Thursday, September 23, 2010

6.5 Tests of Heart

Physician's Notebooks 6  - - See Homepage.
5. Useful Tests of Heart, Update 12 December 2018
Chest X-ray shows enlargement and abnormal shape of heart borders. In middle age it may show calcification of coronary arteries or aorta. It may show heart tumor. When an abnormality is seen, a 2nd rotated view may give more info. Advantage of chest X-ray is that it is easy to get and often needed for other condition – especially in lung – so at same time you can get double for money. But because of radiation risk its use should be limited to after age 50. Today the echocardiogram has made heart x ray almost obsolete.
Echocardiography (ECG, Ultrasound scan of heart, Echo): The wave energy form called Ultrasound (US) is above audible range of 20,000 cps (cycle per second). Applied to chest wall, it directs ultrasound waves into chest and picks up the reflection from heart structures. It produces useful data in anatomy and function of Heart. It can pick up even small abnormality of size and shape of heart valve. It gives the number values for heart ejection volume per stroke (Stroke Volume and ejection fraction - the Gold Standard of heart failure), and numbers for blood flow through the valves with the heart valve outlines, and for dimensions of main coronary arteries. It can detect areas in the heart of abnormal muscle contraction (including lack of contraction where heart muscle ought to be contracting, hypo- or a-kinesia). This is important in picking out area of new or old, previously unknown myocardial infarction. And, via the special application of a swallowed echo emitter, it can visualize left atrium enlargement and pick up blood clot before it causes a brain stroke. In an application with small bubbles it can pick up "holes in heart" that some persons are born with and that are a cause of mysterious brain emboli from legs. It is best all-around test of Heart, every 5 years routine.
Percutaneous Transluminal Coronary Angiography (PTCA) is a test that starts by passing a spaghetti-thin hollow plastic catheter backward to flow through a major artery, and into the coronary artery origin in the heart. A related test for the anatomy and shape and size of right heart chambers and cardiac function measurement has the catheter punctured into a major right sided vein and passed up into right side of heart. In either case the catheter tip releases dye and may do videos. For a view of the coronary arteries (Coronary angiography) and aorta a dye is injected from tip of catheter positioned at origin of the artery and video is done, outlining the full coronary artery system in living action, and looking for coronary artery blockage from blood clot. Because coronary angiography via catheter is very invasive yet tells very important info about the coronary arteries, increasingly now, a special CT scan of the heart with dye, which is less invasive, is being used as initial angiography (CTA) to delineate coronary arteries. It is useful where doubt exists about the occurrence of a narrowing because it can rule out coronary disease and prevent more risky direct angiography. It is preliminary to angioplasty and stenting, to locate the lesion with minimal invasiveness. MRI is also being developed into an imaging as non invasive coronary angiography (MRA).
My recent experience with CTA: As part of a preliminary decision-making check up whether or not to have an elective major surgery, I got a CTA. Preliminaries were easy: you may eat or drink anything. Because good hydration prevents complications I drank 1 quart of pure water 20 to 30 minutes before the actual CTA. (On my own it's not required) I was asked to change to gown and called into the special x-ray room at 11am. The CT machine is shaped like a big white Donut and your body's torso is moved into the hole in the donut for the x-ray view of. The actual x-rays emanate from the inside of the donut-shaped machine as part of a rotatory x-raying. I lay flat on my back and had EKG and blood pressure monitors done and then was asked to extend my arms up in "banzai" position (In Japan a congratulatory shout meaning "10,000 years" and done by extending arms above body sharply). An IV by catheter was inserted into my arm-crease vein and attached to an automated injection syringe. I was instructed that when the operator says "Take a breath and hold it" to do just that but also not to strain at taking the deepest breath I could, as CTA patients sometimes mistakenly do at that command.
The actual x-raying took about a minute and I got a tolerable heat feeling in the throat and upper chest that lasted several seconds. The whole test was finished after 15 minutes.
The Electrocardiogram (EKG) is standard screening for everyone. It is non invasive, inexpensive and easy. When combined with a step-stress test, it is a good screen for coronary heart disease. Tests of EKG like stress test and Holter monitoring are dealt with in the Electrocardiography chapter. 
Radioactive tracer test of heart muscle has variations but essentially the patient receives a tiny dose of radioactive compound by injection, it localizes in the heart muscle based on blood circulation and then the heart is scanned externally and the defects, indicated by low-radioactivity of the tracer, show the scar of previous myocardial infarction. Hot points of the tracer suggest an acutely damaged area. The test is most useful for detecting an old healed myocardial infarction that may not be picked up by other test. 
Blood Tests can suggest abnormal holes between left and right chambers of heart by detecting the affect of shunting of low-oxygen blood from right side of heart to cause a low-oxygen in the normally high-oxygen blood on left.The low-oxygen blood getting into the arterial circulation stimulates bone marrow to produce too many red blood cells and thus shows a high red blood cell count and high hematocrit (Hct) and high hemoglobin (Hgb). It is subtle because the upper normal Hct and Hgb, especially in men can be as high as 49% and 17 grams per dL so finding high normal Hct and high Hgb may mean a healthy state. But in persons with Hct between 46 and 50% and Hgb between 16 and 18 g/dL, there will be some with heart disease that has interfered with normal oxygenation of blood. This is not about cases with grossly abnormal Hct (>50%) or Hgb (>18 gm/dL) who will show obvious sign of illness; it is the early case that will be discovered in testing.  
  Saturation of Oxygen in Artery Blood SaO2 by Pulse Oximeter: While on Hemoglobin, keep in mind its function in red blood cell (RBC) is to loosely bind oxygen (O2) and be a vehicle for Oto be delivered to the body cells. Normally the Hemoglobin molecules in the RBC become nearly 100% saturated in oxygen-binding in your lungs so the test for low saturation of oxygen in hemoglobin of artery blood (SaO2) is a good measure of shunting of low-oxygenated blood from right to left side of heart or of poor oxygenation through the lungs or from low oxygen in outside air. And since SaO2 can be measured easily, inexpensively and non-invasively by the pulse oximeter clip on finger without taking a sample of blood, it ought to be done routinely. While breathing normal room air at rest, the SaO2 ought to be higher than 95%; if lower than 95%, it ought to raise the suspicion of a right to left heart shunt or bad lung function or low oxygen or carbon monoxide in breathed-in air. 
  A diabetes check (fasting blood glucose and glycosylated hemoglobin), a kidney function check (BUN and Creatinine), serum electrolytes (Na+, K+, HCO3(–)), and a lipid screen should be done as part of heart disease check up. The B-type Natriuretic Peptide (BNP) blood test is a screening test for early heart failure before symptoms or signs start.
          END OF CHAPTER . To read next now, click 6.6 Prevent or Stop the MI Heart Attack

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