Reduce risk factors for heart attackDr. Muneesh Sharma: CCTA is a very robust screening tool which when normal rules out coronary disease
With the advent of the New Year, chief radiologist at Doctors Hospital, Dr. Muneesh Sharma, encouraged people to take the necessary steps to reduce their risk factors for heart attacks. To do their part in warding off a catastrophic event, he says to quit smoking if you smoke; consume lots of fruits and vegetables and foods with a lot of fiber, and avoid foods that have a lot of sugar. To that, a complement of 25 minutes of brisk walking on alternate days, or some form of physical activity on most days of the week is enough for a healthy start.
“Lose weight if you are overweight,” said Sharma, during the first Doctors Hospital Distinguished Lecture Series of 2018 during which he spoke on the topic of Coronary (CT) Angiography (CCTA).
He said that obviously there are drugs that help reduce a person’s risk burden, and he believes statins which can be started early, are under-prescribed drugs.
“Some medicines lower your risk of heart attacks and can help you live longer, but you must take them every day, as directed. Medicines your doctor might prescribe include statins that lower cholesterol, lower blood pressure, aspirin or other medicines that help prevent blood clots, and medicines to treat diabetes and keep it in control,” he said.
“Within these, you would reduce your probability of having a cardiac event. More importantly, if any of the risk factors exist, or if you’re symptomatic for any atypical chest pain it’s important to approach your physician and get screened, get diagnosis, because without diagnosis there is no treatment, and CCTA is a very robust screening tool which when normal rules out coronary disease. And it’s important that you know whether or not you have coronary heart disease when you have symptomology pointing to the same. Because if you don’t do that, then it can lead to a catastrophic event, and lead to significant mortality.”
Sharma, who reads x-rays, CT, MRI and mammograms addressed the screening test — its indications, the procedure, the risks associated, how the results are interpreted, if there are any limitations and what they are.
He described Computed tomography (CT) as a mainstay of imaging. At Doctors Hospital he said they have fairly advanced machines with their 128-slice (which refers to the number of sections it can take within one rotation) — a long way from 30 years ago when CTs initially started they were single slice rotations, one slice per rotation. Sharma said while Doctors Hospital has an advanced machine, there is a 320-slice CT in the market.
The machinery allows for the non-invasive visualization of coronary arteries, which he said is difficult because the heart is constantly beating, the vessels are small and are in motion.
“So for us to be able to see these small vessels without actually putting a catheter in demands a machine that is able to do this very fast and very precise. That’s called temporal [ability to resolve things in very short intervals of time] and spatial [the smallest distance to which it can precisely demonstrate anatomy] resolution. It’s also in three-dimension.”
“Coronary arteries essentially are the blood vessels that supply the heart, so the heart from the day we are conceived … four weeks until the time we die, the heart is beating insistently, consistently, persistently without stopping. And it receives very important blood supply throughout by the coronary arteries, which is the pipeline to this important lifeline. If the coronaries get blocked due to any cause during the course of life, then it has great implications on the heart itself, and thereafter it affects the morbidity and mortality scenario for an individual as well as a community,” said Sharma.
The radiologist said coronary arteries can be affected through congenital birth defects from the time you are born, or it could be acquired.
“Essentially the block in the coronary arteries which supply the heart, leads to angina, commonly known as a heart attack, and it is a major cause of both morbidity and mortality.”
When taking the tests, he said people should be cognizant of what things mean. And that if they are to receive an angiogram, that would refer to the visualization of an artery by putting contrast into it, and can be done in many different ways.
“In normal scenarios, an artery has blood, and it’s not going to be seen any different from other tissues. For us to be able to see the artery different from tissues, and be able to delineate, we need to fill it with something, and that filler is the contrast or the dye. It’s usually iodine-based (Ultravist 370). This dye is injected in a peripheral vein at a very fast rate, the machine then tracks the dye, and once it reaches the optimal density, or high contrast density, it triggers the scan, and the scan happens very fast. All this is done simultaneously with the ECG [electrocardiography] recording of the heart, so that ECG recording allows us to take the images when the heart is at it’s slowest, when the motion is at its slowest.”
He said many times non-diagnostic findings on stress tests lead to a physician asking for an angiogram which can be catheter or CCTA. And that one of the reasons why CCTA has taken up is because 50 percent of patients or more referred for an elective coronary angiogram are found to not have significant coronary artery disease (CAD), which means that an invasive procedure which entails its own set of risks — admission, anesthesia, overnight stay, is being done for no findings — and that’s where this screening tool which is non-invasive becomes important.
