As I peer through the window of my room, I see a serene river flanked by lush greeneries with majestic mountains in the background. The spectacular view of the Malay kampungs on my right next to Fort Margherita and the awesome and new Dewan Undangan Negeri building, and 19th century shop houses on my left tells me I should have visited this beautiful city a long time ago.

If not for a short course in cardiac magnetic resonance (CMR), my trip to Kuching would not have materialised for some time.

So what is it about CMR that has persuaded me to go to the land of the Hornbills? To answer that, it would be best to know a bit about some of the other imaging tests available.

The various imaging modalities of the heart.

The field of cardiology probably has the most number of imaging modalities. They include echocardiography,
nuclear medicine, conventional angiography, computed tomography (CT) scan and, relatively more recently, CMR.

Echocardiography is based on ultrasound looking at moving pictures of the heart, and for decades, it has been the investigative tool of choice to detect valve problems, heart failure and congenital heart disease. Nuclear cardiology uses radioactive isotopes to look at any areas of reduced blood supply called perfusion defect, indicative of significant coronary artery disease (CAD).

CT scans, on the other hand, utilises powerful X-rays to create images of the heart. It is particularly good in imaging the coronary arReader’s Questionteries. Cardiac CT technology started off with the Electron Beam CT scan or EBCT which gives scores based on the amount of calcium in the coronary arteries. EBCT is still being used but has declined in popularity since multi-slice CT scanners or MSCT came into the picture. From 4-slice to 64-slice, MSCT really became popular after it was featured on the Oprah Winfrey Show on October, 2005. The world was then able to see pristine clear pictures of the coronary arteries without the use of dye injected through long catheters inserted into the heart as in a conventional angiogram. Everyone began asking for MSCT. In 2007 alone, 700 MSCT scanners were installed in Asia.

In Malaysia, the ‘CT frenzy’ also took off in similar fashion.

According to Professor Dr. Sim Kui Hian, President of the National Heart Association of Malaysia, it took 20 years for the country to see 35 cardiac catheterisation labs (a place to do conventional angiography and angioplasty) but for the same number of MSCT scanners, it only took two years. If you are in the Klang Valley, you are no more than a few kilometres away from a MSCT scanner. After an hour and about RM2,000 or so later, a 3-D map of your heart with nice pictures of the coronary arteries will be ready for you.

However, as good as MSCT is, it comes with several potential health hazards.

A conventional MSCT scan involves very high ionising radiation dose, in excess of 6mSV, equivalent to more than 300 chest X-rays in one go and between two to three times the radiation dose from a conventional coronary angiogram. The iodine-based contrast agent or dye also has the potential to cause renal problems and allergic reaction.

MSCT scan of the coronary arteries should therefore not be used as a routine scan to screen for CAD in an otherwise healthy individual with no symptoms.

What about CMR? Is it a good alternative to MSCT scan?

CMR is the dawn of a new era in cardiac imaging.

It is an imaging study of the heart using MRI and is said to be the cardiac diagnostic tool of the 21st century. To know more about CMR, let us first understand MRI.

MRI stands for magnetic resonance imaging. It utilises hydrogen ions which are ubiquitous in the body in the form of water molecules (H2O). When a person is placed in a strong magnetic field, these protons will become aligned. As various body tissues have different water content, radiofrequency  fields are used to system atically alter this alignment. These protons will then transmit back as energy and converted into an image.

Compared to CT scan, MRI provides a much greater contrast between the different soft tissues of the body. This makes MRI particularly useful in imaging the brain, muscle, abdominal and cancer cases.

MRI application of the heart as in CMR started in the 1990’s but its widespread use was hampered by the rather poor images generated as the beating heart is a continuously moving organ. CMR then was limited mainly to the study of congenital heart disease (heart defects detected at birth), aortic disease and cardiac tumours such as atrial myxoma.

However, with the advances in MRI technology, the clinical use of CMR has expanded. According to Dr Annuar  Rapaee, Consultant Cardiologist and Chairman of the Society of Cardiac Imaging of Malaysia (SCIM), CMR is now also indicated to study left ventricular function (heart muscle contractility), presence of myocardial
ischaemia (reduced blood perfusion in the heart), anomalous (abnormal origin and structure) coronary  arteries, cardiomyopathies (weak heart) and cardiac valves, among others.

If CMR can give pictures clearer than MSCT, why then does CMR not take off in a big way similar to MSCT four years ago?

While CMR is better than MSCT scan for most diagnostic investigations of the heart, it falls somewhat short when it comes to visualisation of the coronary arteries.

Dr Stephen Harden, Consultant Cardiothoracic Radiologist at Southampton University Hospital, United Kingdom, in his lecture mentioned that CMR in general is relatively safe, with no ionising radiation exposure and for coronary MR, no potentially hazardous contrast agent is used. However, it has not been able to replace MSCT yet as far as non-invasive angiography is concerned.

However, there are cases where coronary MR can be useful. According to Dr Annuar, newer and more advanced MR technology such as that found in 32-Channel MR scanners, very good image resolution can be produced giving nice pictures of the coronary tree. Some cases when coronary MR is used are situations where the use of MSCT is not recommended such as in individuals with renal impairment and known allergy to contrast agents. It can also be done in those who do not wish to be subjected to unnecessarily high radiation dose. Professor Sim also added that with the rapid advances in MR technology, it would not be long before CMR replaces MSCT in virtually all cases including non-invasive coronary angiography.

These are exciting times indeed. Never before have we been able to look into our heart with so much precision and clarity…and it can only get better.

If you have a question for me, please write to haizal@tropicanamedicalcentre.com. See you next Monday.

Dr Haizal Haron Kamar
Consultant Cardiologist
Tropicana Medical Centre

What causes water in the lungs?

I am a 53-year-old woman and I was admitted to a hospital recently with ‘water in the lungs’. The doctor said my heart was swollen and very weak but could not explain to me why. He also mentioned that I would need to have an angiogram. Although I rarely exercise, I lead a fairly healthy life, free of any medical illness before I was hospitalised. What do you think could be the cause of my problem?

Jaswinder
Petaling Jaya

Dear Jaswinder

From what you have said, it sounds like you had cardiac failure with acute pulmonary oedema (water in the lungs). In a recent Heart to Heart article on Aug 3, 2009, I explained the likely mechanism. The most common cause of cardiac failure is still coronary heart disease (CHD) and this is probably why a coronary angiogram was suggested by your doctor as it is potentially correctable. To have CHD, you usually need to have at least one risk factor for getting CHD such as smoking, diabetes, hypertension and abnormal cholesterol level, but not always.

You are likely to have had an echocardiogram, an ultrasound scan of your heart, to confirm that your heart was weak and enlarged. If your angiogram later is normal then you do not have CHD but a condition called dilated cardiomyopathy (DCM), which is what your doctor had told you – swollen weak heart. In most cases of DCM, no cause is found although viral infection, adverse drug effect and alcohol excess have been implicated in some cases. Cardiac magnetic resonance (CMR) is a relatively new but useful investigative tool which may shed some light into the cause of your weak heart. You can read a bit more on CMR in this week’s Heart to Heart article.