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Biomedical subjects

K Fox

Publications and source records attributed to K Fox.

At least 253 records · Page 14Linked to original sources
PubMed1981

Relation between atrioventricular pathways and ventricular response during atrial fibrillation and flutter.

We have analysed the ventricular response as seen on the surface electrocardiogram in patients with paroxysmal atrial fibrillation and flutter in relation to the electrophysiological properties of the corresponding atrioventricular pathways. In 15 patients who had atrial fibrillation with conduction solely through the atrioventricular node, there was a significant correlation between th shortest and mean RR intervals during atrial fibrillation and the functional refractory period, "pre-Wenckebach cycle length", and the shortest ventricular cycle length that resulted from 1:1 atrioventricular conduction. In 18 patients with conduction through an accessory atrioventricular pathway the only good correlation was between the shortest and mean ventricular rate during atrial fibrillation and the "pre-Wenckebach cycle length" and shortest ventricular cycle length during 1:1 atrioventricular conduction. In 12 patients with an atriofascicular bypass tract or rapidly conducting atrioventricular node there was no significant correlation between the RR intervals during atrial fibrillation and the electrophysiological indices; the same lack of correlation was evident in all 11 patients with atrial flutter, all of whom had atrioventricular nodal conduction. The response of atrioventricular pathways to electrophysiological testing, particularly the use of incremental atrial pacing, provides useful guidance in the further management of these atrial arrhythmias.

Adult↗
PubMed1981

Patterns of disturbed myocardial perfusion in patients with coronary artery disease. Regional myocardial perfusion in angina pectoris.

Fifty patients who presented with angina pectoris were studied to examine the disturbances of regional myocardial perfusion during stress. Each patient underwent 16-point precordial mapping of the ECG during an exercise test, and coronary and left ventricular angiography. Regional myocardial perfusion was assessed using an atrial pacing test and a short-lived radionuclide, krypton-81m. Eleven patients had negative exercise tests and uniform increases in myocardial activity of krypton-81m of 98 +/- 18.0% during pacing. Ten patients performed 30,000-43,000 J in positive exercise tests. These patients showed abnormal coronary anatomy and increases in myocardial activity of krypton-81m to remote and jeopardized myocardium at the onset of pacing. However, further pacing produced a decrease in activity in the affected segment of 68.0 +/- 9.0% accompanied by ST-segment depression and angina. Twelve patients achieved 26,000-32,000 J in positive exercise tests and had significant coronary artery disease. Atrial pacing produced increased activity of krypton-81m to remote myocardium. The jeopardized segment at first showed no change and then a decrease in regional activity of krypton-81m (89.0 +/- 17%) accompanied by ST-segment depression and chest pain. Seventeen patients achieved only 7000-22,000 J in positive exercise tests. These patients showed abnormal coronary anatomy and developed decreases in regional activity of krypton-81m to the affected segment of myocardium starting at the onset of atrial pacing and decreasing by 88 +/- 0 7.0% below control. We conclude that different patterns of disturbed myocardial distribution of krypton-81m are present during stress-induced ischemia in patients with coronary artery disease. There was a close temporal relationship between these disturbances and ST-segment depression.

Adult↗
PubMed1980

Interaction between cigarettes and propranolol in treatment of angina pectoris.

To determine whether cigarette smoking interferes with the medical management of angina pectoris, 10 patients with angina pectoris who smoked at least 10 cigarettes a day were studied before, during, and after a standardised maximal exercise test. This was done at the end of four randomly allocated one-week treatment periods during which the patients took glyceryl trinitrate while not smoking, took glyceryl trinitrate while smoking, took glycerly trinitrate and propranolol (380 mg/day) while not smoking, and took glyceryl trinitrate and propranolol while smoking. Carboxyhaemoglobin was measured to ensure compliance. Smoking was associated with a significantly higher heart rate, blood pressure, number of positions with ST-segment depression, and total ST-segment depression after exercise than non-smoking (p < 0.01) whether or not the patients were taking propranolol. These results suggest that smoking aggravates the simple haemodynamic variables used to assess myocardial oxygen requirements and the exercise-induced precordial electrocardiographic signs of myocardial ischaemia. These effects were still evident after treatment with propranolol and represent a hindrance to the effective medical treatment of angina pectoris.

