Echocardiography in Clinical Decision Making for Acute Coronary Syndromes

Background Acute coronary syndromes encompass an array of complex symptoms and presentations. The role of echocardiography in acute coronary syndrome has recently assumed a distinguished role in detecting early and late mechanical complications of acute coronary syndrome paving way for emergent clinical decision-making.Case Presentation Three clinical cases are discussed where emergent used of echocardiography identified mechanical complications of acute coronary syndromes including free wall rupture, ventricular septal defect, and papillary muscle rupture allowing for early decision making.Conclusion Due to its non-invasiveness and accessibility, its utility in rapid assessment of acute coronary syndromes and its complications is promising and may lead to improved outcomes.

2 Abstract Background Acute coronary syndromes encompass an array of complex symptoms and presentations. The role of echocardiography in acute coronary syndrome has recently assumed a distinguished role in detecting early and late mechanical complications of acute coronary syndrome paving way for emergent clinical decision-making.Case Presentation Three clinical cases are discussed where emergent used of echocardiography identified mechanical complications of acute coronary syndromes including free wall rupture, ventricular septal defect, and papillary muscle rupture allowing for early decision making.Conclusion Due to its non-invasiveness and accessibility, its utility in rapid assessment of acute coronary syndromes and its complications is promising and may lead to improved outcomes.

Background
There have been prior studies investigating the utility of echocardiography as a preliminary diagnostic modality in evaluating patients with acute chest pain and suspected acute coronary syndrome (ACS). The results have been promising and its implementation in emergent ACS assessment seems beneficial. These studies will be discussed in detail within the "literature review" section in the manuscript. This case series aims to validate the use of echocardiography as a preliminary imaging modality in ACS. Its use in identifying early and late mechanical complications of ACS can help in rapid clinical decision making to improve outcomes.

Case 1
An 85-year-old female with a past medical history of coronary artery disease, status post drug-eluting stent placement presented to the emergency department after having acute onset chest pain and dyspnea on exertion. The patient was diaphoretic and hemodynamically unstable with hypotension and tachycardia. Physical examination revealed jugular venous distension, tachycardia, and clammy extremities. An initial electrocardiogram showed ST-segment elevations in leads II, III, and aVF with T-wave inversions noted in leads V2-V6 with anterolateral T-wave inversions.
Given the patient's clinical presentation and EKG changes, emergent cardiac catheterization was recommended. Coronary angiography demonstrated a 90% calcific stenosis of the left main coronary artery extending distally to the ostium of the left anterior descending artery and left circumflex artery. The left anterior descending artery showed a 70-80% mid-vessel stenosis with TIMI 2 flow distally and the right coronary artery appeared to be the dominant vessel with 60% stenosis proximally and 70% stenosis distally with probable distal occlusion of the posterolateral branches. There was a patent stent in the mid-portion of the vessel with mild in-stent stenosis.
While severe, three-vessel disease was demonstrated, it was felt that the coronary anatomy could not fully explain the patient's hemodynamic instability nor the acute changes on the EKG. Therefore, a stat bedside transthoracic echocardiogram was performed with the patient on the cath lab table. This revealed a large pericardial effusion with significant thrombus, suggesting free wall rupture (Figure 1-3).
An intra-aortic balloon pump was placed, and inotropic therapy was initiated for concurrent cardiogenic shock. Cardiothoracic surgery was consulted. The patient refused surgical intervention. Per her request, her code status was changed to a DNR-CC arrest. She was transferred to the CCU where she continued to deteriorate 4 and expired shortly thereafter.

