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Biomedical subjects

R W Landymore

Publications and source records attributed to R W Landymore.

At least 55 records · Page 3Linked to original sources
PubMed1987

Malignant hyperthermia: a dilemma for the cardiac surgeon.

Malignant hyperthermia is an inherited disease of skeletal muscle characterized by acute elevations of body temperature. The hyperthermic crisis is triggered by a variety of drugs and by volatile anesthetics or it may occur in response to stress. In this report the authors describe the case of a patient with malignant hyperthermia who underwent emergency aortocoronary bypass surgery for unstable angina. They outline the anesthetic and surgical management for individuals susceptible to hyperthermic crises who require open-heart surgery.

Aged↗
PubMed1986

Spectral analysis of small-amplitude electrical activity in the cold potassium-arrested heart.

Recent reports have suggested that small-amplitude electrical activity may persist following the administration of potassium cardioplegia. This report confirms the presence of small-amplitude electrical activity in the potassium-arrested heart and describes a canine model that may be used to measure microvolt plunge-electrode potentials during ischemic arrest. Thirty-one adult mongrel dogs were placed on cardiopulmonary bypass and underwent 90 minutes of ischemic arrest. The heart was arrested with 10 ml per kilogram of body weight of crystalloid cardioplegia (20 mEq of KCl/L) at 4 degrees C. Core temperature was maintained at 26 degrees C and myocardial temperature, within a range of 8 degrees to 10 degrees C with topical ice-slush saline solution. Cardioplegic solution, 10 ml/kg, was reinfused every 30 minutes during the 90 minutes of ischemia. Electrical activity and transmural temperature were continuously monitored over the anterior surface of the left ventricle with specially designed plunge electrodes. Visual electrical and mechanical activity ceased in each animal after the infusion of cardioplegic solution, and was associated with an isoelectric electrocardiogram. However, microvolt (10(-6)V) small-amplitude electrical activity was recorded at a myocardial temperature of 10 degrees C in each animal during ischemic arrest, and the activity from 6 animals was stored on magnetic tape. Spectral analysis of electrical activity during cardioplegic arrest indicated that the fundamental frequency of small-amplitude electrical activity was in the range of 3.25 Hz. These data confirm the presence of small-amplitude electrical activity in the cardioplegia-arrested heart at 10 degrees C.

Animals↗
PubMed1986

Prevention of neurological injury during myocardial revascularization in patients with calcific degenerative aortic disease.

Neurological injury following myocardial revascularization may result from embolization of atheromatous debris from the diseased ascending thoracic aorta. Eight patients with calcified aortas who underwent elective myocardial revascularization suffered major strokes as a result of manipulation and clamping of the diseased ascending aorta during a 30-month period before July, 1981. computerized axial tomography scans demonstrated multiple cerebral infarctions in each patient. Six patients never regained consciousness and died as a result of neurological injury; 2 patients regained consciousness but were left with major neurological deficits. Later, 21 patients with calcific aortic degenerative disease underwent a specific operative protocol, designed to prevent neurological injury during elective myocardial revascularization. All 21 patients recovered without neurological complications. Specific attention to operative technique allowed this difficult group of patients with incapacitating angina and calcific degenerative aortic disease to have the benefit of coronary bypass.

Aorta, Thoracic↗
PubMed1986

Comparison of cod-liver oil and aspirin-dipyridamole for the prevention of intimal hyperplasia in autologous vein grafts.

