Page 33 - Medicine and Surgery

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Chapter 2: Clinical 29

many stenoses previously thought to be treatable only reduce this to approximately 15–20% and this has been
by bypass grafting. Current practice is for left main stem further reduced with drug-eluting stents. These slowly
disease or triple vessel disease to be treated by bypass release a drug (e.g. sirolimus) over 2–4 weeks to modify
grafting for prognostic reasons with almost all other the healing response.
lesions being considered for angioplasty for symptom
control. In addition, patients with concomitant condi- Coronary artery bypass surgery
tions precluding bypass surgery, e.g. lung disease, may
be considered for angioplasty even for left main stem or Surgery for coronary artery disease is useful in patients
advanced multivessel disease. with severe symptoms despite medical treatment. It has
Early angiography and angioplasty is now being in- also been shown to improve outcome in patients with
creasingly used immediately following a myocardial triple vessel disease or left main stem coronary artery
infarction, in order to reduce the risk of further infarc- disease.
tion. This is especially where the acute event is a limited
or non-ST elevation myocardial infarction. Cardiopulmonary bypass
PTCA (percutaneous transluminal coronary angio- In order to operate safely in a bloodless, immobile field
plasty) is performed under local anaesthetic. A small whilst maintaining an adequate circulation to the rest
balloon is passed up the aorta via peripheral arterial ac- of the body cardiopulmonary bypass is most commonly
cess under radiographic guidance. Once within the af- used. A cannula is placed in the right atrium in order
fected coronary artery, the balloon is inflated to dilate to divert blood away from the heart. The blood is then
the stenosis, compressing the atheromatous plaque and oxygenated by one of two methods:
stretching the layers of the vessel wall to the sides. A stent Bubble oxygenators work by bubbling 95% oxygen
is often used to reduce recurrence. Some stenoses cannot through a column of blood.
be dilated due to calcification of the vessel, small vessel or Membrane oxygenators work by bringing the blood
the position or length of stenosis. During the procedure and oxygen together via a gas permeable membrane.
there is a risk of thrombosis, so patients are given intra- Bubbles are then removed by passing the blood through
venous heparin and aspirin. If stents are used, another asponge. The blood is then heated or cooled as required.
antiplatelet agent (clopidogrel) is also used to prevent Aroller pump compresses the tubing driving the blood
in-stent thrombosis in the first few days/weeks and the back into the systemic side of the circulation at an arte-
patient remains on lifelong aspirin. rial perfusion pressure of between 50 and 100 mmHg.
If the myocardium is to be opened, cross-clamping the
Complications aorta gives a bloodless field; the heart is protected from
The main immediate complication of balloon angio- ischaemia by cooling to between 20 and 30˚C. Systemic
plasty is intimal/medial dissection leading to abrupt ves- cooling also lowers metabolic requirements of other or-
sel occlusion. This, and the problem of late restenosis, gansduringsurgery.Beatingheartbypassgraftingisnow
has been largely resolved with the routine implantation possible using a mechanical device to stabilise the target
of a stent. There is a risk of complications, including surface area of the heart, but access to the posterior sur-
emergency coronary artery bypass surgery, myocardial face of the heart can be difficult.
infarction and stroke (due to thrombosis and plaque,
or haemorrhage) but these tend to be lower than for Coronary artery surgery
coronary artery bypass surgery. More commonly, local The internal mammary artery is the graft of choice
haematoma at the site of arterial puncture may occur. as 50% of saphenous grafts become occluded within
Overall mortality is approximately 0.5%. 10 years. The coronary arteries are opened distal to the
obstruction and the grafts are placed. If the saphenous
Prognosis vein is used, its proximal end is sewn to the ascend-
Depending on the anatomy of the lesion, significant ing aorta. The surgery takes approximately 1–2 hours.
restenosis occurs between 30 and 60% after balloon Once the heart is reperfused, it rapidly regains activ-
angioplasty without stenting. Stent implants generally ity. Ventricular fibrillation is deliberately induced during