General
about Heart Conditions
Coronary artery
disease is stenotic arteriosclerosis - a narrowing of coronary arteries caused
by atherosclerosis. When sufficiently severe this limits blood flow to myocardium
(heart muscle). In its most severe form it occludes (blocks) the coronary
arteries. Coronary heart disease is caused by a build up of fatty matter in
walls of coronary (heart) arteries. These arteries become rough and narrowed on
the inside limiting supply of oxygen-rich blood to the heart muscle. This can
cause chest pain (angina) or increase the risk of heart attack. The fatty
deposit can be removed (coronary angioplasty) or the damaged arteries replaced
(coronary bypass surgery). Patients who have coronary angioplasty are able to
return to work sooner than CABG.
Angioplasty
In coronary
angioplasty a tube (inducer catheter or sheath) is inserted into the femoral
artery in groin. A dye is used so that the narrowed artery can be viewed on
monitor. Thin tube with balloon at tip is carefully threaded to the area of
narrowing in coronary artery. Balloon then inflated for several seconds. This
splits and compresses the fatty material in the artery wall. Opening in artery
enlarged to allow blood to flow more easily. Catheter removed - about three
hour op. In 1990 more than 500,000 patients in USA had a revascularisation
procedure and about 300,000 underwent percutaneous transluminal coronary
angioplasty (PTCA). This increased to 325,000 in 1992 and 362,000 in
1993. Overall about 500,000 angioplasty procedures were performed world wide.
Coronary artery bypass graft (CABG) and PTCA are the two most common
revascularisation treatments for severe coronary artery disease. About 670,000
revascularisation procedures in 1993 (USA) - 309,000 CABG ($30,000) compared to
the 362,000 PTCA ($15,000).
In the early
years (1977-81) with primitive equipment and limited operator experience,
coronary angioplasty was recommended in symptomatic, clinically stable patients
with well-preserved ventricular function who, otherwise, were good candidates
for coronary bypass surgery. Coronary angioplasty was indicated in patients
with single-vessel disease with stenoses (narrowing) and not occlusions
(blockage) that were proximal, discrete and non-calcified and did not involve
arterial segments that were angulated or gave rise to major side branches. With
evolution of both angioplasty hardware and technique, the clinical and
morphological profile (study of structure rather than function) patients
acceptable for coronary angioplasty has widened considerably.
With non-occluded
coronary arteries the clinical outcome of angioplasty is successful in 90%
patients. Angioplasty has lower success rate with stenoses that are long,
eccentric, angulated, calcified, ostial or associated with thrombus. The
success rate is lower in patients with unstable angina of advanced age.
Difficult to manipulate catheter guide wire through an occluded region and
lower initial success rate was seen (65-70%) in angioplasty performed on
occluded lesions. Chronically occluded lesions are less likely to be successful
than recently occluded vessels, in which occlusion is short, tapered, not
calcified and not bridged by collateral vessels. Angioplasty of saphenous vein
grafts less than 4 years old especially with lesions at distal anastomic sites
resulted in favourable outcomes. Success rate and frequency of acute
complications are similar among patients with diseased native arteries but
incidence of restenosis is higher in patients with diseased vein grafts.
Stable Angina
Stable angina
pectoris often recurs in a regular or characteristic pattern. Commonly
recognise angina only after several episodes have occurred and pattern has
evolved. Level of activity of stress that provokes the angina is somewhat
predictable. Pattern changes only slowly. This is "stable" angina -
the most common variety. Comparing angioplasty (PTCA) with medical therapy in
single vessel disease and stable angina revealed PTCA was more effective than
medical therapy in relief of angina. PTCA is not recommended as initial therapy
for stable symptoms and single vessel disease.
Unstable
Angina
Instead of
appearing gradually, "unstable angina" may first appear as a very
severe episode or as frequently recurring bouts of angina. Or an established
pattern may change sharply. May be provoked by less exercise than before or
occur at rest. This needs prompt medical attention. The term "unstable
angina" is also used when symptoms suggest heart attack but diagnosis does
not support this. May have prolonged chest pain and poor response to rest and
medication but no evidence of heart muscle damage either on electrocardiogram
or in blood enzyme test. There is no advantage of PTCA over medical therapy in
unstable angina.
