Intraoperative Diastolic Function by TDI and STE

Perioperative echocardiographic quantification of myocardial function is of great importance in patient management and is increasingly being recommended intraoperatively in spite of some unresolved or under-explored issues. One such issue is the perioperative measurement of diastolic function. Diastolic dysfunction and diastolic heart failure - or as commonly referred to "heart failure with preserved ejection fraction (HFpEF)" - is responsible for some 35 to 50% of heart failures. Intraoperative measurements of diastolic function have a prognostic and management relevance for patients undergoing both cardiac and non-cardiac surgery. However, even recent guidelines on intraoperative transesophageal echocardiography (TEE) have neglected this topic, with the exception of the most recent, which briefly alluded to the role TEE can play in assessing diastolic function, but without addressing the issue of which measurements or views to use.

The clinically prevalent echocardiographic view for assessment of intraoperative diastolic function by tissue Doppler imaging (TDI) is the midesophageal 4-chamber (ME 4C) TEE view. This view, which looks at the heart from the left atrium, is the standard view for evaluating intraoperative global cardiac performance. However, the Doppler angle for assessing diastolic performance is generally much greater than 20° and, as Doppler techniques are known to be angle dependent based on the Doppler equation, using this view may relevantly underestimate TDI velocities. Views from the apex of the heart (i.e. both the deep transgastric long axis view [dTG LAX] TEE view as well as the apical 4-chamber [AP 4C] transthoracic echocardiography (TTE) view) have a cosine angle towards the mitral annular plane excursion near zero, thereby allowing valid measurements according to the Doppler equation. However, TDI velocities are often - and potentially erroneously - reported from the ME 4C TEE view.

The objective of this project is to address a number of important clinical topics regarding diastolic dysfunction in TEE.

Two main objectives will be examined:

• Assess whether or not tissue doppler imaging (TDI) measurements of mitral annular plane velocities and systolic excursion in the midesophageal 4-chamber TEE view (ME 4C) significantly underestimate diastolic cardiac performance compared to the deep transgastric long axis TEE view (dTG LAX) due to intrinsic misalignment of the doppler beam. [i.e. is there a technological limitation?]
• Assess whether or not the difference in mitral annular plane velocities and systolic excursion between the ME 4C and dTG LAX will be underestimated using TDI compared to values derived from speckle tracking echocardiography (STE). [i.e. if there is a technological limitation, does STE show more consistency?]

Two secondary objectives will be examined:

• Determine the influence of frame rates (temporospatial resolution) on STE-derived mitral annular velocities and systolic excursion by conducting STE measurement post cardiopulmonary Bypass (CPB) in atrially paced patients in the 1. midesophageal 4 chamber view (ME 4C) and 2. deep transgastric long axis view (dTG LAX). [i.e. if ST shows more consistency, what are its limitations?]
• Confirm the existence of and explore potential reasons (anesthesia, ventilation, TTE vs. TEE, Doppler alignment) for differences in mitral annular plane velocities and systolic excursion observed preoperatively (i.e. by cardiologists) and intraoperatively (i.e. by anesthetists, intensivists). Specifically, we will compare these values in four views: 1. apical 4-chamber view in TTE (AP 4C) preinduction, 2. apical 4-chamber view in TTE (AP 4C) postinduction, 3. midesophageal 4 chamber view (ME 4C) postinduction, and 4. Deep transgastric long axis view (dTG LAX) postinduction. [i.e. what is the relative contribution of the ignoring the misalignment in angulation compared to other intraoperative factors in explaining the observed underestimation of diastolic velocities and distances seen by cardiologists (AP 4C TTE view) and anesthetist's/intensivist's (ME 4C TEE view)?]