Introduction

COVID-19 is a global pandemic that is predicted to strain healthcare resources. The apex of disease is predicted to occur between April 15 and May 30 at various locations throughout the United States and Canada. As of April 6, 2020, all U.S. states have yet to reach their apex of infection, but there are already widespread reports of personal protective equipment (PPE) shortages, making it challenging to treat COVID-19 patients. To conserve PPE, hospitals have canceled or postponed elective procedures, which will have unknown downstream effects on population health [1]. PPE shortages also increase the risk that healthcare workers may contract COVID-19, which would force them to self-isolate, further worsening the ability to deliver care [1]. In this crisis, it is important to protect our healthcare workers and their ability to deliver care by considering imaging strategies that use the least PPE, decrease exposure to staff, and streamline utilization of imaging equipment [1,2,3].

We are suggesting imaging strategies that aim to alleviate the anticipated strain on hospital resources. They are broadly organized by (1) substituting a noninvasive diagnostic test in place of a semi-invasive or invasive diagnostic test, and (2) consolidating multiple diagnostic tests into one single exam.

Substituting noninvasive diagnostic imaging in place of semi-invasive or invasive diagnostic imaging reduces PPE use and has comparable diagnostic accuracy [4]. In most cases, noninvasive diagnostic imaging is associated with less interactions between the patient and the healthcare worker, which decreases the risk of transmitting a communicable disease such as COVID-19.

Consolidating imaging is another strategy to reduce PPE use and healthcare worker exposure because it may reduce the number of visits a suspected or positive COVID-19 patient makes to the Radiology Department. Consolidation is accomplished by anticipating the future imaging needs of a patient and meeting that need by performing a lower number of more comprehensive studies. This may provide the information likely to be sought later during hospitalization, but with less imaging utilization.

There are varying levels of evidence for our suggested strategies. Suggestions backed by a strong level of evidence may already be routine care at some institutions. For suggestions supported by expert opinion alone, the decision to implement a suggested strategy should depend on the current clinical environment. If hospital resources are not strained, only suggestions with strong evidence may be used. However, if resources are severely strained, suggestions based on expert opinion may be considered. Therefore, we separated suggestions with a strong level of evidence from those based on expert opinion.

This document is organized as follows: (1a) noninvasive diagnostic imaging alternatives supported by strong evidence that can be performed in place of semi-invasive or invasive imaging for specific clinical indications in all patients; (1b) noninvasive diagnostic imaging alternatives supported by expert opinion in place of semi-invasive or invasive imaging in suspected or positive COVID-19 patients; and (2) alternative imaging protocols that can be performed in an attempt to consolidate multiple anticipated imaging exams.

These strategies should only be considered during a time of crisis when healthcare resources are strained. All changes in usual care should consider the additional risks imposed on patients. All changes to usual care should be made after consultation with physicians, administration, and stakeholders, and according to local institutional policies and expertise, balancing the immediate needs of the patient with the obligation to deliver care to the community as a whole.

NASCI recommendations for the use of noninvasive diagnostic imaging alternatives

(1a) Noninvasive diagnostic imaging alternatives supported by strong evidence that can be performed in place of semi-invasive or invasive imaging for specific clinical indications in all patients, particularly COVID-19-positive or COVID-19 suspected patients (Table 1)

Table 1 Alternative imaging in specific clinical scenarios
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Indication 1: Acute chest pain and elevated troponin and equivocal diagnosis of non-ST elevation myocardial infarction (NSTEMI).

Rationale: This approach decreases utilization of diagnostic invasive coronary angiography in the catheterization laboratory, which requires airborne precautions, and replaces the assessment with coronary Computed Tomography (CT), a droplet precaution test [5]. In COVID-19-positive or COVID-19 suspected patients, coronary CT can be used to rule out coronary artery disease as the cause of acute chest pain leaving myocarditis, possibly due to COVID-19, as the leading diagnosis. If coronary artery disease is ruled out, this approach changes management by replacing intensive acute coronary syndrome care with supportive care for acute myocarditis.

Evidence: In patients with suspected acute coronary syndrome (acute chest pain and/or elevated troponin) and equivocal NSTEMI diagnosis, a negative coronary CT may be used to exclude the diagnosis of acute coronary syndrome (ACS), and favor the possibility of non-coronary etiologies, primarily myocarditis [6, 7].

Indication 2: Acute chest pain in patients with negative initial troponin, and intermediate risk for coronary artery disease.

Rationale: This approach accelerates patient discharge by replacing the standard of care which entails 24 h observation, serial enzymes, and EKG, and usually performed in an observation unit, Emergency Department (ED) or inpatient setting. Decreased length of hospital stay limits exposure of healthcare workers and frees beds for COVID-19 patients in need of in-hospital care. Coronary CT can be used to rule out coronary artery disease as the cause of acute chest pain, leaving myocarditis, possibly due to COVID-19, as the leading diagnosis.

