[Adaptation to effort myocardial ischemia]

During PTCA it has been observed that in two sequential coronary occlusions, the second is characterized by less subjective anginal discomfort, less ST segment depression, less myocardial lactate production and lower mean pulmonary pressure than that recorded during the first inflation. The phenomenon is known as "cardiac adaptation to ischemia". PTCA, as a model for controlled, reversible myocardial ischemia must be viewed in a substantially different context from other models concerning different types of ischemia. The purpose of our investigation was to examine the hypothesis that phenomena similar to those observed during PTCA can occur during effort ischemia.

Six patients with stable effort ischemia, fixed ischemic threshold (bpm x mmHg variability less than 3200) and fixed recovery period (variability of time at ST on isoelectric line less than 1 min and variability of rate-pressure product at ST on isoelectric line less than 2000 bpm x mmHg) were studied. Our aim was to study the ischemic threshold (IT) and the recovery period in an exercise test performed a short time after an initial one. The programme consisted of: 1) exercise test at a fixed load (the load was predetermined by the level of ischemia reached in a previous multistage exercise test); 2) exercise test ending at ST decreases 1 mm; 3) recovery period; 4) 2nd exercise test similar to the first one and ending at ST decreases 1 mm, to be performed 3 minutes after the end of recovery period (that is, 3 minutes after ST on isoelectric line). In both exercise tests we registered rate-pressure product at ischemia (RPPI), time to ischemia (TI), rate-pressure product at ST on isoelectric line (rate-pressure product at normalization: RPPN) and time at ST on isoelectric line (time of normalization: TN).

[table: see text] In all pts RPPI in the second exercise test was similar to RPPI registered in the first one, while RPPN in the second exercise test was higher than in the first. In the second exercise test, time to ST on isoelectric line was also shorter.

We think that the shorter recovery period from myocardial ischemia in the second exercise test may be an expression of a "cardiac adaptation to ischemia", a phenomenon which has been previously observed during PTCA.