In this episode of PodMD, Cardiologist Dr Xavier Brennan at Advara HeartCare, will be discussing the use of Cardiac CT in Cardiology.
- Transcript
Please note this is a machine generated transcription and may contain some errors.
*As always, all in this PodMD podcast is intended for health professionals and the comments are of a general nature. Information given is not intended as specific medical advice pertaining to any given patient. If you have a clinical issue with one of your patients please seek appropriate advice from a colleague with expertise in the area.
Today I’d like to welcome to the PodMd studio Dr Xavier Brennan.
Dr Brennan is a Cardiologist at Advara HeartCare in Burwood. He has sub-specialty training in cardiac imaging, with a special interest in heart failure, infiltrative cardiomyopathies and the role of MRI tissue characterisation techniques in cardiac pathology. He is also an accredited CTCA specialist with extensive experience in cardiac CT imaging, which will be the focus of today’s podcast.
We do hope you enjoy this podcast but please remember that the advice here is of a general nature and is not intended as specific advice about a given patient. The views and opinions expressed in this podcast are those of Advara HeartCare, not PodMD.
If you do have a patient on whom you require specific advice then please seek advice from a colleague with appropriate expertise in that area.Xavier, thanks for talking with us on PodMD today.
Xavier: Thank you for having me.
Question 1
The topic of today’s discussion is the use of cardiac CT in cardiology. Can you describe for our listeners what cardiac CT is?Xavier: So that’s a really good question. I’ll start with the CTCA because that is used when patients with cardiac risk factors have symptoms of coronary artery disease, whether it’s exertion or chest pain or shortness of breath. A CTCA uses contrast, which helps evaluate stenosis in the coronary arteries, but it also helps delineate the plaque itself in the arteries, whether it’s soft plaque, which is more high risk, or calcific calcified plaque, which is generally more stable. And as CTCA provides GPs and specialists with a report of all the coronary arteries, the degree of stenosis, the type of plaque, and a very detailed report. A calcium score is generally used as a risk assessment tool to help clinicians better understand their patient in front of theirs risk. It’s generally used if there’s no contrast involved, and it’s used for asymptomatic patients who sort of fall in that intermediate risk Framingham score. So they’ve got a 10 to 20% risk of a cardiac event in the next 5 to 10 years. A calcium score, again, asymptomatic patients in that intermediate risk group, and that CTCA is symptomatic patients with risk factors.
Question 2
Why might a patient need a cardiac CT? And more specifically, how to determine whether they need a Calcium Score or CTCA.Xavier: A patient with IBS is diagnosed using the Rome IV criteria, which are a set of diagnostic guidelines used to identify irritable bowel syndrome (IBS). The patient meets the diagnostic criteria for IBS if he or she has: Recurrent abdominal pain, on average, at least 1 day per week in the last 3 months, and associated with two or more of the following: Related to defecation, Associated with a change in frequency of stool and Associated with a change in form (appearance) of stool.
IBS subtype is determined using the Bristol stool chart which classifies patients into either IBS-C (constipation predominant), IBS-D (diarrhea predominant), or IBS-M (mixed).Question 3
What are the risks/efficacy of the test?Xavier: So it’s important to understand when patients are firstly quite invested in knowing that these scans do have a radiation exposure. Now with the increasing technology that we have and the software processing these scans are every year after getting lower and lower in radiation exposure but a calcium score, for example, has 0.5 millisieverts, CTCAs do have higher radiation exposure.