But he also said the test itself is not just limited to coronaries, and evaluates the calcium burden in the coronary arteries. They can also do a functional assessment of the heart to see for wall/valve motion, ejection fraction.
“It’s much more holistic in evaluation of the heart. We can also evaluate incidental findings outside of the heart such as lung nodules and hiatus hernia.”
To be recommended for CT angio, Sharma said a patient has chest pain or breathlessness, but the physician is not convinced of coronary disease. And that atypical chest pain include right-sided or shoulder pain; is a premenopausal lady, suspected dilated cardiomyopathy, anomalous coronary arteries, aneurysm, ectasia or bridge.
If a patient is asymptomatic he said they have no complaints related to their heart, and want to have a screening test that entails radiation and results in a risk-benefit scenario that needs to be judged.
“If there are significant risk factors — family history of heart disease, persistently high triglycerides, history of smoking or diabetes, ECG abnormality on routine check, equivocal abnormality on routine stress test, moderate to severe hypertension, prior to non-coronary heart surgery in adults — so this entire group, there are certain combinations of risk factors which even in an asymptomatic individual can push the physician to ask for a CCTA.”
Sharma said in 2012, the American College of Cardiology/American Heart Association said is should not be used to screen patients who have no signs or symptoms of CAD. But that it also said that if there are two groups that medical professionals want to say no to — those are the extremely low risk, and the extremely high risk.
“One is a group of patients that have no symptoms, no risk factors. You don’t want to do CCTA for them because you’re giving them radiation, and you know it’s going to be normal. The second group is patients who have a very high risk — you know they have CAD, and actually you don’t want to do CCTA for them because you should do a catheter angio for them and they can simultaneously undergo stenting, angioplasty and surgery. Other than these two extremes, the whole group in between with variable risk factors can actually benefit from a CCTA because you will be able to triage that group of patients who can avoid an invasive procedure.”
The process of having a CCTA performed starts with the patient receiving a form from their physician, which they have to take to the Imaging department where Sharma says the patient can expect to have a conversation with technicians.
“We usually like to look at our patients, have a talk, discuss what drugs they’re taking, take some history, find out about hypertension, diabetes, take their blood pressure, pulse, monitor and see whether or not breath-holding would be an issue as they have to hold their breath for 10 seconds during the test. We do that pre-screening. We may also require prescribing some drugs, depending on the blood pressure and heart rate, before they are given an appointment for an exam in the near future.”
During the actual test, ECG leads are connected to the patient to allow medical personnel to monitor the heart while the scan happens.
“This is the part that is minimally invasive and that is a peripheral IV line through which some drugs may be given, the contrast is injected and the scan performed. We remove the IV and you’re good to go home. There’s no stay, and you’re good to resume your normal activities. Overall, an in and out would be estimated at 30 to 45 minutes for this exam.”
According to the doctor one of the concerns is radiation burden, which also exists with a catheter angio as it involves x-rays too. But he said they can tweak their scan and modify the radiation burden as low as possible, but in certain scenarios they may have to go onto higher radiations to maintain the scan quality. And that a definite contraindication would be if a patient is allergic to contrast. Relative contraindication, he said, is renal failure.
Limitations are not necessarily significant but they do exist, he said.
“A heart rate greater than 70 beats per minute is sometimes a problem, yet we can manage that with IV beta blockers. A heart rhythm that is irregular can be a problem, however we can manage that by modifying the phases and reconstructions. Inability to sustain a breath hold for five seconds is going to be a really sick patient, but otherwise, almost everyone is going to be able to hold their breath for five seconds.”
The ability of cardiac CT to rule out coronary artery disease exceeds a predictive value of 99 percent, which means that when the study is reported normal, it will be normal.
“CCTA detects clinically significant coronary artery stenosis with high accuracy. This makes the test more accurate than stress testing, stress echocardiography, stress thallium, stress MRI and without any stress to the heart,” said Sharma.
“The test is primarily designed for you to see inside the vessel. The spectrum is not just limited to plaque evaluation. It can evaluate congenital anomalies, plaque imaging, aneurysm/Kawasaki disease, before non-coronary cardiac surgery, left bundle branch block because they have a high association with disease, dilated cardiomyopathy, acute coronary syndrome (a good triage tool), coronary venography, stent and bypass graft evaluation.”