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Biomedical subjects

C K Rokkas

Publications and source records attributed to C K Rokkas.

22 records · Page 2Linked to original sources
PubMed1993

Profound systemic hypothermia protects the spinal cord in a primate model of spinal cord ischemia.

Spinal cord ischemia with resultant paraplegia or paraparesis remains an important clinical problem after operations on the thoracoabdominal aorta. Because hypothermia has a protective effect on ischemic neural tissue, we developed a baboon model of spinal cord ischemia to simulate the situation encountered clinically for resection of aneurysms of the thoracoabdominal aorta and to determine whether profound hypothermia produced by hypothermic cardiopulmonary bypass has a protective effect on spinal cord function. After cardiopulmonary bypass was established, the aorta was clamped distal to the left subclavian artery and proximal to the renal arteries for 60 minutes. Group I animals (n = 9) underwent aortic clamping at normothermia (37 degrees C), and group II animals (n = 9) were cooled to a rectal temperature of 15 degrees C before aortic clamping and underwent cardiopulmonary bypass at this temperature until the aorta was unclamped. Of the eight operative survivors in group I, six animals were paraplegic and two were paraparetic, whereas all six group II animals that survived the procedure were neurologically intact (p = 0.0002). The protective effect of hypothermia was associated with blunting of the hyperemic response of spinal cord blood flow (determined by the radioactive microsphere technique) in the lower thoracic and the lumbar segments of the spinal cord after unclamping of the aorta. Profound hypothermia produced by hypothermic cardiopulmonary bypass may be an effective method of protection of the spinal cord in patients undergoing repair of aneurysms of the thoracoabdominal aorta and may reduce the prevalence of ischemic injury to the spinal cord.

Animals↗
PubMed1989

Pericardiocentesis guided by a pulse generator.

This study was performed to compare pericardiocentesis guided by a pacing current applied through the pericardiocentesis needle with the traditional method of monitoring ST segment elevation from the needle tip electrogram. ST segment elevation was measured at 3 mm from the epicardium, after epicardial contact, after epicardial penetration and again at 3 mm from the epicardium after epicardial penetration. Two millivolts of ST segment elevation gave the highest combined positive (86%) and negative (79%) predictive value for epicardial contact by the pericardiocentesis needle between the two groups with the largest difference: 3 mm from the epicardium before contact and after epicardial penetration. Therefore, ST segment monitoring cannot reliably determine the point of epicardial contact. To determine the optimal stimulus strength for pulse generator-guided pericardiocentesis, pacing studies were performed using 2, 4, 6, 8 and 10 mA unipolar stimulus strengths. The pacing studies were performed both with and without a hemodynamically significant pericardial effusion to determine if increased pericardial pressure altered the pacing threshold. A 4 mA unipolar cathodal stimulus was chosen because it captured the ventricle only with direct contact of the epicardium. Ten dogs were instrumented and cardiac tamponade produced so that a subxiphoid approach to the epicardium with the pacing needle electrode could be attempted. During pericardiocentesis, needle tip electrograms were recorded, alternating with pacing attempts using a 4 mA unipolar stimulus. In all 10 dogs, the effusion was entered and epicardium was contacted as indicated by capture. No myocardial perforation or coronary artery or venous injuries were produced. These findings support the use of a pulse generator to guide pericardiocentesis.

Animals↗
PubMed1989

Potential mapping in septal tachycardia. Evaluation of a new intraoperative mapping technique.

A recently developed computer program is capable of rapidly (less than 5 minutes) constructing a series of potential-distribution maps (PDMs) for every msec of a 4-second window of ventricular tachycardia (VT). This study was performed to assess the ability of a series of PDMs to localize the site of earliest activation of VT originating in the interventricular septum. In 12 dogs, 13 morphologies of VT were initiated with programmed electrical stimulation 3-6 days after anterior septal coronary artery infarction. VT was mapped with endocardial and epicardial unipolar electrodes with a multipoint, computer-assisted mapping system. PDMs were compared with activation-time maps, and the former correctly identified the site of earliest activation of all 13 VT morphologies. When PDMs were viewed in sequence on a computer monitor, the site of earliest activation was signaled by abrupt development of a negative potential of less than -3.0 mV. The initial negative point subsequently expanded, and the spread of this negative-potential field correlated with activation sequence. PDMs provide an accurate, unambiguous, rapid means of analyzing large numbers of electrograms acquired with multipoint, computer-assisted mapping systems.

Action Potentials↗