CORRESPONDENCE: LETTER TO THE EDITOR
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Dirar S. Khoury, PhD*,
Mihir Naware, MS,
Jeff Siou, BS,
Andreas Blomqvist, MS,
Nilesh S. Mathuria, MD,
Jianwen Wang, MD, PhD,
Hue-Teh Shih, MD,
Sherif F. Nagueh, MD and
Dorin Panescu, PhD
* Department of Cardiology, Methodist DeBakey Heart and Vascular Center, The Methodist Hospital Research Institute, 6565 Fannin Street, F764, Houston, Texas 77030 (Email: dkhoury{at}tmhs.org).
We thank Dr. Madias both for his support of the study findings (1) and for his endorsement of the clinical relevance. Reliable monitoring of heart failure depends on both the sensor technology and the detection algorithm. The study focused on the former subject, namely, measuring impedance via lead sensors readily available in implanted cardiac resynchronization therapy systems. Although impedance measured in between the left ventricular (LV) lead and the Can yielded the largest and fastest change during heart failure in comparison with only right-side heart electrodes, other impedance vectors using the LV lead also were associated with variable but favorable trends. The study was not designed to determine an optimal detection algorithm on the basis of impedance measurements in part because of limitations of the animal model itself. Therefore, it is premature to conclude with certainty that one lead configuration (i.e., LV-Can) is superior to 1 or more combinations of impedance vectors for monitoring heart failure in patients. Clinical trials will be necessary to address this issue. Several factors could impact trends in impedance measured via different electrode configurations that include: 1) heart and torso anatomy and mass; 2) lead electrode location; 3) type and cause of heart failure; 4) concomitant pharmacologic therapy; 5) pulmonary disease; 6) subcutaneous edema; and 7) skeletal muscle resistivity. Given its scope, the study did not advocate using multiple impedance vectors over a single LV-Can configuration, but rather, speculated on possible benefits of using more than 1 vector for sensing, especially when considering the above foreseeable confounding factors in real-life scenarios. This could be particularly attractive when no additional hardware is required and when the platform circuitry of the implanted system affords monitoring multiple impedance parameters.
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References
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1. Khoury DS, Naware M, Siou J, et al. Ambulatory monitoring of congestive heart failure by multiple bioelectric impedance vectors J Am Coll Cardiol 2009;53:1075-1081.[Abstract/Free Full Text]
Related Article
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Multiple Bioelectric Impedance Vectors in the Monitoring of Congestive Heart Failure
- John E. Madias
J. Am. Coll. Cardiol. 2010 55: 259.
[Full Text]
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