Abstract 1880: Isovolumic Acceleration Of The Myocardium (IVA) Generates The Isovolumic Intraventricular Pressure Gradient; A Novel Index Of Contractility.
The intraventricular pressure gradient (IVPG) during ejection (EIVPG) is a robust index of contractility. An IVPG also occurs during the isovolumic contraction period (iso-IVPG). We hypothesized that IVPG may be related to indexes derived from analysis of tissue Doppler (TDI) derived myocardial velocity, and in particular iso-IVPG would be related to isovolumic acceleration (IVA).
Methods: Seven 30kg sheep were studied. IVPG was derived from simultaneous LV mid-cavity and outflow tract pressure measurements from dual catheter-mounted sensors. IVA of the LV free wall from an apical view was calculated by the rate of change of velocity during isovolumic contraction from colour TDI data (minimum frame rate 200Hz). Measurements were at baseline, increased afterload and with incremental inotropy. The timing of IVA, EIVPG and iso-IVPG relative to the ECG R-wave during baseline and afterload increase were compared.
Results: There was no significant change in any of the three indexes with a 30% increase in aortic systolic pressure. All three indexes showed a graded positive increase with incremental inotropy. The induced changes were mirrored by equivalent changes in iso-IVPG and EIVPG. IVA showed excellent correlation with both EIVPG and also iso-IVPG (r2= 0.99 and 0.95 respectively; linear regression). IVA occurred a mean of 26ms prior to R-wave, whereas iso-IVPG and EIVPG followed the R-wave by 8 ms and 100ms respectively.
Conclusions: Iso-IVPG was shown to be equal to EIVPG under these changes in haemodynamics. Whilst TDI derived index IVA shows excellent correlation with these indexes the relative timing would suggest a direct relationship to the iso-IVPG.