Thrombolytic
therapy
Anticoagulants
that dissolve blood clots. Increasing age strongly associated with denial of
this thrombolytic therapy. Elderly have higher risk of bleeding (rare
intracerebral haemorrhage - bleeding into brain) with this therapy but there is
also the higher risk of dying from acute myocardial infarction. Coronary
thrombolysis is a double edged sword - which edge is sharper? Compared to
thrombolytic therapy, coronary angioplasty is better at restoring anterograde
(previous) flow and less recurrence of ischaemia. Greatest benefit to older
patients and those with anterior infarction (blood supply cut off) or
persistent tachycardia (abnormally rapid heart beat). PTCA has profound
advantages over CABG.
Essentially a
non-surgical alternative. Less expensive and less invasive. PTCA is
catheter-based procedure that directly dilates the vessel at point of
obstruction. Local injury. Discharge within days. CABG is major surgery,
requiring opening of the chest wall. New blood circulation channel is provided
with a lumen frequently larger than the native diseased lumen. Both alleviate
the effects of coronary artery disease but do not correct or alter natural
course of the disease. PTCA preferred over CABG. However, revascularisation is
incomplete and restenosis occurs with PTCA. CABG addresses a more severe
condition compared to PTCA in first time revascularisation. Restenosis remains
its Achilles heel.
Subsequent repeat
of PTCA or a first time CABG after PTCA within one year of initial PTCA
compared to those undergoing CABG surgery as first treatment is 30.5% vs 3.6%
in single vessel disease and 34.5% vs 3.2% in multivessel disease. Higher
prevalence rates of angina also observed in patients having PTCA compared to
CABG (14.6% vs 6.5% for single vessel disease and 17.8% vs 12.1% in multivessel
disease). However, incidence of death, non-fatal myocardial infarction or
cardiac death within one year are similar for both treatments. Relative merits
of PTCA vs CABG difficult to assess. Population, changing techniques,
restenosis. In patients with diabetes mellitus (Type I and II) on oral
hypoglycemic agents or insulin, CABG has a markedly lower five-year death rate
than angioplasty (19% vs 35%).
Higher death rate
not due to complications of procedure itself. In patients without diabetes and
those with diabetes but not on drug treatment, 5-year mortality rate both at
9%. (It would seem that drug treatment raises death rate from 9% to 19 - 35%.)
PTCA still faces several obstacles - despite its success in the intervention of
coronary artery disease. The most daunting is restenosis. Development of wide
variety of new devices for the improvement of percutaneous coronary
intervention. Includes atherectomy catheters, stents, laser devices. Most are
used as adjuncts with balloon angioplasty before (predilate), during (as part
of procedure) or afterward (to improve luminal diameter and reverse or prevent
complications from PTCA). Formidable challenges to coronary interventional
procedures - old (impassable) occlusion, abrupt vessel closure from dissection
and restenosis. Prevention will require intravascular devices to open
obstructed arteries to fullest extent and techniques to inhibit hyperplastic
(overgrowth) response. Combined use of pharmacotherapy (antiplatelet and
antithrombotic agents) with coronary angioplasty devices needed.
Coronary
Artery Bypass Graft
Aortocoronary
bypass surgery means that one or more bypass grafts are implanted between aorta
and coronary blood vessel. If occlusive vascular disease limits blood flow to
heart, bypass graft bridges occluded or diseased heart blood vessel (coronary
artery) and brings new blood to the heart. Two types of blood vessel commonly
used for bypass graft (CABG) - saphenous veins in legs or left or right
internal mammary artery (aka thoracic arteries) of chest wall. Both can be used as
there are other pathways that circulate blood to and from the tissues of chest
and legs. Type of graft depends on the location and amount of blockage in the
coronary arteries.
Saphenous vein
surgically removed and graft sewn from aorta (large artery leaving heart) to
coronary artery below blockage. Oxygen-rich blood flows from aorta through
saphenous vein graft past site of blockage to coronary artery to nourish heart
muscle. Mammary artery kept in tact at its origin and sewn to coronary artery
beyond blockage site. As it is an artery it does not have to be sewn to the
aorta. Arteries have their own oxygen-rich blood supply to offer the heart
muscle. After thoracotomy (opening chest) the left IMA (internal mammary
artery) is harvested. Simultaneously a segment of the saphenous vein is
prepared for the aortocoronary bypass operation. After induction of
extra-corporeal circulation the aorta is X-clamped, the coronary arteries are
exposed, opened and the IMA is anastomosed (sutured) into the coronary artery.
The IMA bypass to the coronary artery now supplies arterial blood to the heart
muscle - bypassing the occluded coronary artery. Re-operations (previously
undergone CABG already) constitute about 11% of all bypass procedures.