Long-term prediction of major ischemic events by exercise thallium-201 single-photon emission computed tomography. Incremental prognostic value compared with clinical, exercise testing, catheterization and radionuclide angiographic data.

OBJECTIVES: This study sought to evaluate the prognostic role of exercise thallium-201 (Tl-201) single-photon emission computed tomography (SPECT) in patients with known or suspected coronary artery disease. BACKGROUND: Compared with planar Tl-201 scintigraphy, Tl-201 SPECT allows enhanced assessment of myocardial perfusion abnormalities. However, the long-term prognostic value of exercise Tl-201 SPECT has not been ascertained and compared with that of other techniques of investigation. METHODS: Predictors of ischemic events were sought in 217 patients with known or suspected coronary artery disease who underwent exercise Tl-201 SPECT, coronary angiography and rest radionuclide angiography and who initially received medical therapy. Predictive values were determined using Cox proportional hazards regression models. RESULTS: During a mean (+/- SD) follow-up period of 70 +/- 19 months, 29 patients had a major ischemic event (cardiac death or myocardial infarction). Total extent of exercise defects was the best independent predictor by Tl-201 SPECT of major events (p < 0.001) and provided additional prognostic information compared with clinical, exercise testing and catheterization variables (p < 0.02). Extent of reversible Tl-201 SPECT perfusion defects provided additional prognostic information compared with extent of irreversible defects (p < 0.001) and was the sole Tl-201 SPECT variable providing additional prognostic information compared with radionuclide left ventricular ejection fraction (p < 0.02). CONCLUSIONS: Total extent of exercise Tl-201 SPECT defects is a powerful long-term predictor of major ischemic events that enhances the prediction provided by clinical, exercise testing and coronary angiographic data. In view of its prognostic significance, extent of reversible Tl-201 SPECT defects might provide original information about improving prognosis by coronary revascularization.

[Atrioventricular block induced by radiofrequency: electrophysiological criteria of success]. / Bloc auriculo-ventriculaire induit par radiofréquence: critères électrophysiologiques de succès.

In a retrospective series of 18 consecutive patients (10 men, average age: 61.6 +/- 9.2 years) who underwent His bundle ablation by radiofrequency current, the authors analyzed the electrophysiological criteria predictive of complete atrioventricular block. A total of 82 radiofrequency bursts were analyzed (average: 4.5 +/- 3.1 bursts/patient) and classified as effective (N = 14, definitive atrioventricular block), ineffective (N = 55, no effect on atrioventricular conduction) or transiently effective procedures (N = 13, reversible Mobitz II atrio-ventricular block). Seven electrophysiological parameters were measured: HV interval, amplitude of atrial (A), Hisian (H) and ventricular (V) potentials, and the A/H, A/V, and V/H ratios before each radiofrequency burst. At the end of the ablation, 14 patients were in complete atrioventricular block and during the following 24 hours, a complete atrioventricular block developed in 3 other patients. The average value of the H potential was comparable in the effective and transiently effective procedures (0.28 +/- 0.20 mV and 0.27 +/- 0.19 mV respectively) and significantly higher than the same parameters in the ineffective group of procedures (0.65 +/- 0.14 mV, p = 0.008). The V/H ratio was progressively greater in effective (5.43 +/- 2.51), transiently effective (8.07 +/- 6.90) and ineffective procedure (14.32 +/- 13.35), p = 0.02; the average value of the A amplitude tended to be higher in the effective procedures (1.03 +/- 0.75 mV) and the transiently effective procedures (0.98 +/- 0.72 mV) than in the ineffective procedures (0.58 +/- 0.79 mV), p = 0.06. On the other hand, the other parameters were comparable in the three groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Regression splines for threshold selection in survival data analysis.

The Cox proportional hazards model restricts the hazard ratio to be linear in the covariates. A survival model based on data from a clinical trial is developed using spline functions with variable knots to estimate the log hazard function. Moreover, the main point of the method is that a knot, seen as free parameters for a piecewise linear spline, represents a break point in the log hazard function which may be interpreted as a threshold value. The likelihood ratio test is used to select the final model and to determine the threshold number for a covariate. Confidence intervals for these threshold values are computed by bootstrapping the data. Two examples illustrate the method.