Extrinsic factors influencing left ventricular conductance in situ

The accuracy of conductance measurement of left ventricular (LV) volume is affected by parallel conductance (Vp) from right ventricular (RV) volume as well as surroundings of the heart. No studies have quantified the extrinsic influences on Vp.

In six anesthetized pigs, using a median sternotomy and pericardial well, implantable cardioverter defibrillator patches, normal saline, or echocardiography gel were introduced and removed. LV end-diastolic pressure (LVEDP) did not change significantly with these interventions. Raw LV conductance was used to estimate end-diastolic volume (LVEDV), end-systolic volume (LVESV), and stroke volume (SV). Saline significantly increased mean +/- SEM calculated LVEDV from 106 +/- 8 to 131 +/- 6 mL and calculated LVESV from 81 +/- 7 to 110 +/- 5 mL; calculated SV decreased from 25 +/- 3 to 21 +/- 2 mL (P < .05, paired t test). Implantable cardioverter defibrillator patches and gel did not significantly change calculated LV volumes. LV conductance was also measured in arrested hearts during LV filling (5 to 60 mL) at four levels of RV volume (RVV). Using a fixed value for Vp, calculated mean LV volume was 30 +/- 3 mL at RVV = 0, 32 +/- 3 mL at RVV = 20, 33 +/- 3 mL at RVV = 40, and 36 +/- 3 mL at RVV = 60 (P < .01, repeated-measures ANOVA).

While implantable cardioverter defibrillator patches and gel have no statistically significant effect, saline and RVV affect LV volume calculations by conductance, requiring special techniques during cardiopulmonary bypass or caval occlusion.