Cardiac CT Update- Virtual Conference by Society of Cardiovascular CT (SCCT), 2020
There are several Radiology Conferences held annually around the world, some really good. Since I am based out of Bangalore, I always thought time spent travelling, adjusting to the jet lag and leaving family and work was such a great hindrance! In this connected world, we were still having all conferences in a physical place. Covid-19 has played that fast tracker role for us, made continued medical education seamless through physical boundaries, for which I am grateful. Also, I used to feel distracted because of the myriad presentations going on in several parallel sessions and you had to choose which session to attend. Even though it provides something for everyone, the focus is somehow lost.
This year’s SCCT, 2020 was virtual with three parallel video channels (which were formerly run out of three different halls). I was able to update and share knowledge from the best in the world! And what a conference….. there were several great presentations, a lot of progress made and guidelines updated. Here are some of the highlights that I found worth sharing.
Developments and Highlights
First and foremost, Covid-19 pandemic Cardiac CTA guidelines and how they have impacted Radiology practice was discussed. Guidelines were on timing of imaging (urgent versus semi-urgent and elective) and the various cardiac indications for Coronary CTA, during the pandemic. Cardiac CT is particularly useful to rule out intracardiac or left atrial appendage thrombus to reduce risk from aerosol generation in transesophageal echocardiography (TEE). Cardiac CT has definite role in ruling out obstructive coronary lesion or abnormal anatomy and avoiding unnecessary admissions. https://www.journalofcardiovascularct.com/article/S1934-5925(20)30125-8/fulltext
Below is a case from JCCT publication this year depicting myocardial injury in Covid-19, Myocardial infarction with non-obstructive coronary arteries (MINOCA) (Fig. 1).
Fig. 1. MINOCA Coronary CTA: 2CH (top row) & SA (bottom row) views: depicting subendocardial myocardial hypoperfusion (42 HU) compared to anterior myocardium (142 HU). Multiplanar reformation with narrow C/W settings (right) and color-coded thin slice 3D VRT (left). (3D postprocessing software (SyngoVIATM, Siemens). https://www.journalofcardiovascularct.com/article/S1934-5925(20)30391-9/fulltext
Coronary Calcium gained a lot of attention this year. In his talk, Dr Michael Blaha emphasized the ‘power of 0 coronary artery calcium (CAC)’. In a patient with ASCVD risk factors, we can assess a person’s coronary age as follows (Fig. 2). If CAC is 0, it downgrades his coronary age and if CAC> 0, then it upgrades his coronary age. Let’s say in a 50 year old with ASCVD risk factors if the CAC is 0, then his calculated coronary age might be 45 years. But, if this patient’s CAC is 100, then his coronary age might be 65 years. Thus, CAC 0 will result in significant changes in therapy.
Fig. 2. MESA Coronary Age Calculator.
Major focus in the talks was emphasising the power of CAC 0 (Fig. 3). In a study by Khurram Nasir et al, JACC 2015, approximately 50% of patients on statins based on ASCVD risk estimator had CAC 0. Now in 2019, in Circulation, the Guidelines on Prevention of Cardiovascular Disease by American College of Cardiology (ACC)/ American Heart Association (AHA) recommend considering CAC scores in decision making to assess risk. They go on to state borderline to intermediate risk patients with CAC=0 do not need statin therapy.
Fig. 3. CAC=0. “Power of zero CAC”
Another noteworthy point made by Dr Michael Blaha is that, ‘Total CAC’ scores are best measures of 5 to 10 year short term risk, while the ‘Percentile’ scores are best measures of lifetime risk. He also explained Agatson score is a logarithmic score for CAC. So, in a person with CAC = 0, may remain at that score for almost half his life. The progress from 0 to 100 CAC may take, for example (hypothetical), 15 years. But, from 500 to 800 may take just about two years or five. This has prognostic significance in patient management. So, patient from 100 to 400 CAC may have intermediate rate of progression like around 5-10 years (hypothetical example).
Coronary artery calcium and data reporting system (CAC-DRS) is the new Calcium score reporting guideline which incorporates reporting CAC in Coronary CTAs as well as Visual scoring on Non gated Chest CT studies.
In future, we may have Machine Learning based Calcium scoring not only on Coronary CTAs, but also on non-gated Chest CT studies, in a paradigm shift. There was 0.98 intraclass correlation coefficient between predicted (automated) and manual calcium scores on both cardiac CT and chest CT scans (Al’Aref SJ et al. Eur Heart J 2019;0:1-9).
