New Q waves after bypass grafting: correlations between graft patency, ventriculogram and surgical venting technique.

New Q waves were observed in 35 (11%) of 321 patients undergoing saphenous vein bypass grafting with an overall mortality rate of 1.1%. Twenty-eight (80%) had postoperative arteriograms and ventriculograms and are reported. Ventricular venting was used intra-operatively in 17 patients and atrial venting in 11. The incidence of new Q wave was 22% in patients with ventricular venting and 5.5% in those with atrial venting (p less than 0.05). Complete or incomplete revascularization did not affect the incidence of new Q waves. New Q waves appeared in a zone of myocardium supplied by a grafted artery in all except two patients with ventricular venting in whom Q waves occurred within the zone of myocardium supplied by diseased ungrafted vessels. In the ventricular venting group, seven (41%) demonstrated an improved or unchanged postoperative ventriculogram and ten (59%) had deteriorated ventriculograms. In 11 patients with atrial venting, nine (82%) showed improved or unchanged postoperative ventriculograms and two (18%) had deteriorated ventriculograms. Ventricular venting patients with improved or unchanged postoperative ventriculograms had 7% graft closure as compared to 5% of those with atrial venting (pNS). Graft closure rate was 44% in ventricular venting and 20% (pNS) of patients with atrial venting who had deteriorated left ventriculograms. These findings indicate poor correlation between new Q waves and graft closure. Improved postoperative ventriculograms corrleated well with graft patency despite new Q waves. The etiology of new post bypass graft Q waves are varied. They include ventricular trauma and conduction delays resulting from surgery or venting, as well as infarction. This may be due to compromised arterial inflow either in nonoperated vessels or in the vessels distal to the anastomosis with patent grafts, or due to occluded grafts.