1. CNR Institute of Clinical Physiology, 54100 Massa, Italy
2. CNR Institute of Clinical Physiology, 20162 Milan, Italy
3. Fondazione Toscana Gabriele Monasterio, 56124 Pisa, Italy
4. Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy
5. CNR Institute of Clinical Physiology, 56124 Pisa, Italy
6. Department of Cardiology, Leiden University Medical Center, 2333 ZA, Leiden, Netherlands