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Biomedical subjects

R W Landymore

Publications and source records attributed to R W Landymore.

At least 37 records · Page 2Linked to original sources
PubMed1991

Recurrent atrial arrhythmias following treatment for postoperative atrial fibrillation after coronary bypass operations.

Ambulatory Holter monitoring was performed in 58 patients during the early convalescence after myocardial revascularization in order to determine the incidence of recurrent atrial arrhythmias following treatment for postoperative atrial fibrillation. Fifteen patients who had undergone coronary bypass and had not developed spontaneous atrial fibrillation following operation served as the controls (group 1). The remaining patients developed spontaneous symptomatic atrial fibrillation after coronary bypass that required digitalization for rate control. Sixteen patients (group 2) continued taking digoxin for 8 weeks following operation, 13 patients (group 3) discontinued digoxin treatment 5 weeks following operation, and 14 patients (group 4) discontinued digoxin treatment 3 weeks following operation. Twenty-four-hour Holter monitoring indicated that asymptomatic atrial fibrillation was common in the treatment groups after digitalization just before discharge from hospital. Atrial fibrillation, however, rarely recurred following discharge from hospital and was never symptomatic. Our data indicate that patients who develop spontaneous postoperative atrial fibrillation should be treated with digoxin for 3 weeks following operation and then drug therapy may be discontinued indefinitely.

Atrial Fibrillation↗
PubMed1991

Effect of aspirin on intimal hyperplasia and cholesterol uptake in experimental bypass grafts.

The effects of aspirin on intimal and medial smooth muscle cell proliferation and cholesterol uptake in experimental bypass grafts were examined in a hypercholesterolemic canine model. Ten animals receiving a 2% cholesterol diet served as controls, while a further 10 animals received the same diet and 160 mg aspirin daily. Segments of external jugular vein were implanted between bilaterally divided femoral arteries. Tissue cholesterol and intimal and medial thicknesses were measured at six weeks. Graft cholesterol had increased 1.7 mumol/g at six weeks in the control group but only rose by 0.28 mumol/g in animals receiving aspirin (P less than 0.002). Intimal and medial smooth muscle cell proliferation was evident in all experimental bypass grafts and was unaffected by aspirin. It is concluded that cholesterol uptake and smooth muscle proliferation may be controlled by different mechanisms, and that aspirin reduces cholesterol uptake but does not prevent smooth muscle cell proliferation in experimental bypass grafts.

Animals↗
PubMed1990

Surgical intervention for drug-resistant ventricular tachycardia.

Endocardial resection was required in 26 patients with sustained drug-resistant ventricular tachycardia. The early mortality rate (within 30 days after operation) was 12%. Two deaths were the result of low cardiac output, and the third death was related to recurrent ventricular septal defect after septal endocardial resection. The survivors of endocardial resection were followed up from 6 to 92 months (mean 43). There were no recurrences of ventricular arrhythmias, and patients did not require antiarrhythmic drug therapy. The late mortality rate after endocardial resection was 19%. There were two late cardiac-related deaths (unrelated to arrhythmias) and three late deaths from noncardiac causes. Complete endocardial resection successfully ablates drug-resistant ventricular tachycardia, but is associated with an increased perioperative mortality rate in those patients who have severely depressed left ventricular function without a well defined left ventricular aneurysm.

Adult↗
PubMed1990

The effects of low, medium and high dose aspirin on intimal proliferation in autologous vein grafts used for arterial reconstruction.

Bilateral femoral vein grafts were implanted in 47 adult mongrel dogs to determine the effects of aspirin on intimal hyperplasia. The animals were fed a commercially-prepared 2% cholesterol diet before and for 6 weeks following operation. Twelve animals served as the controls while the remaining animals were divided into three groups receiving low, medium, and high dose aspirin. Eleven animals received 75 mg of aspirin daily, 11 animals were fed 225 mg of aspirin daily and the remaining 13 animals received 650 mg of aspirin daily. A coagulation profile was carried out before operation and at 2, 4 and 6 weeks following operation. The grafts were harvested at 6 weeks and intimal thickness was measured with a Zeiss computerized interactive image-analyzing system. The prothrombin time, partial thromboplastin time, and platelet count were unchanged in all animals. The bleeding time was prolonged in animals receiving aspirin (P less than 0.02). Intimal thickness measured 4 +/- 0.2 microns before implantation and increased at 6 weeks to 39 +/- 5 microns in the control group. Aspirin failed to reduce intimal hyperplasia. Intimal thickness measured 37 +/- 2 microns in those animals receiving 75 mg of aspirin daily, 35 +/- 3 microns after a daily dose of 225 mg of aspirin and 51 +/- 4 microns in the high dose group receiving 650 mg of aspirin daily. Our data indicates that aspirin fails to reduce intimal proliferation in canine vein grafts which suggests that alternative or combined drug therapy may be necessary to reduce the incidence of late graft failure.

