Overview of Cardiac Imaging
With the advancement of medical technology, we now have the ability to non-invasively see the heart and its blood vessels. Several heart imaging techniques have become vital in today’s heart medicine, helping not only in diagnosing but also in managing various heart diseases and guiding invasive procedures. These techniques include echocardiography (which uses sound waves to create pictures of the heart), myocardial perfusion imaging via nuclear scintigraphy (which uses radioactive tracers to visualize blood flow to the heart), magnetic resonance imaging (which uses magnetic fields and radio waves to create detailed images of the heart), and computed tomography (or CT scan, which uses X-rays to create detailed pictures of the heart).
The best way to visualize the coronary arteries (the blood vessels that supply the heart muscle with blood and oxygen) is still through an invasive procedure called coronary angiography, which is done through coronary catheterization (where a long, thin tube is inserted in an artery or vein in the groin, neck or arm and threaded through to the heart).
Each imaging technique can be used on its own or combined with others, depending on the diagnostic needs. These imaging methods are now routinely used along with medical history, physical examination, and laboratory testing in modern heart medicine.
Moreover, guidelines on when it’s appropriate to use these imaging techniques have become standard. These guidelines help assess the best imaging method for specific patient situations to maximize diagnostic accuracy and cost efficiency, as well as to minimize the patient’s risk.
Equipment used for Cardiac Imaging
Echocardiography is a technique that uses sound waves, similar to ultrasound, to create images of the heart. It sends out sound waves that bounce off the parts of your heart, creating moving images in real time. It’s a bit like how bats see in the dark. Blood or fluid shows up as black, hardened areas look white, and muscle looks grey. For a standard echocardiogram, pictures are taken from several different areas on your chest.
There’s also a version called transesophageal echo, where the device that sends out sound waves is placed on a scope and put down your throat. This method offers clearer pictures of the heart, with less interference from the chest wall and ribs. Because the device doesn’t need to penetrate as far, the image quality is better. This procedure needs a local anesthetic and you need to be sedated. You need to give your consent, and your condition needs to be monitored during the procedure and while you recover afterwards.
In addition to creating images, an echocardiogram can measure how fast blood moves through the heart and vessels. It can also identify areas where blood flow is turbulent which helps to detect issues with the heart valves. There’s a version of echocardiography that’s used during physical activity to check how your heart works under stress. Newer techniques can create three-dimensional images and measure changes in the shape and size of the heart muscle during a heartbeat.
Echocardiograms used to need special equipment in special rooms, but smaller, portable versions have been developed that can be used at the bedside or carried around during medical rounds. These smaller devices can often provide important information quickly and efficiently.
Nuclear imaging uses a radioactive tracer that’s injected into your veins. This tracer gets trapped in the heart muscle cells and gives off rays that can be detected and used to create images of how blood flows in the heart. This can also be done while you’re doing physical activity to check for issues.
Cardiac CT scans use x-rays to create slice-like images of the heart. The x-rays pass through the body, and a computer uses this information to create a detailed picture. Different body parts show up in different shades of grey. A dye is sometimes used to help make the heart chambers and blood vessels stand out more. These pictures can also be made into a three-dimensional image of the heart.
Magnetic resonance imaging (MRI) of the heart uses the water in our bodies to create images. It uses a magnetic field to change the spin of the water molecules, which then emit signals that the machine picks up to create an image. MRI can provide very clear pictures of the heart.
Cardiac catheterization involves inserting a tube into a vein in your wrist or groin, and guiding it up to your heart. This is done under x-ray control. It offers a direct way to look at the heart arteries and is the gold standard in cardiac imaging. It can also measure pressures inside the heart chambers. Cardiac catheterization is not only diagnostic but can also be used to treat heart disease by opening up blocked arteries.
Possible Complications of Cardiac Imaging
Some medical procedures, like transesophageal echocardiography, where a small device is passed down the throat to look at your heart, carry some risks. These can include minor damage to the esophagus (the tube that connects your mouth with your stomach), accidentally inhaling foreign material into the lungs, and complications from sedatives used during the procedure. However, these complications are extremely rare, particularly when the procedure is carried out by experienced doctors.