Evidence: Randomized controlled trials [8, 9] and observational studies [10] have shown that a coronary CT-guided approach has similar safety outcomes and decreased length of hospital stay compared to standard of care in intermediate risk patients with negative initial troponin.

Indication 3: Patients in need of urgent cardioversion with indication to rule out left atrial appendage (LAA) thrombus for stroke prevention.

Rationale: This approach replaces transesophageal echocardiography (TEE), which requires airborne precautions, with cardiac CT with delayed phase (droplet precautions) to exclude the presence of an LAA thrombus in patients with arrhythmias. Cardiac CT with delayed phase can be used to rule out the presence of LAA thrombus.

Evidence: Cardiac CT with delayed images has comparable sensitivity and specificity to TEE to exclude the presence of LAA thrombus [11]. Studies utilizing cardiac CT instead of TEE in the imaging workup for LAA thrombus before left atrial (LA) ablation have shown no difference in adverse outcomes such as stroke or embolic events [12, 13].

Indication 4: Patients with severe aortic stenosis with cardiac decompensation, in need of acute aortic valve replacement, surgical, or transcatheter.

Rationale: CT angiography (CTA) in patients in need of urgent Transcatheter Aortic Valve Replacement (TAVR) or Surgical Aortic Valve Replacement (SAVR) can replace TEE for assessment of TAVR eligibility. CTA approach would reduce the exposure from airborne to droplet precautions. Dedicated pre-TAVR CTA could guide the selection of the type of intervention and might preclude the need for pre-procedure TEE [14]. This imaging also includes the added benefit of evaluating proximal coronary arteries for stenosis [15, 16].

Evidence: CTA is an accurate imaging modality to determine eligibility for TAVR based on valve sizing and peripheral arterial access with evaluation of coronary arteries [17].

Indication 5: Patients with acute symptomatic prosthetic or native heart valve dysfunction or suspected endocarditis.

Rationale: Cardiac CT with retrospective gating can delineate prosthetic heart valve morphology and identify the reason for cardiac decompensation, such as the presence of a vegetation or thrombus. Cardiac CT can determine if the perivalvular region is involved and thus influence a change in management from medical therapy to surgical intervention. Urgent Cardiac CT with functional analysis may provide sufficient information to guide the next treatment step without the need for TEE.

Evidence: Cardiac CT functional native or prosthetic valve assessment has similar accuracy to TEE for diagnosis of endocarditis or vegetations [18].

(1b) Noninvasive diagnostic imaging alternatives supported by expert opinion in place of semi-invasive or invasive imaging for indications other than listed in 1a and only in COVID-19-positive or COVID-19 suspected patients (Table 2)

Table 2 General recommendations for noninvasive alternatives to semi-invasive or invasive imaging
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There are multiple clinical scenarios that require imaging with diagnostic invasive coronary angiography or TEE in a patient with COVID-19 or suspected COVID-19 that are not listed in Sect. 1a. On a case-by-case basis, it may be determined as reasonable to perform Coronary or Cardiac CT in place of these other semi-invasive or invasive tests. Because this substitution is considered reasonable, but evidence related to specific clinical indications is not present, these recommendations are based on expert opinion. Therefore, a decision to employ these protocols should be based on clinical need in the setting of the evolving crisis. For example, the protocols may be used differently in COVID-19 patients who are severely ill versus stable.

1. Substitution of coronary CT for catheter coronary angiography in known COVID-19 and COVID-19-suspected patients.

Rationale: This strategy leads to conservation of PPE. It reduces risk of transmitting infection to healthcare workers and reduces time for disinfecting the imaging suite compared to angiography suite, which maximizes availability of diagnostic services. Cleaning after a CT examination is based on droplet precautions, whereas diagnostic angiography and TEE are based on airborne precautions, a more time intensive cleaning process.

2. Substitution of cardiac CT for TEE in known COVID-19 and COVID-19-suspected patients.

Rationale: Same as above.

(2) Alternative imaging that can be performed in an attempt to consolidate imaging, supported by expert opinion, in COVID-19-positive or COVID-19 suspected patients (Table 3)

Table 3 List of protocols that can be used for consolidating imaging
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If possible, the number of CT imaging exams should be consolidated (reduced) in known COVID-19 and COVID-19-suspected patients by changing the imaging protocol to a more comprehensive.

