Recognition of myocardial infarction after cardiac surgery and its relation to cardiopulmonary bypass

Reversible diastolic dysfunction after successful coronary artery bypass surgery. Assessment by transesophageal Doppler echocardiography

To assess the potential effects of coronary artery bypass surgery on left ventricular diastolic filling, 12 patients, aged 65 +/- 11 years, were studied by serial transesophageal Doppler echocardiograms. Doppler measures of mitral inflow velocity were made before, immediately after, 4 h after, and 20 h after cardiopulmonary bypass (CPB). Left atrial pressure was directly measured and controlled at 10 +/- 2 mm Hg for each study period. Mitral maximal early inflow velocity (E)/maximal atrial velocity (A) ratios and atrial filling fractions were calculated as indexes of diastolic function from maximal E and A velocities and their time velocity integrals, respectively. Data sets were available for serial comparison in 11 patients and were also compared with an age-matched control group of normal values. The results of E/A ratios were as follows: control group--1.4 +/- 0.2; before CPB--1.7 +/- 0.6; immediately after CPB--1.0 +/- 0.2 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); 4 h after CPB--0.8 +/- 0.2 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); and 20 h after CPB--1.3 +/- 0.4. Atrial filling fractions were as follows: control group--0.29 +/- 0.05; before CPB--0.25 +/- 0.06; immediately after CPB--0.43 +/- 0.07 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); 4 h after CPB, 0.46 +/- 0.07 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); and 20 h after CPB--0.35 +/- 0.06. Alterations in Doppler indexes of left ventricular filling occurred immediately after CPB and persisted 4 h after CPB. These indexes returned to baseline values by 20 h after CPB. This suggests reversible diastolic dysfunction in patients after coronary artery bypass surgery.

Assessment of the immediate effects of cardiopulmonary bypass on left ventricular performance by on-line pressure-area relations

BACKGROUND

Pressure-volume relations have been established as useful measures of left ventricular (LV) performance. Application of these methods to the intraoperative setting have been limited because of difficulties acquiring LV volume data. Transesophageal echocardiographic automated border detection can measure LV cross-sectional area as an index of volume, which can be coupled with pressure data to construct pressure-area loops on-line. The purpose of this study was to evaluate intraoperative LV performance in patients undergoing coronary bypass surgery before and immediately after cardiopulmonary bypass using on-line pressure-area relations.

METHODS AND RESULTS

Studies were attempted in 13 consecutive patients. Simultaneous measures of LV cross-sectional area, LV pressure, and electromagnetic flow probe-derived aortic flow recorded on a computer work station interfaced with the ultrasound system. Pressure-area loops were compared with simultaneous pressure-volume loops constructed from pressure and flow data during inferior vena caval occlusions before and after bypass. Pressure-volume calculations (end-systolic elastance, maximal elastance, and preload-recruitable stroke work) were then applied to pressure-area loops with area substituted for volume data. Changes in stroke force from pressure-area loops were closely correlated with changes in estimates of stroke work from pressure-volume loops for individual patients before bypass (r = .99 +/- .03, SEE = 5 +/- 2%, n = 10) and after bypass (r = .96 +/- .05, SEE = 5 +/- 2%, n = 9). Pressure-area estimates of end-systolic elastance, maximal elastance, and preload-recruitable stroke force decreased significantly from before to after cardiopulmonary bypass in the 7 patients with paired data sets. Load-dependent measures of LV function (stroke volume, cardiac output, and fractional area change) were unchanged after surgery in these same patients.

CONCLUSIONS

Intraoperative pressure-area loops may be acquired and displayed on-line using transesophageal echocardiographic automated border detection and readily analyzed in a manner similar to pressure-volume loops. LV performance was depressed immediately after cardiopulmonary bypass compared with before. On-line pressure-area relations may be clinically useful to assess LV performance in patients undergoing cardiac surgery in whom load and contractility may be expected to vary rapidly.

