Cardiac effects of thoracic epidural analgesia before and during acute coronary artery occlusion in open-chest dogs

Abstract

The effects of thoracic epidural analgesia (TEA) on myocardial performance and metabolism and on the severity of an acute myocardial ischaemia, were studied in eight anaesthetized open-chest dogs. TEA reduced mean arterial blood pressure (AP) by 26%, heart rate (HR) by 20%, left ventricular dP/dt by 37%, and myocardial oxygen consumption by 27%. Although arterial concentrations of free fatty acids, glucose and lactate were unchanged, their myocardial uptake was reduced in proportion to the reduction in mechanical activity of the heart. Acute ischaemic injury was estimated from epicardial ECG recordings 10 min after occlusion of a branch of the left anterior descending coronary artery. In seven of eight dogs TEA caused a substantial reduction in the severity of the acute myocardial ischaemic injury. In the eight dogs investigated, the sum of ST segment elevations in epicardial ECG recordings was reduced from 34.0 ± 3.4 to 23.3 ± 2.8 mV (mean ± SEM, P<0.01). After restoration of AP¯ and HR to control values with phenylephrine and atrial pacing, the favourable effect of TEA on myocardial ischaemic injury was abolished. It is concluded that TEA effected a reduction in the severity of myocardial ischaemia in open-chest dogs, mainly through reduction of myocardial mechanical activity with a consequent reduction of myocardial metabolism.

Key Words:

• coronary artery occlusion
• epicardial ECG
• myocardial ischaemia
• myocardial metabolism
• myocardial oxygen consumption
• myocardial performance
• phenylephrine
• thoracic epidural analgesia