The other things to be aware of, particularly with CTCAs, is because we’re giving contrast, we do need to know the patients renal function. At my centre in Advara Heartcare Burwood, Sydney, if people have an EGFR of less than 30, we don’t go ahead with the CTCA. And if the EGFR is between 30 and 45, we pre hydrate them, withhold any nephrotoxic medications and liaise with their nephrologists. Other things to be aware of before performing the scan. With the CTCA, we need the heart rate around 70 and patients who are on that need to be on beta blockers. So if patients have a history of moderate or severe asthma, that can be a relative contraindication. If they have a contrast allergy, again we might reconsider doing the scan or giving them pre meds of hydro steroids or antihistamines. And then there are other factors to take into account as the patients body habitus and if they’ve got tachyarrhythmias or very high heart rates, then the image quality of the scan can be low and it might not be the most imaging modality. And then I guess the one of the other things to be aware of is in patients who’ve had a bypass before or have diffuse coronary calcification, particularly in renal failure patients, you can get a lot of calcium blooming in the artery and that just makes reporting the scan very technically difficult as well. So they’re kind of the main things to be aware of. But look, there’s some really great efficacy with these tests. A CTCA compared to stress echo or nuclear medicine scan has a very high sensitivity of in some studies up to 96% and it also has a very high specificity. So as I mentioned before, CTCA’s direct visualisation of the plaque. So when I see a patient, I can tell them where there stenosis is, is it a high risk plaque, is it calcium and that really helps guide you know my treatment in terms of cholesterol, cholesterol lowering agents, blood pressure and whether they need to go on aspirin. So they really are a great test for to have for the diagnosis and management of coronary artery disease.Question 4
How is a cardiac CT performed?Xavier: So cardiac CT can be performed in private radiology rooms or in hospital settings. A calcium score is a non-contrast scan, so the patient preparation is relatively straightforward. It can take mostly sort of 5 minutes or so. The patients need to lie flat. They need to have a cannula. And again body habitus and those sorts of things do play a role in terms of picking the right patient for the scanner. With the CTCA there’s more preparation involved. They need a cannular for the IV contrast. They need their heart rate to be at 70 beats per minute. Even when I was training 5 or 10 years ago, we needed to get the heart rates down to about 55 Beats per minute. So the technology of the scanner is really making it a lot easier for scanned patients now as we’re not needing to give beta blockers or ivabradine to get the really good quality imaging. Once the patient’s in the scanner, they’re sort of guided by a radiologist, a radiographer. Sorry. And they have to hold their breath sometimes for up to 8 to 15 seconds. And that’s just to help with the timing of the image acquisition. Once the image is acquired of the heart, the post processing can be a bit of time. The radiographer make sure the image quality is adequate. They then sort of trace through all the coronary arteries and the software is then reviewed by the cardiologist and we sort of make changes to different vessels to make sure we’ve looked at in all the different angles. And when we write our final report with a degree of stenosis across all the main arteries, we make sure that you know, we’ve looked at it in different phases and that if we’re writing that someone has a severe stenosis greater than 70%, that that’s the most accurate measurement and assessment we can get for the scan. And post scan, And I’m sure GP’s will be aware, but in the report they’ll often see they have minimum minimal plaque which is less than 25% stenosis.Mild coronary artery plaque which is up to 50% moderate 50 to 69 and severe stenosis which is greater than 70%. So that detailed report only in the CTCA’s whereas the calcium score is a new numerical value of calcium around the artery that doesn’t reflect the degree of stenosis that we can see in the ctca.
Question 5
Have there been any developments in treatment in the last years or are there any in trials or development now?Xavier: So yeah, look, there’s two studies I’ll touch on. The 1st is probably the seminal paper for CTCA in primary care and it was called the Scott Hart trial, which was published in 2018 in the New England Journal of Medicine. And what that looked at was 4000 patients with stable chest pain. They were randomised to just standard care of stress, ECG and other functional imaging versus a CTCA and that standard care baseline. They’ll followed up for five years. And the primary endpoint was death from coronary artery disease and non fatal MI. And what they found was the group who got the CTCA had lower rates of deaths from coronary artery disease and lower rates of non fatal MI. They also found the CTCa group were more likely to be put on preventative cardiac medication and antianginal therapies. So overall this was a really big trial in helping give robust evidence to using CTCA for stable chest pain. And then one thing that’s just sort of evolving and it’s probably not prime time in cardiology just yet, but I think it may be in the next 5 to 10 years is something called fractional flow reserve on cardiac CT. Again, this is for CTCA’s, and fractional flow reserve is already used in invasively in the Cath lab in hospital to help Interventional Cardiologists guide which lesions they stent, by using physiological studies to look for any pressure differences across the lesion and whether it’s significant and needs a stent. so FFR on cardiac CT involves the data from the CT being sent to a core lab, which at the moment I think is mostly overseas in the UK or the US. They use that data from the CT to reconstruct the coronary arteries and use mathematical equations to measure flow, pressure and resistance, and then that model sent back to the cardiologist to look at the lesions, and these are lesions that are mostly intermediate or severe. And is there a hemodynamic drop in blood pressure or flow across that lesion that would mean the patient would require an invasive test? So these techniques are approved by the FDA in the US but not readily available just yet in Australia. And I think as software and things change, they will slowly become cheaper and faster processing time and hopefully be processed in Australia and what that will mean is patients can go for an angiogram and only need the vessel stented an image that that has a significant lesion and that hopefully will reduce contrast exposure and risk for patients that they’re having less time in invasive procedures and really targeted stenting procedures in the sort of the next in the in the future.
