Cardiology diagnostic tests and procedures
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
The diagnostic tests in cardiology are methods of identifying heart conditions associated with healthy vs. unhealthy, pathologic, heart function.
Bedside
History
Obtaining a medical history is always the first "test", part of understanding the likelihood of significant disease, as detectable within the current limitations of clinical medicine. Yet heart problems often produce no symptoms until very advanced, and many symptoms, such as palpitations and sensations of extra or missing heart beats correlate poorly with realtive heart health vs disease. Hence, a history alone is rarely sufficient to diagnose a heart condition.
Auscultation
Auscultation employs a stethoscope to more easily hear various normal and abnormal sounds, such as normal heart beat sounds and the usual heart beat sound changes associated with breathing versus heart murmurs.
Laboratory
Blood tests
A variety of blood tests are available for analyzing cholesterol transport behavior, HDL, LDL, triglycerides, lipoprotein little a, homocysteine, C-reactive protein, blood sugar control: fasting, after eating or averages using glycosylated albumen or hemoglobin, myoglobin, creatine kinase, troponin, brain-type natriuretic peptide, etc. to assess the evolution of coronary artery disease and evidence of existing damage. A great many more physiologic markers related to atherosclerosis and heart function are used and being developed and evaluated in research.
| Test Name | Lower/normal risk | High risk | Cost $US (approx) |
|---|---|---|---|
| Total Cholesterol | <200 mg/dL | >240 mg/dL | |
| LDL-C | <100 mg/dL | >160 mg/dL | $150* |
| HDL-C | >60 mg/dL | <40 mg/dL | |
| Triglyceride | <150 mg/dL | >200 mg/dL | |
| Blood Pressure | <120/80 mmHg | >140/90 mmHg | |
| C-reactive protein | <1 mg/L | >3 mg/L | $20 |
| Fibrinogen | <300 mg/dL | >460 mg/dL | $100 |
| Homocysteine | <10 µmol/L | >14 µmol/L | $200 |
| Fasting Insulin | <15 µIU/mL | >25 µIU/mL | $75 |
| Ferritin | male 12–300 ng/mL female 12–150 ng/mL |
$85 | |
| Lipoprotein(a) - Lp(a) | <14mg/dL | >19mg/dL | $75 |
| Calcium Heart Scan | <100 | >300 | $250-600 |
(*) due to the high cost, LDL is usually calculated instead of being measured directly
source: Beyond Cholesterol, Julius Torelli MD, 2005 ISBN 0-312-34863-0
Electrophysiology
Electrocardiogram
Electrocardiography (ECG/EKG in German vernacular. Elektrokardiogram) monitors electrical activity of the heart, primarily as recorded from the skin surface. A 12 lead recording, recording the electrical activity in three planes, anterior, posterior, and lateral is the most commonly used form. The ECG allows observation of the heart electrical activity by visualizing waveform beat origin (typically from the sinoatrial or SA node) following down the bundle of HIS and ultimately stimulating the ventricles to contract forcing blood through the body. Much can be learned by observing the QRS morphology (named for the respective portions of the polarization/repolarization waveform of the wave, P,Q,R,S,T wave). Rhythym abnormalities can also be visualized as in slow heart rate bradycardia, or fast heart rate tachycardia.
Holter monitor
A Holter monitor records a continuous EKG rhythm pattern (rarely a full EKG) for 24 hours or more. These monitors are used for suspected frequent rhythm abnormalities, especially ones the wearer may not recognize by symptoms. They are more expensive than event monitors.
Event monitor
An Event monitor records short term EKG rhythm patterns, generally storing the last 2 to 5 minutes, adding in new and discarding old data, for 1 to 2 weeks or more. There are several different types with different capabilities. When the wearer presses a button on the monitor, it quits discarding old and continues recording for a short additional period. The wearer then plays the recording, via a standard phone connection, to a center with compatible receiving and rhythm printing equipment, after which the monitor is ready to record again. These monitors are used for suspected infrequent rhythm abnormalities, especially ones the wearer does recognize by symptoms. They are less expensive than Holter monitors.
Cardiac stress testing
Cardiac stress testing is used to determine to assess cardiac function and to disclose evidence of exertion-related cardiac hypoxia. Radionuclide testing using thallium or technetium can be used to demonstrate areas of perfusion abnormalities. With a maximal stress test the level of exercise is increased until the patient heart rate will not increase any higher, despite increased exercise. A fairly accurate estimate of the target heart rate, based on extensive clinical research, can be estimated by the formula 220 beats per minute minus patient's age. This linear relation is accurate up to about age 30, after which it mildly underestimates typical maximum attainable heart rates achievable by healthy individuals. Other formulas exist, such as that by Miller (217 - (0.85 × Age)) and others[2]. Achieving a high enough heart rate at the end of exercise is critical to improving the sensitivity of the test to detect high grade heart artery stenosis.
Medical imaging
Coronary catheterization
Coronary catheterization uses pressure monitoring and blood sampling through a catheter inserted into the heart through blood vessels in the leg to determine the functioning of the heart, and, following injections of radiocontrast dye, uses X-ray fluoroscopy, typically at 30 frames per second, to visualize the position and size of blood within the heart chambers and arteries. Coronary angiography is used to determine the patency and configuration of the coronary artery lumens.
Echocardiogram
Echocardiography uses ultrasonic waves for continuous heart chamber and blood movement visualization. In recent times, it has become one of the most commonly used tools in diagnosis of heart problems, as it allows non-invasive visualization of the heart and the blood flow through the heart, using a technique known as Doppler.
Intravascular ultrasound
Intravascular ultrasound, an imaging methodology using specially designed, long, thin, complex manufactured catheters attached to computerized ultrasound equipment to visualize the lumen and the interior wall of blood vessels.
Positron emission tomography
Positron emission tomography, an imaging methodology for positron emitting radioisotopes. PET enables visual image analysis of multiple different metabolic chemical processes and is thus one of the most flexible imaging technologies. Cardiology uses are growing very slowly due to technical and relative cost difficulties. Most uses are for research, not clinical purposes. Appropriate radioisotopes of elements within chemical compounds of the metabolic pathway being examined are used to make the location of the chemical compounds of interest visible in a PET scanner constructed image.
Computed Tomography Angiography
Computed Tomography Angiography (CTA), an imaging methodology using a ring-shaped machine with an X-Ray source spinning around the circular path so as to bathe the inner circle with a uniform and known X-Ray density. Cardiology uses are growing with the incredible developments in CT technology. Currently, multidetector CT, specially the 64 detector-CT are allowing to make cardiac studies in just a few seconds (less than 10 seconds, depending on the equipment and protocol used). This images are reconstructed using algorithms and software. Great development and growth will be seen in the short term, allowing radiologists to diagnose cardiac artery disease without anesthesia and in a non-invasive way.
Magnetic resonance imaging
Magnetic resonance imaging (originally called nuclear magnetic resonance imaging), an imaging methodology based on aligning the spin axis of nuclei within molecules of the object being visualized using both powerful superconducting magnets and radio frequency signals and detectors. Cardiology uses are growing, especially since MRI differentiates soft tissues better than CT. The principle difficulty with current implementations, for Cardiology uses, is the difficulty of imaging the ever moving heart structures, more so than with CT because MRI is much slower. However, there is a promising future in cardiac MRI.