Vascular Diseases consist of a range of diseases affecting the blood vessels in the body. It can be divided into two big groups, which are arterial diseases and venous diseases. The more common arterial diseases are aneurysms, which is an abnormal dilatation of the blood vessels, and peripheral vascular diseases, which is narrowing of the blood vessels in any part of the body. The most common venous diseases seen in everyday life is varicose veins.
Treatment options available for vascular diseases consist of both conventional open surgery as well as the more modern endovascular intervention.
An aneurysm is an abnormal dilatation or ballooning of the blood vessel. This can occur in the vein, artery, aorta or heart muscle. Depending on the site of aneurysm, the following terms are used: venous aneurysm, arterial aneurysm, aortic aneurysm and ventricular aneurysm.
To distinguish between true dilataion of the artery from a generalised ectasia or enlargement of the blood vessel, arterial aneurysm is defined as a focal dilatation of at least 50% of the expected normal diameter of the artery.
Abdominal aortic aneurysm (AAA) is by far the commonest aneurysm. It occurs in the abdominal aorta, which is the part of the aorta that courses from the diaphragm to the groin and supplies blood to the abdominal viscera (organs) and the lower limbs. Approximately 95% of the aneurysms are infrarenal, i.e. they are below the kidney arteries.
The aneurysm that extends above the kidney arteries is called a suprarenal aneurysm. An aneurysm that occurs in the chest is called a thoracic aneurysm.
Atheroslerosis is the commonest cause of AAA. The atherosclerosis is secondary to hypertension, smoking, diabetes mellitus, hyperlipidaemia and ageing.
Occasionally, in patients with long-standing hypertension, there may be a split in the inner wall of the aorta, allowing blood to seep into the media layer of the vessel, splitting the wall into two halves.
The thinned out wall weakens and causes dilatation. This is termed dissecting aneurysm. It commonly occurs in the thoracic aorta and may extend all the way down to the abdomen, causing a dissecting thoraco-abdominal aneurysm.
In developing countries, infection is an infrequent cause of aneurysm formation. Not all bacteria have the propensity to get lodged in the wall of a rapidly flowing aorta.
Bacteria that cause aneurysms include Salmonella typhi (the cause of typhoid fever), Mycobacteria tuberculosis (that causes tuberculosis) and staphylococcus infection. With the advent of penicillin, syphilitic aneurysm is very rare now. It used to be a common cause of thoracic aneurysm.
People with Marfan syndrome, a form of congenital anomaly that is associated with deranged connective tissue synthesis, are prone to develop AAA.
Open repair of an abdominal aortic aneurysm (AAA).
It appeared that some people with atherosclerosis develop narrowing (stenosis) or blockage (occlusion) of the aorta or arteries. Yet in other groups, the artery or aorta just ballooned out. Are they really the same pathologic process giving rise to different end results?
Extensive research has been conducted to elucidate the mechanism underlying aortic aneurysms. Under the microscope, the wall of the normal aorta contains not only vascular smooth muscles but also collagen fibres and elastin, which are organised in concentric layers.
In AAA, elastin fragmentation and degeneration occurs, leading to the loss of load bearing capacity and resultant dilatation. It would appear that AAA is really a degenerative disease of the aortic wall. That would explain why it occurs commonly in elderly patients, some with no predisposing illnesses.
AAA is a common disease in Western countries. The prevalence of the disease varies from 3% to 10 % in those above 50 years of age. There are no studies in Asia to determine the incidence and prevalence of this disease.
Judging from the incidence and prevalence of diseases that are associated with atherosclerosis, like ischaemic heart disease, stroke and kidney failure, in Asian patients, it is reasonable to assume that the incidence and prevalence of AAA would not be any less. Published data from Asian hospitals show that the incidence of AAA repair is increasing every year.
People with AAA usually have no symptoms. Occasionally, some may notice a pulsatile mass in the abdomen, while some would notice a hard lump in the tummy that has grown larger. Some of the asymptomatic aneurysms are diagnosed when the patient presents for a check-up with his general practitioner.
More often, the aneurysm gets picked up when the patient comes to the hospital for an unrelated illness, like repair of a hernia or for urinary retention.
If the aneurysm leaks, the blood seeps through the posterior peritoneum, adjacent to the spine, and the patient would experience backache.
The classical presentation is of a previously well elderly patient who suddenly develops a severe backache not relieved by rest or painkillers. If the patient is pale and there is a pulsatile mass palpable, it is almost certain that the patient has a leaking AAA.
If the aneurysm ruptures, torrential bleeding would occur into the peritoneal cavity. The patient would present with a sudden onset of abdominal pain and hypotension. Only about 50% of the patients would survive the journey to the hospital. Of those who are lucky to arrive at the hospital and undergo immediate surgery, only about 50% of the operated patients survive.
