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Special Investigations In Cardiology III: Cardiac Catheterisation, Interventional Radiology And Angiography
Method of Catheterisation
The right and left sides of the heart can be catheterised, using special catherters. The pressure in the different chambers can be recorded during catheterisation and this helps in identifying anatomical abnormalities.
Blood can be sampled from different locations for estimation of oxygen (Oxymetry) and this helps to examine left-to-right or right-to-left shunts. Cardiac output and cardiac index can be calculated by oxymetric studies in the aortic and pulmonary arterial blood. Normal cardiac index is 2.8 to 4.2 liter/min/m2. Reduction below 2.4 indicates abnormality. Pressure tracing of the ventricles enables detection of obstruction to ventricular filling, outflow obstructions, intactness of interventricular septum, presence of large septal defects, and also permits the calculation of the systolic ejection time. Systolic ejection time is the interval between the end of isometric contraction and the end of ejection.
A suitable catheter can be passed into the right side of the heart and manipulated into the pulmonary artery and advanced till it gets impacted in a small branch. Measurement of the pressure at this site (Pulmonary wedge pressure) reflects the left atrial pressure.
Upper limit of normal pulmonary artery pressure is 30/14 mmHg. Rise in right ventricular end diastolic pressure above 8mm Hg and left ventricular end diastolic pressure above 12 mmHg is indicative of ventricular failure or restriction to ventricular filling due to pericardial disease or myocardial fibrosis.
Siemens interventional radiography
Selective angiocardiography is the imaging of the different cardiac chambers after injecting dye into them. This method helps in visualising the cardiac chambers and sequential flow of the dye during the different phases of the cardiac cycle. Angiocardiography clearly demonstrates the anatomical and functional abnormalities in the heart. Mitral incompetence, mitral stenosis, aortic stenosis, aortic incompetence, tricuspid and pulmonary valve lesions, cardiac aneurysms and complex congenital malformations can be fully visualised.
Coronary angiography is the method of demonstrating the right and left coronary arteries after selective catheterisation using special catheters. Angiocardiographic studies still provide invaluable information in several disorders when all the modern non-invasive methods fail. Therefore this investigation is frequently resorted to, particularly in the pre-operative assessment of cardiac lesions.
This term is used to indicate therapeutic procedures undertaken along with the radiological studies. This specialty is fast expanding. The procedures include coronary angioplasty, (recanalising stenosed coronary renal artery) and embolisation of bleeding vessels (e.g, embolisation celiac axis to arrest intractable hematemesis melena).
Digital subtraction angiography: In this technique, the bony cage and soft tissue shadows eliminated by computer-aided subtraction which makes the vascular anatomy stand out prominently. Enhancement of vascular image obtained by elimination of other shadows enables one to visualise lesions in the major arteries (Cerebral, thoracic, visceral, peripheral) by venous injection of small doses of contrast media.
© 2013 Funom Theophilus Makama