Characterization of Repolarization Alternans in the Coronary Artery Disease

Repolarization alternans (RA), an electrophysiologic phenomenon consisting on everyother-beat changes of the repolarization morphology (amplitude, shape, and, sometimes, polarity) unaccompanied by gross changes in the heart-cycle length, is generally recognized as a promising electrocardiographic (ECG) predictor of sudden cardiac arrest (SCA; Bloomfield et al., 2006, Chow et al. 2006, Ikeda et al., 2006, Klingenheben et al., 2000, Leino et al., 2009, Maeda et al., 2009, Narayan, 2006, Rosenbaum et al., 1994, Sakaki et al., 2009, Salerno-Uriarte et al., 2007, Stein et al., 2008), that is one of the leading causes of death in developed countries (over 300,000 lives per year in the U.S.; Montagnana at al., 2008, Zheng et al., 2001). On the ECG tracing, RA consists of an alternation of either the ST-segment (Nearing et al., 1991, Rosenbaum et al., 1994), or the T-wave, or even the U-wave (Habbab & el-Sherif, 1992). Macroscopic and, thus, visible RA (like that reported in Fig. 1) is quite rare. After being first reported by Hering in the early 1900s (Hering, 1909), RA has later on been occasionally observed in patients affected by various diseases, among which ischemia (Kleinfeld & Rozanski, 1977), long QT syndrome (Schwartz & Malliani, 1975, Zareba et al., 1994) and ventricular arrhythmias (Verrier et al., 2003). Recent investigations on RA rely on automatic detection of microvolt RA from the digital ECG signal by means of specifically designed techniques, among which the spectral method (implemented in the commercial ECG machine CH2000 and Heartwave, Cambridge Heart Inc., Bedford, MA; Smith et al., 1988, Rosenbaum et al., 1994, Rosenbaum et al., 1996), the complex demodulation method (Nearing et al., 1991, Nearing & Verrier, 1993), the modified moving average method (implemented in the commercial ECG machine CASE-8000, GE Medical Systems, Milwaukee, WI; Nearing & Verrier, 2002), the Laplacian likelihood ratio method (Martinez & Olmos, 2005, Martinez et al., 2006), our adaptive match filter method (Burattini et al., 2008, Burattini et al., 2009b) and others (Burattini et al., 1999, Martinez & Olmos, 2005). Microvolt RA has been found to be much more common than visible RA (Adachi et al., 1999, Chow et al., 2007, Ikeda et al., 2006, Klingenheben et al., 2000, Narayan et al., 2006, Narayan et al., 2007, Reddy et al., 1984) and linked to inducible (Narayan and Smith, 2000, Rosenbaum et al., 1994, Smith et al., 1988) as well as spontaneous (Bloomfield et al., 2006, Klingenheben et al., 2000, Maeda et al., 2009, Narayan, 2006, Verrier et al., 2003) ventricular arrhythmias.