Atherosclerosis: Practical Implications for Pathologists
Section 5 -
Coronary Artery Bypass Grafts
This 47-year-old male had a myocardial infarction at age 39 years.
Investigations showed that this heavy smoker had hyperlipidemia, hypertension and diabetes mellitus. He
was not a lightweight. At age 41 years, he once again developed chest pain and was investigated. He had
three vessel CAD and underwent CABG with three vein grafts (RCA, intermediate and OM1) and a left
internal thoracic artery graft to the LAD. He had recurrent episodes of congestive heart failure
necessitating hospitalization. He underwent orthotopic heart transplantation. His explanted heart was
available for review.
Coronary Artery Bypass Grafts:
With over a half a million coronary artery bypass graft operations performed in North America
alone,for myocardial revascularization, coronary artery bypass grafts remain the most frequently
performed surgical procedure, worldwide. They also therefore account for the largest amount of resources
used in cardiovascular medicine, certainly more than other single procedure. The average cost of such a
procedure, was $45,000, about ten years ago. Today, it must be much more. The operative mortality
associated with coronary artery bypass surgery in all comers is about 2%. First time elective surgery in
patients with a grade II or III ventricle is, in many centers, is less than 1.6%. Outcomes are somewhat
worse for emergent procedures and the consistent predictors of mortality after coronary artery bypass
surgery are emergent or urgent surgery, patient's age, previous cardiac surgery, female sex, a poor left
ventricular rejection fraction, degree of stenosis and the number of foci of such stenosis of the left
main coronary artery and the number of arteries stenosed. The history of angina pectoris, ventricular
arrhythmias, congestive heart failure, mitral valvular incompetence, obstructive lung disease, diabetes
mellitus, renal dysfunction are all other comorbid factors which worsen the morbidity and mortality.
Metanalysis of randomized trials of coronary artery bypass graft vs. medical therapy show that the
CABG group does have a lower mortality and morbidity than the medically treated group at five and ten
years with a 39 and 17% risk reduction respectively. 
A quick look at coronary artery surgery lists shows that more than 10% of cases and in some
institutions 15 - 20% of cases are redo coronary artery bypass graft procedures( these numbers appear to
be changing -downward , at least at our center. Perhaps more of the patients are getting stents in their
bypass grafts and in the native vessels.. The indications for re operation include worsening of native
coronary artery disease, inadequate revascularization and graft failure (early as well as late). The
mortality for redo surgery is higher, at 2 - 10%.
Over 1 million coronary artery bypass grafts are performed worldwide annually. Of these, over half
are performed in the United States, significant numbers in the other Western countries and increasing numbers in the developing countries. A heavy
price to pay for playing catch-up with regard to industrial development! The principle surgical
approach to the therapy of ischemic heart disease / coronary artery disease has been direct
revascularization. Studies show improved survival amongst cohorts of surgically treated patients when
compared to those treated medically or those treated with percutaneous, transluminal interventions. It
is important to remember that in the recent past (close to three decades now), improvements in surgical
technique, equipment and coronary perfusion have improved survival, decreased morbidity, decreased
mortality from coronary artery bypass graft surgery (performed the first or second time. Significantly
improved anesthesia and post-operative care, has reduced the length of time patients spend in hospital
With the more recent improvement and increased availability of less invasive techniques for coronary
artery bypass graft surgery, surgeons are able to provide direct revascularization or bypass grafts to
patients whose medical conditions would in the past, have prohibited the standard open approach to
Prior to the development of coronary artery bypass graft surgery (CABG), several innovative techniques
were used to "improve" blood flow to the ischemic myocardium. Some were probably partly successful but
most were not and all have since been abandoned at least in their original forms.
Vineberg procedure is by far the precursor of today's direct revascularization and it entailed the
implantation of the internal thoracic artery into a tunnel in the myocardium on the anterior surface of
the left ventricle .
Coronary artery arteriography or cinecoronary arteriography by Sones and Shirey of the Cleveland
Clinic in the late 1950's provided the foundation for coronary artery bypass graft surgery (CABG).
Angiography permitted the accurate placement of CAB grafts. In these initial studies, the mortality rate
was 12%, with massive improvement over previously mortality rates, of nearly 50%.
The next advancement was the introduction of direct anastomoses of the left internal thoracic artery
(LITA) to the
LAD . The long-term efficicacy of cardiac revascularization is established by
three randomized studies. The European study of 768 randomized men, followed up to eight years, showed
that survival was significantly improved in patients with significant three-vessel disease and in
patients with significant stenosis of the proximal LAD Ca. As compared with medically treated patients,
late mortality was reduced by 53% after five years and amongst those patients with three-vessel disease,
the five-year mortality was lower by 66%. The patients with significant disease of the proximal LADCa,
five-year mortality were diminished by 50%, by surgery.