The combination of aspirin and dipyridamole is currently used to prevent intimal hyperplasia and to improve long-term vein graft patency following myocardial revascularization. Preliminary studies indicate that cod-liver oil, rich in eicosapentaenoic acid, an unsaturated fatty acid, may also be effective in the prevention of intimal hyperplasia. Twenty-four mongrel dogs were used to compare the effectiveness of aspirin-dipyridamole and cod-liver oil on vein graft intimal hyperplasia following arterial bypass. Forty-eight segments of undistended autologous external jugular vein were interposed between bilaterally divided femoral arteries. All animals received a 2% cholesterol diet for 1 week before and 6 weeks after operation. Eight controls received the diet alone. Eight other animals received dipyridamole (2.5 mg per kilogram of body weight) two days before operation and dipyridamole (2.5 mg/kg) and aspirin (30 mg/kg) daily for 6 weeks after operation. Another 8 animals received cod-liver oil containing 1.8 gm of eicosapentaenoic acid daily 1 week before and for 6 weeks following operation. Serum cholesterol increased similarly in all groups; it rose from 4.5 +/- 0.2 mm/L to 8.3 +/- 0.8 mm/L in the controls, to 7.2 +/- 0.5 mm/L in the aspirin-dipyridamole group, and to 7.1 +/- 0.5 mm/L in the cod-liver oil group (p less than 0.01). Prothrombin time, partial thromoboplastin time, total platelet counts, and bleeding times were unchanged. Intimal hyperplasia was measured at 6 weeks with a Zeiss computerized microscope; 376 +/- 25 measurements were made from each graft. The intima increased from 4.5 +/- 0.2 to 83 +/- 10 micron in the control dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Effects of cod-liver oil on intimal hyperplasia in vein grafts used for arterial bypass.

Cod-liver oil rich in eicosapentaenoic acid, an unsaturated fatty acid, has been shown to inhibit platelet aggregation. To determine the effect of this acid on vein-graft intimal hyperplasia, 46 segments of undistended external jugular vein were interposed between the bilaterally divided femoral arteries of 26 mongrel dogs. The animals received a 2% cholesterol diet for 1 week before and 6 weeks after the operation. Eight control animals received the diet alone, eight received cod-liver oil containing 1.8 g of eicosapentaenoic acid daily, for 1 week before and 6 weeks after operation, and seven animals received 1.8 g of eicosapentaenoic acid daily for 6 weeks after operation. Intimal thickness was measured at 6 weeks with a Zeiss computerized interactive image analysing system from multiple cross-sections of vein graft; 395 +/- 10 measurements were made from each graft. The intima measured 4 +/- 0.2 micron (SEM) before implantation and increased to 83 +/- 10 micron in the controls. Eicosapentaenoic acid administered before and after operation reduced intimal hyperplasia to 24 +/- 2.5 micron (p less than 0.001) and to 30 +/- 5 micron in animals receiving eicosapentaenoic acid after operation only (p less than 0.001). These results indicate that the acid inhibits intimal hyperplasia of canine vein grafts but that it is more effective when given before operation (p less than 0.01).

Animals↗
PubMed1986

Reduction of intimal hyperplasia in canine autologous vein grafts with cod-liver oil and dipyridamole.

To determine the effects of cod-liver oil and a combination of cod-liver oil and dipyridamole on vein-graft intimal hyperplasia, 76 segments of undistended jugular vein were interposed between bilaterally divided femoral arteries in 38 mongrel dogs who received a 2% cholesterol diet. Ten control animals received the diet alone, 8 received cod-liver oil containing 1.8 g of eicosapentaenoic acid daily 1 week before and for 6 weeks after operation, and 20 dogs received 1.8 g of eicosapentaenoic acid and 75 mg of dipyridamole daily 1 week before and for 6 weeks after operation. A similar and significant (p less than 0.01) increase in serum cholesterol was observed in all three groups. Prothrombin, partial thromboplastin and clotting times and the platelet count were unchanged in the controls and in those receiving cod-liver oil. Clotting time increased in the animals receiving a combination of cod-liver oil and dipyridamole (p less than 0.001). Measurements (406 +/- 27) of intimal thickness were made from each graft. Intimal thickness was 3.7 +/- 0.1 micron before implantation and increased to 78 +/- 8 micron after in the controls. Cod-liver oil limited the increase in intimal thickening, to 24 +/- 3 micron (p less than 0.001); cod-liver oil and dipyridamole further reduced the increase in intimal thickening, to 17 +/- 1.4 micron (p less than 0.001). The data indicate that a combination of cod-liver oil and dipyridamole is more effective than cod-liver oil alone in reducing canine vein-graft intimal hyperplasia (p less than 0.03).

Animals↗
PubMed1986

Effect of small-amplitude electrical activity on myocardial preservation in the cold potassium-arrested heart.

