Dissection of heart can be done by many ways but for routine medicolegal examinations following two methods are commonly used: 1. Inflow-outflow method 2. Ventricular slicing method.
1.Inflow-outflow method-In this method the direction of blood flow is followed. Openings of superior and inferior vena cava are cut and joined to enter into right atrium after which the auricular appendage is opened by one small incision. Right ventricle is opened by cutting along the lateral margin of right ventricle through the tricuspid opening.
After that each slice examined from apex to base. Then the basal portion is opened according to inflow outflow method.
The portion between the openings of the pulmonary veins is cut, left atrium is incised along the lateral wall. The incision is further extended to the mitral valve. Through the mitral opening the lateral wall of the left ventricle is cut to enter into left ventricle. From apex another incision is given along the interventricular septum to expose aortic valves. A series of transverse incisions along the course of Left Coronary Artery, Right Coronary Artery and Circumflex Artery are made to examine the coronary arteries. 2. Ventricular slicing method – This method is also called Short Axis Method. For the evaluation of CAD or other cardiac pathology this method is preferred because in this method greater area of myocardium is exposed for examination. First of all, the flat diaphragmatic surface of the heart is placed on a paper towel to avoid slippage during incision process. Then incisions parallel to the AV groove is given at 1 to 1.5 cm intervals with the help of sharp cutting knife by bold one or two slices with precautions avoiding sawing movements which may produce hesitation marks. Slices obtained in this dissection corresponds to short axis plane produced in 2D Echocardiography.
3. Others Methods :
a]. Base of heart method-To display all heart valve intact at the cardiac base, this method is employed. Best method for demonstrating the relationship between valves themselves as well as with adjacent coronary arteries and AV conductive system. b]. Long axis method-Three points are marked to demarcate the long axis plane initially. First on the cardiac apex, second on the right aortic sinus near coronary ostium and third near the mitral valve annulus between right and left pulmonary veins. The heart is cut along the demarcated long axis plane from apex to base passing through mitral and aortic valves. c]. Four chamber method-Heart is divided into two parts and each part shows all the four chambers. A long knife is used, and incision made through the apex and extending to acute margin of right ventricle and obtuse margin of left ventricle and the interventricular septum after that the upper half of the heart is opened according to inflow-outflow method. d]. Window method-Heart is fixed by perfusion and windows of various sizes removed from the chambers and great vessels of the heart with scalpel and such window blocks are used for histological examination. This method is beneficial for the dry museum specimen preparation using paraffin, plastination or other materials. e]. Unrolling method-Used to demonstrate opacified coronary artery in single plane. The ventricular free walls and the ventricular septum is unrolled after doing postmortem coronary angiography. Unrolling involves considerable mutilation of the heart and may be useful for research purposes. Unrolling techniques used are following. Lumb and Hardey technique, Schlesinger technique and Reiner Technique. Among them the Reiner technique is the simplest. f]. Partitioning method-Used for the detailed assessment of ventricular hypertrophy. Each ventricle is weighed separately after removal of epicardial fat and coronary vessels and separating the specimen from ventricular septum. Biventricular atrophy would show abnormal ratio. The normal ratio is LV + S: RV is 2.3 to 3.1: 1. In left ventricular hypertrophy the ratio is greater than 3.6 :1 and the weight of LV + S is more than 225 gm Whereas in Right ventricular hypertrophy the ratio is less than 2:1 and weight is more than 80 gm. g]. Examination of conduction system-Basically a histological process, three tissues SA node, AV node and AV bundles are prepared. This technique is used when pathology in conducting system is suspected.