Alterations in myocardial hydrogen ion concentration after temporary coronary occlusion: a sign of irreversible cell damage.

Alterations of hydrogen ion (H+) concentration in the myocardium of 60 cats were determined before release of coronary ligation of 30, 45, 60, 90 or 180 minutes' duration, or 5, 30 and 90 minutes after release of the occlusion, by pressing pH indicator paper on unfixed frozen heart sections. The H+ concentration had clearly increased (pH less than 6.0) in a transmural extension in the left ventricle before release of the coronary ligature. This elevated H+ concentration persisted some time in the subendocardial region despite release of the coronary occlusion, thus proving that the so-called no reflow phenomenon exists in involved myocardium after temporary coronary occlusion. A diminished H+ concentration (pH 7.4) was found in the border zone between the acid-reacting area and the normal muscle when the coronary occlusion lasted 180 minutes before release of the ligature or 30 minutes after release of the occlusion when the previous period of temporary occlusion had been longer than 30 minutes. Although areas manifesting an acid reaction vanished or diminished in size after release of coronary occlusion, the extent of alkaline-reacting zones showed no reduction in size, and muscle cell necrosis developed in these alkaline-reacting areas. It is assumed therefore that an alkaline reaction of the myocardium is an early sign of irreversible muscle cell damage.