CORRESPONDENCE: RESEARCH CORRESPONDENCE
Left Ventricular Wall Motion Abnormalities Induced by Squatting: A New Echocardiographic Stress Test for the Diagnosis of Coronary Artery Disease
P. Anthony N. Chandraratna, MD, FRCP, FACC*,
Rajiv Maraj, MD,
Ghasan Tabel, MD,
Arash Vahdat, MD and
Lalkrushna Malaviya, MD
* Long Beach VA Medical Center (111C), 5901 East Seventh Street, Long Beach, CA 90822 (Email: premindra.chandraratna{at}med.va.gov).
To the Editor: Stress echocardiography is useful for diagnosing coronary artery disease (CAD) (1,2). Expense, potential for complications, and the time factor are potential disadvantages of these techniques. Thus, there is a need for a simple, inexpensive, rapid, and safe echocardiographic stress test.
Squatting increases left ventricular afterload and preload (3–5). This study tested the hypothesis that squatting will produce left ventricular wall motion abnormalities (WMA) in patients with CAD.
The study population consisted of 15 normal male subjects (group 1) (age range 34 to 75 years, mean 57 years) and 42 male patients (mean age 63 years, range 31 to 84 years) who had coronary angiography (group 2). The institutional committee on human research approved the study protocol. Informed consent was obtained from all subjects.
The standing (3 min of quiet standing) heart rate and blood pressure were recorded. Parasternal long- and short-axis and apical four-, two-, and three-chamber views were obtained in the standing position. The subjects were asked to squat, for 2 min. Blood pressure, heart rate, and echocardiograms were recorded. The echocardiogram was repeated after standing.
A 16-segment model was used for analysis of echocardiographic images. A squatting stress echocardiogram was considered positive if there was a new or worsening WMA during squatting. An isolated fixed WMA was not considered a positive result. A stenosis of 50% or greater was considered significant.
Continuous variables are presented as mean and standard deviation and were compared using the Student t test. A p value of <0.05 was considered significant.
The heart rate and blood pressure responses to squatting are summarized in Table 1. Group 1 subjects had normal left ventricular global and regional function while standing. There were no WMA while squatting.
In group 2, five patients had a baseline WMA. New or worsening WMA occurred during squatting in 35 patients. Twelve patients developed a WMA in the left anterior descending coronary artery territory, five had WMA in the circumflex coronary artery territory, seven had WMA in the right coronary artery territory, and seven had normal wall motion. Eleven had WMA in multiple territories. All WMA resolved on standing within 1 min. None of these patients developed chest pain, arrhythmias, or hypotension. The sensitivity, specificity, and accuracy of squatting echocardiography for diagnosis of the CAD were 92%, 80%, and 91%, respectively. The sensitivity, specificity, and accuracy of squatting stress echocardiography for the diagnosis of multivessel CAD were 33%, 92%, and 50%, respectively.
Echocardiograms from a patient in group 1 are depicted in Figure 1, and an example of a patient in group 2 is shown in Figure 2.
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Figure 1 End-systolic frames during standing (left) and squatting (right) in a normal subject. Note the triangular shape of the apex during standing and squatting. LV = left ventricle.
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Figure 2 Echocardiogram of a patient in group 2. Left ventricular (LV) function was normal in the standing position. The LV apex had a triangular appearance at end-systole. An extensive wall motion abnormality developed during squatting (arrows). The distal posterior septum, apex, and distal posterolateral wall became akinetic, and the distal half of the LV became dilated and circular. The wall motion abnormality and the ventricular shape normalized on standing.
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Lewis et al. (3) observed that squatting produced an increase in left ventricular dimension in end-diastole and end-systole. The heart rate decreased, and blood pressure, stroke index, and cardiac index increased.
Stress echocardiography performed in conjunction with treadmill testing and dobutamine infusion is associated with increases in heart rate, blood pressure, and contractility. In contrast, squatting increases myocardial oxygen consumption by augmenting afterload and preload.
There are some advantages to squatting as a stress test. The absence of marked changes in heart rate during squatting makes comparison with the baseline echocardiogram and interpretation of stress-induced WMA easier than when tachycardia is present. Ventricular dilatation that occurs with squatting facilitates analysis of wall motion. The rapid recovery of wall motion after squatting reduces the risks of adverse sequelae. No ventricular arrhythmias, chest pain, or hypotension were noted during squatting.
There are some limitations to squatting as a stress test. Patients with knee or hip disease, or extreme obesity may not be able to squat. The sonographer also has to squat during the procedure, and only those with adequate echocardiography windows are suitable for testing.
The mechanism by which squatting induces WMA is uncertain. A potential mechanism is unmasking of subclinical segmental dysfunction in normokinetic segments subtended by stenotic coronary arteries. Yuda et al. (6) have demonstrated subclinical left ventricular dysfunction in patients with CAD and normal ejection fraction. A second potential mechanism is the induction of myocardial ischemia. Although the absence of angina in our patients does not support ischemia as a mechanism, it does not exclude ischemia.
In summary, squatting induces WMA in segments subtended by coronary artery stenoses. These preliminary data underscore the potential usefulness of squatting echocardiography as a stress test. Studies in which squatting is compared with a currently accepted stress test are needed to assess the value of this novel test.
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References
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2. Quinones MA, Verani MS, Haichin RM, Mahmarian JJ, Suarez J, Zoghbi WA. Exercise echocardiography versus 201T1 single-photon emission computed tomography in evaluation of coronary artery disease. Analysis of 292 patients Circulation 1992;85:1026-1031.[Abstract/Free Full Text]
3. Lewis BS, Lewis N, Gotsman MS. Effect of standing and squatting on echocardiographic left ventricular function Eur J Cardiol 1980;11:405-412.[Medline]
4. Sharpey-Shafer EP. Effects of squatting on the normal and failing circulation BMJ 1956;1:1072-1074.[Medline]
5. O’Donnell TV, McIlroy MB. The circulatory effects of squatting Am Heart J 1962;64:347-356.[CrossRef][Web of Science][Medline]
6. Yuda S, Fang ZY, Marwick TH. Association of severe coronary stenosis with subclinical left ventricular dysfunction in the absence of infarct J Am Soc Echocardiogr 2003;16:1163-1170.[CrossRef][Web of Science][Medline]
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