A four-shock Bayesian up-down estimator of the 80% effective defibrillation dose.

INTRODUCTION: New defibrillation techniques are often compared to standard approaches using the defibrillation threshold. However, inference from thresholding data necessitates extrapolation from reactions to relatively ineffective shocks, an error prone procedure requiring large sample sizes for hypothesis testing and large safety margins for defibrillator implantation. In contrast, this article presents a clinically validated statistical model of a minimum error, four-shock defibrillation testing protocol for estimating the 80% effective defibrillation strength for a given patient (ED80). METHODS AND RESULTS: A Bayesian statistical model was constructed assuming that the defibrillation dose-response curve is sigmoidal, and the ED80 is between 150 and 750 V. The model was used to design a minimum predicted error testing protocol and estimates. To prospectively validate the testing protocol and estimates, 170 patients received voltage-programmed biphasic testing. Four fibrillation episodes were induced and terminated in each patient according to the Bayesian up-down protocol. In addition, a validation attempt was made at the estimated ED80 rounded up to the nearest 50 V. In order to estimate the safety margin, in 136 patients, a defibrillation attempt was made at the rounded ED80 + 100 V. Of the 170 attempts at the rounded ED80, 143 (84%) attempts terminated fibrillation. Of the 136 attempts at the rounded ED80 + 100 V, 133 (98%) were effective. CONCLUSIONS: The four-shock Bayesian up-down protocol is the first clinical protocol to accurately predict an ED80 voltage. A 100 V increment above the ED80 provides an adequate safety margin. This simple and accurate method for estimating a highly effective defibrillation dose may be a valuable tool for population-based clinical hypothesis testing, as well as defibrillator implantation.

Mitral valve repair combined with aortic valve replacement.

BACKGROUND AND AIMS OF THE STUDY: Combined aortic and mitral valve replacement continues to result in significant morbidity and mortality. Although mitral repair has improved the results of mitral valve surgery, its influence on combined aortic valve replacement has not been assessed. METHODS: We reviewed 38 consecutive patients who underwent aortic valve replacement (AVR) and mitral repair (MR) between 1985 and 1995. The average age was 57 years; 20 were men and 18 women. Nineteen patients were considered high risk: six had previous cardiac surgery, three were on chronic dialysis, two required emergency surgery for low output syndrome, one had a chronic tracheotomy for chronic lung disease, and seven had left ventricular ejection fraction < 30%. MR consisted of ring application alone in 28 patients, chordal shortening in nine, posterior leaflet transfer in six and posterior leaflet resection in four. AVR was accomplished with 21 bioprostheses, 14 mechanical and three allograft valves. The mean (+/-SD) cross-clamp time was 133 +/- 41 min. Additional procedures included coronary bypass in six patients and tricuspid procedures in three. RESULTS: There were no operative deaths. Six patients died between 4 and 73 months postoperatively. Patient survival was 75% five and 67% 10 years after surgery. The causes of death were heart failure (two cases), and respiratory failure, drug overdose, electrolyte imbalance and unknown (one each). Logistic risk analysis was significant for females and rheumatic valve disease, bacterial endocarditis, and degenerated valve patients. During follow up there were no valve failures or endocarditis, but three embolic episodes occurred without permanent sequel. CONCLUSIONS: With increased surgical expertise, improved myocardial protection of MR combined with AVR offers excellent short- and long-term results, optimal chordal preservation, no valve failure and no endocarditis; it is the ideal choice where anti-coagulation is contraindicated. The prolonged cross-clamp time was well tolerated.