New insights into the physiology of retrograde cardioplegia delivery.
Although retrograde cardioplegia (RC) is being increasingly used in clinical practice, its physiology is unclear. Because the microvascular architecture of the coronary venous system is different from that of the arterial system, we hypothesized that myocardial perfusion would be different during RC compared with anterograde cardioplegia (AC) delivery. To better understand these differences, three groups of dogs were studied during similar RC and AC flow rates. Radiolabeled microsphere-derived microvascular flow underestimated total cardioplegia flow by 66% during RC. For the same flows, the first-pass extraction fractions of 201Tl and 99mTc were significantly less during RC compared with AC despite adjusting for microsphere loss. Myocardial contrast echocardiography (MCE), however, provided an accurate estimation of AC and RC flow rates. In addition, the rate of myocardial cooling for most of the left ventricular myocardium was similar for AC and RC at the same flow rates, as long as the flow rates were brisk. It is concluded that microvascular and nutrient flows are significantly lower at the same flow rates during RC compared with AC due to loss of RC at different microvascular sites. Unlike microspheres and diffusible radioisotopes, MCE can provide a reliable measure of myocardial flow during RC delivery. Furthermore, myocardial cooling is similar in most of the myocardium during high-flow RC and AC, which suggests that the clinical benefits of RC are probably related to myocardial cooling and that substrate replenishment may be better achieved at the same flow rates and myocardial temperatures with AC rather than RC.
Villanueva
F S
FS
Cardiovascular Division, University of Virginia School of Medicine, Charlottesville 22908, USA.
Spotnitz
W D
WD
Glasheen
W P
WP
Watson
D D
DD
Jayaweera
A R
AR
Kaul
S
S
D000388:Air; D000818:Animals; D001831:Body Temperature; D002314:Cardioplegic Solutions / Q000008:administration & dosage*; D003287:Contrast Media; D003331:Coronary Vessels; D004285:Dogs; D004452:Echocardiography; D006321:Heart / Q000503:physiopathology; D006324:Heart Arrest, Induced / Q000379:methods*; D006439:Hemodynamics; D008833:Microcirculation; D008863:Microspheres; D017256:Technetium Tc 99m Sestamibi; D013794:Thallium Radioisotopes; D014680:Veins
D002314:Cardioplegic Solutions; D003287:Contrast Media; D013794:Thallium Radioisotopes; D017256:Technetium Tc 99m Sestamibi