Detecting acute coronary syndrome in the emergency department: the answer is in seeing the heart: why look further?

Abstract

The emergent assessment of chest pain continues to represent a major medical challenge. In the USA alone, 6 million patients annually present to emergency departments with chest pain. The time-honoured application of clinical assessment, electrocardiography, and markers of myocardial injury (e.g. troponins) definitively identify only 20–30% of patients with acute coronary syndrome (ACS); indeed, biochemical markers are frequently normal in the early hours of pain. Conversely, many admissions pending normal results are unnecessary and take much of the patient time and cause anxiety as well as costing billions of dollars. Worryingly, 5% of patients with ACS are discharged inadvertently, representing a source of significant mortality ( 25%) and litigation. Therefore, there is an urgent demand for effective risk stratification tools. Can pathophysiological principles help identify the ideal test? A direct relationship between myocardial blood flow (MBF) and regional function (RF) is well recognized in acute ischaemia; RF diminishes with diminishing MBF and at 25% of resting MBF, RF abates completely. Importantly, these RF abnormalities persist for hours even after reperfusion (myocardial stunning). Consequently, despite the lack of overt myocardial necrosis as evidenced by normal troponin levels, a significant risk of future events may exist in patients with myocardial stunning owing to flowlimiting coronary disease. In addition, when only 20% of the myocardium (especially endocardium) is infarcted, wall thickening is abolished; RF is therefore exquisitely sensitive to perfusion defects and precedes electrocardiographic or biochemical defects. As a tribute to the accuracy of these pathophysiological syntheses, comprehensive clinical studies have confirmed the comparability of rest RF as assessed by 2D echocardiography and rest perfusion as assessed by SPECT in the diagnosis of ischaemia. Both have been reported to provide a sensitivity and a negative predictive value of .90% in patients with acute chest pain for ischaemia and represent powerful independent predictors of hard cardiovascular endpoints. Nevertheless, despite its diagnostic–prognostic equality to SPECT, its greater availability, its rapid bedside utility, the wealth of structural information rendered, and advances that may further enhance the performance of 2D echocardiography, there has been a lingering suspicion among some that perfusion combined with RF as assessed by gated-SPECT may better reflect and hencemore accurately assess the underlying pathophysiology of acute ischaemia. These suspicions have been heightened by suggestions that the accuracy of echocardiography may be blunted by a failure to fully characterize all myocardial segments, insensitivity to subtle RF defects, and failure to adequately visualize the endocardial border. These criticisms have recently become potentially fully addressable through the advent of gas-filled shell-bound intravenously injected microbubble contrast agents that safely opacify the left ventricle, facilitating endocardial border definition and RF analysis. Furthermore, by being intravascularly confined, these agents also have the capacity to assess myocardial blood volume and velocity, and hence myocardial perfusion (MP). By virtue of combining both RF and MP assessments in a single technique, with a superior ability to judge perfusion compared with SPECT, myocardial contrast echocardiography (MCE) has the potential of becoming the ideal stratification tool in patients with chest pain. This potential of MCE has been realized in the report by Rinkevich et al. which represents a landmark study due to both the size and the scope of their study. Their 2 year follow-up study in more than 1000 patients is impressive and empowers them to confidently advocate the use of early MCE to assess patients presenting to their emergency department with chest pain. Not surprisingly, they show that RF is the best predictor of both shortand long-term cardiovascular endpoints. Moreover, while confirming that MP provides an incremental prognostic value, they demonstrate that this increment is essentially confined to those with abnormal RF; those with abnormal RF and normal MP

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Cite this paper

@article{Senior2005DetectingAC, title={Detecting acute coronary syndrome in the emergency department: the answer is in seeing the heart: why look further?}, author={Roxy Senior and Houman Ashrafian}, journal={European heart journal}, year={2005}, volume={26 16}, pages={1573-5} }