The updated ESR 2019 guidelines. They observed In a metanalysis that for diagnosing obstructive coronary artery disease using CTA (computed tomography angiography), in patients with stable chest pain in important subgroups, CT had high sensitivity and specificity, and therefore, the European Society of Cardiology has now accepted Coronary CTA as Class IB indication, which means test of choice for initial imaging in patients with stable chest pain, along with any function non-invasive study/ imaging stress test. They further qualify, this test of initial choice should be based on your ability to get good quality images, based on equipment, patient factors and expertise available. They also recommended that a Coronary CTA can complement stress testing and vice versa, i.e. you can first assess by coronary CTA and if needed, get additional ischemia information from stress testing as need. On the other hand, if stress imaging is equivocal, add a Coronary CTA for the patient’s investigation.
When we look at the patient profile in the same study by Konnet et al, in the European Heart Journal, they observed that that except men aged> 70 years, in the rest of the population the Pre-test probability of a clinically significant CAD is < 50%.
Burns et al studied Triple rule out CTA versus the Coronary CTA and concluded that the former did not result in statistically significant difference in diagnostic yield.
Plaque morphology was a hot topic with recent advancements. Fat Attenuation Index (FAI) is a functional marker of inflammation in the peri-coronary fat. FAI mapping is associated with increased risk of adverse cardiac event. Together with vulnerable plaque features (plaque remodelling, spotty calcification, fat attenuation, napkin rim), Fat attenuation index features FAI has additive value in predicting cardiac risk (Fib. 4). FAI is associated with cardiac risk in patients with plaque and in patients without plaque, as an independent marker of inflammation in the pericoronary fat.
Fig. 4. Eur Heart J, Volume 40, Issue Supplement_1, October 2019, ehz745.0049, https://doi.org/10.1093/eurheartj/ehz745.0049 (European Society of Cardiology).
Hyperintense T1 signal indicative of intraplaque haemorrhage is associated with worse coronary outcomes, just like carotid artery intraplaque T1 hyperintensity is associated with strokes.
In Congenital Heart disease, the dual phase, biventricular and two phase venous Contrast CT protocols were again highlighted which were laid out in SCCT Consensus document. In a 2018 American College of Cardiology document, they have laid out recommendations for use of CT/MRI for Interval Follow up of patients with Adult Congenital Heart Disease in months. The role of 3D printing was highlighted and we are looking to move to a future based on CT Virtual Reality for pre-surgical planning in complex cases.
This year also saw clear guidelines for Competitive Athletes (CA), when to use Cardiac CT, Cardiac MR (CMR) and TEE. Specifically, few key points include, Aortic sinus or ascending aortic dilatation (40 mm in males and 34 in women) need evaluation with gated CTA or CMR. However, these modalities are not recommended as ‘screening’ or ‘first line strategy’ before participation in competitive sports. CA presenting with possible cardiac chest pain should be evaluated beginning with TTE and coronary artery origins and course outlined. Gated CTA or CMR should be considered the next best options, in case of suboptimal assessment by TTE. For CA patients with syncope, start investigating with TTE and move next to gated CTA or CMR (individualize for each case) for structural or valvular heart disease evaluation.
Myocardial rest and stress CT Perfusion (CTP) with Coronary CTA imaging is now recommended for anatomic and functional information presence and severity of stenosis and ischemia, as having good accuracy when compared to Cardiac MRI, SPECT invasive coronary angiography, PET and invasive fractional flow reserve. They recommend Cardiac CT Perfusion imaging may be performed with Coronary CTA in patients with high risk for obstructive CAD or high Calcium or indeterminate/ equivocal coronary stenosis or if they have undergone prior coronary interventions. The CTP protocols based on pre-test probability are depicted below (Fig. 5).
Fig 5. Comparison of CT Perfusion acquisition protocols.
Transcatheter aortic valve replacement/ implantation (TAVR/ TAVI) assessment using CTA now stands updated with recommendations by SCCT for contrast protocol, contouring, annular plane identification, measurements and bicuspid valve grading.
Cardiac CTA is a rapidly evolving technology with expanding use of case scenarios to include myocardial perfusion and deep learning. Updates have been made in CAC and Coronary CTA guidelines and plaque morphology assessment. Pandemic related Cardiac CTA guidelines have emerged for near future.
Dr Deepali Saxena MBBS, DNB, Cardiothoracic Imaging Fellowship (USA)
Senior Consultant Radiologist,
Lead Cardiac Imaging & Specialist Chest Imaging,
Manipal Hospitals Radiology Group