Clots in leg veins – DVT – can travel to the heart chambers and into the arteries of the lung, causing chest pain, breathlessness, and even sudden death. By Michael Lim

MADAM A had been on a cruise ship for a month and had been gradually developing chest pains and progressive shortness of breath for over three weeks. As she was breathless even at rest, she had to be transferred to the hospital because of her symptoms.

On further evaluation with ultrasound scans of the lower limb veins, she was found to have developed clots in her leg veins, a condition called deep vein thrombosis (DVT). The clots had dislodged from her leg veins and travelled into the main vein of the body (called inferior vena cava or IVC) leading into the right heart chambers.

The clots then passed from the IVC through the right side of the heart chambers into the arteries of the lung (pulmonary arteries) where they were lodged and thus, obstructed blood flow into some of the lung arteries. This resulted in less blood flow to the lungs and less oxygen, causing chest pain and breathlessness.

This was confirmed within minutes with a computed tomography (CT) scan of the lung arteries which took seconds to perform. Previously, to confirm the presence of clots in the lung arteries, a plastic tubing or catheter had to be inserted through the leg veins into the right side of the heart to take X-ray images of the lung arteries after contrast injection. This is unnecessary now as the CT scan is safe, non-invasive, has less radiation, is more accurate and gives immediate results.

Causes of deep-vein clots

DVT is not uncommon in those who have been immobile for a period of time including those travelling long distance via plane or train, prolonged hospitalisation following surgery, third trimester pregnancy and post-pregnancy. One of the greatest tragedies is to have a post-partum mother collapsing because of large clots from the leg veins being dislodged and causing massive obstruction of blood flow into the lung arteries, resulting in sudden death.

Less commonly, it can be caused by genetically “thick” blood, oral contraceptives and excessive production of red blood cells. For Madam A, she was given an injection of blood-thinning medication and improved gradually over the next few days.

As she had residual DVT , a special “umbrella like” device was inserted through her leg veins into the IVC to act as a safety net to prevent further large clots from going into the lung arteries. This device can be left in the IVC permanently or it can be removed several months later when all the clots in her veins have dissolved.

Within a week, she had flown off to join her friends on the cruise. She was given oral blood-thinning medication which she will take until the clots in the leg veins and lung arteries dissolve completely.

‘Kinking’ of veins

Unlike the arteries where the force of the heart-pumping action pushes the blood forwards, flow in the leg veins is passive. The blood in the veins is propelled forward by the contraction of the leg muscles compressing the leg veins and pushing the blood forward.

There is a series of one-way valves inside the leg veins which prevents the blood from flowing backwards. Unlike arteries which have thicker walls, veins have thin walls. Hence, if the leg is bent excessively such that the thigh and calf forms a less than 90-degree angle, the main leg vein behind the knee becomes “kinked”; it is like bending a straw and kinking it. “Kinking” the leg vein will slow down the blood flow in the leg veins and hence increases the likelihood of clot formation.

Preventing deep-vein clots

Hence, if you are going on a long-distance trip, make sure you move your legs regularly to improve vein circulation. Keep your leg at a greater than 90-degree angle to prevent “kinking” of the leg vein. Keep yourself well hydrated as dehydration will “thicken” the blood and increase the likelihood of clot formation.

If you have to lie in bed after surgery, it may be necessary to wear compression leg stockings or be given blood-thinning medication to prevent DVT. Operations such as heart bypass graft surgery, hip surgery, knee surgery and gynaecologic surgery are associated with increased risk of developing DVT.

Recognising deep-vein clots

If you develop leg swelling, you will need to consider the possibility of DVT especially if the leg swelling is more severe on one leg. For pregnant women and those in the post-delivery period, if there is leg swelling predominantly in one leg, it is essential to get an ultrasound of the leg veins to look for clots.

If the DVT becomes extensive and the clots extend towards the IVC, the blood clots will obstruct blood flow from both legs and hence cause swelling in both legs.

The simplest way to confirm the presence of clots in the leg veins is an ultrasound scan. However, if the clots are present only in the veins in the pelvis, it may sometimes be difficult to detect them on an ultrasound scan. In such instances, if there is a very high likelihood of DVT, a CT scan of the pelvic veins and IVC may be useful if there are no contra-indications.

For those who have DVT and the clots have travelled to the lungs, insertion of an umbrella-like device in the IVC may be necessary if the lung artery clots are large and there is significant residual clot in the leg veins.

There are many types of these devices and the best will be to consider those that give the patient the option of having it as a temporary retrievable device that can be removed at a later date or leaving it in the IVC as a permanent device.

These devices are called IVC filters. If clots reach the lung, the patient will have shortness of breath and can have chest pains on either side when clots obstruct the flow to the lung tissue and damage the lung.

The IVC filters have been shown to prevent recurrent episodes of a clot travelling to the lung by acting as a safety net to trap it. In most instances, the clots will dissolve with blood-thinning medication and in rare occasions, surgery may be required to remove massive clots which cause a significant drop in blood pressure by causing severe obstruction to the lung circulation.

The aim is to dissolve the clots as soon as possible and to prevent recurrent clots in the lung. Recurrent clots in the lung can lead to a condition called pulmonary hypertension which means elevated high blood pressure on the right side of the heart chambers; this condition can lead to heart failure and reduce long-term survival.

Hence, if you adre on oral contraceptives, have been in bed for a few days after surgery, have just returned from a long flight or are pregnant and you notice progressive shortness of breath, you may need to look beyond the heart and consider the presence of DVT.