Clinical analysis:
Free wall rupture is a known complication of myocardial infarction that occurs typically within the first five days after MI in about one-half of cases and within two weeks in over 90 percent of cases. It leads to rapid accumulation of blood within the pericardium and resultant tamponade. It results from severe myocardial tissue necrosis with perforation. In most cases, the left anterior descending artery is involved but the phenomenon can occur with any coronary vessel.
Survival depends primarily upon the rapid recognition of myocardial rupture and provision of immediate therapy.
Echocardiography can quickly identify mechanical complications of myocardial infarction in hemodynamically unstable patients. Although, many acute cases of free wall rupture cause death, some cases may be subacute allowing time for intervention. Utilizing echocardiography in a patient with hemodynamic instability and presumed cardiogenic shock can accurately recognize the severity of myocardial infarction and catch early mechanical complications that allow for more rapid intervention.
In our patient's presentation, the presence of the pericardial fluid and thrombus increased the concern for an acute/subacute free wall rupture. Percutaneous revascularization of the coronary artery disease would likely not have changed the outcome.

Case 2
A 59-year-old male with a past medical history of type 2 diabetes mellitus presented with acute onset chest pain and hemodynamic instability with a heart rate of 127 beats per minute and a systemic blood pressure of 51/29 mmHg. Initial EKG Unfortunately, the patient's stay was further complicated by a number of comorbid conditions. He continued to deteriorate clinically and ultimately after extensive discussion with the involved family, further care was withdrawn. The patient was extubated and died shortly thereafter.

Clinical Analysis:
Development of VSD due to myocardial ischemia requires extensive tissue deterioration and perforation leading to open communication between the left and right ventricles. It leads to massive left to right shunting of oxygenated blood, reduces cardiac output ultimately resulting in cardiogenic shock. Similar to free wall rupture as previously discussed, use of echocardiography in a hemodynamically unstable patient can quickly identify mechanical complications of myocardial infarction. In addition, a VSD is difficult to distinguish from severe mitral 6 regurgitation clinically. The rapid use of echocardiography can identify shunting through the necrotic myocardium providing rapid confirmation of the diagnosis as well as assessment of size and severity.

Case 3
An 82-year-old female presented for an elective left hip revision after multiple prior procedures complicated by infection. During her hospital stay she developed severe left-sided chest pain. EKG revealed atrial fibrillation with rapid ventricular response and troponin was elevated at 3.6 ng/ml. The patient was deemed to be of unacceptably high risk for valve replacement. She was treated with intravenous antibiotics and discharged home with strict follow up.

Clinical Analysis:
Acute papillary muscle rupture is a frequently lethal complication of endocarditis as well as acute myocardial infarction. Echocardiography in the setting of acute hemodynamic decompensation in a patient who may have either of these diagnoses, can rapidly identify valvular pathologies and aid in the differentiation of these clinical entities. In a patient who presents with sudden onset chest pain and an elevated troponin, and in the appropriate clinical scenario, the rapid use of an echocardiography can distinguish the cause of the decompensation and is invaluable in avoiding unnecessary procedures (e.g coronary angiography).

Advantages
The rapid use of echocardiography as a clinical decision-making tool in the setting of acute coronary syndrome carries a number of potential advantages. These include early detection of regional wall motion abnormalities confirming a likely ischemic etiology and potentially for anatomical localization, a rapid estimation of left ventricular function, early recognition of mechanical complications, and perhaps most importantly recognition of alternate etiologies with the potential to decrease unnecessary invasive procedures. We will discuss each of these components in further detail.

Diagnostic utility and clarification
Echocardiography stands as a fairly rapid, noninvasive, and accurate test to detect early myocardial dysfunction. [1] Given that wall motion abnormalities may manifest prior to the development of EKG changes or a troponin elevation, it also has the potential for ruling in ischemia early on. [2] Perhaps one of the best uses of echocardiography is in the setting of mixed or atypical presentations of chest discomfort. In this setting, it plays a crucial rule in ruling out other known culprits such as tamponade, endocarditis, or pericarditis where cardiac catheterization would commit the patient to additional risks without the potential for benefit. One recent study investigating the use of echocardiography in the evaluation of ACS in the pre-hospital setting demonstrated the sensitivity and specificity of prehospital transthoracic echocardiography for non-ST segment elevation myocardial infarction at 90.9% and 100% respectively. [5] This demonstrates clear potential for the use of echo as a standardized initial evaluation strategy.
In addition, the FoCUS exam can detect contraindications to certain cardiac mechanical support devices that may have resulted from ACS. Several examples include the Impella that has a contraindication in patients with LV thrombus, the Intra-aortic balloon pump that has an absolute contraindication to moderate to severe aortic regurgitation, and the Tandem Heart Devices that are contraindicated with left atrial thrombus. Any suspicion of these findings before or during cardiac catheterization by physical examination or by catheterization findings should lead to further evaluation by FoCUS exam before proceeding with mechanical circulatory support.