Animals↗
PubMed1990

Pulmonary complications following myocardial revascularization with the internal mammary artery graft.

A total of 106 patients participated in a clinical investigation to determine the incidence and etiology of pulmonary complications following myocardial revascularization with the internal mammary artery graft; 39 patients (group I), undergoing valve replacement or myocardial revascularization with vein grafts, served as control. The mammary artery was used for revascularization in the remaining patients. The pleura was opened during the dissection of the mammary graft in 34 patients (group II), but was left intact during harvesting of the internal mammary artery in 33 patients (group III). Inspiration and expiration chest X-rays were obtained during the first 3 months of convalescence to determine the presence of pleural fluid, the position of the left hemidiaphragm, and to asses diaphragmatic movement. Pleural effusions, left lower-lobe atelectasis, and elevation of the left hemidiaphragm were observed in all groups after operation, but were more commonly observed in those patients undergoing revascularization with the mammary artery graft. Postoperative chest X-rays just prior to discharge from hospital were normal in 69% of the control group, only 9% of patients in group II who had pleurotomy during mammary artery dissection, and 42% of group III. By 3 months, however, 95% of patients in groups I and II had normal chest X-rays, whereas 53% of patients in group II had persistent loss of left-lung volume related to the presence of left-lower-lobe atelectasis, left pleural effusions and organization of the postoperative hemothorax.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1990

Culture-negative endocarditis probably due to Chlamydia pneumoniae.

A 59-year-old man had culture-negative endocarditis (clinical evidence compatible with endocarditis and histopathologic evidence of a recent episode of endocarditis) and serology compatible with a recent episode of Chlamydia pneumoniae infection. The conclusion was that this episode of culture-negative endocarditis was probably due to C. pneumoniae.

Antibodies, Bacterial↗
PubMed1990

A miniature voltmeter for monitoring small amplitude electrical activity in the hypothermic arrested myocardium.

A measurement system which is capable of detecting microfibrillation in the hypothermic, arrested heart has been developed. It is shown that this system can reliably measure microfibrillation signals as low as 10 microV in amplitude. Using this system, it has been shown that even after the heart has been rendered visibly arrested using cold potassium, it may still be producing a low level of electrical activity. It has also been shown that the presence of this microfibrillation during the period of the cold potassium administration and visible arrest, is very highly correlated with the decrease in high energy phosphates (ATP), mitochondrial injury, and a decreased cardiac function post-operatively. Using the information obtained from this first measurement system, a miniature, battery powered voltmeter has been designed and fabricated. This voltmeter has been tested using the initial measurement system as reference and produces the same information concerning the small signal electrical activity (i.e.: same waveform and RMS value). Because this voltmeter is battery powered and is, therefore, completely isolated from all electrical equipment in the operating theatre, it can be used to monitor the presence, or absence, of microfibrillation in the human heart. Of greatest importance, however, is the fact that the voltmeter can serve as a monitoring device which will indicate when the potassium should be administered in order to render the heart both mechanically and electrically arrested.

Animals↗
PubMed1990

Effect of hypothermia and cardioplegia on intramyocardial voltage and myocardial oxygen consumption.

