Charles E. Denbow

COMPUTED TOMOGRAPHY SCANNING

Recent advances in computerised tomography whereby slices of the body are reproduced in image form has revolutionised the diagnosis of coronary artery disease with the aid of multidetector scanners (MDCT).

Recent studies have shown that this diagnostic modality (especially the ultramodern 64 slice model now available in Jamaica) allows for non-invasive imaging of the coronary arteries with such clarity to reliably assess the degree of coronary stenosis ( narrowing).

The MDCT is highly sensitive in diagnosing the presence of coronary calcium, which, except in patients with chronic renal failure, is invariably associated with hardening of the arteries. Conversely, the absence of calcium on the coronary CT scan virtually rules out coronary atherosclerosis. When the MDCT is negative for calcium, coronary disease is absent in 96-99 per cent of patients.

The original concerns that this technique would lead to overdiagnosis of coronary artery disease have not proved to be valid, and the radiation exposure to the patient has been shown to be comparable to or below that produced by conventional coronary angiography depending on the scanner and the protocol used. Additionally, this investigation, while far from cheap, is approximately half the cost of cardiac catheterisation and conventional coronary angiography.

AVAILABILITY

X-Ray and Diagnostic Ultrasound Consultants Limited. COST: EXPENSIVE ($20,001 to $100,000).

CARDIAC CATHETERISATION AND CONVENTIONAL CORONARY ANGIOGRAPHY

This procedure involving the introduction of cardiac catheters into the cardiovascular system followed by the measurement of pressures and oxygenation of the blood in the different chambers of the heart was first done in Jamaica at the University Hospital of the West Indies (UHWI) in the mid 1950s.

Coronary Angiography whereby X-ray dye is injected into the coronary arteries in order to locate any narrowed areas was introduced here by Dr. Edward Chung, the author, and others in 1994 at the UHWI.

For many years, coronary angiography was viewed as the 'gold standard' for coronary investigations. However, with the advent of the MDCT, many cardiologists believe that many patients can now be successfully investigated by CT scanning, avoiding the small risk and high cost of conventional angiography.

The main advantages of conventional coronary angiography are clear diagnosis of coronary stenoses (narrowing) and if balloon angioplasty is necessary, it is easy to proceed to this. The disadvantages are some risk of vascular complications and its cost.

AVAILABILITY

University Hospital of the West Indies Heart Institute of the Caribbean. COST: more than $100,000.

MAGNETIC RESONANCE IMAGING (MRI)

Magnetic Resonance Imaging (MRI) is a relatively-new technique which has been applied to a variety of organs especially the nervous system, muscles, bones and joints but also to the cardiovascular system. The principle involved here is that a special machine receives signals emitted by the nuclei of the cells of different body tissues - a detailed image of the relevant organ is then produced by the machine.

When applied to the cardiovascular system, the images produced allow the diagnosis of disorders of the cardiac muscle, valvular, congenital, neoplastic and ischaemic heart diseases. In addition, diseases of the aorta may be easily detected.

AVAILABILITY

St. Joseph's MRI, University Hospital. COST: $20,001 to $100,000.

There are other miscellaneous investigation which may be helpful in assessing patients with cardiac disease such as complete blood count, thyroid function tests, pulmonary function tests, blood oxygenation (oximetry) and perfusion lun scan.

Addendum

With respect to the locations where cardiac investigations are available locally, Mobay Hope Medical Centre also offers the following investigations - echocardiography, treadmill exercise testing, and ambulatory electrocardiography ( holter monitoring).

Charles E. Denbow is Professor of Medicine and consultant cardiologist at the University of the West Indies (Mona).