One of our most influential Echocardiographers, Dr Luigi had his concern about Tau measurement in MR patients. Fact is quite a few cardiologists asked similar questions. Let me take this chance to address the issue.
Tau happens within isovolumic phase of diastole, which means three approaches are available to measure it. One is to insert a catheter into the LV. This is the invasive method well accepted as a gold standard to assess diastolic function during basic research. The other two need measuring either MR or AI CW Doppler spectrum. Both the formulas and their verification had been published. The MR Tau has already been in Mindray’s Echo machines since 2017.
Dr Luigi’s concern is true. We cannot measure Tau in pts with mitral regurgitation in whom there is no isovolumic phase. Yet, if we are planning to measure Tau in MR pts, we can carefully manoeuvre the probe to achieve the isovolumic phase. Most cases are satisfactory.
In normal studies where there is no MR or AI, we cannot measure Tau in an Echo lab. Dr JD Thomas can measure it, but his method bears logic flaws. After dominance of non-invasive Tau measurement for more than two decades, Tau is died in daily clinic.
Chances of MR or AI increase dramatically in HF pts, usually we tend to have interests to measure Tau in these pts.
Another issue is Tau is indispensible sometimes.
Just as our Echo giant Dr Jae K. Oh mentioned above. In some severe HF pts, the assessment of diastolic function could be confusing without Tau. To my knowledge, almost all of those pts we can measure Tau, the measurement always suggest severe diastolic dysfunction.
The last but not the least, Tau can only be measured non-invasively in pts with either MR or AI, similar like dp/dt or PISA. It is amazing for it is indispensable sometimes. The strength of Tau comes from its direct relationship to cardiac muscle power, which leads us from special Tau to general Tau, and finally reveals symmetry of cardiac function assessment. Dr Sherif Nagueh’s vision about the “symmetry” is:
It might be very helpful in the assessment of cardiac function in the future, especially for RV and diastolic function.