VENTRICULAR COUPLING VIA THE PERICARDIUM - NORMAL VERSUS TAMPONADE

Objective: The aim was to examine how regional variations in pericardi al pressure affect the mechanical coupling between the ventricles. Met hods: Canine hearts from 14 dogs (14.5-18 kg) were removed and placed in cold cardioplegia solution. Balloons were inserted into the left an d right ventricles and the atria. Pericardial pressure over the left v entricle (Pclv) and the right ventricle (Pcrv) was measured with thin balloon catheters. Ventricular and pericardial pressures were measured , and ventricular and pericardial coupling was calculated, under contr ol conditions and with increases in pericardial tension and fluid. Res ults: At baseline, regional differences in pericardial pressure occurr ed [Pclv>Pcrv, 4.0(SD 0.9) v 2.9(0.6) mm Hg, p<0.05]. Ventricular coup ling via the pericardium was defined as DELTAPclv/DELTAPcrv for right ventricular volume increases and DELTAPcrv/DELTAPclv for left ventricu lar volume increases. This ratio increased more after increasing right ventricular volume than after increasing left ventricular volume [DEL TAPclv/DELTAPcrv>DELTAPcrv/DELTAPclv, 1.14(0.33) v 0.51(0.15), p<0.05] . Increasing the pericardial tension by clamping the pericardium incre ased pericardial pressures, yet did not alter the regional variations in pressure [PcLv>Pcrv, 8.4(2.2) v 6.4(2.5) mm Hg, p<0.05] or pericard ial coupling DELTAclv/DELTAPcrv>DELTAPclv/DELTAPcrv, 1.18(0.46) v 0.54 (0.16), p<0.05]. In contrast, creating a mild tamponade increased peri cardial pressures, eliminated regional differences in pressure. and al tered the coupling between ventricles [DELTAPclv/DELTAPcrv almost-equa l-to DELTAPclv/DELTAPcrv, 0.95(0.11) v 1.05(0.08), p=NS]. These region al differences in pericardial pressure might have a geometrical basis. In four in vivo canine experiments using cine magnetic resonance, the short axis radius of curvature for the right ventricle was greater th an for the left ventricle [38.3(4.4) mm v 29.2(3.8) mm, p<0.05]. Concl usions: The pericardium partially protects right ventricular filling: regional differences in pericardial pressure normally occurred with lo wer pericardial pressure over the right ventricle, and left to right v entricular coupling was less. This protection of right ventricular fil ling was lost with even a small pericardial effusion.