AAA is a disease of the elderly
people aged over 50 years old. The diagnosis is suspected in patients who are smokers, hypertensive and in those with a family history of AAA. The tests that are usually performed in the diagnosis of AAA include:
Abdominal x-ray – The routine abdominal x-ray outlines the aorta if there is calcium deposition in the intima. AAA could be seen by tracing the outline of the intima.
Ultrasound – This uses a high frequency ultrasound waves sent through the skin. The returning echoes form an image on the screen. The size of the aneurysm can be measured.
CT scan – Computerised axial tomography gives an accurate estimate of the size of the aneurysm. This is by far the best form of investigation to plan treatment. The only drawback is the contrast that needs to be administered, which may cause allergy in susceptible patients or result in kidney derangement in patients with poor kidney function. With the advent of 64-slice CT angiogram, an image of the aorta with its renal arteries and other mesenteric arteries can be depicted clearly.
Aortography – Before the introduction of CT angiogram, an aortogram is indicated in complicated aneurysms to show the relationship of the renal arteries and mesenteric arteries relative to the aneurysm. This is important if the aneurysm involves the suprarenal aorta, in which case, reimplantation of the renal or mesenteric arteries may be required.
Not all AAA require treatment. The basic principal is to weigh the risk of repair against that of leak or rupture. Given that aneurysms occur mostly in elderly patients, some of them with associated heart, lung and kidney problems, any surgical repair entails a risk to life.
An aneurysm of less than 4cm has an annual risk of rupture of less than 1%. An aneurysm of 6cm has an annual risk of rupture of at least 10% and that of 6.5cm has an annual risk of rupture of 20%, increasing exponentially. In the UK and the US, most vascular surgeons would agree that any aneurysm above 5.5cm must be repaired.
An elective repair (i.e. repair in a predetermined date so that the patient can be optimally prepared) carries a mortality of around 5%.
An emergency operation carries a mortality of at least 50%. It makes sense that if the risk of rupture is high, the aneurysm must be repaired electively.
Asians are generally of smaller build compared to their Western counterparts. It is prudent that the assessment for repair should not be based on absolute size of the aneurysm. What about the smaller aorta in Asians – wouldn’t that increase the risk of rupture if we waited until it reaches 5.5cm?
Dr Teoh MK and group had done a study in the early 1990s on the aorta size of Malaysians in Hospital Kuala Lumpur. It was noted that our aorta size is about 10% less than that of Caucasians, both in male and female populations, and in patients with or without cardiovascular disorders.
Based on this data, I would recommend a repair for any AAA that has reached a size of 5cm.
In patients who are younger, say in their 50s, we know that repair would be required ultimately as the aneurysm grows by about 10% or 0.5cm per year. Some doctors advocate repair when the diameter reaches beyond 4cm. This is contentious and a policy of wait and see is by far the best approach.
This is an age-old repair technique, successfully performed since the 1950s. In the US, an estimated 40,000 AAA repairs are carried out annually.
This repair entails general anaesthesia. Through a midline incision in the abdomen, the aorta is exposed and controlled. The aneurysm is then clamped at both ends to prevent blood from getting into the aneurysm.
A synthetic graft is then implanted, sutured to the healthy portion of aorta. The aneurysmal wall is then used to wrap around the graft.
This repair is generally safe with a mortality rate of less than 5%. Extensive pre-operative assessment of the heart and lungs are usually carried out before the operation. The patient is usually nursed in the Intensive Care Unit for a day. The total length of hospital stay is about a week to 10 days.
Endovascular repair (EVAR)
This is a newer form of repair where a pre-fabricated graft is inserted into the aneurysm through the femoral arteries. Two small incisions are made in the groin to expose the femoral arteries and the graft treaded carefully into the aneurysm under fluoroscopic (Cine X-Ray) guidance.
This technique was introduced in the 1980s by Dr Parodi. This promised to be a less invasive procedure whereby a long abdominal incision was avoided and could reduce the operative mortality.
The initial enthusiasm of this minimally invasive device has decreased with time. With more widespread usage of this device, new problems emerged. There have been no long-term studies of this modality of therapy and the device is being constantly modified and some have been withdrawn from the market.
The main complications that have emerged include endoleaks (leakage of blood through a collateral branch) and stent migration (the stent slipped out of position).
More studies are being conducted to have these problems rectified.
Due to the uncertainty of its long-term results and the potential complications, patients need to be monitored with periodic CT scans, initially at one month post implantation of graft, then at six months and then at yearly intervals.
It costs about two-and-a-half to three times the cost of an open repair. Coupled with the need for periodic scans, its cost-effectiveness has been questioned.
Recent studies in Europe like the EVAR and DREAM trials have shown that it has decreased perioperative mortality by about 3% in follow-up of patients up to four years. However, judging from its costs and complications, and the lack of long-term follow up data, this procedure is recommended only to high-risk patients.