Adult↗
PubMed1980

Myocardial infarction in the dog: effects of intravenous propranolol.

The effects of propranolol on myocardial perfusion and metabolism during acute myocardial infarction were studied in 18 mongrel dogs. A reversible snare was placed on the left anterior descending coronary artery; regional myocardial perfusion was continuously measured using the short-lived isotope krypton-81m, and myocardial metabolism was assessed using the epicardial electrocardiogram and measurement of release of creatine kinase activity from the affected segment of myocardium. Six dogs with no arterial occlusion acted as "sham operated" dogs; six others in which the snare was occluded acted as a control group and a third group of six were given propranolol, 0.5 mg/kg, 30 minutes after coronary occlusion. All variables were recorded before and for 5 hours after coronary occlusion. Dogs treated with propranolol showed a significant improvement in regional myocardial perfusion to the affected segment, decreased loss of electrically active myocardium at the end of each experiment for any given degree of early S-T segment elevation and a delay in the local release of creatine kinase activity compared with that in the control dogs. These results suggest that propranolol exerts a beneficial effect on the progress of ischemic myocardial damage when given shortly after the onset of infarction.

Animals↗
PubMed1980

Praecordial surface mapping after exercise in evaluation of propranolol for angina pectoris.

The effect of propranolol on ST depression in the praecordial 16 lead electrocardiogram was observed in 52 patients before and after treatment, both at rest and after exercise. In a further 20 patients exercise tests repeated on separate days two months apart showed that the technique gave reproducible results. A variable relation between symptomatic relief and praecordial exercise-induced ST segment depression was noted. Use of a single fixed-position chest lead (V5) was shown to be less accurate. The relief of symptoms alone is probably an inadequate guide to the success of medical treatment, which should control not only angina but also the manifestations of ischaemia on the praecordial electrocardiogram.

Angina Pectoris↗
PubMed1979

Precordial electrocardiographic mapping after exercise in the diagnosis of coronary artery disease.

A technique is described for recording the precordial electrocardiographic body surface map before and after exercise. The technique provides an extra dimension to the conventional exercise electrocardiogram because a measurement can be made of the area and severity of S-T segment changes that are projected onto the front of the chest. Sixteen lead isopotential surface maps were recorded before and after exercise in 109 patients with angina who subsequently underwent coronary arteriography. In addition, exercise electrocardiograms were obtained in 53 of these patients using three orthogonal leads and in all patients using a single chest unipolar chest lead. Precordial surface mapping after exercise was found to have a greater sensitivity (95 percent) than electrocardiography using either the orthogonal leads (68 percent) or a single chest lead (64 percent) (P less than 0.01). The specificity of the three techniques did not differ significantly (P greater than 0.05). The technique of precordial surface mapping after exercise improves the ability to diagnose coronary artery disease and can easily be applied to clinical practice.

Adult↗
PubMed1979

Krypton-81m in the physiologic assessment of coronary arterial stenosis in man.

Fifteen patients with frequent anginal chest pain underwent diagnostic cardiac catheterization. After coronary arteriography a specially designed cardiac catheter was seated in the aortic root, permitting the continuous infusion of krypton-81m into the right and left aortic sinuses. A gamma camera, areas of interest and a visual display unit were used to record images and the regional myocardial equilibrium of activity before, during and after a standarized atrial pacing test. The unique physical properties of krypton-81m allowed the continuous imaging and recording of moment to moment changes in regional myocardial perfusion. This investigation revealed that when the coronary arteriogram was normal or revealed lumonal stenosis of less than 50 percent, regional myocardial perfusion was uniform at rest and during stress. Two patients with a previous history of myocardial infarction had defects of regional perfusion at rest and during stress. Krypton scintigraphy demonstrated reversible regional defects in myocardial perfusion during stress in seven patients with greater than 70 percent stenosis of one or more coronary arteries. Alterations in regional myocardial perfusion occurred within 30 seconds of the start of atrial pacing in all the patients and preceded the onset of electrocardiographic signs of ischemia or chest pain.