Intramyocardial voltage and myocardial oxygen consumption were measured in the fibrillating heart between the temperatures of 37 degrees C and 25 degrees C and in the arrested heart after infusion of potassium cardioplegic solution in 10 adult mongrel dogs. Electrical activity from the myocardium was recorded using specially designed plunge electrodes, and intramyocardial voltage was monitored by an in-line voltmeter. Myocardial oxygen consumption gradually decreased from 5.8 +/- 0.6 ml O2/min at 37 degrees C to 2.3 +/- 0.5 ml O2/min at 25 degrees C. In contrast, hypothermia did not cause a similar decrease in intramyocardial voltage which remained within a range of 1.8 +/- 0.5 mV to 2.4 +/- 0.5 mV between the temperatures of 37 degrees C and 25 degrees C. The infusion of potassium cardioplegic solution resulted in a dramatic decrease in voltage to 43 +/- 5 microV, and myocardial oxygen consumption fell to 0.5 +/- 0.3 ml O2/min. Our data demonstrated that the mean voltage of the fibrillating heart remains constant between the temperatures 37 degrees C and 25 degrees C and myocardial oxygen consumption decreases with hypothermia, which suggests that voltage does not correlate with the level of myocardial oxygen consumption. Myocardial oxygen consumption and intramyocardial voltage, however, decrease dramatically when cardioplegia is instituted.

Animals↗
PubMed1989

The measurement of afterload, vascular input impedance, and power distribution in aorto-femoral bypass.

The effects of aorto-femoral bypass grafts on the vascular input impedance, and the ratio of pulsatile to total power were studied in eight dogs. Unilateral ileo-femoral stenosis was simulated and comparisons were made between the input impedance and power distribution in healthy and simulated disease situations. Input impedance magnitude spectra and phase were displayed graphically and it was shown that the presence of the simulated disease increases the ratio of pulsatile to total power as measured in the abdominal aorta from 7.5 to 14.8% (p less than 0.05). This suggests that the presence of the stenosis creates an impedance mismatch thus causing reflected waves to propagate proximally towards the heart. It was concluded that the way in which the heart transfers fluid power into the arterial bed was compromised by the presence of the ileo-femoral partial stenoses. It is further suggested that the system described in the paper makes it possible to quantitatively assess afterload, vascular input impedance and cardiovascular power distribution as a quasi-real time diagnostic procedure.

Anastomosis, Surgical↗
PubMed1989

Monitoring the voltage of the myocardium during cardioplegia arrest.

Electrical activity was monitored with specially designed plunge electrodes in 19 animals undergoing 3 h of cardioplegic arrest. Electrical activity was recorded on electromagnetic tape and intramyocardial voltage was monitored with an inline voltmeter. Haemodynamic function was assessed before bypass and following 3 h of ischaemia and 45 min of reperfusion. Intramyocardial voltage during normothermic fibrillation measured 2.4 +/- 0.4 mv. Infusion of cardioplegia initiated a complete electrical arrest in all animals and reduced intramyocardial voltage to 33 +/- 7 mu v. Small amplitude electrical activity was present in 9 of 19 animals. Intramyocardial voltage increased to 108 +/- 12 mu v with the onset of small amplitude electrical activity and spectral analysis of the wave form indicated that the fundamental frequency was in the range of 3.08 Hz. Small amplitude electrical activity during cardioplegic arrest was associated with significant post-arrest depression of left ventricular function. Our data confirms that the presence of small amplitude electrical activity impairs myocardial functional recovery and suggests that continuous intramyocardial voltage monitoring may be used to guide the administration of cardioplegia during cardioplegic arrest.

Adenine Nucleotides↗
PubMed1989

Effects of low-dose marine oils on intimal hyperplasia in autologous vein grafts.

The effects of low-dose cod-liver oil on intimal hyperplasia of vein grafts were examined in 45 adult mongrel dogs undergoing peripheral arterial reconstruction. Fifteen animals served as the control group, 15 animals were fed a fish-oil supplement containing 240 mg of eicosapentaenoic acid daily, and a further 15 animals received 480 mg of eicosapentaenoic acid daily. Segments of undistended external jugular vein were anastomosed to bilaterally divided femoral arteries. The grafts were harvested at 6 weeks and intimal thickness was measured with a computerized interactive image analyzing system. Serum cholesterol level, prothrombin time, partial thromboplastin time, bleeding time, and platelet counts were measured before the operation and at 2, 4, and 6 weeks after the operation. Plasma levels of thromboxane B2 and prostaglandin F1 alpha and serum levels of eicosapentaenoic acid were measured before and 4 weeks after the operation. Serum cholesterol level increased similarly and significantly in all animals. Serum levels of eicosapentaenoic acid rose proportionately with the oral ingestion of fish oil but did not affect coagulation parameters. Plasma thromboxane B2 and prostaglandin F1 alpha were not significantly affected by the ingestion of marine oils. Intimal thickness was 39 +/- 5 microns in the control dogs. Ingestion of 240 mg of eicosapentaenoic acid reduced intimal thickness to 24 +/- 3 microns at 6 weeks (p less than 0.01). Increasing the dose by a factor of 2 did not decrease intimal thickness further, the intima being 23 +/- 2 microns (p less than 0.005). Our data indicate that small doses of fish oil will reduce intimal proliferation in autologous vein grafts and that marine oils may exert their beneficial effects on intimal hyperplasia by a mechanism other than their known effects on prostanoid metabolism.

