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J Appl Physiol 103: 729, 2007; doi:10.1152/japplphysiol.00450.2007
8750-7587/07 $8.00
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LETTER TO THE EDITOR

Reply to Madias

To the Editor: We appreciate the interest of Dr. Madias (1) in our recent study. Indeed, we were most interested in his suggestion that magnified T-wave amplitude may acutely contribute to the elevated T-wave alternans (TWA) that we observed in dogs subjected to volume overload (2). This topic is timely given recent clinical studies that T-wave amplitude varies with the site of pacing (3) and studies using T-wave amplitude to identify at-risk individuals with long QT syndrome (4).

Accordingly, we additionally analyzed T-wave area and peak amplitude from the surface ECG for each dog in our volume overload study at baseline, midinfusion, peak infusion, and in the postdiuresis phase. Both T-wave indexes were computed semi-automatically from digital ECG data using custom software written in Labview (National Instruments, Austin, TX; Ref. 5). T-wave area was integrated using the trapezoid method from the ECG J-point to the T-wave offset, defined by visual return of the T-wave to the TP baseline. When T-waves were inverted or biphasic, absolute areas were summated. T-wave peak amplitude was defined as the absolute maximum voltage deviation from the TP segment.

We observed a weak linear relationship between T-wave area and TWA amplitude, measured as voltage of alternation (Valt, mV), with a correlation coefficient R = 0.40 (P = 0.08), and between T-wave peak voltage and Valt (correlation R = 0.42; P = 0.06). Actual T-wave areas did not differ with volume overload and, normalized to baseline values for each dog, were 1.21 ± 0.44 (midinfusion), 1.06 ± 0.25 (peak infusion), and 1.06 ± 0.30 [postdiuresis; P = not significant (NS)]. Similarly, T-wave peak amplitudes did not alter significantly with volume challenge and, normalized to baseline, were 0.90 ± 0.24 (midinfusion), 1.08 ± 0.33 (peak infusion), and 0.87 ± 0.85 (postdiuresis; P = NS).

Thus, although TWA magnitude in our study (Valt) may reflect T-wave amplitude, elevated TWA magnitude with volume overload did not relate to T-wave amplitude per se. This may reflect our small series. However, these results agree with preliminary clinical data from our laboratory that TWA is sensitive to T-wave magnitude, although the extent to which T-wave magnitude fluctuates according to the Brodie effect (1) remains unclear. Further clinical studies are needed to examine how ventricular dilatation alters T-wave magnitude, shape and beat-to-beat dynamics, and their potential arrhythmic consequences in patients with structural heart disease and volume overload.

GRANTS

This work was supported by a grant from the National Institutes of Health (SBIR-1R43HL-80815-1) and from the American Heart Association, Western Regional Affiliate to S. M. Narayan (0265120Y).

FOOTNOTES


Address for reprint requests and other correspondence: S. M. Narayan, Electrophysiology Service, VA San Diego, Univ. of California San Diego, Box 111A, 3350 La Jolla Village Dr., San Diego, CA 92161 (e-mail: snarayan{at}ucsd.edu)

REFERENCES

  1. Madias JE. Effect of acute volume overload on the magnitude of T-wave alternans. J Appl Physiol. doi:10.1152/japplphysiol.00346.2007.
  2. Narayan SM, Drinan DD, Lackey RP, Edman CF. Acute volume overload elevates T-wave alternans magnitude. J Appl Physiol 102: 1462–1468, 2007.[Abstract/Free Full Text]
  3. Berger T, Hanser F, Hintringer F, Poelzl G, Fischer G, Modre R, Tilg B, Pachinger O, Roithinger FX. Effects of cardiac resynchronization therapy on ventricular repolarization in patients with congestive heart failure. J Cardiovasc Electrophysiol 16: 1–7, 2005.[CrossRef]
  4. Restier-Miron L, Fayn J, Millat G, Denjoy I, Rodriguez-Lafrasse C, Rubel P, Chevalier P. Spatiotemporal electrocardiographic characterization of ventricular depolarization and repolarization abnormalities in long QT syndrome. J Electrocardiol. 2007 Feb 19; [Epub ahead of print].
  5. Narayan SM, Smith JM, Schechtman KB, Lindsay BD, Cain ME. T-wave alternans phase following ventricular extrasystoles predicts arrhythmia-free survival. Heart Rhythm 2: 234–241, 2005.[CrossRef][Web of Science][Medline]

Sanjiv M. Narayan1
Darrel D. Drinan2
Robert P. Lackey2
Carl F. Edman2
 1University of California and 2PhiloMetron Incorporated, San Diego, California





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