The Veteran's Administration long-term CABG survival study in 686 patients having stable angina
followed for an average of 11.2 years. The seven-year survival showed a statistically significant
survival benefit of 77% with surgical therapy compared with 70% survival with medical treatment. This
benefit diminished by eleven years of observation but a survival advantage persisted eleven years in
surgical patients with three-vessel disease and impaired left ventricular function and in those with high
clinical risk defined by pre-operative ST segment depression. The coronary artery surgery study (CASS)
showed survival data on 780 patients with stable angina and ejection factions greater than 35%, assigned
to receive medical or surgical therapy. At eight years follow-up, 87% of the surgically treated patients
were alive as compared with 84% of those receiving medical therapy. While this was not statistically
significant, the trend favored surgical therapy. The benefits of direct revascularization surgery - CABG
- decreased progressively with time. This is due primarily to the development of disease in the
saphenous vein graft, resulting in gradual stenosis and ultimately occlusion of the vein grafts.
The left internal thoracic artery (LITA) grafts appear to be "resistant" to atherosclerosis and the
improved late patency of these bypass grafts improves the patient's survival. Today, many other vessels
such as the right internal thoracic artery (RITA), radial artery and the gastroepiploic artery are
available or are being used for vascular bypass grafts to coronary arteries.
Minimally Invasive Approaches :
In recent years, coronary artery bypass procedures have been performed using alternate incisions with
and without cardiopulmonary bypass. In all cases, cardiopulmonary bypass is available as an option,
should the need arise. Minimally invasive techniques are used to reduce morbidity of surgery and permit
early hospital discharge, as well as to avoid the difficulties associated with a sternotomy and the
cosmetic difficulty of a long mid chest incision! Today, minimally invasive direct coronary artery
bypass graft procedures are proposed as alternatives to percutaneous transluminal coronary angioplasty
(PTCA) for single vessel disease of left anterior descending coronary artery. The heart is exposed
through a 10.0 cm transverse parasternal incision and a bypass is created from the LITA to the LAD
directly or with an interposed segment of inferior epigastric artery or radial artery. A variety of
techniques are used to help make the anastomosis with the beating heart.
OPCAB Surgery - Off Pump Coronary Artery Bypass :
This procedure is performed using a standard median (middle) sternotomy and access to coronary artery
is achieved by accurate placement of pericardial stay sutures to rotate and lift the heart. A relatively
bloodless field is obtained and pedicle arterial grafts used for bypass. This procedure is believed to
reduce the incidence of stroke and other organ injury caused by embolization of atherosclerotic debris.
These pedicle arterial grafts, allow a no-touch technique with regard to the aorta.
The availability of sutureless connectors for the proximal anastomosis was supposed to allow for allow
for easier aorto-saphenous vein graft proximal anastomosis. These are not particularly effective and
their use has not gained significant momentum.
There are many reports about long-term data regarding coronary artery bypass grafts. Rahimtoola et al
reporting on procedures performed between 1974 and 1988 (n=7026) reported a 2.1% operative mortality and
a 10 and 15-year survival probability of 74 +/- 1 and 55 +/- 2%
respectively . Sarjeant et
al reported a series of 9600 patients followed for up to 20 years. Freedom for re -intervention at one,
ten and fifteen years were 99, 89 and 72% respectively. They concluded that patients were "relatively
free of the need for intervention for the first decade after coronary artery bypass surgery".
Approximately 50% of patients surviving more than ten years required reintervention . From
most studies, the patency rate for saphenous vein bypass grafts ranges from 40 to 50% at ten years. The
patency rates of various free or pedicled arterial conduits is lessestablished.
3. Complications:The important perioperative
complications are stroke, wound infection, myocardial infarction and graft thrombosis. Stroke includes
permanent stroke and transient ischemic attacks, as well as delirium. Permanent neurologic deficits
ranges from 0.8 to 5.2% and the mortality associated with this may be as high as 38%. Surgery for
coronary artery disease has "come of age" over the past 25 years. Direct revascularization means
predictable relief of angina and improved quality of life, in 80 to 90% of patients. Patient survival is
improved. The use of multiple arterial grafts in revascularization, should improve patient outcomes even
further both, regarding graft survival and quality of survival.
With the use of different types of bypass grafts on the same hearts , it is interesting to see and
note the type and degree of change in the bypass graft in the same individual and ofcourse the same
Case 4 a: This 45 year old came to heart transplantation , 3 years after
having undergone CABG (X3) with a LITA to the LAD, a free radial graft to the OM and an SVG to the RCA.
The findings will be discussed briefly.
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