RESUMO
BACKGROUND: Sustained tachyarrhythmia resulting in fetal hydrops is often refractory to medical therapy. Fetal atrioventricular node ablation associated with epicardial fetal pacing has the potential to be an effective procedure for this morbid association. METHODS: To assess the feasibility of therapeutic fetal heart block, we developed a technique of intrauterine cryosurgical ablation of fetal atrioventricular node without the need for cardiac bypass in 8 fetal lambs. Complete heart block was obtained by applying the cryoprobe over the coronary sinus. Fetal pacing was then performed to allow fetal survival. RESULTS: Complete heart block was achieved in 100% of the fetal lambs. Postoperative evaluation revealed persistent atrioventricular block. The hearts were studied at different postoperative times. Morphologic evaluation of the area containing the cryosurgical lesion revealed varied extension of necrosis of the atrioventricular node and hemorrhage, with involvement of the His bundle and proximal right bundle branch. CONCLUSIONS: This procedure is technically feasible and offers an alternative approach to the treatment of drug-resistant, life-threatening fetal supraventricular tachyarrhythmias associated with hydrops fetalis.
Assuntos
Nó Atrioventricular/cirurgia , Criocirurgia , Coração Fetal/cirurgia , Animais , Nó Atrioventricular/patologia , Modelos Animais de Doenças , Estudos de Viabilidade , Doenças Fetais/cirurgia , Necrose , Ovinos , Taquicardia Supraventricular/cirurgiaRESUMO
Epicardial fetal pacing via thoracotomy has the potential of being a safer and more reliable procedure to treat congenital complete heart block (CHB) associated with fetal hydrops refractory to medical therapy. To assess the acute electrophysiological characteristics of two ventricular epicardial leads, a new experimental model of fetal heart block induced by cryosurgical ablation of the AV node without the need for fetal cardiac bypass was performed in 12 pregnant ewes at 110-115 days gestation. A modified screw-in lead (1 1/2 turns) was used in six fetal lambs and a stitch-on lead in the other six lambs. CHB was achieved in 100% of the fetal lambs, with no ventricular escape rate noticed in any of the lambs. The acute stimulation thresholds were consistently low for both leads, with lower values for the screw-in lead at pulse duration below 0.9 msec (P < 0.03). Current measured at voltage threshold with pulse width below 0.5 msec was lower for the screw-in lead (P < 0.048). Stimulation resistance, measured during constant-voltage pacing, was not statistically different between the two leads (441.8 +/- 13.7 omega for the screw-in lead vs 480.2 +/- 59.2 omega for the stitch-on lead). No significant differences (P > 0.20) were found in R wave amplitude between the two electrodes. Slew rates were significantly higher in the screw-in group than in the stitch-on group (1.40 +/- 0.2 vs 0.62 +/- 0.2 V/sec, P = 0.04). This model of CHB is a simple and reproducible method to assess fetal pacing. We find the screw-in electrode to be a better option when fetal pacing is indicated.
Assuntos
Estimulação Cardíaca Artificial , Doenças Fetais/terapia , Bloqueio Cardíaco/terapia , Animais , Nó Atrioventricular/patologia , Nó Atrioventricular/fisiopatologia , Modelos Animais de Doenças , Eletrocardiografia , Desenho de Equipamento , Feminino , Doenças Fetais/patologia , Doenças Fetais/fisiopatologia , Coração Fetal/patologia , Coração Fetal/fisiopatologia , Idade Gestacional , Bloqueio Cardíaco/patologia , Bloqueio Cardíaco/fisiopatologia , Frequência Cardíaca Fetal/fisiologia , Marca-Passo Artificial , Gravidez , Ovinos , Toracotomia , Função Ventricular/fisiologiaRESUMO
In 100 consecutive neonates with birth weights < or = 2500 gm (range, 540 to 2500 gm; median, 2200 gm), major congenital heart disease (excluding patent ductus arteriosus, isolated atrial septal defect, and ventricular septal defect) was diagnosed between January 1987 and January 1991; 46 had ductus-dependent lesions. Of the 100 neonates, 30 had genetic aberrations or significant associated congenital anomalies. The four most common cardiac diagnoses were tetralogy of Fallot with or without pulmonary atresia (n = 16); coarctation of the aorta (n = 12); transposition of the great arteries (n = 11); and common atrioventricular canal (n = 11). The hospital survival rate for the entire group of 100 neonates was 70%. The patients were separated into three groups on the basis of the time of intervention. Group 1 (early intervention) included 62 infants. These neonates (including 31 with ductus-dependent lesions) had surgical or catheter intervention during the initial hospitalization (median age, 9 days), all at weights < or = 2500 gm. The hospital survival rate was 81% (50/62); survival rates for palliation (78%, 18/23) and for correction (82%, 32/39) were similar. There were 26 neonates in group 2 (late intervention). These neonates did not have surgical intervention during the initial hospitalization. All were managed medically; survivors were discharged and had surgical procedures later (at a median age of 4.3 months). Six neonates (23%) died during medical management; all 20 survivors returned and had surgical procedures, with 90% survival. Overall survival rate for this group was 69% (18/26). The remaining 12 patients (group 3) had complicating features that precluded intervention; none survived. On the basis of these results, we conclude that early intervention, even with corrective surgery, can be performed in low birth weight neonates with an acceptable mortality rate. Prolonged medical therapy to achieve further weight gain did not appear to improve the survival rate.