LETTERS TO THE EDITOR
Coronary flow reserve assessment from average peak velocity profiles alone must be judged with caution
Philipp A. Kaufmann, MDa and
Rolf Jenni, MD, MSEEa
a Division of Cardiology, University Hospital Zürich, CH-8091 Zürich, Switzerland
We enjoyed the study by Caiati et al. (1) on contrast-enhanced transthoracic second harmonic Doppler echocardiography with adenosine for noninvasive coronary flow reserve (CFR) assessment, which confirmed the very similar data from their recent study using dipyridamole (2). Although the results are interesting, we would like to comment on methodologic issues.
First, it should be emphasized that the assessment of CFR by using the ratio of hyperemic to basal peak velocity is not entirely correct, as it relies on the assumption of an invariate shape of the velocity profile. In fact, the error introduced by changes of the flow velocity profile has been shown to be as high as 11% (3).
Second, the spatial resolution in this study does not allow vessel visualization. No accurate CFR assessment can be done by velocity information alone, without knowing the exact vessel size, unless this variable cancels out because vessel size remains constant. However, it is a well-documented fact (see, for example, reference 6 of the study [4]) that adenosine leads to significant coronary dilation, severely affecting the relation between coronary flow velocity and volumetric flow, thus introducing an error of up to 40%. This problem is usually addressed by using nitroglycerin before the baseline measurement to achieve maximal dilation throughout the study. However, this was not done in the study by Caiati et al. Thus, the authors’ statement that "vessel size does not change with respect to the baseline so vessel size cancels out" is simply untrue, and this is emphasized by a recent study reporting that such a lack of epicardial coronary dilation response to adenosine is diagnostic for microvascular disease (5). These two facts may add up to a substantial underestimation of CFR and, at least in part, explain why the normal value in this study (2.88) is considerably lower than that obtained after predilation with nitroglycerin (3.4) (4) or with other established methods such as positron emission tomography (3.5–4.0) (6).
Third, the authors use an infusion rate of 0.5 to 2 ml/min of echo contrast agent, referring to a previous report (2) quoting two studies (7,8) in which the infusion rate was 2 ml/s. We wonder whether there might have been a typing error or additional data justifying a slowing of the infusion rate by a factor 60.
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References
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1. Caiati C, Zedda N, Montaldo C, Montisci R, Iliceto S. Group-enhanced transthoracic second harmonic echo Doppler with adenosine: a noninvasive, rapid and effective method for coronary flow reserve assessment. J Am Coll Cardiol. 1999;34:122–130[Abstract/Free Full Text]
2. Caiati C, Montaldo C, Zedda N, Bina A, Iliceto S. New noninvasive method for coronary flow reserve assessment: contrast-enhanced transthoracic second harmonic echo Doppler. Circulation. 1999;99:771–778[Abstract/Free Full Text]
3. Jenni R, Büchi M, Zweifel HJ, Ritter M. Impact of Doppler guidewire size and flow rates on intravascular velocity profiles. Cathet Cardiovasc Diagn. 1998;45:96–100[CrossRef][Medline]
4. Rossen JD, Quillen JE, Lopez AG, Stenberg RG, Talman CL, Winniford MD. Comparison of coronary vasodilation with intravenous dipyridamole and adenosine. J Am Coll Cardiol. 1991;18:485–491[Abstract]
5. Reis SE, Holubkov R, Lee JS, et al. Coronary flow velocity response of adenosine characterizes coronary microvascular function in women with chest pain and no obstructive coronary disease. J Am Coll Cardiol. 1999;33:1469–1475[Abstract/Free Full Text]
6. Schelbert HR. Assessment of blood flow and substrate metabolism in the myocardium of the normal human heart. Schwaiger M. Cardiac Positron Emission tomography. Boston, Dordrecht, London: Kluwer Academic Publisher; 1996. p. 191
7. Iliceto S, Caiati C, Aragona P, Verde R, Schlief R, Rizzon P. Improved Doppler signal intensity in coronary arteries after intravenous peripheral injection of a lung-crossing contrast agent (SHU508A). J Am Coll Cardiol. 1994;23:184–190[Abstract]
8. Caiati C, Aragona P, Iliceto S, Rizzon P. Improved Doppler detection of proximal left anterior descending coronary artery stenosis after intravenous injection of a lung-crossing contrast agent: a transesophageal Doppler echocardiographic study. J Am Coll Cardiol. 1996;27:1413–1421[Abstract]
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P. A. Kaufmann, M. Namdar, F. Matthew, M. Roffi, S. V. Aschkenasy, B. van der Loo, G. Sutsch, T. F. Luscher, and R. Jenni
Novel Doppler Assessment of Intracoronary Volumetric Flow Reserve: Validation Against PET in Patients With or Without Flow-Dependent Vasodilation
J. Nucl. Med.,
August 1, 2005;
46(8):
1272 - 1277.
[Abstract]
[Full Text]
[PDF]
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