1. Fondazione G. Monasterio CNR-Regione Toscana, Via Aurelia Sud, 54100 Massa, Italy
2. Fondazione G. Monasterio CNR-Regione Toscana, Via Giuseppe Moruzzi, 1, 56124 Pisa, Italy
3. Department of Statistics, National Research Institute, National Research Council, 56121 Pisa, Italy
4. Clinical Cardiology Unit, University of Cagliari, 09042 Monserrato, Italy