Special Dissection Procedures

Dissection of Hearts with Developmental Malformations

The malformed heart presents challenges that often require a customized approach to dissection. A solid knowledge of normal cardiac anatomy is essential. Even then, if the prosector encounters a puzzling abnormality, he or she should limit dissection of portions of the organ block and seek additional input. This may entail consulting the local pediatric cardiologist or sending the fixed, nondissected specimen to a cardiac pathologist.

The first step in the evaluation of the malformed heart at autopsy is to understand the clinical diagnosis. In this age of echocardiography and other sophisticated noninvasive methods, as well as cardiac catheterization and angiography, the anatomy has often been defined accurately during life. However, there are some instances in which the anatomy cannot be defined from the echocardiogram with certainty. This is particularly true for fetal echocardiograms, for which the fetus may not be positioned to present the anatomy to best advantage. With improvements in imaging, the key clinical questions at autopsy increasingly are not about the congenital anomaly itself, but rather about the acquired defects in the anomalous organs. It is essential to have an informed concept of the expected cardiac anatomy, including surgical intervention, before dissection. This can be augmented by any of a number of standard textbooks of pediatric cardiology, all of which include sections describing cardiac anatomy and pathophysiology associated with the malformations.

Regardless of prior clinical documentation of malformations, each case should be approached in a consistent manner. The possibility of unexpected malformations is a chief reason why the pediatric autopsy must be detailed and systematic (see Chapter 5 ). As in routine autopsies, the heart and lungs are inspected in situ, and the relative size of the heart within the thorax is assessed. Similarly, in every pediatric autopsy, it is important to dissect the great arteries and their major branches before evisceration; the prosector should document the relation of the great vessels and any anomalous course of branch vessels so that accommodations in the dissection may be made if necessary. In addition, the position of the descending thoracic aorta relative to the spine, course of the pulmonary veins, and location of the anterior and posterior descending coronary arteries should be noted. The position of the abdominal organs and presence of polysplenia or asplenia may be the first indication of a heart malformation; in general, these complex heterotaxy syndromes warrant prudent, meticulous dissection and probably consultation with a specialist.

When the anatomy has been defined in situ, the organs are removed en bloc. From the posterior aspect, the course of the inferior vena cava should be noted. If the pulmonary veins course in the usual fashion—that is, do not connect with a vessel below the diaphragm—the thoracic organs can be separated from the rest of the block. In a case of suspected cardiovascular malformation (including subdiaphragmatic connection of the pulmonary veins), these organs remain together. In our institutions, we usually perfuse and fix the nondissected heart overnight through a cannula placed in the orifice of one of the venae cavae; it is not absolutely necessary to occlude the aorta or its major branches during perfusion. Although this enhances the final appearance of the specimen, the risk of artifactual injury may not be worth the improvement compared with simple immersion of the specimen in fixative. Following fixation, the heart is generally opened along the lines of blood flow (as shown by the solid arrows in Fig. 4-17 ), taking care to probe valve orifices before cutting. Hearts with malformations often contain shunts, and the prosector must use caution in opening the heart.

Although it is beyond the scope of this chapter to describe the approaches to dissection of the various cardiac malformations, suffice it to say that advance knowledge of the expected anatomy, as well as a common-sense approach, is adequate for all but the most complex lesions. One should never cut through a defect (or the septum). Anatomic relationships should be maintained to the best extent possible. In pediatric pathology, too little dissection is often preferable to too much. Besides the lines-of-blood-flow method of dissection, there is the “windows method,” in which the chambers are opened by incisions that are not carried through the valves. The windows method is superior to the standard method for keeping the specimen in proper anatomic appearance but not as good for inspecting the cardiac valves. For certain defects, it may be advisable to use an adaptation of both methods. Finally, it is important to show the autopsy specimen to the treatment group; the clinicians are usually best positioned to place the anatomic findings in proper perspective.

Dissection of Hearts with Medical Devices

The prevalence of medical devices within hearts at autopsy is increasing, and many of them can be critical components of the postmortem analysis. The medical record often indicates that devices have been placed, but their positions within the heart are not entirely predictable. A simple radiograph of the isolated heart ( Fig. 6-1 ) is helpful in planning the dissection. Epicardial pacemaker wires, seen as wispy wires in the apical portion of Figure 6-1 , can be pulled straight off before cutting. Endocardial/luminal pacemaker wires are discussed below. Coronary artery bypass grafts can be traced from the proximal anastomoses; examination of them is explained in greater detail in Chapter 8 . Clips and other devices used to exclude blood from the left atrial appendage can be left in place with the usual dissection methods for the heart.