Recent reports indicate that small-amplitude electrical activity may be present in the cold potassium-arrested heart. Twenty-four mongrel dogs were placed on cardiopulmonary bypass and cooled to a rectal temperature of 26 degrees C. Myocardial preservation was provided with a combination of systemic hypothermia 26 degrees C. potassium (20 mEq/L) crystalloid cardioplegic solution (10 ml/kg) infused initially and every 30 minutes during 90 minutes of ischemic arrest, and topical hypothermia. Myocardial temperature was maintained between 8 degrees and 10 degrees C. Electrical activity and transmural myocardial temperature were monitored with specially designed plunge electrodes. Left ventricular stroke work index, cardiac index, and maximum rate of rise of left ventricular pressure were measured before bypass and 45 minutes after ischemic arrest. Biopsy specimens were taken before bypass and at 15 and 45 minutes after ischemic arrest. The specimens were used to measure adenosine triphosphate and to analyze electron microscopic ultrastructure. Small-amplitude electrical activity was present in 16 of 24 animals during cardioplegic arrest. Cardiac index decreased 18 ml/min/kg (not significant), left ventricular stroke work index fell by 0.28 +/- 0.1 gm-m/beat/kg (p less than 0.007), and maximum rate of rise of left ventricular pressure decreased 409 mm Hg/sec (p less than 0.01) in the eight animals without small-amplitude electrical activity. Adenosine triphosphate concentration was unchanged and electron microscopic ultrastructure was well preserved. In contrast, small-amplitude electrical activity (16 animals) resulted in a decrease in cardiac index of 67 ml/min/kg (p less than 0.001), a decrease in left ventricular stroke work index of 0.79 +/- 0.8 gm-m/beat/kg (p less than 0.001), and a fall in maximum rate of rise of left ventricular pressure of 775 mm Hg/sec (p less than 0.001). Adenosine triphosphate concentration decreased from 25 to 21 mumol/gm (p less than 0.04) and electron microscopic ultrastructure was poorly preserved (p less than 0.001). This study demonstrates that small-amplitude electrical activity in the cardioplegia-arrested heart at 10 degrees C impairs myocardial preservation.

Adenosine Triphosphate↗
PubMed1986

Myocardial metabolism and hemodynamic responses with fentanyl-enflurane anesthesia for coronary arterial surgery.

Ten patients for coronary vein grafting had induction of anesthesia with fentanyl (30 micrograms/kg), followed by enflurane-oxygen sufficient to decrease systolic blood pressure by 27% before intubation. Enflurane was continued in concentrations to maintain blood pressure below that with patients awake. All patients had preserved ventricular function and effective beta-blockade. Studies of hemodynamic functions and myocardial blood flow and oxygenation were done before induction, six times during anesthesia, and twice postoperatively. The blood pressure decrease on induction and before bypass was due to reduced cardiac index without decreased heart rate or systemic resistance. Stroke work index decreased 47% on induction and remained below awake level throughout. Coronary sinus blood flow decreased 26% after intubation and remained so before bypass. Without change in coronary resistance, coronary sinus oxygen content increased 30% on induction and stayed elevated before bypass. Normal lactate extraction continued after induction and increased before bypass; mean extraction decreased after bypass, with one or two hearts producing lactate in the first 24 postoperative hr. Fentanyl-enflurane-oxygen maintained a steady mild hemodynamic depression during the operation and soon afterward, which preserved myocardial oxygenation.

Anesthesia↗
PubMed1986

Myocardial metabolism and hemodynamic responses with isoflurane anesthesia for coronary arterial surgery.

Isoflurane-oxygen was given for induction and maintenance of anesthesia to ten patients having coronary artery bypass grafts. All had preserved ventricular function without hypertension or other cardiac lesions; treatment with beta-blocking drugs was maintained until the operation in all patients. Cardiac output, arterial and central pressures, coronary sinus (CS) blood flow, arterial and CS oxygen, Hb, and lactate contents were measured before, six times during, and twice after anesthesia. On induction, systolic arterial pressure was purposely reduced 33% along with systemic resistance by increasing the concentration of isoflurane; cardiac index, heart rate, and coronary flow did not change. Coronary resistance decreased 23% and CS oxygen content increased 56%; but in three of ten patients myocardial lactate production took place, evidence of global ischemia. Induction of anesthesia was not smooth in three patients. Controlled hemodynamic depression could be maintained with isoflurane-oxygen, but the frequency of myocardial lactate production before and after perfusion was greater than with other general anesthetics. Isoflurane dilated portions of the coronary bed but, because anaerobic metabolism occurred concomitantly, the theory that redistribution of flow can take place resulting in ischemic areas of ventricle is supported.

