#Cardiotwitter: Continuing with timing. Timing can easiest be determined by Doppler, by the start of flows and the closing clicks of valves. The timing by Tissue Doppler is less obvious, but can be done, when the correct events are understood. 
1/ IVC duration is shortened by rate of force development, which again is a function of preload and contractility, however also increased HR, by force-frequency relationship. Time to AVC depends on the SBP, I.e. afterload, so IVC is both preload, afterload and HR dependent.
2/ LVET is related to SV. Thus, just as IVC, it increase with preload and contractility. But on the contrary, LVET decreases with afterload (⬇️ SV). And finally, it decreases with HR. Thus, for LVET to be useful, HR correction must be applied (LVETc).
3/ But is LVETc useful? I was taught by Liv Hatle that it was useful in assessing low flow - low gradient AS. A patient with low EF will have a low LVETc, if it is near normal, it means the gradient is real, if substantially reduced, it’s the LV function.
4/ Though I’ve never seen any studies, I’d think that the same would be the case if LVEDV and SV are low (in that case LDDDE doesn’t work), but a low SV and normal LVETc would be suspicious. Could be case for a nice study, although the gold standard for AS might be troublesome.
An example, Patient with EDV 56 ml, EF 68%, MAPSE 6 mm and S’ 4.4 cm / S- LVETc is 408 ms, despite low SV. (Although here the gradient is high enough).
5/ But how to correct for HR? Bazett's formula QTc = QT/ SQR(RR), a non linear correction, is on observations on mechanical systole, nearly lost in history, and applied to electrical systole by Bazett in 1920. Normal values, however, only gives upper cut off for arrhythmia risk.
6/ Weissler ahajournals.org/doi/pdf/10.116… did a linear regression against HR, LVETC = LVET+1.7*HR with normal mean (SD) 413 (10) in men, and LVET+1.6*HR with normal 418 (11) in women. This gives lower normal values, which are more interesting hemodynamically
7/ As the relation between HR and RR-interval in fact is non linear (hyperbolic, not quadratic), it seems both corrections may be fair. In an exercise study, we found Bazett’s formula to be a bit better, but the relation of LVET to HR seems to be fairly linear anyway.
So, I'll come back to the relations of Tissue Doppler to AVC and IVR, which are as complex as in pre ejection
