| Abstrakt: |
Cold hyperkalemic solutions were infused intermittently into the aorta of 16 dogs subjected to a 2 hour period of aortic clamping while on cardiopulmonary bypass (CPB). In one group (eight dogs), the coronary anatomy was left intact; in a second group, a critical stenosis was created prior to CPB on the proximal circumflex (Cx) artery and left in place throughout the experiment. Regional and global left ventricular (LV) function were measured before CPB and 30 minutes after cessation of bypass, at which time the heart had been reperfused for 1 hour. Ultrasonic microcrystals were implanted in the subendocardial area of both the Cx and left anterior descending (LAD) arteries to allow measurement of regional function, i.e., percentage of fiber shortening (%ΔL) and velocity of systolic shortening. Overall LV performance was measured by calculating LV pressure, its first derivative dp/dt, end-diastolic pressure (LVEDP), cardiac output index (COI), and stroke work index (SWI). LV function showed some deterioration after CPB in both groups. Deterioration was more severe in animals with a narrowed Cx artery (Group II), as measured by LVEDP (p < 0.013) and peak positive dp/dt (p < 0.04). Indeed, LVEDP remained the same in Group I (4.4 to 5.2 mm Hg) and rose significantly in Group II (6.6 to 11.2 mm Hg). Likewise, peak positive dp/dt returned to 84% ± 52% of preischemic values (1,776 to 1,480 mm Hg) in Group I compared to 60% ± 4% (1,725 to 1,033 mm Hg) in Group II. For the other indices of global LV function, the difference between the two groups was not statistically significant. Regional function was affected differently in the two groups. On the average. Group I animals showed no change in both Cx and LAD areas. Conversely, in group II, %ΔL decreased by 41% ± 14% (average 13.3% to 7.3%) and maximum velocity of systolic shortening dropped significantly (23.3 to 5.8 mm/sec) in the Cx area. The level of significance between the two groups in the Cx area was, respectively, 0.015 and 0.001 for percentage and velocity of shortening. Thus global LV function, on the whole, is well preserved by cold potassium cardioplegia during prolonged aortic clamping. On the other hand, under similar conditions, the presence of a critical coronary artery narrowing leads to inadequate myocardial protection and poor recovery of regional LV function. |
