| Abstrakt: |
Myocardial blood flow (MBF) regulation in collateral dependent myocardium (CD) of patients with coronary artery disease has not been fully elucidated. To this purpose, 19 patients with stable angina, no previous myocardial infarction and isolated occlusion of the left anterior descending (n=14) or left circumflex (n=5) coronary artery were evaluated. MBF measurements were obtained off-therapy, using dynamic positron emission tomography and nitrogen-13 Ammonia, at baseline, during atrial pacing tachycardia and after i.v. dipyridamole (0.56mg/kg over 4min). MBF in CD and remote regions were compared with MBF values Obtained in 13 normal subjects. At rest, MBF was similar in CD and in the remote myocardium (0.61±0.11 vs 0.63±0.17 ml/min/g), both values were lower than normal (1.00±0.2 ml/min/g, p<0.01). During pacing MBF increased to 0.84±0.25 and 1.11±0.39 ml/min/g in CD and contralateral areas, respectively (p<0.05 vs baseline); both these values were lower (p<0.01) than normal (1.86±0.61 ml/min/g). Dipyridamole induced a further increase in MBF in remote areas (1.36±0.57 ml/min/g, p<0.01 vs pacing) but not in CD (0.93±0.37 ml/min/g, ns vs pacing); both values were reduced (p<0.01) with respect to normals (3.46±0.78 ml/min/g). Dipyridamole MBF in CD was slightly lower in patients with poor than in those with well developed collaterals (0.75±0.29 vs 1.06±0.38ml/min/g, respectively, p=0.06). however, the former showed a higher flow inhomogeneity (CD/control flow ratio: 0.58±0.10 vs 0.81±0.22, respectively, p±0.02). Despite so different coronary anatomy (one vessel occluded the other normal), a linear, direct correlation was observed between flow reserve of CD and remote regions (r=0.83, P<0.01). Thus, despite resting hypoperfusion, CD maintains a residual perfusion reserve that can be almost fully utilized during moderate increases in oxygen consumption. A global microvascular disorder affects the adaptation to chronic coronary occlusion. |
