by admin | July 1, 2016 8:50 am
Atherosclerosis is a condition in which cholesterol, fatty substances, calcium, cellular-waste-products, and fibrin start depositing on the walls of coronary arteries of the heart. These arteries are vital for supplying oxygen-rich blood to the heart. High cholesterol and triglyceride[1] levels in the blood, hypertension, type 1 diabetes, obesity, a diet high in saturated fat, physical inactivity, and smoking are risk factors for Atherosclerosis.
Over time, these deposits harden, forming what is called a plaque. The plaque gradually grows in size, thereby restricting the heart flow in that artery. When the growth and constriction are severe, there is said to be a blockage in the heart. Heart blockages are serious and affect overall, long-term health. They must be detected early and removed through one or more means.
One of the earliest minimally-invasive and still widely-used diagnostic procedures for detecting coronary blockages is the Angiogram (also called Angiography or Arteriogram). In this, the doctor inserts a long, thin tube called a catheter in one of the major blood vessels in either the leg or groin and gently threads it to the heart. A dye is inserted into the heart, and its flow through the arteries is watched using X-ray equipment. This helps identify the blockages. The type of X-ray used is a CT scan. Hence the procedure is also called CT Angiogram.
Despite their wide usage, Angiograms come with their limitation. As Dr. Amal Louis, a reputed cardiologist[2] at Kauvery Hospital, Chennai, opines, “merely identifying the number and extent of blockages is not enough. This is just the anatomical aspect of stenosis and not the full story. Also, this test is not foolproof. So, there are more advanced techniques by which doctors can examine the blood vessel and plaque in more detail. This includes the presence of a clot, image of the blood vessel walls, the content of the plaque, how much cholesterol is there in it, etc. Basically the physiological aspects of the blockage”.
So what are these techniques? Considering that this is a constantly evolving field, we are only showcasing some of the methods.
In patients with severe calcification of the arteries, a conventional angiogram may not provide accurate results. For such patients, Ultra High-Resolution CT or UHRCT is used. This technique uses equipment that can generate ultra-high resolution images of the arteries and hence the blockages. The equipment can provide a detector width of 0.25 mm which helps overcome partial volume effect limitations, a common problem with traditional angiograms. Various studies have been conducted to show the accuracy of this equipment compared to conventional Angiogram.
It is also called Endovascular ultrasound or endovascular echocardiography. The doctor uses a special catheter fitted with a tiny ultrasonic transducer at one end. The other end is connected to a computer workstation which converts high-frequency sound waves from the transducer into real-time images on the computer monitor. Sound waves from the transducer bounce off the artery’s walls and are captured by the transducer as echoes. A computer then converts these echoes into images on the monitor to generate pictures of the coronary arteries or other blood vessels. Depending on the type of blood vessel being analyzed, different sized catheters are used.
The procedure has several advantages. IVUS can show the entire artery wall and provides vital information around the amount and type of plaque deposits. It does not use ionizing radiation, so it is safe. It can provide clear pictures of soft tissues that cannot be captured by X-ray. The procedure requires little or no special preparation. However, it is often used along with another procedure, such as angiography.
OCT is the optical analog of IVUS. Instead of ultrasound employed in IVUS examinations, near-infrared light with a wavelength of about 1,300 nm is used here. Red blood cells, water, lipids, and protein absorb this wavelength at relatively low levels. A rotating, glass-fiber-optic system is used to direct coherent infrared light reflected within the tissue to create a detailed image of the tissue with extraordinarily high resolution, along with cross-sectional tomographic images like the ones obtained through IVUS.
Since the speed of light is greater than ultrasound, an interferometer is used to measure the back-scattered light. Further, the axial resolution achieved with OCT is 10-20 microns, while it is typically only 100-200 microns with IVUS. The resolution achieved withOCT is also superior to other non-invasive coronary imaging techniques such as cardiac magnetic resonance (CMR) and computer tomography coronary angiography (CTCA).
In this technique, the patient receives a small amount of adenosine drug through an IV hooked to the arm. The drug acts as a vasodilator. That is, it makes the coronary arteries open like it would if the patient is exercising. This increases the blood flow and simulates the effect of a treadmill test or some other exercise for patients who cannot exercise for various reasons.
The medication is given in a small dose to ensure an increase in heart rate is slight.A small amount of MRI dye called gadolinium is injected into a vein while the person is resting when they receive the adenosine. An MRI scanner takes pictures of the gadolinium dye as it flows through the heart. This creates computer images of the patient’s heart for the doctor to review. This technique is suitable for understanding blockages in the larger arteries.
This is a less-expensive improvement over an older technology called Fractional Flow Reserve (FFR). FFR, like the Cardiac MRI Stress test, also uses adenosine for vasodilation and then measures the pressure difference as blood flows through a blocked artery. In contrast, iFR measures the pressure during a specific point in the cardiac cycle. In studies conducted, patients who underwent this procedure had fewer Percutaneous Coronary Intervention (PCI), Coronary Artery Bypass Grafting[4] (CABG or bypass), and revascularization rates.
Dr. Amal Louis, Senior Cardiologist talks about latest techniques which are far superior to the traditional Angiogram.
Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai, Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.
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