Stress echocardiography has evolved considerably over the last three decades. The prognostic value of stress echocardiography is now well established, with the ability to risk-stratify patients into low (<1%), intermediate (1-5%) or high (>5%) risk groups. This article addresses the current role of stress echocardiography in stratifying risk, its influence on patient outcome and management decisions.
by Dr S. S. Yao, Dr S. Bangalore, Dr X. Zhang, & Dr F. A. Chaudhry
Stress echocardiography was first introduced in 1979 and represents the natural merger of cardiovascular stress testing with two-dimensional echocardiography. The rationale for its use is that either physical exercise (treadmill or bicycle) or pharmacologic (dobutamine or dipyridamole/adenosine) stress will result in ischemia. Myocardial ischemia is manifested as a regional wall motion abnormality, which then serves as a marker for the location, severity and extent of obstructive coronary stenoses. The applications of stress echocardiography have broadened substantially since its introduction as a diagnostic test for CAD. Primarily, the expanded applications of stress echocardiography relate to its prognostic efficacy and influence on clinical outcomes.
Table 1 summarises the different variables, important in identifying risk and predicting prognosis, which will be discussed in detail in the following sections.
Risk stratification and prognosis in patients with known or suspected ischemic heart disease.
An important objective of noninvasive testing is to identify patients at risk for future cardiac events. The application of prognostic testing is based on the premise that in patients identified as being at highest risk for adverse outcomes, there can be intervention to alter the natural history of their disease process, thereby reducing subsequent risk.
We and others have demonstrated that the presence of normal wall motion (peak wall motion score index, WMSI = 1.0) during stress echocardiography confers a benign prognosis [1]. These low risk patients generally only require counseling in regard to risk factor modification.
Patients with mild to moderate wall motion abnormalities (peak WMSI = 1.1-1.7) have an intermediate risk of cardiac events. The ideal management strategy for these patients is unclear. Rather than an invasive management approach of catheterisation and revascularisation with its inherent risks, patients with an intermediate risk of cardiac events may, perhaps, experience lowering of their risk for future cardiac events by aggressive risk factor modification, and referral to catheterisation only for refractory symptoms. In addition, resting Ejection Fraction (EF) should have an important influence on the appropriate management approach in such patients. An initial noninvasive management strategy may be cost-effective and avoid unnecessary invasive procedures. Conversely, high risk patients with WMSI >1.7 and especially those with EF ≤45% are at a significant risk of cardiac events [Figure 1]. Such high risk patients should be appropriately referred for consideration of cardiac catheterisation and potential coronary revascularisation in order to modify and reduce their cardiac risk.
Extent and severity of myocardial wall motion abnormality as predictors of prognosis.
The prognostic utility of stress echocardiography derives from its ability to quantify the magnitude of “jeopardised” (i.e. potentially ischemic) myocardium during exercise or pharmacologic stress testing. Specifically, stress echocardiography measures two indices of ischemia: a) ischemic extent and b) maximal severity. Ischemic extent reflects the area of myocardium (number of segments) that is abnormal, whereas maximal severity reflects the maximal magnitude of abnormal wall motion within a designated segment, both quantified at peak stress. Ischemic extent reflects the number of new stress-induced wall motion abnormalities, and corresponds roughly to the number of stenosed coronary arteries. Maximal severity reflects the magnitude of ischemia within a designated myocardial segment and reflects the severity of a subtending coronary stenosis within a given coronary artery vascular territory. Estimation of both ischemic extent and maximal severity variables by stress echocardiography provides a functional depiction of a “noninvasive” coronary angiogram, and accurate prognostic assessment of the amount of jeopardised myocardium.
We have demonstrated that prognostic risk stratification by stress echocardiography can be established using both separate and combined functions of the extent and severity of wall motion abnormalities [2]. Ideally, a continuum of risk can be defined based upon varying degrees of extent and severity of wall motion abnormalities. Stable patients with normal stress echocardiography or those with mild and non-extensive wall motion abnormalities (single vessel CAD or mild ischemia) are at low (<1%/year) to intermediate (1-5%/year) cardiac risk, and may be considered for an initial strategy of aggressive risk factor modification and optimal medical therapy.
On the contrary, patients manifesting severe and/or extensive stress-induced wall motion abnormalities are at intermediate-high cardiac risk (>4%/year) and should warrant consideration for referral to catheterisation and potential coronary revascularisation in order to modify and reduce their risk [Figure 2]. Moreover, a prognostic model of risk stratification is important since a defined threshold for aggressive management can be applied individually according to a given patient’s clinical characteristics and other co morbidities.
Prediction of MI vs cardiac death by stress echocardiography.
Stress echocardiography is an effective technique for differential risk stratification of patients for the outcome specific endpoints of cardiac death and non-fatal myocardial infarction (MI) [3]. Patients with EF <30% are at very high risk of cardiac death (>4%/year) and these patients should be managed actively with aggressive medical management, assessment of viability, revascularisation if needed and early consideration of device therapy and cardiac resynchronisation therapy. In patients with EF ≥30%, peak wall motion score index can further risk-stratify this subgroup. There are three risk categories, namely a high-intermediate risk group (WMSI >1.7) (cardiac death rate 2.5-4%/year) who may benefit from aggressive medical management and consideration for revascularisation; a low-intermediate risk group (WMSI 1.1-1.7) (cardiac death rate 1.0-2.5%/year) may benefit from aggressive medical management and consideration for revascularisation for symptom relief only. Finally there is a low-risk group (WMSI 1.0) (cardiac death rate <1.0%/year) who may benefit from risk factor modification [Figure 3].
