The document provides an overview of cardiac surgery and the anatomy of the heart. It describes the shape and borders of the heart as well as the chambers and valves. It then discusses the coronary arteries and dominance. It provides details on cardiopulmonary bypass, including the circuit and components. It lists alternative uses of CPB. It also summarizes the main methods of myocardial protection during surgery, including cardioplegic arrest and intermittent clamping. Finally, it outlines some common incisions used for cardiac surgery like median sternotomy and thoracotomies.

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Cardiac Surgery
Surgical Anatomy of the Heart
Shape of the heart is that of a three-sided pyramid located in the middle
mediastinum, enclosed by the serous and fibrous pericardium. The right border
consists of the right atrium, the inferior border is made up mostly by the right
ventricle, with a small portion of the left ventricle which forms the apex. The
left border formed mostly by the left ventricle & partially by left atrium, The
anterior (sternocostal) border is made mainly by the right ventricle, the
diaphragmatic surface is 1/3 by RV & in 2/3 by LV and the posterior the (base)
of the heart is mainly by the left atrium.
Cardiac chambers and valves:
The right atrium is an elongated chamber lies between the opening of the
superior and inferior venae cavae while the left atrium lies behind it. It drains
the venous return form heart itself through the coronary sinus. Its main
communication with the RV is through the tricuspid valve. The left atrium
receives pulmonary venous drainage via pulmonary veins which drain into the
posterior portion of the left atrium. The bicuspid mitral valve(anterior &
posterior cusps) guards the left side atrioventricular connection.
The right ventricle is located anteriorly. The inflow is via the tricuspid valve.
Flow enters the right ventricle into a large sinus portion and a smaller
infundibulum or outlet portion just proximal to the pulmonary valve. A septum
lies between the inflow and outflow portions of the right ventricle and thus lies
adjacent to the pulmonary valve (3 cusps: left ant, right ant & posterior) which
forms the outlet. The LV is characterised by its muscular wall which is three
times thicker than that of the RV. The aortic valve is composed of three
smilunar cusps (non-coronary, left coronary & right coronary), forming the
outlet of the LV.
Blood supply of the heart: These consist of a left main coronary artery (LMS ~
1.5 cm ) which bifurcates to the circumflex coronary (CX) artery and left
anterior descending coronary artery (LAD). The orifice of the left main coronary
artery lies in the left coronary sinus. The orifice of the right coronary (RCA)
artery arises from the right coronary sinus. The right coronary artery has a first
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branch called an acute marginal artery which supplies the free ventricular
surface and may also give off a conal branch which supplies the infundibulum of
the right ventricle. The right coronary artery continues to bifurcate into a
posterior descending artery (PDA) as well as a
continuing posterior ventricular branch, also
called a posterolateral branch or LV extension
branch. The dominance of the coronary arteries is
determined by which side, i.e. right or left,
supplies the posterior descending artery. In 90%
of people, the posterior descending artery is a
continuation of the right coronary artery; in 10%
it is a continuation of the circumflex coronary
artery or the left anterior descending coronary artery.
Basic Principles of Cardiopulmonary Bypass (CPB) & Myocardial
protection:
Cardiopulmonary bypass is a process by which systemic venous blood is taken
from the patient, transferred to a pump oxygenator and delivered back to the
arterial circulation of the patient. Cardiac
surgery is unique in that an
extracorporeal circulation system is
required for open cardiac. The bypass
circuit consists of a single venous
cannula in two stages or two different
venous canulas according to the type of
surgery, the venous line drains down to a
reservoir the. The reservoir’s blood then
enters a hollow fiber membrane pump
oxygenator (Fig) with a temperature regulating device in the proximal portion of
the system and the oxygenator just distal to this. Once the blood passes through
the membrane where the CO2/O2 exchange takes place, the blood travels
through a 40 micron filter and then back into the arterial circuit of the patient
and then to the ascending aorta via the arterial canula. The filter serves to
remove particulate and gaseous emboli. The arterial circuit has a purge line
which can remove gross air. Cooling in cardiopulmonary bypass is done at
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approximately 1°C per minute. The advantages of cooling are that it decreases
the metabolic requirement of the body organs, in particular, the brain and the
heart. However, disadvantages are that it may increase bleeding after coming off
bypass because of stunning of the coagulation enzyme systems, and it may
induce myocardial edema by impairment of enzyme system
Alternative uses of CPB machine:
1. Rewarming from profound hypothermia,
2. Resuscitation in severe respiratory failure,
3. As an adjunct in pulmonary embolectomy,
4. In single and double lung transplantation
5. In cardiopulmonary trauma
6. Resection of highly vascular tumours
7. Tumours invading large blood vessels (e.g. renal or hepatic tumours
extending into inferior vena cava, right atrium or even pulmonary arteries
Methods of Myocardial protection:
Principle: To obtain a bloodless operative field, the ascending aorta is usually
cross-clamped once CPB has been established and blood is diverted away from
the heart. The heart ceases to eject and, as a result of inhibition of coronary
blood flow, becomes anoxic. Permanent myocardial damage will develop within
30-45 min. Therefore, most cardiac operations require some form of myocardial
protection.
1. Cardioplegic arrest
Most methods now involve combinations of topical cooling by ice appilcation
and intracoronary infusions of cardioplegic solutions. Most solutions contain
potassium as the arresting agent. Potassium arrests the heart in diastole by
depolarisation of the membrane. Cold (4-10 ° C) isotonic crystalloid or chilled
blood solutions aid myocardial protection by reducing metabolic requirements
through local hypothermia.
2. Intermittent cross-clamp fibrillation
Ventricular fibrillation is induced by a small electrical charge. The heart does
not eject and is relatively still, but not bloodless. To perform an operative
procedure such as coronary artery bypass grafts, the aorta is cross-clamped to
render the heart ischaemic. The heart can tolerate short periods (10-20 minutes)
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of intermittent ischaemia, providing the heart is reperfused and allowed to beat
in between.
3. Total circulatory arrest
The metabolic rate of all organs of the body is reduced by 50% with every 7°C
drop in temperature. So, with the pump switched off at 18°C, circulatory arrest
can be tolerated for 20-30 minutes.
Common incisions used to approach the Heart
1)Median Sternotomy
The most common approach for operations on the heart and aortic arch is the
median sternotomy. The skin incision is made from 1-2 cm below jugular notch
to just below the xiphoid process.
2) Bilateral Transverse Thoracosternotomy (Clamshell Incision)
The bilateral transverse thoracosternotomy (clamshell incision) is an alternative
incision for exposure of the pleural spaces and heart.
3) Anterolateral Thoracotomy
The right side of the heart can be exposed through a right anterolateral
thoracotomy. The patient is positioned supine, with the right chest elevated to
approximately 30 degrees by a roll beneath the shoulder.
4)Posterolateral Thoracotom
A left posterolateral thoracotomy is used for procedures involving the distal
aortic arch and descending thoracic aorta. With left thoracotomy, cannulation for
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