Europace Advance Access originally published online on June 6, 2008
Europace 2008 10(7):893; doi:10.1093/europace/eun141
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LETTERS TO THE EDITOR
Spinal cord stimulation and T-wave alternans
Mount Sinai School of Medicine of the New York University,
Division of Cardiology,
Elmhurst Hospital Center,
79-01 Broadway,
Elmhurst, NY 11373,
USA
Tel: + 1 718 334 5005
Fax: + 1 718 334 5990
E-mail address: madiasj{at}nychhc.org
Ferrero et al.1
in a study published online in the Europace Journal evaluated T-wave alternans (TWA) before and after spinal cord stimulation (SCS) to ascertain whether this SCS alters the arrhythmic substrate and thus has an effect on TWA. The authors evaluated three patients with ischaemic cardiomyopathy, who had undergone implantation of both implantable cardioverter/defibrillator (ICD) for sudden cardiac death prophylaxis and an SCS device for intractable angina. T-wave alternans was elicited during pacing via the ICDs while the SCS was switched off (baseline) and after 2 and 24 h of SCS. This sequence was again repeated in 2 months to check the reproducibility of the findings. In a total of 18 TWA studies, the authors reported that TWA, which was positive in the three patients at baseline, remained positive, but decreased in amplitude after 2 h of SCS, and became negative after 24 h of SCS. This suggests that SCS ameliorates the arrhythmic substrate in a time-dependent fashion.
Recently, it has been speculated that TWA amplitude may be T-wave amplitude-dependent, and thus values of TWA may need adjustment by the corresponding T-wave amplitudes.2,3 Studies of patients treated with SCS who have undergone ambulatory electrocardiogram (ECG) monitoring have documented some amelioration of the frequency of ST-segment changes due to episodes of myocardial ischaemia.4 I am not aware of any specific studies of the exact changes in the ECG, particularly of the ST-segment and the T-wave, in response to SCS. As the three patients in the study of Ferrero et al. acted as their own controls on two occasions, it would be of interest to evaluate whether the amplitudes of the TWA had any relationship to the corresponding T-wave amplitudes of surface ECGs of intracardiac electrograms at the three different phases of the study. As the authors used the spectral method for assessing TWA, it would be more appropriate to adjust the amplitudes of the TWA by the area under the J–T curve of the corresponding ECGs or electrograms. A crude way would be to adjust the values of the amplitude of the TWA by the T-wave amplitude of the corresponding ECGs or ICD electrograms. Have the authors noted any changes in the ST-segments or the T-waves in surface ECGs or the ICD electrograms among the three-study phases that could account (confounding variable) for the changes in the amplitude of TWA?
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[1] Ferrero P, Castagno D, Massa R, De Luca A, Castellano M, Chirio C, et al. Spinal cord stimulation affects T-wave alternans in patients with ischaemic cardiomyopathy: a pilot study. Europace (2008) 10:506–8.
[2] Madias JE. Reproducibility of T-wave alternans in congestive heart failure: a theoretical argument. Pacing Clin Electrophysiol (2006) 29:800–2.[CrossRef][Medline]
[3] Madias JE. A proposal for a T-wave alternans index. J Electrocardiol (2007) 40:479–81.[CrossRef][Medline]
[4] Sanderson JE, Ibrahim B, Waterhouse D, Palmer RB. Spinal electrical stimulation for intractable angina—long-term clinical outcome and safety. Eur Heart J (1994) 15:810–4.
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