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Special Investigations In Cardiology II: The Significance Of Echocardiography
In principle, this method records the reflection of pulsed ultrasound from various parts of the heart studied in different directions. Ultrasound of 1-7 megahertz frequency is generally used. The earlier machines used time-motion mode display, but later versions permitted two-dimensional imaging. Colour coding has also been introduced for specialized investigations. The echocardiogram can be visualised on a fluorescent screen, photographed or recorded on tapes to be examined on a video screen for future use.
In the echocardiogram, the anterior right ventricular wall, both sides of the interventricular septum, mitral valve, posterior left ventricular wall, pericardium, walls of the aorta, aortic valves, pulmonary artery and valves, pulmonary veins, posterior left atrial wall, both atria, and the tricuspid valve can be identified distinctively. Incorporation of Doppler echography in echocardiography helps in assessing abnormal flow of blood as occurring in septal defects and valvular incompetence. Being a simple easily available and non-invasive procedure the use of echocardiography has become an integral part of cardiological studies. With its use, invasive investigations such as catheterisation and angiocardiography can be avoided in many cases.
Interpretation of the Echocardiograph
- DIagnosis of mitral valve lesions, especially mitral stenosis
- Assessment of the thickness of the cardiac muscle, internal dimensions of the chambers, presence of thrombi or new growths and calcification.
- Assessment of the chamber size during diastole and systole so as to determine the ejection fraction and other parameters of ventricular function.
- Identification of abnormal movements of the ventricular wall which occur in aneurysms or firbrous scars.
- Demonstration of vegetations of heart valves as in infective endocarditis.
- Detection of pericardial effusion.
In the diagnosis of valvular stenotic lesions, echocardiography is most useful, but in the assessment of regurgitant lesions, this method is less helpful.
Isotopic investigations: Availability of radionucleides such as 99mtechnetium (half-life g hrs) and 201thallium (half life 73 hrs) has enabled isotopic studies to assess blood flow and myocardial perfusion. Isotopic studies are also non-invasive.
Flow studies: 99mTechnetium compounds are used for dynamic flow studies. These include:
- delineation of the various cardiac chambers during systole and diastole (nuclear angiocardiography)
- calculation of ejection fraction
- evaluation of congenital cyanotic heart diseases
- demonstration of akinetic segments of the ventricular wall following myocardial infarction, and
- quantification of intracardiac shunts.
Myocardial Scanning: For this purpose 201thallium which is concentrated in the myocardium is employed. This isotope behaves similar to potassium and its concentration in the myocardium depends on the myocardial blood flow. Areas of diminished perfusion can be detected as "cold: areas in ischemic heart disease. Appearance of cold areas during exercise is an indication of stress induced ischemia. 201thallium studies are employed.
- To assess myocardial perfusion during rest and exercise;
- study the configuration of the myocardium, especially hypertrophy;
- to detect the presence of myocardial infarct and its extent; and
- for the evaluation of post-bypass surgery patients.
Modern instruments incorporate computer facilities and video screen and these have considerably improved their usefulness.
© 2013 Funom Theophilus Makama