Impact of stress echocardiography on patient outcome
Stress echocardiography is now an established technique for diagnosis, risk stratification and prognosis of patients with known or suspected coronary artery disease. However, the impact of stress echocardiography on patient outcomes and coronary revascularisation was previously unclear. In our study, we assessed 3121 patients (60 ± 13 years, 48% male) undergoing stress echocardiography (41% treadmill, 59% dobutamine) [4]. Follow-up data were obtained (2.8 ± 1.1 years) for subsequent coronary angiography, revascularisation: percutaneous coronary intervention (PCI) or coronary artery bypass surgery (CABG), and confirmed hard events: non-fatal myocardial infarction (n = 76) or cardiac death (n = 83). Stress echocardiography studies were normal (pWMSI = 1.0) in 66% and abnormal (pWMSI >1.0) in 34% of patients. Early coronary angiography (30 days following stress echocardiography) was performed in only 35 patients (1.7%) with normal stress echocardiography and 267 patients (25.5%) with abnormal stress echocardiography (p<0.0001). Late coronary revascularisation (2 years following stress echocardiography, PCI% or CABG%) occurred in 80 patients (2.8%, 1.1%) with pWMSI = 1.0, 123 patients (13.5%, 7.3%) with pWMSI = 1.1-1.7 and 102 patients (12.7%, 9.6%) with pWMSI >1.7 [Figure 4]. Multivariate logistic regression analysis identified pWMSI as the strongest predictor of coronary angiography (RR 2.04, 95% CI 1.67-2.5), revascularisation (RR 1.91, 95% CI 1.68-2.17) and cardiac events (RR 2.45, 95% CI 2.09-2.88). All data were statistically significant p <0.0001. Patients with markedly abnormal stress echocardiography (pWMSI >1.7) had a significantly higher cardiac event rate than those who did not undergo coronary revascularisation (9.6%/year vs. 2.9%/year, p < 0.05). Stress echocardiography is an effective gatekeeper for coronary angiography and revascularisation. A normal stress echocardiography study (pWMSI = 1.0) confers a benign prognosis (0.8%/year), and is associated with a low rate of early coronary angiography (1.7%) and late revascularisation (2.8% PCI, 1.1% CABG). Stress echocardiography impacts clinical decision making in higher risk patients (pWMSI ≥1.1) with significantly increased coronary angiography, PCI and CABG rates. Patients with markedly abnormal stress echocardiography (pWMSI >1.7) were most likely to benefit from coronary revascularisation.
Conclusions
Stress echocardiography has evolved during the past 30 years to become a mainstay in the diagnostic and prognostic armamentarium of clinical cardiologists. Stress echocardiography provides diagnostic and prognostic information in a broad range of patient subsets and plays an integral role in the management of patients with known or suspected CAD. Stress echocardiography has demonstrated significant incremental prognostic value when added to clinical and adjuvant testing information. Stress echocardiography is an essential tool in defining cardiac risk and in identifying patients who are most likely to benefit from additional invasive diagnostic testing. Stress echocardiography significantly influences clinical patient outcomes while impacting clinical decision making and use of limited cardiology resources.
Future developments
In stress echocardiography future developments are likely to be targeted at refinements in methodology and quantitation in order to increase reproducibility of interpretation, decrease subjectivity and improve accuracy. These potential enhancements include the incorporation of myocardial strain, strain rate imaging, tissue Doppler and 3D/4D imaging. Furthermore, advances in myocardial contrast echocardiography would ideally allow the simultaneous evaluation of myocardial
function and perfusion.
References
1. Yao S, Qureshi E, Sherrid MV, Chaudhry FA. Practical applications in stress echocardiography: risk stratification and prognosis in patients with known or suspected ischemic heart disease. J Am Coll Cardiol 2003; 42: 1084-1090.
2. Yao S, Qureshi E, Syed A, Chaudhry FA. Novel stress echocardiographic model incorporating the extent and severity of wall motion abnormality for risk stratification and prognosis. Am J Cardiol 2004; 94(6): 715-719.
3. Bangalore S, Yao S, Chaudhry FA. Prediction of myocardial infarction versus cardiac death by stress echocardiography. J Am Soc Echocardiogr 2009; 22(3): 261-7.
4. Yao S, Bangalore S, Shah A, Silva-Encisco J, Chaudhry FA. Impact of Stress Echocardiography on Patient Outcome: An Effective Gatekeeper for Coronary Angiography. Circulation 2008; 118S849 (abst).
The authors
Siu-Sun Yao, MD, FASE,
Sripal Bangalore, MD,
Xiaoqian Zhang, MD,
Farooq A. Chaudhry, MD, FASE
Department of Medicine,
Division of Cardiology,
St. Luke’s-Roosevelt Hospital Center,
Columbia University College
of Physicians and Surgeons,
New York, NY,
USA
Contact address: Farooq A. Chaudhry, MD, St. Luke’s-Roosevelt Hospital Center, Division of Cardiology, 1111 Amsterdam Avenue, New York, NY 10025. Tel (212) 523-4298.
Fax (212) 523-5989.
E-mail chaudhr@chpnet.org
