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ORIGINAL ARTICLE

Evaluation of continuous normothermic blood cardioplegia using Phosphorus 31 nuclear magnetic ressonance

Carlos A. M BarrozoI; Imtiaz S AliI; Anthony L PanosI; Owaid Al-NowaiserI; Keith W ButlerII; Nicholas HaasII; Tomás A SalernoI; Roxanne DeslauriersII

DOI: 10.1590/S0102-76381992000400010

ABSTRACT

An isolated, blood perfused pig heart model was adapted for metabolic studies using 31 P NMR spectroscopy during continuous normothermic blood cardioplegia (CNBC). The experiment comprised two groups: In Group I (n=5) the hearts were subjected to 1 hour of CNBC. In Group II (n=5) a 20 min period of ischemia was introduced in the middle of the period of CNBC. Left ventricular function was assessed, in the beating heart, prior to the period of CNBC and after 60 min of cardioplegia, using an intra-ventricular balloon. During the entire period of the experiment, spectra were obtained using a 4.7 T/30 cm bore BrukerTM Biospec 31P NMR spectrometer with 2 min of resolution. At the end of the experiments myocardial biopsies were taken for ATP and phosphocreatine (PCr) analyses using high performance liquid chromatography (HPLC). ATP and PCr were maintained after the period of cardioplegic arrest (Group I). However the Group II, complete loss of PCr was shown after 14 ± 2 min of normothermic ischemia, followed by an increase of inorganic phophate (Pi) and decrease of intracellular pH. Following reperfusion after CNBC, PCr, pH and Pi returned normal values in 3 min. Left ventricular function, assessed by end-systolic elastance, was maintained at 100±10% of control in Group I. In the Group II, left ventricular function was 88 ± 7% (p<0.05) of the control. HPLC analyses of the myocardial biopsies showed normal values for Group I, ATP (24 ± 3 µmol/g dry weight) and PCr (55 ± 14 µmol/g dry weight), but in Group II, despite normal levels of PCr after reperfusion, the ATP levels decreased to 21 ± 3 µmol/g dry weight at the end of the experiments. These results showed that cardiac metabolism was seriously compromised after 14 min of normothermic ischemia and left ventricular function had decreased (Group II). However in Group I, in which CNBC was used without interruptions, function and metabolism were preserved, suggesting this is the ideal technique to protect the heart during cardiac surgery.

RESUMO

Um modelo isolado de coração de porco perfundido com sangue foi adaptado para o uso de fósforo 31 ressonância nuclear magnética (31 pRNM) em estudos de espectroscopia do metabolismo cardíaco durante cardioplegia sangüínea contínua e normotérmica (CSCN). O experimento foi dividido em dois grupos: Grupo I (n=5): os corações foram submetidos a 1 hora de CSCN. Grupo II (n=5): um período de 20 minutos de isquemia normotérmica durante o período de 1 hora de CSCN 17. A função do ventrículo esquerdo (VE) foi avaliada, com o coração batendo, utilizando um balão intraventricular, antes do período de parada cardioplégica e a seguir, quando o coração foi novamente perfundido com sangue normokalêmico. Durante todo o protocolo, análise espectroscópica do metabolismo cardíaco foi obtida utilizando-se 4.7 T/30cm Bruker TM Biospec 31 p RNM com uma resolução de 2 minutos para cada resultado. Ao final dos experimentos biópsias miocárdicas foram obtidas para análise de ATP e fosfocreatina (PCr) utilizando cromatografia liqüida de alta "performance" (HPLC). Não houve perda significante de ATP e PCr durante o período de parada cardioplégica com CSCN (Grupo I). Contudo, no Grupo II, a análise espectroscópica demonstrou perda completa de PCr após 14 ± 2 minutos durante a isquemia normotérmica acompanhada de aumento de fosfato inorgânico (Pi) e diminuição do pH intracelular. Quando reperfundido com CSCN, PCr, pH e Pi retornaram aos valores normais em 3 minutos. A função do VE avaliada através da elastância sistólica final foi mantida em 100 ± 10% dos valores obtidos antes da parada cardioplégica no Grupo I. No Grupo II, a função do VE foi de 88 ± 7% (p<0,05) dos valores precedentes à parada cardioplégica. Os resultados das biópsias do miocárdio demonstraram manutenção dos níveis normais de ATP (24 ± 3 µmol/g dry weight) e PCr (55 ± 14 µmol/g dry weight) no Grupo I, porém no Grupo II, apesar dos níveis normais de PCr após a reperfusão, os níveis de ATP diminuíram para 21 ± 3 µmol/g dry weight ao final do experimento. Este experimento demonstrou que o metabolismo cardíaco deteriorou após 14 minutos de isquemia normotérmica com conseqüente diminuição da função do VE (Grupo II). Porém, quando a cardioplegia sangüínea contínua e normotérmica foi utilizada sem interrupções (Grupo I) o metabolismo cardíaco e a função de VE foram preservadas, sugerindo que essa é a maneira ideal para se proteger o coração durante cirurgia cardíaca.
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