Echocardiographic assessment of myocardial viability
Echocardiographic assessment of myocardial viability: Diastolic wall thickness will give an idea regarding the myocardial viability. Thin and hyperdense myocardium is likely to be scarred and non viable. Dobutamine stress echocardiography documents the contractile reserve of the myocardium and hence indicate viability. Myocardial perfusion is assessed by myocardial contrast echocardiography. Strain and strain rate imaging is done by tissue Doppler and speckle tracking. There are various methods of assessing diastolic dysfunction using Doppler and tissue Doppler echocardiography.
End diastolic wall thickness (EDWT)
End diastolic wall thickness (EDWT) is one of the simplest methods to screen for myocardial viability, which cardiac surgeons check most often. EDWT more than 5.5 mm has a sensitivity of 94%, albeit with a low specificity of 48% for detection of myocardial viability. With EDWT less than 5-6 mm, less than 5% will be viable, while with thickness above that viability is considered to be more than 50%.
Dobutamine stress echocardiography
Pharmacological stress echocardiography can be done using dobutamine, adenosine or dipyridamole. Low dose dobutamine echocardiography is useful in assessing myocardial contractile reserve. Parasternal and apical views can be used to assess the response in 16-17 myocardial segments. Higher doses of dobutamine can be used to check whether there is any biphasic response indicating ischemic viable myocardium. The response to dobutamine can be divided into four types. In monophasic or sustained response, low dose dobutamine increases the contraction, which is further enhanced in high dose. In biphasic response, low dose enhances contraction while high doses decreases the contraction. Another type is ischemic response, in which both low dose and high dose produces decrease in contraction. In non phasic response, there is hardly any contraction of the segment through out. Roughly forty percent will have a non phasic response while nearly one third can have a biphasic response. Sustained response may be noted in nearly one fifth and worsening may be noted in 15% . Biphasic response had the highest predictive value for recovery of function after coronary angioplasty. Nonphasic and monophasic responses predicted poor recovery of function while ischemic response was in between. Dobutamine stress echocardiography (DSE) has been noted to have better specificity than nuclear imaging. DSE has a fair value in prognostication as well.