Calculation Of Left Ventricular Relaxation Time Constant (Tau) In Dogs With Mitral Regurgitation By Continuous-wave Doppler

PART ONEObjective To establish the model of acute ischaemic left heart failure with mitralregurgitation in beagles.Methods①The construction of mitral regurgitation (MR)animal model: A catheterwas sent into left ventricle through the carotid artery in15experiment beagles, then abiopsyclamp was put into the mitral valve nearby through the catheterization andchordae tendineae was pinched under the guidance of echo in order to construct mitralregurgitation．②The construction of acute ischaemic left ventricular (LV) diastolic heartfailure:15beagles with MR were further processed with coronary microembolization bymicrospheres repeatedly.Results①In15experiment dogs, the ventricular morphology showed that bothvalve and chordae had been broken in one dog, caused severe MR; one of the valveswas broken in one dog; the chordae tendineaes were broken in all the other thirteendogs, causing moderate MR. One dog with natural mild MR was with broken chordaetendineae. Continuous wave Doppler showed that the MR peak velocity was483±1.12cm／s, the maximun pressure gradient was162.7±1.8mmHg.②12modelsof acute ischaemic left diastolic heart failure with mitral regurgitation were established.2dogs were microembolised four times,5dogs were microembolismed5-6times,4dogs were microembolismed8times,1dog was microembolismed9times. Leftventricular end-diastolic pressure is equal or greater than5mmHg be defined as modelsuccessful. The steady-state model need1.5hours. The left ventricular end-diastolic pressure (LVEDP),-dP/dtmax, Tau-c of successful model were increasedsignificantly(p<0.05).Conclusion This method is safe, feasible and easily successful in constructing theMR animal model under the guiding of transthoracic echocardiography．Coronarymicroembolization with microspheres is a sueeessfull way for establishing the acuteischaemic left diastolic heart failure. PART TWOObjective To explore the new method for noninvasively measuring the time constantof left ventricular relaxation (Tau) in animals with mitral regurgitation bycontinuous-wave Doppler.Methods The acute ischaemic left diastolic heart failure with mitral regurgitation wasproduced in12dogs. Dobutamine Hydrochloride or Esmololhydrochloride had beenapplied to change the hemodynamic states.In different hemodynamic states, leftventricular pressures, left atrial pressures, curves of dP/dt and continuous-wave mitralregurgitant spectra were synchronously recorded. Doppler spectra were postly processedthrough Matlab workstation.Results39hemodynamic status had been obtained in12dogs. Mean value of eachthree continuous cardiac cycle. Calculation the parameters in different hemodynamicstates, dP/dtmax:-494.79mmHg/s～-4864.24mmHg/s, mean-dP/dtmax:-1832.35±827.81mmHg/s; LAP:2.03mmHg～84.99mmHg, mean LAP:41.64±23.92mmHg;PLV:34.86mmHg～139.36mmHg, mean PLV:73.44±25.29mmHg; PAO:55.23mmHg～180.92mmHg, mean PAO:99.95±34.52mmHg.Tau-c (Tau-catheter)and Tau-d(Tau-doppler ultrasound) correlated closely with this standard (r=0.85).Tau-c(Tau-catheter):48.76±17.60ms, Tau-u（Tau-doppler ultrasound）:49.33±18.79ms had nodifferences (P>0.05).Conclusion Choose the three points:(t1,1m/s),(t2,2m/s) and (t3,3m/s)in mitralregurgitant velocity spectrum descending branch to calculate Tau. This methoddemonstrates that the Doppler mitral regurgitant velocity profile can be used to providea direct and noninvasive measurement of ventricular relaxation time constant (Tau).