In Reply:-Drs. Borges and Coulson suggest that perfusion to the myocardium is preferable to ischemic preconditioning. Although the technique of perfusion during surgical anastomosis seems to be an excellent option for many patients, it may not be appropriate for some patients. According to their case report, they had prophylactically cannulated the femoral artery in case cardiopulmonary bypass was required. Therefore, they were effectively able to manage arrhythmias and hypotension after occlusion of the right coronary artery using a perfusing cannula connected from the side port of a femoral artery DLP cannula. On the other hand, in our patient, cardiopulmonary bypass with cross-clamping of the aorta was planned. Only after median sternotomy and harvesting of the right and left internal mammary arteries was completed was it clear that the patient had a “porcelain” aorta and that aortic cross-clamping would not be feasible. Because this patient had significant atherosclerosis of his major arteries including femoral and axillary arteries, an appropriate arterial cannulation site was not available. Had we been able to cannulate the femoral arteries, we would have opted for femoral artery bypass.
Dr. Lennon suggests that the phenomenon of ischemic preconditioning did not occur because there was no electrocardiographic evidence of myocardial ischemia during the preconditioning interval. However, absence of ST-segment or T-wave changes during the preconditioning interval does not indicate that transient ischemic episodes did not occur. Furthermore, transesophageal echocardiography is a more sensitive monitor for myocardial ischemia and perhaps may have demonstrated regional wall motion abnormalities in the absence of electrocardiographic changes, although we do not routinely use transesophageal echocardiographic monitoring. Importantly, myocardial ischemia that is sufficient to induce preconditioning may not be detectable with the currently available clinical monitors (i.e., electrocardiography and transesophageal echocardiography). It has been shown that ischemic preconditioning in humans does occur after brief periods of coronary artery occlusion, despite the absence of electrocardiographic changes during the occlusion period. Jacobsohn et al. did not observe any ST-segment or T-wave changes during ischemic preconditioning but documented beneficial effects of preconditioning such as improved myocardial contractility. Although it cannot be concluded with certainty that ischemic preconditioning in our patient preserved the myocardial function, the absence of perioperative myocardial infarction, as suggested by serial electrocardiographic and cardiac enzyme determinations, suggests that the myocardium may have been protected during coronary artery clamping and cardiac standstill.
Finally, Dr. Lennon misinterpreted our rationale for using adenosine in this patient. We did not give adenosine for the purpose of preconditioning. After we were unable to effectively decrease the patient's heart rate with esmolol, we gave adenosine for the sole purpose of providing intermittent, brief periods of cardiac standstill so that the surgeons could complete the anastomosis. As we stated in our discussion, there are no reports that suggest that intermittent cardiac standstill produced by the administration of adenosine mimic ischemic preconditioning.
Girish P. Joshi, M.B., B.S., M.D., F.F.A.R.C.S.I.
Paige Latham, M.D.
Department of Anesthesiology and Pain Management; University of Texas Southwestern Medical Center; 5323 Harry Hines Boulevard; Dallas, Texas;email@example.com
(Accepted for publication July 30, 1998.)