Animals↗
PubMed1988

Transvenous closure of acquired ventricular septal defects.

Post infarction ventricular septal defect is an uncommon but frequently fatal complication of myocardial infarction. In this report a method for creating experimental ventricular septal defects is described and the use of a transvenous balloon catheter for closure of septal perforations reported. Ventricular septal defects were created with a specially designed punch in 25 adult mongrel dogs. Severe hemodynamic compromise occurred immediately following septal perforation in 15 animals which failed to permit sufficient time to pass the transvenous balloon catheter. However, passage of the catheter and occlusion of the ventricular septal defect was accomplished in the remaining 10 animals. Perforation of the ventricular septum resulted in a marked left-to-right shunt as indicated by changes in interventricular pressure and a step-up in the right ventricular PO2 saturations. Passage of the double balloon catheter and inflation of the balloons prevented left-to-right shunting and completely occluded the ventricular septal defect. Further refinements of this experimental catheter may result in the development of a balloon catheter that may be used to stabilize patients after spontaneous ventricular perforation, thus allowing them to recover from their infarction and undergo delayed repair of the ventricular septal defect.

Animals↗
PubMed1988

Effect of various low-dose concentrations of verapamil cardioplegia on small-amplitude electrical activity during cardioplegic arrest.

The effect of verapamil cardioplegia on atrioventricular conduction was examined in 19 dogs. During 90 minutes of ischemic arrest, five dogs received multidose potassium cardioplegia, containing 1.2 mg/L of verapamil (group 1), five received potassium cardioplegia containing 600 micrograms/L of verapamil (group 2) and nine animals received cardioplegia containing 300 micrograms/L of verapamil (group 3). Atrioventricular conduction was measured in all groups before bypass, after 90 minutes of ischemia and after 45 minutes of reperfusion. Specially designed plunge electrodes were used to monitor the electrical status of the heart during arrest in group 3 and, in addition, left ventricular function and concentration of high-energy phosphates were determined before and after ischemic arrest. Conduction was prolonged in four group 1 dogs and in two group 2. Atrioventricular conduction was measured in six group 3 dogs; five had prolonged conduction and one experienced second-degree heart block. Small-amplitude electrical potentials were recorded from the myocardium in two of nine dogs in group 3. Persistent electrical activity was associated with continued use of high-energy phosphates and resulted in decreased left ventricular function after 90 minutes of ischemic arrest. Our data indicate that small doses of verapamil will delay atrioventricular conduction and will not prevent small-amplitude electrical activity.

Animals↗
PubMed1988

Evaluation of delivery systems for oxygenated cardioplegia.

The oxygen-carrying capacity of four delivery systems for blood and crystalloid cardioplegia was evaluated: nonoxygenated crystalloid cardioplegia, crystalloid cardioplegia oxygenated with a bubbler system and with a membrane system and, finally, blood cardioplegia delivered by the Shiley-Buckberg system. The nonoxygenated crystalloid cardioplegic solution delivered 0.56 ml of oxygen/dl of solution, the bubbler oxygenating system delivered 3.2 ml/dl and the membrane oxygenating system made available 3.7 ml/dl. Blood cardioplegia delivered 4.2 ml/dl when oxygen-carrying capacity was corrected for the shift in the oxyhemoglobin dissociation curve that occurs with hypothermia. There appears to be no advantage between blood and oxygenated crystalloid cardioplegia with respect to the ability of these solutions to provide oxygen to the myocardium during ischemic arrest. However, the bubbler oxygenating system is superior to the membrane and blood delivery systems in that it could administer cold cardioplegia at any time during the operation. In contrast, the membrane and blood cardioplegia delivery systems both depend on integral heat exchangers which limit the delivery of cold cardioplegia to the period of hypothermia.

