Elevated coronary vascular resistance in the presence of reduced resting blood flow distal to a severe coronary stenosis.

Vascular reserve in underperfused myocardium has recently been described. This seemingly paradoxical observation conflicts with older concepts of the coronary circulation which hold that flow deficits do not develop until reserve is fully exhausted. To examine this phenomenon in greater detail in an animal model mimicking a fixed human coronary artery stenosis, we analysed the records of 25 carefully selected, sedated pigs all instrumented with a rigid intralumenal coronary stenosis (82% lumenal diameter reduction). Each animal satisfied the following criteria: 1) perfused myocardial mass beyond the stenosis was within a narrow weight range (16 to 24 g); and 2) post stenosis (distal) epicardial (Epi) and endocardial (endo) flows were less than or equal to 90% of respective flows in a region perfused by the non-stenosed circumflex (CX) coronary artery. Accordingly, distal flow was reduced compared to circumflex zone flow (p less than 0.01) in the Epi (173 +/- 51 to 113 +/- 32 ml . 100g-1 . min-1), Endo (146 +/- 39 to 116 +/- 27) and transmural (Tm) regions (164 +/- 45 to 124 +/- 31). Despite a flow deficit and constant severity of stenosis, distal zone Tm resistance (0.55 +/- 0.21 mmHg/ml . 100 g-1 . min-1) exceeded the minimum level achievable with intravenous infusion of adenosine (0.25 +/- 0.07) in a separate group of eight animals without a stenosis. Distal transmural resistance also varied over a five fold range (0.27 to 1.33) and in 20/25 animals exceeded the highest level (0.37) seen in non-stenosis animals during adenosine infusion.(ABSTRACT TRUNCATED AT 250 WORDS)