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The Journal of Cardiovascular Surgery 2000 Dicembre;41(6):807-17

lingua: Inglese

Importance of heart rate for acute hibernation in isolated blood-perfused piglet hearts

Sommerschild H. T. *, Grund F. *, Offstad J. *°, Ilebekk A. *, Kirkebøen K. A. **

From the *Insti­tute for Experi­mental Uni­ver­sity of ­Oslo, °Depart­ment of Car­di­ology, Rik­shos­pi­talet Med­ical Depart­ment B
**Depart­ment of ­Anaesthesia, ­Ullevål Hos­pital Oslo, ­Norway


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Back­ground. Hiber­nating myo­car­dium may ben­efit ­from revas­cu­lar­iza­tion. ­There are sev­eral experi­mental ­models for ­acute hiber­na­tion. In ­intact ­hearts low-­flow ­ischemia ­causes ­time-depen­dent meta­bolic alter­a­tions, ­termed “meta­bolic adap­ta­tion”. In iso­lated ­heart prep­ar­a­tions meta­bolic ­responses to low-­flow ­ischemia ­vary, and ­signs of meta­bolic adap­ta­tion are not con­sis­tently ­found. In iso­lated ­hearts ­global ­ischemia may ­cause brad­y­cardia ­unless the ­hearts are ­paced. We hypoth­e­sized ­that the ­lack of con­sis­tent meta­bolic adap­ta­tion to low-­flow ­ischemia in iso­lated ­hearts ­might be due to brad­y­cardia ­during ­ischemia. In ­this ­study we inves­ti­gated the influ­ence of ­heart ­rate on metab­olism and func­tion in an iso­lated ­heart prep­ar­a­tion.
­Methods. Iso­lated ­blood-per­fused ­piglet ­hearts ­were sub­jected to 120 min 10% ­flow. In ­groups A (n=9) and B (n=4) ­hearts ­were not ­paced ­during ­ischemia, in ­groups C (n=5) and D (n=5) ­hearts ­were ­paced at pre-­is­chemic ­heart ­rate ­during ­ischemia.
­Results. ­Without ­pacing, ­heart ­rate ­declined to ≈1/3 ­during ­ischemia and anaer­obic metab­olism ­showed a ­slight ­decline ­over ­time. ­With ­pacing, pro­duc­tion of pro­tons, pCO2 and lac­tate ­showed a ­bell-­shaped ­curve ­which ­peaked at 20-25 min of ­ischemia, fol­lowed by a sub­se­quent ­decline ­towards the end of ­ischemia (­overall p<0.001 for all). How­ever, reper­fu­sion ­revealed ­impaired ­recovery of func­tion in ­paced ­hearts com­pared to non-­paced ­hearts (53±7% vs 77±4%, p<0.05) con­com­i­tant ­with ­higher ­release of crea­tine ­kinase (455±93 IU/100 g vs 106±13 IU/100 g, p<0.01).
Con­clu­sions. ­When ­heart ­rate is ­allowed to ­decline ­during low-­flow ­ischemia in iso­lated ­piglet ­hearts, ­signs of meta­bolic adap­ta­tion are not evi­dent. ­When ­hearts are ­paced ­during ­ischemia ­time-depen­dent alter­a­tions in anaer­obic metab­olism ­occur, resem­bling obser­va­tions ­seen in ­intact ­beating ­hearts. How­ever, ­paced ­hearts ­also ­show indi­ca­tions of ­increased cel­lular ­injury, indi­cating ­that in ­paced ­hearts the meta­bolic con­se­quences are ­mostly due to ­increased irre­ver­sible ­cell ­injury. ­Thus, the ­model for ­acute hiber­na­tion ­with 10% ­flow in iso­lated ­blood-per­fused ­piglet ­hearts are crit­i­cally depen­dent on brad­y­cardia ­during ­ischemia.

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