1348420 - Myocardial work index as a marker of fibrosis in hypertrophic cardiomyopathy

Background: Myocardial fibrosis in hypertrophic cardiomyopathy (HCM), as assessed by late gadolinium enhancement (LGE) by cardiac MRI (CMR) is associated with adverse outcomes. Myocardial work index (MWI) is a novel technique that can detect subtle abnormalities in systolic myocardial function by echocardiogram. It incorporates non-invasive blood pressure measurement into global longitudinal strain (GLS), thereby eliminating the effects of afterload on LV function. Studies have shown some correlation between focal fibrosis by CMR as assessed by LGE and MWI in HCM. However, the association between MWI and diffuse interstitial fibrosis as assessed by T1 and ECV has not been yet examined. We aimed to examine the association between MWI and the presence, degree, and distribution of LGE, T1, and ECV in patients with HCM. Additionally, we aimed to establish a cutoff MWI value associated with LGE >15%.

 


Methods:

HCM patients who had a CMR with LGE, T1, and ECV assessment and transthoracic echocardiogram with myocardial index were identified from the Hartford Hospital Inherited Cardiovascular Disease Clinic’s clinical database. All CMR and echocardiograms were reviewed by cardiologists with level 3 training in CMR and echocardiography, respectively (figure 1). We examined the association between the presence and extent (number of segments) of abnormal MWI and LGE, T1, and ECV.  Receiver operator characteristics curve (ROC) analysis was used to determine the MWI cutoff to predict extensive myocardial fibrosis by CMR (i.e., LGE >15% of the total LV mass).


 


Results:

Out of 18 patients, 44% were males, and the mean age was 45+/-17 years. 27% of the patients had obstructive HCM (LV outflow gradient >30 mmHg). The average maximum wall thickness was 2.1+/-0.8 cm. There was a significant association between the number of segments with abnormal MWI and the number of segments with LGE (r=0.55, p=0.02). There was a significant association between abnormal global MWI (MWI < 1270 mmHg% for males and < 1310 mmHg% for females) and extensive LGE (LGE >15% of the total LV mass) (r=0.53, p=0.02). Only 2 of the 9 patients with severe LGE had normal global MWI. Global MWI < 1317mmHg% had 91% sensitivity and 71% specificity for extensive LGE (figure 2).  There was an association between the LGE % of the total LV mass and the global MWI but it did not reach statistical significance (r=0.44, p=0.07).  There were no significant associations between the presence and number of segments with abnormal MWI and T1 or ECV.

 


 


Conclusion:

Our study has found a significant correlation between abnormal MWI and the presence and severity of LGE among HCM patients. Thus, a CMR should be considered in every HCM patient with abnormal MWI, and MWI might be used for risk stratification in patients who cannot undergo a CMR. We found no significant association between MWI and T1 and ECV. Larger studies are needed to confirm our findings and for better characterization of these associations.