Early Assessment of Strain Echocardiography Can Accurately Exclude Significant Coronary Artery Stenosis in Suspected Non-ST-Segment Elevation Acute Coronary Syndrome
J Am Soc Echocardiogr. 2014 May;27(5):512-9.
Dashlett, T, et al.
Abstract
Background:
Many patients with suspected non-ST-segment elevation acute coronary syndrome (NSTE-ACS) do not have significant coronary artery disease. The current diagnostic approach of repeated electrocardiography and cardiac biomarker assessment requires observation for >6 to 12 hours. This strategy places a heavy burden on hospital facilities. The objective of this study was to investigate whether myocardial strain assessment by echocardiography could exclude significant coronary artery stenosis in patients presenting with suspected NSTE-ACS.
Methods:
Sixty-four patients presenting to the emergency department with suspected NSTE-ACS without known coronary artery disease, inconclusive electrocardiographic findings, and normal cardiac biomarkers at arrival were enrolled. Twelve-lead electrocardiography, troponin T assay, and echocardiography were performed at arrival, and all patients underwent coronary angiography. Significant coronary stenosis was defined as >50% luminal narrowing. Global myocardial peak systolic longitudinal strain was measured using speckle-tracking echocardiography. Left ventricular ejection fraction and wall motion score index were calculated.
Results:
No significant stenosis in any coronary artery was found in 35 patients (55%). Global peak systolic longitudinal strain was superior to conventional echocardiographic parameters in distinguishing patients with and without significant coronary artery stenosis (area under the curve, 0.87). Sensitivity and specificity were calculated as 0.93 and 0.78, respectively, and positive predictive value and negative predictive value as 0.74 and 0.92, respectively. Feasibility of the strain measurements was excellent, with 97% of segments analyzed.
Conclusions:
Myocardial strain by echocardiography may facilitate the exclusion of significant coronary artery stenosis among patients presenting with suspected NSTE-ACS with inconclusive electrocardiographic findings and normal cardiac biomarkers.
Review
by Frederick Conlin M.D.
Acute coronary syndrome is responsible for up to 25% of hospital admissions and the standard workup of repeated sets of cardiac enzymes, ECGs, stress testing, and angiography is time consuming and costly. Identifying patients at low risk and discharging them early would be ideal. The authors hypothesize that myocardial strain may have a role in NSTE-ACS evaluation by pinpointing who is low risk and sparing them unnecessary hospital stays and testing.
Myocardial strain by speckle-tracking is a technique based on 2-D imaging that tracks myocardial deformation during a cardiac cycle. Strain is a measure of change in length of an object and is calculated as: . Where L0 is the baseline length and L1 is the final length. An object that shortens such as myocardium will have a negative strain. Strain can be measured in the radial (transmural), circumferential, or longitudinal directions. In this study they examined longitudinal strain measured by speckle-tracking. When ultrasound encounters a tissue the pulse becomes distorted in a way that is dependent on the composition of that tissue. There are reflectors within the myocardium that will produce constant “speckles” throughout the cardiac cycle. These are referred to as natural acoustic markers. These markers can be used as reference points to measure the shortening or strain in an angle independent fashion.
In this small prospective study, 64 patients with suspected NSTE-ACS without known coronary disease, inconclusive ECG findings, and a normal first set of cardiac enzymes were enrolled. An echocardiographic evaluation of three apical imaging planes was obtained to include all the myocardial walls. Peak systolic longitudinal strain was measured as the maximum value of myocardial shortening. Coronary angiography was also performed in all patients and significant stenoses were defined as 50% narrowing (they designated >75% as severe stenosis).
Of the patients enrolled, 55% did not have significant stenosis while 45% did have significant stenosis by angiography. LVEF, wall motion score index, and strain were evaluated for all patients and all measures differed significantly between patients with and without coronary stenosis. However, global longitudinal strain was found to be superior to LVEF, wall-motion score index, and GRACE risk scale when used to separate patients with significant coronary artery disease from those without. The investigators performed a separate analysis of their data and found that a strain cutoff of -21% predicted 93% of the patients with coronary artery disease.
This is the first study designed to assess the feasibility of strain to rule out significant coronary disease, prior studies have demonstrated that in patients hospitalized with angina who have significant coronary artery stenosis, longitudinal strain is impaired. Limitations of the study include that it was performed only on patients without known coronary disease. This is an important distinction as strain can remain impaired even after revascularization so the utility of this modality to stratify risk of ACS in patients with documented CAD is unknown. Next, this is a relatively small study and included only patients in the emergency room with recent complaints of angina. Finally, the results of strain analysis are known to vary among vendors, machines, and software versions so cutoffs may not be easily extrapolated from one to the other.
While this is a small study with some limitations, it demonstrates that strain may have a role in the interrogation of NSTE-ACS and in conjunction with ECG, biomarkers, and risk factors strain may in the future aid in the early discharge of patients at low risk for significant coronary artery stenosis. As our understanding and technology improves, strain may also have a greater role in perioperative monitoring and management.