The Journal of Thoracic and Cardiovascular Surgery, Vol 72, 52-56, Copyright © 1976 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Monitoring of midmyocardial and subendocardial pH in normal and ischemic ventricles
GL Hicks, A Hill and JA DeWeese
Midmyocardial and subendocardial pH monitoring was used as an indirect
method for continuous evaluation of regional canine myocardial ischemia.
Left ventricular midmyocardial pH (pHm) at 4 mm. depth was monitored in 10
dogs, under resting conditions, by means of a 5 mm. Beckman pH probe. pHm
was 6.96 +/- 0.03, recorded at myocardial temperatures of 35 to 37 degrees
C. Ischemia was then produced by snare occlusion of the proximal left main
coronary artery for 2 minutes. pHm decreased to 6.87 +/- 0.03 (p less than
0.01) at 1 minute and 6.80 +/- 0.04 (p less than 0.005) in 2 minutes. When
flow was restored, pHm returned toward normal within 2 minutes (pH 6.86 +/-
0.03) and at 5 minutes had returned to control values (pH 6.93 +/- 0.03).
In another 5 dogs under similar conditions, pHm at 4 mm. and subendocardial
pH (pHe at 8 mm.) were measured. Baseline pHm (6.97 +/- 0.01) and pHe (6.84
+/- 0.02) levels were significantly different (p less than 0.0005). After 2
minutes of ischemia, pHm was 6.82 +/- 0.03, whereas pHe decreased to 6.78
+/- 0.04 (p less than 0.1). Five minutes after snare release, pHe remained
at 6.73 +/- 0.07; pHm (6.93 +/- 0.03) returned to control values. Both pHm
(6.93 +/- 0.02) and pHe (6.84 +/- 0.09) levels were normal 15 minutes after
release of the snare. The midmyocardium and subendocardium have different
pH levels which can be monitored. Ischemia produces different pH patterns
in these layers. pHm returns to control values within 5 minutes after 2
minutes of ischemia, whereas pHe remains depressed for at least 5 minutes.
pH monitoring provides an accurate and simple method for on-line evaluation
of endocardial ischemia.
