Brazilian Journal of Cardiovascular Surgery (Sep 2006)
Avaliação experimental de novo eletrodo para implante de marca-passo em fetos Experimental assessment of a new electrode for fetal pacing
Abstract
OBJETIVO: O bloqueio atrioventricular total (BAVT) fetal apresenta mau prognóstico quando associado à hidropisia. O implante de marca-passo pode melhorar as chances de sobrevida fetal. Este estudo analisa as características eletrofisiológicas do novo eletrodo de marca-passo fetal, a hemodinâmica e metabolismo fetal sob freqüências cardíacas variadas. MÉTODO: O novo eletrodo (formato de "T") foi implantado no coração de cinco fetos de cabras. O débito cardíaco fetal foi medido com fluxômetro. O BAVT foi obtido por meio da crioablação do nó atrioventricular fetal. Os parâmetros eletrofisiológicos, hemodinâmica e metabolismo fetal foram analisados sob diversas freqüências cardíacas. RESULTADOS: O eletrodo fetal apresentou baixos limiares agudos, sem falhas no comando do estímulo. A curva do limiar de estimulação permaneceu relativamente constante para larguras de pulso acima de 0,5 mseg. A resistência foi de 1050,4 ± 76,6 ohms; e a onda R foi de 8,6 ± 5,6 mV. A freqüência cardíaca fetal abaixo de 60 bpm produziu baixo débito cardíaco fetal e hipotensão arterial (pOBJECTIVE: The prognosis of congenital complete heart block (CHB) is very poor when manifested with fetal hydrops. Fetal pacing may improve the survival rate. This study aims to assess the electrophysiological characteristics of a new lead, as well as fetal hemodynamic and metabolism under different fetal heart rates. METHODS: The new lead (T-shaped) was deployed into the myocardium of five fetal goats. Fetal cardiac output was measured by a flow transducer. CHB was achieved by cryosurgical ablation of fetal AV node. Electrophysiological parameters, hemodynamic and metabolic behavior of the fetus under different fetal heart rates were evaluated. RESULTS: The acute stimulation thresholds were consistently low. The voltage strength-duration curve remained relatively constant at pulse widths > 0.5 msec. The stimulation resistance was 1050.4 ± 76.6 ohms, and the sensed fetal R wave was 8.6 ± 5.6 mV. Fetal heart rate bellow 60 bpm was associated to low cardiac output and low blood pressure (p<0.05). Fetal bradycardia also determined oxygen saturation drop parallel to low cardiac output, with severe hypoxia below 60 bpm. CONCLUSION: The new lead allows for a less invasive procedure and stable fixation to the myocardium that may prevent lead dislodgement after fetal recovery. It seems to be compatible with safe chronic stimulation. This study suggests that a gradual increase in the fetal rate beginning on 80 bpm after implantation would be more adaptive and adequately augment fetal cardiac output.
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