Adult↗
PubMed1979

Assessment of coronary venous bypass graft function using krypton-81m.

Fifteen patients with intractable angina pectoris underwent coronary angiography and coronary arterial bypass graft surgery. After the operation, a continuous infusion of krypton-81m was delivered into each graft. A gamma camera and multichannel analyzer were used to record the regional myocardial distribution of perfusion provided by each graft. The disappearance of myocardial activity at the end of each infusion was used to calculate the flow per unit volume in the myocardial distribution provided by each vessel. Myocardial perfusion provided by the grafts to all the major coronary arteries were recorded individually as high spatial resolution images. Myocardial flow rates in the distribution of each graft were measured using the washout of krypton-81m. The rates were 0.5 to 2.0 ml/g per min in the 13 patients with no evidence of previous myocardial infarction. Krypton-81m was infused into grafts to the left anterior descending coronary artery in two patients with a history and electrocardiographic evidence of previous anterior myocardial infarction. The grafts provided poor perfusion to the anterior and apical portions of the ventricles. An experimental model of myocardial perfusion was used to demonstrate that the washout of krypton-81m can be used to measure flow per unit volume within or above the physiologic range.

Angina Pectoris↗
PubMed1979

The effects of nifedipine on acute experimental myocardial ischemia and infarction in dogs.

We studied 25 anesthetized and thoracotamized dogs before and during 5 hours of acute regional myocardial ischemia. Krypton-81m (81mKr) was infused constantly into the aortic sinuses. The myocardial equilibrium of this tracer was used to image and assess the distribution of regional myocardial perfusion using a gamma camera and digital computer. The epicardial ECG was recorded, S-T segment elevation and the loss of R and appearance of Q waves were measured, and the plasma activity of creatine kinase (CK) was determined in aortic and coronary venous blood throughout these experiments. Ten dogs underwent left anterior descending coronary artery (LAD) narrowing for 5 hours and received no drugs. Five dogs received nifedipine 13 microgram/kg, and another five received 1.0 microgram/kg intravenously 30 minutes after LAD narrowing. Those dogs receiving nifedipine, 13 microgram/kg, showed a 30% fall in aortic pressure, a 12% rise in heart rate, and an extension of regional ischemia. The ECG showed an extension of infarct size, and CK release into the coronary vein appeared earlier than in the controls. Dogs receiving nifedipine, 1 microgram/kg, showed a 12% fall in blood pressure, no rise in heart rate, an improvement in regional perfusion, and ECG signs that suggested limitation of infarct size. There also was delayed release of coronary venous CK. The effects of nifedipine on the natural history of regional myocardial perfusion, the electrocardiogram, and enzyme release from the heart were dose related and cannot be generalized. These observations warrant further clinical investigation to improve the use of this agent in man.

Animals↗
PubMed1979

'Bradycardia-tachycardia' syndrome 8 yr after correction of Fallot's tetralogy.

A 13-yr-old boy presented with atrial flutter 8 yr after surgical correction of tetralogy of Fallot; antiarrhythmic therapy caused depression of the sinoatrial node, with syncope. Disordered sinoatrial function and intraventricular conduction were demonstrated by intracardiac electrography, and appear to have resulted from the operation. Sinoatrial disease may be responsible for supraventricular arrhythmias or syncope long after operative correction of Fallot's tetralogy and may be one of the explanations for the tendency of such patients to die suddenly.

Adolescent↗