Acute myocardial dysfunction and recovery: a common occurrence after coronary bypass surgery

To evaluate whether acute myocardial dysfunction was common in the early postoperative period, serial hemodynamic measurements and radionuclide evaluation of ventricular function were performed before and after operation in 24 patients undergoing elective coronary bypass surgery. All patients had uncomplicated surgery, and no patient sustained an intraoperative infarction. In 96% of patients, significant depression in right and left ventricular ejection fraction was seen postoperatively, reaching a nadir at 262 +/- 116 min after coronary bypass. Left ventricular ejection fraction was 58 +/- 12% preoperatively and 37 +/- 10% at trough. Right ventricular function displayed a similar pattern. These findings were also associated with depressed cardiac and left ventricular stroke work index despite maintenance of adequate ventricular filling pressures and mean arterial pressure. The depression in ventricular function was partially reversible within 8 to 10 h after surgery. Left ventricular ejection fraction had increased to 55 +/- 13% at 426 +/- 77 min after coronary bypass and showed complete recovery within 48 h. Left ventricular end-systolic and end-diastolic volume index increased significantly postoperatively, but recovery in left ventricular ejection fraction was mostly due to decreases in end-systolic volume index (50 +/- 22 ml at trough and 32 +/- 16 ml at recovery). Depressed myocardial function was independent of bypass time, number of grafts placed, preoperative medications or core temperatures postoperatively. Postoperative therapy with pressors or inotropic agents delayed but did not prevent the occurrence of postoperative ventricular dysfunction. Despite improvements in operative techniques and methods of myocardial protection, postoperative left ventricular dysfunction continues to be common in patients undergoing cardiopulmonary bypass surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Recognition and quantification of myocardial injury by means of plasma enzyme and isoenzyme activities after cardiac surgery

Serial plasma enzyme determinations were carried out in 32 patients who underwent cardiac surgery with the aid of extracorporeal circulation. Plasma creatine kinase (CK), the cardiospecific isoenzyme of CK (CKMB), and alpha-hydroxybutyrate dehydrogenase (HBDH) were determined from the onset of surgery up to 100 to 120 hours after operation. From the plasma enzyme activities, the total amount of enzyme released by the injured heart into the circulation could be calculated using mathematical equations solved numerically by means of a computer. The calculated amount of CK, CKMB, and HBDH released by the heart correlated well with (1) postoperative mortality, and (2) peak activities of the respective enzymes. The calculated amount of any of the 3 enzymes released showed poor or no correlation with (1) electrocardiographic criteria of myocardial infarction, (2) duration of cardiopulmonary bypass, and (3) duration of total aortic cross-clamping. This study shows that the extent of myocardial injury after surgery can be assessed quantitatively using the calculated amounts of enzyme released, as well as using peak plasma activities of CKMB and HBDH.

Late sequelae of perioperative myocardial infarction

The late suquelae of myocardial injury occurring at the time of direct myocardial revascularization are unknown. Fifty of 500 consecutive patients undergoing aortocoronary bypass grafting developed both electrocardiographic and enzymatic evidence of myocardial injury. They were matched with 50 patients of similar age, sex, history of previous infarction, severity of angina, degree of coronary arteriosclerosis, and level of ventricular function as determined by preoperative angiographic studies. The conduct of the operation was identical in each group except for prolongation of total cross-clamp time in those patients with myocardial injury. The total number of vessels grafted, the conduit used, and the operative mean graft flow were similar. Results of treadmill stress testing at 24 to 36 months were not significantly different between groups. Angina status, long-term survival, graft patency, and ventricular function were not adversely affected by intraoperative myocardial injury. However, postoperative ventricular function and stress test performance were related to graft patency.

Left ventricular function and adrenergic hyperactivity before and after saphenous vein bypass

Forty patients with severe angina pectoris were studied before and two weeks after saphenous vein bypass surgery (SVG) in order to assess the effect of this operation on left ventricular performance as judged by systolic time intervals (STI). The patients were divided into two groups: group I included 29 patients in whom no postoperative infarction occurred and group II was composed of 11 patients with postoperative infarction. For group I the PEP/LVET was 0.39 +/- 0.01 preop and slightly but significantly increased at 0.42 +/- 0.004 (P less than 0.025) two weeks postop. The mean preop PEP/LVET was 0.33 +/- 0.01 for group II and dramatically increased to 0.54 +/- 0.02 (P less than 0.001) after surgery. Another striking abnormally was a marked shortening of electromechanical systole (QS2I), which was uniformly present in the postoperative studies. Follow-up studies in 16 patients and urinary catecholamine determination in five patients suggested excessive adrenergic activity was responsible for the abbreviated QS2I. This phenomenon must be considered when interpreting the results of SVG on left ventricular function.