Question 6
When should a GP refer?Xavier: As I’ve sort of touched on it, first of all, it depends on the GPs location. Some of these services like a ctca or calcium score may not be readily available in rural or regional areas. So it’s always important to be aware that other functional testing might be your only modality. Where calcium score and ctca is available, a calcium score again is a risk assessment tool, so GPs should refer calcium scores if the patients are asymptomatic and fall into that intermediate risk Framingham heart score table. Again calcium scores aren’t Medicare rebatable, so it’s important to educate patients there is a cost of generally between 150 and $200 depending on the centre. And then CTCAs there’s some centres where, I know at Advara we have streamline referrals where GP can refer directly for a CTCA, but generally speaking as a GP they should refer to a cardiologist or a specialist suggesting for a CTCA to be performed, because obviously with the CTCA there’s patient preparation that’s involved. So they do need a clinical review before just being approved for the scan, the good thing about CTCA is most patients who have exertional symptoms will fall under the Medicare eligibility criteria and they will be bulk billed for the scan. Other patients where you know, you might consider a ctca rarely if patients are asymptomatic but have a familial hyperlipidemia where they’ve got very elevated LDL’s and they’ve got a very strong family history. I find sometimes in rooms patients want to get the CTCA even if they have to pay for it. So that might be something GP just to be aware of that there are some patients who are at extreme high risk of cardiac disease and the CTCA will often that more detailed report even though the patients may have to pay 6 or $700. The information they get to help guide their treatment of coronary artery disease can be quite beneficial.
Question 7
What role does the GP play in the treatment of the condition?Xavier: Yeah. So GP’s play a critical role in the treatment of coronary artery disease. Often with these reports, you know, once you get a calcium score and you know the patient might be moderate risk and a calcium score of 100, the GP then can use that information to help guide the treatment of that patient, whether that’s non pharmacologically and recommending diet and exercise changes or looking for patients cholesterol and hypertension. And really, being aggressive with sort of modifying those to the most up-to-date guidelines. And I find sometimes with my patients that they might not fully understand the Ctca report of the calcium score report and GP’s I think, really have a critical role to help explain those reports, educate the patients and help guide them on how best to modify their risk factors to lower their risk of cardiac disease.
Concluding Question
Thank you for your time here today in the PodMD studio. To sum up for us, could you please identify the three key take home messages from today’s podcast on Cardiac CT.Xavier: So yeah, I think the first takeaway is just remembering for CTCa, their best indicator for anyone with cardiac symptoms and risk factors, and also to be aware about the contraindications of renal failure, body habitus or already known diffuse calcification across the heart arteries. A calcium score is generally used in asymptomatic patients to help guide their risk assessment tool. And a calcium score can be referred by GPs, CTCA’s generally need a specialist referral. The second take home message is the journey doesn’t start with the scan, It’s using that information from their CTCa or calcium score to help optimise patients cardiac risk. So. Once you’ve got the report, you can now you’ve got that information, you can increase their statin dose, monitor their blood pressure, start them on aspirin for primary prevention If they’ve got diabetes, and discuss with them, you know, stopping smoking, diet and exercise strategies as well. And I think the final point is just Communication between, like cardiologists and GP is really important in this area, so if GP’s have a patient they’re concerned about loss of risk factors and they’re not sure which scan to order. You know, cardiologist, just call up your local cardiologist or someone you know and they can help guide you through this decision making process. Because even myself as a cardiologist who deals with this day in, day out, it’s sometimes you’ve really gotta stop and think is what is the best scan to order for my patient. So I think communication is really important with the clinicians involved. But also the patients that’s you know it educating the patients about what this scan has showed and what the patients can do to improve their heart health going forward once they have their report from the calcium score or the CTCA.
Thanks again for your time Xavier and the insight’s you’ve provided.
Xavier: Thanks for having me.
