Quantitative echocardiographic methods for patients with acute coronary syndrome

Abstract

Background: The aim of this thesis was to evaluate two diagnostic and two prognostic quantitative echocardiographic methods for patients with acute coronary syndrome (ACS).

Methods: Velocity tracking (VeT) presents the longitudinal tissue Doppler velocities of the left ventricle (LV) as a bull’s eye plot giving an easy three dimensional understanding of both the global and regional function of the LV in regard to longitudinal velocities, systolic as well as diastolic.

The state diagram ,also derived from tissue Doppler imaging (TDI), gives a schematic view of the timing of the different phases of the cardiac cycle both on a global and segmental level, from this diagram we get the State index based on myocardial performance index (MPI) both on a global level and its intersegmental variation. Both methods were compared to wall motion score (WMS) and ejection fraction (EF) in a population with ACS without previously known heart disease. We included 20 NSTEMI patients and 10 controls for the VeT study and 49 NSTEMI patients and 21 controls for the State index study.

For prognostic evaluation we tested peak systolic velocity (PSV) and four different dyssynchrony parameters in two studies. PSV is an easy accessible parameter derived from TDI. As dyssynchrony parameters we examined septal-lateral delay, post systolic index (PSI), myocardial performance index (MPI) and time to peak systolic 2D strain both as a global mean and with the standard deviation (SD) as a measurement of intersegmental variation. We included 227 unselected patients with NSTEMI and used a combined endpoint of death, readmission due to heart failure and new MI.

Results: Both diagnostic methods were shown to be sensitive to acute ischemia but only the state index showed significantly better diagnostic value compared to WMS with an AUC of 0.87 (WMSI 0.66 p=0.008). VeT had comparable results to that of WMS regarding both ischemia and regional information.

PSV showed a strong association with outcome in respect to our combined endpoint when compared to all other tested echo methods with a AUC of 0.74. When adjusting for known risk factors PSV remained independent when the other echo parameters did not. The dyssynchrony parameters did carry some prognostic information but were not of incremental value to that of conventional parameters such as EF and WMS.

Conclusion: Both VeT and the State index showed a strong diagnostic value but only the State index was significantly stronger compared to EF and WMSI. Both these promising methods need to be evaluated further in a larger prospective study.

For risk stratification after ACS PSV seems to be a robust and easily obtained echocardiographic parameter that carries independent prognostic information with incremental value to that of known strong predictors such as NT pro BNP and eGFR. Mechanical LV dyssynchrony parameters seem to carry some significant prognostic information but in comparison to conventional echo parameters there was no or little incremental value of this information.