Research Article Intra-QT Spectral Coherence as a Possible Noninvasive Marker of Sustained Ventricular Tachycardia Gianfranco Piccirillo, 1 Federica Moscucci, 1 Alessandro Persi, 1 Daniele Di Barba, 1 Maria Antonella Pappadà, 1 Pietro Rossi, 2 Raffaele Quaglione, 1 Bich Lien Nguyen, 1 Francesco Barillà, 1 Matteo Casenghi, 3 and Damiano Magrì 3 1 Dipartimento di Scienze Cardiovascolari, Respiratorie, Nefrologiche, Anestesiologiche e Geriatriche, Policlinico Umberto I, “Sapienza” University of Rome, Viale del Policlinico No. 155, 00185 Roma, Italy 2 Division of Cardiology, S. Giovanni Calibita Fatebenefratelli Hospital, Isola Tiberina, Piazza Ponte dei Quattro Capi, 39 186 Roma, Italy 3 Dipartimento di Medicina Clinica e Molecolare, S. Andrea Hospital, “Sapienza” University of Rome, Via di Grottarossa 1035/1039, 00189 Roma, Italy Correspondence should be addressed to Gianfranco Piccirillo; gianfranco.piccirillo@uniroma1.it Received 18 March 2014; Accepted 28 May 2014; Published 15 July 2014 Academic Editor: Jason Ng Copyright © 2014 Gianfranco Piccirillo et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Sudden cardiac death is the main cause of mortality in patients afected by chronic heart failure (CHF) and with history of myocardial infarction. No study yet investigated the intra-QT phase spectral coherence as a possible tool in stratifying the arrhythmic susceptibility in patients at risk of sudden cardiac death (SCD). We, therefore, assessed possible diference in spectral coherence between the ECG segment extending from the  wave to the T wave peak (QT  ) and the one from T wave peak to the T wave end (T e ) between patients with and without Holter ECG-documented sustained ventricular tachycardia (VT). None of the QT variability indexes as well as most of the coherences and RR power spectral variables signiicantly difered between the two groups except for the QT  -T e spectral coherence. he latter was signiicantly lower in patients with sustained VT than in those without (0.508±0.150 versus 0.607±0.150,  < 0.05). Although the responsible mechanism remains conjectural, the QT  -T e spectral coherence holds promise as a noninvasive marker predicting malignant ventricular arrhythmias. 1. Introduction A prospective multicenter study indicates the myocardial temporal repolarization dispersion, measured with the beat- to-beat QT variability index (QTVI), as a marker predicting cardiac death without speciically predicting sudden cardiac death (SCD) in patients with chronic heart failure (CHF) [1]. A possible explanation might be that QTVI results in a better electrocardiographic (ECG) marker for the severity of CHF than for SCD, being closely inluenced also by the severity of let ventricular dysfunction and neurohu- moral activation [2–5]. Nonetheless, the QTVI is custom- arily calculated together with another marker that assesses changes in myocardial temporal repolarization, namely, the spectral coherence between the QT and RR intervals [2–5]. he QT-RR spectral coherence uses a value ranging from 0 to 1 to express whether the two ECG signals yield coherent oscillations over time, and it reaches maximum when QT and RR interval oscillations proportionally correspond [2– 5]. Unfortunately, this speciic index is more complex to calculatethan the simple correlation between the myocardial action potential duration and the diastolic interval expressed with ventricular electrical restitution curves. Indeed, QT-RR interval spectral coherence evaluates temporal patterns in oscillating signals whereas regression curves or lines measure QT variations as a function of RR interval variations. In healthy subjects, QT-RR interval spectral coherence tends to remain relatively low (less than 0.400) but it logically tends to decrease further in CHF (less than 0.300) [2–5]. Because Hindawi Publishing Corporation BioMed Research International Volume 2014, Article ID 583035, 9 pages http://dx.doi.org/10.1155/2014/583035