Rationale: Hospitalized patients often have multiple CT examinations performed during their hospitalization, sometimes in rapid succession. Each of these examinations requires resources and exposes clinical staff to the risk of infection. If a crisis situation is present, and resources are strained, it may be advantageous to predict future imaging needs and attempt to consolidate imaging by ordering a more comprehensive exam in place of multiple exams. For example, a Triple Rule-Out (TRO) protocol CT likely yields all the information contained in a CT Pulmonary Angiogram (CTPA), with the added evaluation of the aorta and coronary arteries. Likewise, a TRO protocol CT is likely to evaluate coronary arteries as well as a coronary CT, with the added benefit of evaluating for aortic disease, pulmonary embolism, and the entire lung for pulmonary parenchymal disease.

Extending the information routinely gathered from a coronary CT, CTA or CTPA is pertinent in COVID-19 patients because studies have suggested a high incidence of myocarditis in COVID-19 and other studies have reported an increased incidence of pulmonary embolism in viral pneumonia [24].

As an example, myocarditis has been described as common in COVID-19 patients with ARDS or who are severely ill and is associated with a poor prognosis [19, 20]. The diagnosis can be suggested by an elevated troponin in a patient with no known history of cardiac disease. However, in some cases, myocardial ischemia from epicardial coronary disease may still need to be excluded. In that setting, a Coronary CT may be used to evaluate the coronary arteries. However, if the lung parenchyma also needs to be evaluated, a TRO study may provide that needed additional information.

Substituting one study for another should be decided on a case-by-case basis, and considered only if appropriate resources and expertise are available. The risks associated with the protocol change should also be considered. Adding intravenous contrast to an examination is associated with risk, and an individual patient’s renal status and potential for allergic reaction should be considered. Anecdotally, COVID-19 patients may suffer increased rates of renal dysfunction, and this should be considered before administering contrast. Using cardiac gating may increase radiation and duration in the radiology suite interacting with technologists. Nitroglycerin and beta-blockers are not required for TRO imaging but may be used if it is justified by the risk/benefit ratio of a given patient. In summary, cardiac-gating and cardiac medications should only be employed if it is likely to obviate the need for a future study and is an acceptable risk/benefit for the patient.

Additional information

Summary of other Society guidelines or statements

Several societies have contributed guidelines or strategies related to imaging patients with COVID-19. Most of these recommendations have focused on changing the first-line imaging study for purposes of protecting staff, cleaning equipment, and deferment of non-emergent imaging studies to a later date. These guidelines have not addressed imaging for the purpose of reducing scarcity of resources.

A brief summary of society statements is included below.

Radiological Society of North America, American College of Radiology, Society of Thoracic Radiology [21]

  • Guidelines for reporting CT findings in COVID-19 patients

  • Radiology Department Preparedness for COVID-19: Radiology Scientific Expert Panel

Society of Cardiac Computed Tomography [22]

  • PPE use and equipment cleaning when patients with confirmed or suspected COVID-19 are imaged.

  • Guidelines for delaying imaging for specific cardiac indications

  • Substitution of noninvasive diagnostic imaging for other forms of imaging to reduce exposure

American Society of Echocardiography [23]

  • PPE used for echocardiography

  • Guidelines for delaying imaging for specific cardiac indications

  • Substitution of noninvasive diagnostic imaging for other forms of imaging to reduce exposure

American College of Cardiology’s Interventional Council and the Society of Cardiovascular Angiography and Intervention [5]

  • Recommendation to deferred elective cardiac catheterization cases for the purposes of conserving PPE

Group definitions

COVID-19 patients :

Patients with a positive RT-PCR result within the last 14 days or patients within RT-PCR result over 14 days ago, but still experiencing symptoms believed to be caused by COVID-19

Suspected COVID-19 patients :

Patients with unexplained lower respiratory tract symptoms and a pending or single negative RT-PCR.

Non-COVID-19 patients :

Patients without lower respiratory tract symptoms or with lower respiratory tract symptoms but a negative RT-PCR result for COVID-19 and an alternative source of infection.

Protocol definitions

Diagnostic angiography :

Invasive catheter-based angiography for imaging only and not intervention.

Coronary CT :

ECG–gated CT of the heart and proximal aorta with contrast injection optimized for coronary artery of enhancement. Consider prefacing this study with ECG-gated Coronary calcium score CT.

Cardiac CT: :

ECG-gated Cardiac CT with contrast injection optimized for imaging of cardiac chambers and/or valve morphology with or without 90 s delay.

CT angiography (CTA) :

Thoracic CT with contrast injection optimized for systemic arterial enhancement (i.e. aortic).

CT chest unenhanced :

Thoracic CT without intravenous contrast administration.

CT chest with contrast :

Thoracic CT with intravenous contrast administration, usually imaging at a 70 s delay.

CT pulmonary angiography (CTPA) :

Thoracic CT with intravenous contrast administration optimized for pulmonary artery enhancement.

Triple-rule-out (TRO) :

ECG-gated thoracic CT with intravenous contrast administration optimized for imaging of pulmonary and coronary arteries, and aorta.