Influence of isoflurane on ischaemic heart disease in patients with coronary steal prone anatomy.

It is postulated that patients with ischaemic heart disease (IHD) and coronary steal prone anatomy (CSPA) may develop myocardial ischaemia under isoflurane anaesthesia. This study was conducted in 50 patients undergoing coronary artery bypass grafting. Among these 10 patients (20%) had CSPA, as evidenced by coronary angiography. Anaesthesia was induced with fentanyl, midazolam and thiopentone and maintained with isoflurane in oxygen after endotracheal intubation. Patients were continuously monitored with automated ST segment analysis of electrocardiogram (ECG) and transoesophageal echocardiography (TEE). The end-tidal concentration of isoflurane was maintained at 1.2%, which is equal to one minimum alveolar concentration. Haemodynamic parameters were maintained within 20% of baseline values with either the use of phenylephrine or increasing the depth of anaesthesia by using midazolam and fentanyl. ST changes were measured after 80 ms of J-point in ECG and TEE monitored for occurrence of new regional wall motion abnormalities during the study period. ST changes more than +/-1.0 mm were considered as an indication of myocardial ischaemia. Out of 10 patients having CSPA, 50% developed significant ECG changes during isoflurane anaesthesia at an endtidal concentration of 1.2%. In patients not having CSPA new ischaemia was not observed. Our study indicates necessity of close monitoring of patients with IHD and CSPA during isoflurane anaesthesia to identify new ischaemia and institute appropriate measures.