Coronary Artery Stents

Coronary artery stents require careful handling during autopsy. Knowing their location by medical record or autopsy radiograph allows those segments of the epicardial arteries to be isolated carefully and removed from the heart, remembering that they are easily bent or compressed with handling. The segments should be decalcified as needed, and the lumen should be examined by looking in each end. Cross sections should be made until only a small portion of adjoining artery extends beyond the stent. These portions adjoining the stent often are sites of intimal proliferation and should be assessed for restenosis. For an extremely detailed analysis of in-stent stenosis or thrombosis, the stented segments can be sent to specialty laboratories for plastic-embedding and specialized microtomy. We find it practical in most cases to open the stented segment in layers as demonstrated in Figure 6-2 , because this leads to the least disruption of the luminal contents. This allows microscopic examination of any luminal coagulum for signs of being an antemortem thrombus, which is often indicated by its platelet-rich nature, confirmed by anti-CD61 immunohistochemistry (see Fig. 9-12 ).

Ventricular Assist Devices

Ventricular assist devices are likewise becoming more prevalent in developed countries. They most commonly support the left ventricle, but right ventricular and biventricular devices exist. They come in an assortment of sizes and shapes, growing smaller with each redesign, and now almost always are fully implanted in the chest, with percutaneous wires extending to external control units. The earlier models usually take blood into the device from a hole in the apex of the left ventricle and route output to the aorta. More devices are being introduced, however, that are contained within the cavity of the left ventricle extending transluminally to the ascending aorta. Ventricular assist device designs are evolving rapidly, and before the autopsy the prosector should review the design of the device if it is identified in the medical record. Figure 6-3 shows a typical device, as of year 2015, in which it is helpful to assess the luminal contents of the inlet, outlet, and device lumen for infection or thrombus. The solid tissue at the anastomoses should also be examined. As with any medical device, the pathologist should determine whether the device is subject to tracking by the U.S. Food and Drug Administration (FDA) and notify the appropriate health care provider and/or manufacturer. Information regarding tracking of medical devices is available at the FDA website.

Valve Implants

Valve implants (traditional prosthetic replacements, annuloplasty rings, and transcatheter prostheses) usually require modification of the dissection of the heart. In most cases, it is unnecessary to sever the device or remove it. The objective is to gain an adequate view by making cuts up to but excluding the manufactured material. The type of valve implant, its position, and its diameter should be recorded; there are several good references that can be useful for identification of the valve type. Again, the valve disorder and cardiac anatomy must be considered in the appropriate pathophysiologic context.

Prosthetic valves should be examined for paravalvular channels as evident from probe-patent channels or frank dehiscence. Any other pathologic changes—such as fractures, thrombus, infective material, overgrowth of endocardial pannus, or degenerative changes in the leaflets—should also be described and sampled for histologic examination. The mobility of the leaflets must be ascertained. To examine for perivalvular “ring” abscess, the valve should be photographed in situ and then perimeter sutures may be cut and the valve removed. Figure 6-4 shows examination of a transcatheter valve, which is becoming increasingly common.

Electronic Medical Devices, Including Pacemakers and Defibrillators

Electronic medical devices have become a regular part of modern therapeutics, and the autopsy pathologist should expect to encounter them at autopsy with increasing regularity. These include older instruments such as implantable cardiac pacemakers but also newer implanted devices such as defibrillators; Holter monitors; cerebellar stimulators; spinal cord, peripheral nerve, and diaphragmatic/phrenic nerve stimulators; drug infusion pumps; insulin pumps; and glucose monitors. Little has been written on how the pathologist should handle these devices at autopsy, although the excellent article by Weitzman stands out. Table 6-1 describes some of the more common electronic medical devices, and Box 6-1 summarizes Weitzman's recommendations for their examination. Again, information regarding tracking of medical devices is available at the FDA website.

In most cases, the presence of an implantable device in a decedent will not significantly alter the autopsy procedure. Defibrillators, however, present a potential risk to autopsy personnel and should be turned off by the cardiologist or cardiology technician before autopsy. (Safety recommendations are presented in Chapter 3 .) Virtually all hearts in patients with defibrillators or pacing wires will have a significant pathologic lesion, and the method of dissection must be the one best suited for the underlying disease process. For the lines-of-blood-flow method, luminal wires can be left in place; the short-axis method requires removal of wires before slicing the ventricles. The distal ends of the wires are usually embedded into the myocardium with 1 to 2 turns of a right-hand “corkscrew” tip, which can be removed with a few turns. If the wires need to be cut, make sure the device is deactivated. The course of the wire within the heart and the position of its point of contact with the cardiac muscle should be described; wires that have been in place for months are tethered by reactive fibrosis at the points of contact. The generator and the full length of the wire should be inspected for evidence of infection, thrombus, insulation cracks, or other abnormality. In cases of sudden unexplained death, the generator should be sent to the manufacturer for evaluation.