The detection of intra-operative myocardial ischaemia. Preliminary experience with the right-sided precordial lead.

The value of monitoring the right precordial lead, V4R, to detect peri-operative ischaemic events during coronary artery surgery was studied in 60 patients. Thirty-four patients had only left-sided coronary disease (Group 1). The other 26 patients had both left-sided occlusive coronary artery disease and significant right-sided occlusive lesions on coronary angiography (Group 2). Lead sensitivity was estimated, assuming that all ST segment changes were true positive responses. Sensitivity using a single lead was greatest for lead V5 in the two groups (73% for Group 1 and 69% for Group 2). Sensitivity in Group 1 for lead II was intermediate (55%), whereas sensitivity for lead V4R was only 9%. In Group 2, on the other hand, lead V4R was 54% sensitive and lead II only 31%. The combination of leads V4R and V5 increased the sensitivity to 92% in Group 2, whereas lead II or V5 combined with V4R failed to improve sensitivity in Group 1. The monitoring of lead V4R allowed detection of 23% of the ischaemic episodes in Group 2 that would have passed undetected if only lead II and V5 were monitored. These results demonstrate the value of an additional right precordial lead during coronary artery bypass grafting in patients with right-sided occlusive disease.