Adult↗
PubMed1987

Effect of force on anastomotic suture line disruption after carotid arteriotomy.

Static and dynamic forces exerted on 6-0 polypropylene suture material after carotid arteriotomy were measured in 22 adult mongrel dogs. Force was measured in 11 normotensive animals (Group I) before and 6 weeks after carotid artery repair. Force was measured in the remaining animals during normotension and induced hypertension before and 6 weeks after operation. The tensile strength of each suture used in the study was measured by the manufacturer. The mean force required to break a 6-0 polypropylene suture measured 436.9 +/- 2 g, whereas knotting of the suture decreased the tensile strength to 316.9 +/- 3.9 g (p less than 0.001). The static and dynamic axial forces exerted on the suture after carotid arteriotomy in Group I was in the range of 26 g and decreased to 18 g at 6 weeks, whereas the 45 degree force exerted during the static dynamic phase measured in the range of 23 g and decreased to 16 g at 6 weeks (not statistically significant). The axial and 45 degree forces exerted on 6-0 polypropylene suture material in Group II under normotensive conditions were in the range of 14 g after carotid arteriotomy and ranged between 12 to 14 g at 6 weeks. Systolic hypertension did not result in a significant increase in axial or 45 degree forces during static or dynamic measurements, both in the range of 15 g after carotid arteriotomy. Measurements were similar at 6 weeks and ranged between 14 and 16 g. Our data indicate that 6-0 polypropylene suture material is an appropriate choice for repair of the carotid artery and that the suture material has sufficient inherent tensile strength to withstand forces generated in the neck region. Furthermore, our data indicate that spontaneous carotid artery suture line disruption is most likely related to damage to the suture strand during carotid artery repair rather than an inherent weakness in the suture material.

Animals↗
PubMed1987

Prevention of myocardial electrical activity during ischemic arrest with verapamil cardioplegia.

The effect of potassium cardioplegia and potassium cardioplegia containing verapamil hydrochloride on myocardial preservation and electrical activity during prolonged aortic occlusion was examined in 40 adult mongrel dogs. Twenty-four animals (Group 1) received potassium cardioplegia, and 16 animals (Group 2) received potassium verapamil cardioplegia. Potassium or potassium verapamil cardioplegia, 10 ml per kilogram of body weight, was administered after application of the aortic cross-clamp and at 30-minute intervals during the 90-minute arrest. Myocardial temperature was maintained within a range of 8 degrees to 10 degrees C with topical ice saline solution, and electrical activity was monitored with specially designed plunge electrodes. Plunge electrode activity was recorded from the myocardium during arrest in 16 of the 24 animals in Group 1; no electrical activity was present in the animals in Group 2 (p less than .001). The addition of verapamil to potassium cardioplegia increased the tolerance of the myocardium to prolonged ischemia and resulted in less depletion of high-energy phosphate stores and better preservation of mitochondrial ultrastructure and left ventricular function. These data suggest that verapamil augments the preservation provided by potassium cardioplegia by initiating and maintaining a more complete electrical arrest.

Animals↗
PubMed1987

Anatomical studies to support the expanded use of the internal mammary artery graft for myocardial revascularization.

The internal mammary artery pedicle graft is frequently used for coronary bypass. Five internal mammary artery pedicle grafts, harvested but not utilized for coronary bypass, underwent histological examination. The histological studies demonstrated that the vasa vasorum were confined to the adventitia and did not penetrate the media of the internal mammary artery. These observations indicate that the media is nourished entirely from the lumen and suggest that harvesting the internal mammary artery as a free graft would not subject the wall of the artery to ischemic injury. Subsequent to these studies, we used the right internal mammary artery as a free graft to revascularize the distal circumflex coronary artery in 12 patients. The free graft was anastomosed to marginal branches of the circumflex and was then brought up to the left internal mammary artery pedicle graft and anastomosed end-to-side. This procedure has not resulted in excessive postoperative bleeding or sternal infections, and has relieved the anginal syndrome in all 12 patients.

Aged↗