Myocardial ischemia is not a prerequisite for the stimulation of coronary collateral development.

To understand better the temporal sequence of coronary collateral development and the factors that may govern that development, dogs were chronically instrumented with left circumflex (LCf) Doppler flow probe, ameroid constrictor, balloon occluder, and left atrial and aortic catheters. Collateral blood flow was measured at least weekly or when the coronary artery occluded. The reactive hyperemic response (RH) to a 15-second LCf occlusion was recorded three times per week. Most LCf arteries occluded during the 4th week after surgery. Two patterns of coronary collateral development were observed. In 11 animals collateral flow did not change for 2 or 3 weeks; peak RH and flow debt repayment, indexes of coronary vascular reserve, changed little. The next week there was an abrupt increase in collateral flow from approximately 15% of normal to 100%. This increase was coincident with a sudden loss of coronary vascular reserve and therefore suggests myocardial ischemia was the principal stimulus. However, in 11 dogs collateral flow increased gradually over 3 to 4 weeks as indexes of RH slowly decreased. The greatest increase in collateral flow occurred while peak RH was still approximately twice baseline flow, representing 80% of peak flow measured 1 week after surgery. Therefore in these animals ischemia is less likely to have been the major stimulus of coronary collateral development.