Lofland Gk

Ventricular Cryosurgery: Short-term Effects on Intramural Electrophysiology

The acute effects of cryothermia on regional electrophysiology were examined in order to devise a means of localizing and monitoring the intramural progression of ventricular cryolesions during a two-minute period of cryothermia application. Intramural unipolar electrograms were recorded from multipoint plunge electrodes placed in the left ventricle in 15 dogs. Epicardial, intramural, and endocardial applications of cryothermia were then employed, and changes in the unipolar peak-to-peak amplitude (UPPA) of electrograms were recorded. The location and depth of the ultimate permanent cryolesion could be predicted by noting locations of those electrograms demonstrating a decrease in the UPPA to less than 30% of the control values. Such electrophysiological monitoring of the region of myocardium undergoing cryothermic ablation provides a means of limiting the ultimate cryolesion to the desired location and depth within the ventricular wall. This allows precise placement of cryolesions in specific areas of the left ventricle for the treatment of ventricular tachyarrhythmias by selectively ablating arrhythmogenic ventricular myocardium without inducing injury in surrounding nonarrhythmogenic myocardium.

Late Fractionated Potentials and Continuous Electrical Activity Caused by Electrode Motion

Late fractionated potentials, recorded during cardiac mapping to find the source of a ventricular arrhythmia, have been ascribed particular localizing value. Re‐entry is assumed when these highly amplified and filtered recordings span diastole during tachycardia. The purpose of this study was to see if such potentials can occur artifactually. A saline soaked 7 ± 2 ± 3 cm sponge was sewn to the epicardium of the right ventricle in five non‐infarcted, open‐chest dogs. Two bipolar button electrodes, one with 1 mm and one with 1 cm interelectrode spacing, were attached to the outer surface of the sponge and a bipolar wire hook electrode was placed just under the outer surface of the sponge. Thus all three electrodes were 3 cm from the nearest myocardium yet still subjected to cardiac motion. The electrodes were recorded at gains of 4,000–40,000 and filtered to pass 50–300 hertz. One to three rapid deflections were recorded during the QRS from all electrodes. In seven of the 15 electrode recordings, two or three additional deflections, 100–200 μV in amplitude, occurred after the QRS. These late potentials were fractionated and recurred reproducibly from cycle to cycle. In two cases, these late fractionated potentials could be made to span diastole by rapid pacing to Simula te tachycardia. Clamping the sponge to eliminate motion between the sponge and electrode caused this late activity to disappear. Thus, in highly amplified and filtered recordings, electrode motion can cause artifacts resembling late fractionated potentials and continuous electrical activity.

Aortic thrombosis in neonates and infants

Aortic thrombosis in the neonate occurs most frequently as a complication of umbilical artery catheterization. There is still controversy concerning the appropriate management of this problem. Complications associated with umbilical artery cannulation are numerous and include renal failure, which may necessitate peritoneal dialysis. Because of this possibility, we illustrate and advocate a retroperitoneal approach to the abdominal aorta for thromboembolectomy.

Reversal of Flow through Chronic Coronary Collateral Vessels

The purpose of this study was to determine whether blood flow through chronic collateral vessels may reverse its direction to supply acutely ischemic myocardium. Ameroid constrictors were placed on the circumflex coronary artery (CCA) of 12 dogs to promote collateral flow (CQ) from the left anterior descending (LAD) to the CCA. Twelve weeks later, myocardial blood flow (MBF) was determined (ml/g/min) using radioactive tracer microspheres. Control LAD subepi-cardial (EPI) and subendocardial (ENDO) flows were 1.17 ± 0.11 and 1.00 ± 0.10 (Mean ± SEM), respectively. CCA EPI and ENDO flows were 1.25 ± 0.12 and 1.12 ± 0.20, respectively. The LAD was then occluded, and MBF to the CCA bed decreased by an average of 0.31 ± 0.03 ml/g/min (P < 0.005). This decrease in MBF quantitated the amount of CQ from the LAD to the CCA bed. An aortocoronary bypass graft was anastomosed to the distal CCA and MBF to the LAD bed immediately increased by an average of 0.30 ± 0.02 ml/g/min (P < 0.005). This increase in MBF represented reversed CQ from the CCA to the acutely ischemic LAD bed. It had a normal transmural distribution (ENDO/EPI = 0.9). Four hours later, total reversed CQ to the LAD bed remained unchanged, but was redistributed toward the EPI (ENDO/EPI = 0.6). These data document that chronic collateral vessels are capable of immediate and sustained conduction of CQ in a retrograde direction and suggest that these collateral vessels may play a role in limiting the degree and transmural extent of ischemic injury when a perioperative myocardial infarction occurs in the vascular bed of a nonbypassed coronary artery.