiograms (CTA) are routinely performed for pulmonary vein mapping prior to ablation. We measured 3D left atrial volume (LAV) using a simple semi-automated CTA method in

Myocardial contractility and afterload in aortic stenosis

Background In aortic stenosis(AS) with normal left ventricular ejection fraction(LV EF), circumferential and longitudinal systolic strains(CSt, LSt) are reduced but the underlying mechanisms are uncertain. Conventional indices of afterload(A) per unit of myocardium are suboptimal for strain analysis and based on inaccurate assumptions about myocardial properties, while conventional contractility(C) indices address LV chamber, not myocardial properties. We have shown that the product of end-systolic pressure(P) and volume(V), divided by LV mass(M), or (PV/M), is a more effective index of A than conventional wall stress(Mirsky, J. Biophys. 1969) for strain analysis, while the ratio of strain to PV/M is an effective strain-based index of C. These methods were used to evaluate the mechanism of reduced LV strain in AS with preserved EF.

Myocardial contractility indices based on strain imaging

Background The principal determinants of chronic left ventricular (LV) dysfunction are reduced myocardial contractility and afterload excess due to adverse LV remodeling. To determine the relative contribution of each to a given instance of LV dysfunction, reliable quantitative indices of both myocardial contractility and afterload are needed. At the LV chamber level, ventricular volume and LV pressure can be used in a ventricular elastance model. But at the myocardial level, afterload must be normalized per unit of myocardium, conventionally done using wall stress (WS) calculations, while myocardial function is best characterized as systolic myocardial deformation, or strain (ST). Prior experimental model studies have suggested that the ratio of strain to afterload may be an effective contractility index. However, this has not been evaluated in human disease. We have recently shown that a nongeometric LV end-systolic afterload index (NGI, = (end-systolic LV pressure(P) × volume (V))/LV mass(M), or PV/M), may be superior to conventional circumferential WS (CWS) as a quantitative measure of afterload at the myocardial level, and correlates more closely than CWS with circumferential ST(CST), Therefore, we evaluated the ratios CST/CWS and CST/PV/ M, as candidate contractility indices in normals(NL) and in patients with nonischemic dilated cardiomyopathy(CM).

Afterload quantitation for evaluation of myocardial strain

Background Systolic myocardial strain is load dependent, but the CMR literature largely disregards effects of myocardial afterload on strain and strain rate. This may reflect well known limitations of conventional myocardial afterload assessment using wall stress analyses, which are based on erroneous assumptions about left ventricular(LV) geometry and/or myocardial material properties. Therefore, we compared the utility of a nongeometric afterload index (NGI) derived from LV pressure(P) volume(V) and mass, which requires no assumptions about material properties, to that of conventional noninvasive end-systolic circumferential stress(CWS) as determinants of CMR LV circumferential strain(CST), ejection fraction(EF) and strain rate(SR) in normals(NL) and patients with nonischemic dilated cardiomyopathy(CM).

EVALUATION OF DIASTOLIC FUNCTION BY CARDIAC MAGNETIC RESONANCE IMAGING USING A NOVEL FEATURE TRACKING TECHNIQUE AND COMPARISON WITH ECHOCARDIOGRAPHY IN HEALTHY SUBJECTS

Left ventricular diastolic function is not routinely evaluated by cardiac magnetic resonance imaging (MRI). Feature Tracking (FT-MRI) is a novel tissue tracking method, which can be easily used to derive myocardial velocity. We sought to determine the feasibility of evaluating diastolic function by

Validating feature tracking MRI for the assessment of strain rate in patients with various hemodyanamic states

Background Myocardial strain rate (SR) is a valuable measurement in assessing myocardial mechanical properties, which can be compared between subjects in the setting of various hemodynamic states. Featur et racking (FT) is an ovel method to assess SR off-line on cine images acquired in routine cardiac MRI. In this study we sought to assess SR using the FT method in a group of patients and to validate the relation of SR to LV ejection fraction (LVEF) and left ventricular end diastolic pressure (LVEDP) measured during cardiac catheterization. Methods Mean age of the cohort was 59 years with 32 patients being male (61%). The average LVEF was 49±15%, LVEDV 90±38 mL/m2 and LVEDP 14±7 mmHg. The average circumferential SR was higher in patients with a normal LVEF (≥50%) -1.6±0.4s-1 versus patients with a low LVEF (<50%) -0.7±0.4s-1 (p<0.001). Significant dif- ferences were also noted in average radial SR in patients with normal LVEF 2.1±0.8s-1 versus 0.9±0.5</s-1 (p<0.001) in patients with a low LVEF. While average strain rates were consistently higher in patients with a normal LVEF, there is a lack of linear correlation between circumferential SR and radial SR with LVEF (p=0.241 and 0.987, respectively). In contrast, among patients with low LVEF, the correlation was excellent with r=0.810 (p<0.001) for circumferential SR and r=0.730 (p=0.002) for radial SR. In univariate analysis LVEDP significantly correlated with circumferential SR and radial SR (r=0.579, p<0.001 and r=-0.438, p=0.001, respectively). However, in am ultivariate regression model including LVEDP, LVEF, LVEDV, and LVESV as covariables to assess their relationship to circumferential SR and radial SR, LVEDP was not significantly asso- ciated with either SR measurements while LVESV and LVEF were significantly associated with circumferential SR and radial SR. Conclusions FT-MRI is a promising method to assess SR in off-line standard cine images. SR assessed by FT is sensitive to change in global LV dysfunction yet independent of LV preload condition. Funding None.