Adult↗
PubMed1985

Current status of surgery for ventricular tachyarrhythmias.

This article outlines the accepted histopathologic and electrophysiologic theories underlying the etiology of medically refractory ventricular tachyarrhythmias. It delineates the indications and techniques for the electrophysiologic study of the ventricle. Finally, the surgical procedures available as well as their indications and results are elucidated.

Animals↗
PubMed1985

Intimal hyperplasia in autogenous vein grafts used for arterial bypass: a canine model.

Late vein graft occlusion following myocardial revascularisation is usually the result of progressive intimal hyperplasia which ultimately leads to vein graft thrombosis. Considerable attention has recently been directed towards the development of optimal platelet-inhibiting drug regimens designed to prevent intimal hyperplasia in autogenous vein grafts. This report describes an animal model that reliably reproduces short-term intimal hyperplasia in autogenous vein grafts, thus facilitating the study of platelet-inhibiting drug regimens for the prevention of intimal hyperplasia. 28 segments of undistended jugular vein were implanted end-to-end between bilaterally divided femoral arteries in 14 mongrel dogs. Seven control animals (CON) received a non-lipid diet one week before and for 6 weeks following vein implantation. A further seven animals received a 2% cholesterol diet throughout the study. Serum cholesterol was measured at 4.06 +/- 0.6 mmol X litre-1 in the CON and did not change significantly throughout the study. Serum cholesterol rose from 3.9 +/- 0.4 to 8.5 +/- 0.8 mmol X litre-1 in the lipid-supplemented animals (p less than 0.001). Vein grafts were harvested at 6 weeks and fixed in formaldehyde. Precise measurements of intimal thickness in microns were measured from multiple vein graft cross-sections with a Zeiss computerised interactive image analysing system. A mean of 102 +/- 15 measurements were made from each vein graft cross-section. Intimal thickness of autogenous vein grafts prior to implantation were similar in both groups and measured 4.15 +/- 0.4 micron. Intimal thickness increased in CON animals to 23.3 +/- 3 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Encircling endocardial resection with complete removal of endocardial scar without intraoperative mapping for the ablation of drug-resistant ventricular tachycardia.

Encircling endocardial resection, with complete removal of endocardial scar unguided by intraoperative mapping, was employed in 10 patients with drug-resistant sustained ventricular tachycardia. Reproducible sustained ventricular tachycardia was induced in all patients preoperatively with programmed electrical stimulation. A trial of conventional antiarrhythmics had failed in all 10 patients; seven patients required frequent cardioversion, and three patients required overdrive suppression with temporary transvenous pacing. Encircling endocardial resection was performed in all patients, with complete removal of endocardial scar; partial reimplantation of the mitral apparatus was required in nine patients. Eight patients underwent aneurysmectomy, and the nine patients who required concomitant aorta-coronary bypass received a total of 13 grafts (mean 1.3 grafts per patient). There were no spontaneous postoperative arrhythmias. One patient without postoperative clinical arrhythmias, who had required daily preoperative cardioversion, had inducible ventricular tachycardia with postoperative programmed electrical stimulation, but not after loading with procainamide. Mean follow-up was 17.3 months. Eight patients are alive and well. There were two late deaths. One patient died with recurrent ventricular septal defects 2.5 months following extensive septal encircling endocardial resection, and one patient was readmitted after 4 months with massive pulmonary embolus and right-sided heart failure. This early experience suggests that this procedure, with complete removal of endocardial scar, successfully ablates reentrant ventricular tachycardia. We believe that the procedure will prove to be more effective than localized endocardial resection because the encircling procedure removes all ventricular sites that have the potential to generate reentrant ventricular tachycardia.

Aged↗
PubMed1985

Cod-liver oil in the prevention of intimal hyperplasia in autogenous vein grafts used for arterial bypass.

