A rapid hemodynamic monitor of acute ischemia during cardiac procedures: changes in relaxation via a continuous left ventricular pressure-derivative loop.
BACKGROUND
Procedures that induce ischemic pre-conditioning during cardiac surgery will require a rapidly visualized hemodynamic monitor of acute ischemia. This study investigated the utility of a continuous loop tracing of left ventricular pressure (LVP) plotted against its derivative (dP/dt) as a visual beat-to-beat monitor of acute changes in myocardial relaxation due to global ischemia.


METHODS
In 11 dogs, LVP, recorded via a micromanometer-tip catheter, was plotted against dP/dt as a continuous loop. The angle of the loop during relaxation is inversely related to tau, the time constant of isovolumic relaxation. The angle was measured before and during: infusion of dextran to increase pre-load, infusion of nitroprusside to reduce after-load, and a 30-s occlusion of the left main coronary artery to induce temporary global ischemia.


RESULTS
The relaxation angle of the loop did not change with dextran or nitroprusside infusion. During left main occlusion, the angle increased from 57 +/- 7 degrees to 92 +/- 3 degrees (P < 0.001), reflecting markedly impaired relaxation. In five of nine cases, the angle became greater than 90 degrees, rendering the monoexponential model of pressure decay inapplicable. However, the beat-to-beat progression of the angle could easily be followed visually.


CONCLUSIONS
The LVP-dP/dt loop is a readily visualized, continuous display of beat-to-beat changes in myocardial relaxation. It provides a dynamic and specific display of immediate changes in relaxation during global ischemia, even when the exponential model of pressure decay is not applicable. The loop may be useful for guiding procedures that induce ischemic pre-conditioning or post-conditioning during cardiac surgery.
Department of Surgery, Louisiana State University Medical Center, and Department of Surgery, Tulane University, New Orleans, Louisiana, USA. hsilber@jhmi.edu
Harry A
HA
Silber
William M
WM
Gottliebson
Douglas P
DP
Lohmann
Willam R
WR
Rank
Watts R
WR
Webb
Peter V
PV
Moulder
D000818:Animals; D003971:Diastole; D004285:Dogs; D006339:Heart Rate; D008991:Monitoring, Physiologic; D009200:Myocardial Contraction; D017202:Myocardial Ischemia / Q000503:physiopathology*; D016277:Ventricular Function, Left