Cardiac CT scans expose you to a certain type of radiation which has been known to have harmful side effects. While the risk of developing cancer from these scans is difficult to figure out and probably small, there is still a chance. Therefore, the risks and benefits of these imaging tests need to be discussed before going ahead. Repeat scans and scans done on young patients should be given extra thought, due to possible accumulated exposure to radiation.
In many heart imaging tests such as cardiac CT scans, and catheterizations, contrast agents are used to improve the images. However, there’s a risk that these agents can harm the kidney, especially those with pre-existing kidney conditions or diabetes. In such cases, the risk of developing chronic kidney disease is quite high. Cardiac magnetic resonance imaging (CMR), which uses a magnetic field to create pictures of your heart, is not suitable for patients with any metallic implants like pacemakers or defibrillators because they might interfere with the magnetic field used in the tests.
The most invasive heart test is cardiac catheterization, where a thin tube is inserted into a blood vessel leading to your heart. This carries the most risk of harm, including kidney injury due to the use of contrast agents, a heart attack, stroke, heart rhythm problems, and bleeding from the vessel where the catheter was inserted. There’s no absolute rule on who shouldn’t have cardiac catheterization, but there are some conditions, like severe heart failure, serious infections in the blood, a recent stroke or acute kidney failure, which might make the test a bad idea.
What Else Should I Know About Cardiac Imaging?
Echocardiography is a test that uses sound waves to create pictures of the heart. This can show the size of the heart’s chambers, how thick the heart’s walls are and if there are any structural issues with your heart. It also helps doctors assess how well your heart is contracting and how much blood it’s pumping out with each beat (left ventricular ejection fraction).
One type of echocardiography, called transesophageal echocardiography, can spot lesions (known as vegetations) on heart valves and blood clots within the heart. This test can give a clear view of an appendage off the left chamber of the heart, which is often hard to see. In people with kidney problems, this test is commonly used to check for a tear in the large blood vessel leading from the heart (aortic dissection).
An echocardiogram can also be done while you exercise, to see if your heart functions properly under stress. If you can’t exercise, the test is performed while you’re given medicine that makes your heart work hard, as if you were exercising. If there are changes in the movement of the heart’s walls, this may signal areas where the heart isn’t getting enough blood.
Radionuclide imaging is a test that uses small amounts of radiation to examine the heart. It’s especially useful in people known or suspected to have heart disease, not just for diagnosing it, but also for grading how severe the disease is and predicting your risk of a heart attack. Radioactive substances are used to show which parts of the heart muscle are getting adequate blood flow. Areas getting insufficient blood are highlighted as possible areas where the heart muscle is deprived of oxygen (ischemic areas).
Heart CT scans can provide a 3D picture of the heart’s blood vessels without needing an invasive test like coronary catheterization. They can also spot calcium deposits in the coronary arteries, which can indicate coronary artery disease. Especially in cases where aortic dissection is suspected, these scans have become the first choice for quickly checking the heart’s blood vessels.
MRI scans of the heart provide detailed images of the heart’s structure and function. They can give sharper images of the blood vessels and tissues of the heart compared to CT scans. These scans can also highlight areas of the heart muscle affected by a lack of oxygen and find scar tissue from past heart attacks. They can assess the performance of valves and the flow of blood in your heart too.
Coronary angiography, done using cardiac catheterization, gives a detailed view of the heart’s anatomy and states of disease. It can also be used to carry out treatments that restore blood flow to the heart. This is the preferred treatment in emergencies like heart attacks. Other tools used during cardiac catheterization include intravascular ultrasound and fractional flow reserve assessment. Intravascular ultrasound can visualize the inside and the wall of blood vessels which is useful for checking possible plaques. Fractional flow reserve assessment measures the flow of blood through a narrow part of a coronary artery. Procedures such as valve replacements or repairs are often guided by cardiac imaging tools.