Cod-liver oil, rich in eicosapentaenoic acid, an unsaturated fatty acid, was administered to 14 mongrel dogs to determine if this acid would prevent platelet-mediated intimal hyperplasia. Twenty-eight 1 cm segments of undistended jugular vein were interposed between bilaterally divided femoral arteries. Seven control animals were fed a 2% cholesterol diet 1 week before and for 6 weeks after the operation. A further seven animals received cod-liver oil capsules containing 1.8 gm of eicosapentaenoic acid daily 1 week before and for 6 weeks after autogenous vein implantation, in addition to the lipid-supplemented diet. Baseline serum cholesterol was 4.6 +/- 0.4 mmol/L. The rise in serum cholesterol was similar in the two groups and increased to 7.4 +/- 0.6 mmol/L (control group) and to 6.8 +/- 0.2 mmol/L (eicosapentaenoic acid group) (p less than 0.001). Prothrombin time, partial thromboplastin time, bleeding time, and platelet counts were unchanged in the two groups. Vein grafts, harvested at 6 weeks, were fixed in formaldehyde. Mean intimal thickness was measured from multiple vein graft cross sections with a Zeiss computerized interactive image analyzing system. A mean of 140 +/- 11 measurements were computed from each graft. Marked intimal hyperplasia occurred in the control group and increased from 4.3 +/- 0.3 to 86.4 +/- 14 micron. In contrast, a high eicosapentaenoic acid diet inhibited intimal hyperplasia, with intimal thickness only increasing from 4.0 +/- 0.4 to 24.8 +/- 2.7 micron (p less than 0.001). These data indicate that eicosapentaenoic acid inhibits platelet-mediated intimal hyperplasia and suggest that cod-liver oil could be used to prevent intimal hyperplasia in vein grafts used for myocardial revascularization.

Animals↗
PubMed1984

Encircling endocardial resection for sustained drug-resistant ventricular tachycardia.

Localized endocardial resection guided by intraoperative mapping has been used recently to manage patients with drug-resistant ventricular tachycardia. Although not uniformly successful, this procedure is superior to simple aneurysmectomy. This report describes the authors' early experience with encircling endocardial resection with complete removal of endocardial scar in seven patients with drug-resistant, sustained, ventricular tachycardia, as identified by electrophysiologic studies. Intraoperative mapping was not used. Although no spontaneous clinical arrhythmia occurred after operation, ventricular tachycardia could be induced in one patient, but not after loading with procainamide. This was the only patient who required long-term antiarrhythmic therapy. There were no operative deaths, but one patient died 21/2 months after endocardial resection with recurrent ventricular septal defects and another died after 4 months. Our early experience indicates that encircling endocardial resection effectively eliminates re-entrant ventricular tachycardia and identifies ventricular septal defect as a potential postoperative complication following extensive septal endocardial resection.

Aged↗
PubMed1984

Effects of crystalloid and blood cardioplegic solutions on myocardial cooling during myocardial revascularization.

Cardioplegic protection during ischemic arrest is impaired in patients with serious coronary artery disease, resulting in large regional temperature gradients and impaired myocardial cooling. Recent data have suggested that the viscosity of cardioplegic solutions may affect their distribution beyond coronary artery stenosis. This study compared the effects of asanguineous and blood cardioplegic solutions on myocardial cooling in 26 such patients who underwent elective myocardial revascularization; 15 were subjected to blood cardioplegia and 11 to crystalloid cardioplegia. One litre of blood or asanguineous cardioplegic solution was infused into the aortic root at a constant infusion pressure. Samples for viscosity determination were taken from both cardioplegic solutions during their infusion. Regional myocardial temperature was measured distal to coronary artery obstructions following administration of the cardioplegic agent. Although the viscosity of the blood solution was 250% greater than the asanguineous solution, regional myocardial temperatures were not significantly different beyond the coronary artery stenosis. Regional temperature was reduced to less than 15 degrees C after infusion of the cardioplegic agent in regional myocardium with a normal coronary circulation. Marked temperature gradients were observed distal to a critical stenosis, with temperatures ranging between 18 degrees C and 20 degrees C for stenosis, and about 23 degrees C for obstruction. The authors conclude that the marked difference in viscosity between crystalloid and blood cardioplegic solutions does not significantly affect their distribution beyond a coronary artery stenosis.

Blood↗