The time-velocity integral (TVI) measurements of pulmonary venous and transmitral flows
As LV chamber stiffness increases, antegrade trans-micuspid blood flow and pulmonary venous return are affected during atrial contraction because of the increase in chamber pressure. The original invasive study by Rossvoll O, et al. found that pulmonary venous flow reversal beyond the duration of the mitral A wave indicated an exaggerated increase in late left ventricular diastolic pressure. A pulmonary venous systolic fraction <0.4 indicated a significant increase in ventricular filling pressures(36). Based on this, Kazunori Okada et al. (37)proposed to indirectly reflect LV chamber stiffness by velocity-time integral measurements of pulmonary venous and transmicuspid blood flow. The TVI measurements of pulmonary venous and transmitral flows refer to the measurements of the TVI of the backward pulmonary venous (PV) flow during atrial contraction (IPVA) and the ratio of IPVA to the PV flow TVI throughout a cardiac cycle (FPVA) by echocardiography. In addition, the TVI of the atrial systolic forward transmitral flow (IA) and the ratio of the IA to the transmitral TVI during a cardiac cycle (FA) also need to be measured (Figure 2D). Kazunori Okada et al. reported the FPVA/FA and IPVA/ IA are well correlated with the LV chamber stiffness (r = 0.79 and r = 0.81) and LV end-diastolic pressure (r = 0.73 and r = 0.77) in 62 patients who underwent cardiac catheterization. The areas under the ROC curve to discriminate LVEDP >18mmHg were 0.90 for IPVA/ IA (Optimal cut-off value 0.51, Sensitivity 83%, Specificity 80%, P <0.001)and 0.93 for FPVA/FA(Optimal cut-off value 0.47, Sensitivity 83%, Specificity 82%, P <0.001).
Unfortunately, only one study has been conducted in the literature on the exploration and application of TVI, and its accuracy in assessing LV chamber stiffness remains to be confirmed. In the meanwhile, these indicators are not applicable to patients with dyssynchrony of atrial activity caused by synchronized atrial activity due to arrhythmias such as atrial fibrillation, atrial flutter and complete atrioventricular block, and left ventricular catheterization and echocardiography cannot be performed at the same time. In addition, although there was a good correlation between IPVA/IA and chamber stiffness, IPVA/IA was angle dependent. More in-depth studies in different populations with larger samples are further needed.