Early identification of mechanical complications of myocardial infarction
Echocardiography remains the most accessible and reliable initial imaging modality to evaluate for structural cardiac disease. The management of life-threatening complications of ACS including ventricular free wall rupture, ventricular septal defect, acute papillary muscle rupture, ventricular aneurysm, cardiac tamponade, and ventricular thrombus formation all benefit from early recognition. While a thorough physical exam can frequently raise suspicion for one of these complications, it invariably requires imaging confirmation.
A patient presenting with cardiogenic shock and a newly auscultated murmur raises 9 suspicion for a mechanical complication of an MI. An urgent, focused echocardiogram offers the possibility of immediate visualization of the VSD, imaging and quantification of new valvular regurgitation and also allows the rapid identification of a pericardial effusion associated with free wall rupture. [6] Mechanical complications of myocardial infarction carry a poor prognosis without immediate surgical intervention; coronary angiography in such situations may delay such life-saving surgery.
It is also important to mention that such complications can also present as late complications of ACS, where the door to balloon time will not be considered or in patient with STEMI who have been treated with thrombolytics and transferred to PCI capable facilities. The use of echocardiography may be prudent and a rapid assessment by an experienced ultrasonographer can help evaluate for these complications before proceeding with cardiac catheterization.

Reduction in unnecessary cardiac catheterizations
Prompt echocardiography in ACS has the potential to reduce unnecessary cardiac catheterizations as well as associated morbidity and mortality. Emergent coronary angiography is indicated when a thrombotic or embolic cause of ACS is suspected.
In the absence of a strong indication, it may delay other more appropriate therapies and expose the patient to an invasive procedure with its concomitant risks In cases such as left ventricular thrombus, echocardiography may both confirm the need for catheterization (i.e. LV thrombus with associated wall motion abnormality) and decrease complication rates by identifying the need to avoid left ventricular catheterization.

Potential disadvantages
The additional step of performing echocardiography in cases of suspected acute coronary syndrome also carries potential drawbacks. In many institutions, the ability to obtain an echocardiogram may be limited. If the etiology of ischemia is otherwise clear, any additional imaging reduces time to potential revascularization. Therefore, such utilization of echocardiography relies upon a rapidly available, appropriately trained technician and physician.

Delaying time to the catheterization lab
Current guidelines for the treatment of ST-segment elevation myocardial infarction recommend a 90-minute door-to-balloon time at a catheterization capable facility.
Any delay for additional imaging should be avoided unless mechanical complications are suspected. A delay in care has to be carefully balanced relative to its potential benefit. Patients to be targeted are those with troponin elevation without an obvious type 1 MI and patients in whom the diagnosis of a mechanical complication will significantly affect their outcomes.
The purpose of the previously established FoCUS exam is to perform a more limited, high-yield examination by a skilled provider. Loss of time remains an unavoidable drawback of adding additional diagnostic testing. A useful test must be incorporated into a system of implementation that allows for timely performance and interpretation. This will allow for meaningful clinical impact.

