surgery.Cardiac surgery 1.(dr.aram)


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surgery.Cardiac surgery 1.(dr.aram)

  1. 1. CARDIAC SURGERY 2012 Cardiac SurgerySurgical Anatomy of the HeartShape of the heart is that of a three-sided pyramid located in the middlemediastinum, enclosed by the serous and fibrous pericardium. The right borderconsists of the right atrium, the inferior border is made up mostly by the rightventricle, with a small portion of the left ventricle which forms the apex. Theleft border formed mostly by the left ventricle & partially by left atrium, Theanterior (sternocostal) border is made mainly by the right ventricle, thediaphragmatic 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 thesuperior and inferior venae cavae while the left atrium lies behind it. It drainsthe venous return form heart itself through the coronary sinus. Its maincommunication with the RV is through the tricuspid valve. The left atriumreceives pulmonary venous drainage via pulmonary veins which drain into theposterior 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 smallerinfundibulum or outlet portion just proximal to the pulmonary valve. A septumlies between the inflow and outflow portions of the right ventricle and thus liesadjacent to the pulmonary valve (3 cusps: left ant, right ant & posterior) whichforms the outlet. The LV is characterised by its muscular wall which is threetimes thicker than that of the RV. The aortic valve is composed of threesmilunar cusps (non-coronary, left coronary & right coronary), forming theoutlet 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 leftanterior descending coronary artery (LAD). The orifice of the left main coronaryartery 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 1
  2. 2. CARDIAC SURGERY 2012branch called an acute marginal artery which supplies the free ventricularsurface and may also give off a conal branch which supplies the infundibulum ofthe right ventricle. The right coronary artery continues to bifurcate into aposterior descending artery (PDA) as well as acontinuing posterior ventricular branch, alsocalled a posterolateral branch or LV extensionbranch. The dominance of the coronary arteries isdetermined by which side, i.e. right or left,supplies the posterior descending artery. In 90%of people, the posterior descending artery is acontinuation of the right coronary artery; in 10%it is a continuation of the circumflex coronaryartery or the left anterior descending coronary artery.Basic Principles of Cardiopulmonary Bypass (CPB) & Myocardialprotection:Cardiopulmonary bypass is a process by which systemic venous blood is takenfrom the patient, transferred to a pump oxygenator and delivered back to thearterial circulation of the patient. Cardiacsurgery is unique in that anextracorporeal circulation system isrequired for open cardiac. The bypasscircuit consists of a single venouscannula in two stages or two differentvenous canulas according to the type ofsurgery, the venous line drains down to areservoir the. The reservoir’s blood thenenters a hollow fiber membrane pumpoxygenator (Fig) with a temperature regulating device in the proximal portion ofthe system and the oxygenator just distal to this. Once the blood passes throughthe membrane where the CO2/O2 exchange takes place, the blood travelsthrough a 40 micron filter and then back into the arterial circuit of the patientand then to the ascending aorta via the arterial canula. The filter serves toremove particulate and gaseous emboli. The arterial circuit has a purge linewhich can remove gross air. Cooling in cardiopulmonary bypass is done at 2
  3. 3. CARDIAC SURGERY 2012approximately 1°C per minute. The advantages of cooling are that it decreasesthe metabolic requirement of the body organs, in particular, the brain and theheart. However, disadvantages are that it may increase bleeding after coming offbypass because of stunning of the coagulation enzyme systems, and it mayinduce myocardial edema by impairment of enzyme systemAlternative 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 arteriesMethods of Myocardial protection:Principle: To obtain a bloodless operative field, the ascending aorta is usuallycross-clamped once CPB has been established and blood is diverted away fromthe heart. The heart ceases to eject and, as a result of inhibition of coronaryblood flow, becomes anoxic. Permanent myocardial damage will develop within30-45 min. Therefore, most cardiac operations require some form of myocardialprotection.1. Cardioplegic arrestMost methods now involve combinations of topical cooling by ice appilcationand intracoronary infusions of cardioplegic solutions. Most solutions containpotassium as the arresting agent. Potassium arrests the heart in diastole bydepolarisation of the membrane. Cold (4-10 ° C) isotonic crystalloid or chilledblood solutions aid myocardial protection by reducing metabolic requirementsthrough local hypothermia.2. Intermittent cross-clamp fibrillationVentricular fibrillation is induced by a small electrical charge. The heart doesnot eject and is relatively still, but not bloodless. To perform an operativeprocedure such as coronary artery bypass grafts, the aorta is cross-clamped torender the heart ischaemic. The heart can tolerate short periods (10-20 minutes) 3
  4. 4. CARDIAC SURGERY 2012of intermittent ischaemia, providing the heart is reperfused and allowed to beatin between.3. Total circulatory arrestThe metabolic rate of all organs of the body is reduced by 50% with every 7°Cdrop in temperature. So, with the pump switched off at 18°C, circulatory arrestcan be tolerated for 20-30 minutes.Common incisions used to approach the Heart1)Median SternotomyThe most common approach for operations on the heart and aortic arch is themedian sternotomy. The skin incision is made from 1-2 cm below jugular notchto just below the xiphoid process.2) Bilateral Transverse Thoracosternotomy (Clamshell Incision)The bilateral transverse thoracosternotomy (clamshell incision) is an alternativeincision for exposure of the pleural spaces and heart.3) Anterolateral ThoracotomyThe right side of the heart can be exposed through a right anterolateralthoracotomy. The patient is positioned supine, with the right chest elevated toapproximately 30 degrees by a roll beneath the shoulder.4)Posterolateral ThoracotomA left posterolateral thoracotomy is used for procedures involving the distalaortic arch and descending thoracic aorta. With left thoracotomy, cannulation for 4