CORRESPONDENCE: LETTER TO THE EDITOR
Vasodilator Therapy in Cardiac FailureWhat Was New Is Old
Michael F. O'Rourke, MD, DSc* and
Wilmer W. Nichols, PhD
* Suite 810, St Vincent's Clinic/University of New South Wales, 438 Victoria Street, Darlinghurst, Sydney NSW 2010, Australia (Email: m.orourke{at}unsw.edu.au).
The paper by Mullens et al. (1) and editorial comment by Yancy (2) draw attention to use of vasodilators in treatment of acute and chronic refractory cardiac failure. The importance of left ventricular (LV) afterload is stressed, but this is described only in terms of peripheral resistance as the ratio of mean arterial pressure and cardiac output, with the latter requiring and justifying right heart catheterization. There is a problem with this approach over and above the risks of Swan-Ganz catheter use; peripheral resistance is only part of LV afterload, which is best expressed as aortic input impedance (3,4). In addition to peripheral resistance, impedance also considers aortic stiffness and wave reflection, and the effects of vasodilator drugs on these (3–5). In the recent articles, brachial systolic pressure is taken as an index of LV afterload, but this is considerably higher than aortic and LV systolic pressure, especially in patients with cardiac failure and during use of vasodilators (4–6). Vascular impedance in cardiac failure during use of vasodilator drugs is not mentioned in either article, but has been described in major journals over the past 3 decades, and forms the basis for modern treatment of this condition (3,4). Central aortic pressure also can be estimated accurately through noninvasive methods (4,6), as can indices of arterial stiffness and wave reflection (4,5).
Persons wishing to apply the principles described by Mullens et al. (1) and Yancy (2) are advised to consider these issues. They can measure LV afterload better, and avoid invasive catheterization completely. They can also obtain a more accurate measure of mean arterial pressure from integration of the arterial pressure waveform using applanation tonometry, rather than estimating this from the inaccurate formula of diastolic + one-third pulse pressure (4).
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Footnotes
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Please note: Dr. O'Rourke is a founding director of AtCor Medical Pty Limited, manufacturer of systems for analyzing the arterial pulse.
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References
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1. Mullens W, Abrahams Z, Francis G, et al. Sodium nitroprusside for advanced low-output heart failure J Am Coll Cardiol 2008;52:200-207.[Abstract/Free Full Text]2. Yancy CW. Vasodilator therapy for decompensated heart failure J Am Coll Cardiol 2008;52:208-210.[Free Full Text] 3. Pepine CJ, Nichols WW, Conti CR. Aortic input impedance in heart failure Circulation 1978;58:460-465.[Abstract/Free Full Text] 4. Nichols WW, O'Rourke MF. McDonald's Blood Flow in Arteries: Theoretical, Experimental and Clinical Principles5th edition. London: Hodder Arnold; 2005291–6, 435–50, 464–502. 5. Laurent S, Cockcroft J, Van Bortel L, et al. Expert consensus document on arterial stiffness: methodological issues and clinical applications Eur Heart J 2006;27:2588-2605.[Abstract/Free Full Text] 6. Agabiti-Rosei E, Mancia G, O'Rourke M, et al. Central blood pressure measurements and antihypertensive therapy: a consensus document Hypertension 2007;50:154-160.[Free Full Text]
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