Literature review
There have been prior studies investigating the utility of echocardiography as a preliminary diagnostic modality in evaluating patient with acute chest pain and suspected acute coronary syndrome (ACS). The results of these studies have been promising and its implementation in emergent ACS assessment seems beneficial. [9][10][11][12][13][14][15][16][17] Table 1 reviews nine studies that measured the accuracy of echocardiography as a 11 predictor of cardiac events by assessing the presence and absence of wall motion abnormality. The primary endpoints for these studies range from major endpoints such as myocardial infarction, to revascularization, angiographic findings of coronary artery disease, and abnormal study findings. [11,17] The positive predictive value (PPV) of the various studies is variable ranging from 31-100 % but it is important to note that the PPV correlates with low-risk and highrisk patients. Conducting echocardiography for assessment of ACS in the high-risk population, such as the study by Mohler and colleagues [17], reveals a high PPV in high-risk patients. This study identified all patients with new wall motion abnormality; of those, myocardial infarction was identified in 43% giving a PPV of 100% and a negative predictive value (NPV) of 57%.
However, in the low-risk population, echocardiogram seems to be less predictive. In the study with Sabha and colleagues [11], who had a lower-risk population, the overall prevalence of a cardiac events was 17 % giving echocardiography a PPV of 31% and NPV of 98%. In addition, Krontos and colleagues [9] found that the PPV and NPV between echocardiography and electrocardiography in the low-risk population were similar with a PPV of 44% and 60% and a NPV of 98% and 44% respectively.
Overall, echocardiogram is more useful in evaluating for acute coronary syndrome in moderate to high risk populations. Its value in low-risk populations is nonsuperior to a standard electrocardiogram.

Prior case series regarding the use of echocardiography in ACS
A case series investigating the use of echocardiography by ER physicians to identify clinically significant acute occlusive coronary artery lesions concluded that ultrasound-trained Emergency Physicians can identify significant wall motion abnormalities. These cases involved high-risk patients in whom echocardiography would not have changed management. The strengths of this study included real-life cardiac function assessment and quicker assessment than laboratory data could allow. Some of the drawbacks include body habitus which may make it difficult to obtain certain views, interpretation of images that varied from provider to provider, and the ability to identify new versus old wall motion abnormalities. [19] Another more recent study investigated the use of echocardiography in the evaluation of ACS in the pre-hospital setting. The study demonstrated very high sensitivity (90%) and specificity (100) for the early detection of NSTEMI. [5]

Suggested implementation strategy
Wall motional abnormalities in acute coronary syndrome may occur before electrocardiographic changes and before chest pain. [18] Suggested implementation of echocardiography in acute coronary syndromes, is in a moderate-to-high risk patient presenting with chest pain in the emergency department after an initial electrocardiogram is negative for STEMI. . This may aid in identifying new wall motion abnormalities for early identification of a probable ischemic etiology while blood work is pending.
A moderate-to-high risk patient who presents with an ST elevation myocardial infarction (STEMI), may benefit from emergent echocardiography just prior to cardiac catheterization if this does not delay door-to-balloon time. This may be especially useful in patients with hemodynamic compromise to identify possible mechanical complications of the MI in whom further interventions prior to coronary angiography (e.g circulatory support, surgical consultation) may be critical. The assessment should be performed by a trained ultrasonographer in the emergency department or on the cath table immediately preceding the procedure. (Table 2) 13

Conclusion
The use of echocardiography in the acute setting is a valuable tool in the early assessment of a hemodynamically unstable patient. It can provide a rapid assessment of the likelihood of ischemic myocardial disease, the degree of global and wall motion abnormality, and it can identify mechanical and valvular complications that allows for early recognition of life-threatening processes. The utilization of echocardiography in the acute setting may allow more rapid and appropriate intervention thereby reducing morbidly and improving outcomes.

Availability of data and materials
Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.

Competing interests
There are no financial and non-financial competing interests for this manuscript

Funding
No funding sources were used for this manuscript

Authors' contributions
PH assisted in conceptualization, data curation, analysis, investigation, methodology, writing, revision, and editing ZN assisted in conceptualization, data curation, analysis, investigation, methodology, writing, revision, and editing SM assisted in data curation, writing, editing, revisions, and supporting RS assisted in revisions, analysis, investigating and supporting EE assisted in conceptualization, data curation, analysis, investigation, methodology, writing, revision, editing, and supervision   Parasternal long view showing closure of the VSD using an ASD occluder Flowchart.pdf Flowchart.pdf