Current concepts: converting enzyme inhibitors in coronary artery disease

Can clonidine, enoximone, and enalaprilat help to protect the myocardium against ischaemia in cardiac surgery?

OBJECTIVE

To evaluate whether clonidine, enoximone, and enalaprilat reduce ischaemia-related myocardial cell damage in cardiac surgery.

DESIGN

Prospective randomised controlled trial.

SETTING

Clinical investigation in a cardiac anaesthesia department of a university hospital.

PATIENTS

88 consecutive patients undergoing coronary artery bypass surgery.

INTERVENTIONS

After induction of anaesthesia patients continuously received the alpha 2 agonist clonidine (group 1, n = 22), the phosphodiesterase (PDE) III inhibitor enoximone (group 2, n = 22), the angiotensin converting enzyme (ACE) inhibitor enalaprilat (group 3, n = 22), or saline solution as placebo (control group, n = 22). The infusion was stopped immediately before the start of cardiopulmonary bypass.

MAIN OUTCOME MEASURES

The ST segment was analysed and the activity of creatine kinase isoenzyme MB (CKMB), cardiac troponin T (TnT), and the BB isoenzyme of glycogen phosphorylase (GPBB) were measured before the start of infusion (baseline), after weaning from cardiopulmonary bypass (CPB), at the end of surgery, 5 h after CPB, and on the morning of the first and third postoperative days.

RESULTS

Biometric data and time of cross-clamping were not significantly different in the four groups. Changes in the ST segment indicating ischaemia were least common in the enalaprilat group (P < 0.05). Postoperatively, CKMB activity was significantly higher in the clonidine and the control groups. Both new markers of myocardial cell damage increased more after CPB and postoperatively in the control patients (TnT peak: (mean (SD)) 3.99 (0.35) microgram/1; GPBB peak: 82 (15) ng/ml) and the clonidine-treated group (TnT peak: 3.80 (0.3) microgram/1; GPBB peak: 85 (14) ng/ml). Enalaprilat-treated patients showed the smallest overall changes in standard (CKMB) and new serological markers of myocardial ischaemia (TnT peak: 0.71 (0.1) microgram/1; GPBB peak: 44 (14) ng/ml).

CONCLUSIONS

In patients treated with enalaprilat before CPB, both new, more sensitive markers of ischaemic myocardial tissue damage increased significantly less than in an untreated control group. Those treated with enoximone also had lower plasma concentration of TnT and GPBB than the control group, whereas clonidine did not reduce the concentration of these markers of myocardial ischaemia. Pharmacological interventions, such as the continuous infusion of the ACE inhibitor enalaprilat, before start of CPB may help to protect the heart against ischaemia/reperfusion injury.

Influence of intravenous administration of angiotensin-converting enzyme inhibitor enalaprilat on cardiovascular mediators in cardiac surgery patients

The renin-angiotensin system (RAS) is important in controlling and maintaining cardiovascular homeostasis. In a randomized, prospective study, the response to intravenous (i.v.) administration of the angiotensin-converting enzyme (ACE) inhibitor enalaprilat (0.06 mg/kg) on important controllers of the circulation was investigated in 14 patients undergoing aortocoronary bypass grafting with a mean arterial blood pressure (MAP) > 85 mm Hg after induction of anesthesia. Fourteen patients received saline solution as placebo (control group). Endothelin (ET), atrial natriuretic peptide (ANP), catecholamine (epinephrine, norepinephrine) plasma levels, and ACE activity were measured from arterial blood sampled before injection of enalaprilat or NaCl solution (baseline values), 10 min and 30 min thereafter, immediately before the start of cardiopulmonary bypass (CPB), immediately after CPB, and at the end of surgery. MAP, heart rate (HR), cardiac index (CI), and systemic vascular resistance (SVR) were also monitored. ACE activity was similar at baseline in both groups; after i.v. injection of enalaprilat, it significantly decreased (from 35.1 +/- 11 to 4.4 +/- 1.0 U.min-1.L-1 30 min after injection) and remained reduced until the end of the operation (295 +/- 31 min after injection). ANP plasma levels were increased beyond normal (> 100 pg/mL) at baseline in both groups. They increased significantly in the control patients, but remained almost unchanged in the enalaprilat-treated patients within the entire study period. Plasma concentration of ET also increased only in the control group and was increased after CPB (8.6 +/- 1.2 pg/mL at the end of the operation).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiorespiratory response of intravenous angiotensin-converting enzyme inhibitor enalaprilat in hypertensive cardiac surgery patients

Twenty-four patients undergoing elective coronary artery bypass surgery were studied. Either the angiotensin-converting enzyme (ACE) inhibitor enalaprilat, 0.06 mg/kg, (n = 12), or saline solution (= control group; n = 12), was randomly and blindly administered intravenously when the mean arterial blood pressure (MAP) increased to 90 mmHg after induction of anesthesia. Cardiorespiratory parameters were studied before injection, during the subsequent 30 minutes, precardiopulmonary bypass (CPB), post-CPB, and at the end of surgery. MAP was significantly reduced 5 minutes after administration of enalaprilat. The peak reduction of blood pressure was observed after 30 minutes (from 98 +/- 4 to 68 +/- 8 mmHg). Even immediately before CPB (112 +/- 12 minutes after injection of enalaprilat), MAP and systemic vascular resistance were significantly lower than baseline values. Heart rate remained almost unchanged in both groups. Cardiac index increased slightly in the enalaprilat patients (maximum: +0.75 L/min/m2 20 minutes after injection). Filling pressures (central venous pressure, pulmonary capillary wedge pressure) were also significantly reduced by enalaprilat. There were no differences from the control patients with regard to changes in right ventricular hemodynamics (right ventricular ejection fraction, right ventricular end-diastolic volume, right ventricular end-systolic volume), pulmonary gas exchange (PaO2), or intrapulmonary right-to-left shunting (Qs/Qt). VO2 increased only in the enalaprilat patients (from 179 +/- 28 to 230 +/- 30 mL/min) (p < 0.05). Cardiorespiratory parameters did not differ between the two groups post-CPB.(ABSTRACT TRUNCATED AT 250 WORDS)