Zanobetti et al, in their contribution in the September 1, 2009, issue of The American Journal of Cardiology , showed that air pollution and traffic caused increases in the magnitude of T-wave alternans (TWA) detected on 24-hour Holter electrocardiographic monitoring (HEM) in 48 patients with various manifestations of coronary artery disease. The investigators, using time-domain modifying moving average analysis of HEM, reported maximum TWA magnitude (TWA-MAX) in each 30-minute interval of the 24-hour HEM period, using data only from modified lead V 5 . Increases in TWA-MAX were associated with the previous 2-hour ambient black carbon level and with being in traffic in the previous 2 hours, thus revealing an impact of air pollution on TWA.
Experience in interpreting HEM reveals a large intraindividual variation of the amplitude of T waves in patients and normal subjects alike. Such variation pertains also to the morphology and polarity of the T waves, but for the sake of the present discussion, I will focus only on the amplitudes of the T waves. These changes in the T waves can occasionally be linked to changes in heart rate, posture, type of activity, and being awake or asleep, but this is not always the case. Often such major changes in the amplitudes of T waves occur in the absence of heart rate changes and symptoms, in patients and in normal subjects. A case in point (the first HEM of 1 day’s reading session) is that of a 37-year-old man, a frequent user of hospital services, but without any pathology having been detected, with a history of illicit drug use, who complained of palpitations. Only rare premature atrial and ventricular beats were detected on HEM. His echocardiographic results were normal, with a left ventricular ejection fraction of 60%. Figure 1 shows an increase in the T-wave amplitude (compare the top and bottom panels) in 2 portions of HEM, separated by 4 hours. There was a difference in heart rate of 14 beats/min, with the slower heart rate being associated with the taller T waves. Also, in both panels, there was some variation of successive T waves, probably of respiratory origin.
