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J Thorac Cardiovasc Surg 1996;111:432-442
© 1996 Mosby, Inc.

CARDIOPULMONARY BYPASS, MYOCARDIAL MANAGEMENT, AND SUPPORT TECHNIQUES

EFFECTS OF CARDIOPLEGIA ON VASCULAR FUNCTION AND THE "NO-REFLOW" PHENOMENON AFTER ISCHEMIA AND REPERFUSION: STUDIES IN THE ISOLATED BLOOD-PERFUSED RAT HEART

Sponsored by Mark V. Brainbridge

London, United Kingdom

Supported by the Joint Research Board of St. Bartholomew's Hospital and St. Thomas' Hospital Heart Research Trust (STRUTH).

Address for reprints: Vincenzo Argano, MD, FRCS, Cardiothoracic Surgery Department, 3rd floor Q.E. II Block, St. Bartholomew's Hospital, West Smithfield, London EC1A 7BE, United Kingdom.

Abstract

The ability of cardioplegia to protect against cardiac contractile dysfunction caused by ischemia and reperfusion is well established. The effects of cardioplegia on vascular injury and the no-reflow phenomenon, however, remain controversial. We used the blood-perfused rat heart to study the effect of St. Thomas' Hospital cardioplegic solution on postischemic endothelium-dependent and endothelium-independent vascular function, the extent of the no-reflow phenomenon, and the temporal relationship between postischemic vascular and contractile function. Isolated rat hearts (16 per group) perfused with blood from a support rat at 60 mm Hg were subjected to 10, 20, 30 or 40 minutes of global ischemia and 40 minutes of reperfusion at 37° C. Eight hearts in each group also received cardioplegia (45 mm Hg for 2 minutes) before ischemia. Left ventricular developed pressure was measured with an intraventricular balloon. At the end of reperfusion, a bolus of 250µg nitro-L-arginine methyl ester was infused to assess endothelium dependent vascular function. After a 20-minute washout, 25µg sodium nitroprusside was infused to assess endothelium-independent vascular function. Fluorescein (1 ml, 1% weight/volume) was then infused to assess no-reflow; this involved freezing the hearts, cutting them into transverse sections (10 x 1 mm), video recording the sections under ultraviolet light, digitizing the images, and analyzing density of fluorescence. No-reflow was defined as a flow of less than 5%. Compared with nonischemic control responses, endothelium-independent vascular function was significantly decreased only after 30 and 40 minutes of ischemia (48.1% ± 3.8% and 24.3% ± 7.4%, p< 0.05), but it was significantly protected by cardioplegia (66.6% ± 3.9% and 64.5% ± 5.2%, p< 0.05). A significant reduction in endothelium-dependent vascular function was observed after 40 minutes of ischemia (-31.8% ± 6.6% vs -50.4% ± 1.6% in control hearts, p< 0.05), and again this was improved by cardioplegia (-45.0% ± 3.4%, p< 0.05 vs ischemic group). Areas of no reflow were present after 30 and 40 minutes of ischemia (11.9% ± 6.8% and 33.4% ± 14.1% of left ventricular mass), and at each time period they were significantly decreased by cardioplegia (0.7% ± 0.4% and 3.8% ± 1.6%, p< 0.05). Postischemic contractile dysfunction was observed before any vascular alteration was apparent. After only 20 minutes of ischemia, the postischemic recovery of left ventricular developed pressure fell to 56.7% ± 4.0%, but both endothelium-dependent vascular function and endothelium-independent vascular function were unaffected. In conclusion, vascular alterations are apparent only after prolonged periods of ischemia, longer than those required to observe contractile dysfunction, and cardioplegia protects against postischemic endothelium-dependent and endothelium-independent vascular dysfunction and reduces the extent of the no-reflow phenomenon. (J THORAC CARDIOVASC SURG 1996;111:432-42)

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