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Biomedical subjects

B Lown

Publications and source records attributed to B Lown.

At least 145 records · Page 8Linked to original sources
PubMed1981

Prognosis of medically treated patients with coronary-artery disease with profound ST-segment depression during exercise testing.

Reproducible and profound (greater than 2 mm) ST-segment depression during exercise testing in patients with coronary heart disease is associated with multivessel involvement. In these patients, coronary-artery bypass surgery has been recommended even when symptoms are absent. However, there are few long-term follow-up data regarding the prognosis when such patients are treated medically. Among 212 men with coronary-artery disease in whom profound ST-segment depression could be reproduced with exercise, 142 who had no other type of heart disease and were not receiving digitalis drugs had a mean ST-segment depression of 2.9 mm. Follow-up has lasted an average of 59 months: 11 patients have died (annual mortality, 1.4 per cent), and nine have had bypass operations (1.3 per cent per year). Survival correlated with exercise tolerance but not with degree of ST depression, peak heart rate, or peak blood pressure during exercise. We conclude that such ST-segment depression is not associated with a poor prognosis. There is rarely a need to resort to cardiac surgery; medical management is highly successful and associated with a low mortality.

Adult↗
PubMed1981

Lignocaine prophylaxis in acute myocardial infarction: an evaluation of randomised trials.

Although lignocaine has been used in coronary care units for almost two decades, its role in preventing ventricular fibrillation (VF) during acute myocardial infarction (MI) is still debated. Of fifteen randomised trials of lignocaine prophylaxis, most showed no apparent benefit. When the data from all fifteen trials were pooled and a summary relative risk estimate calculated, there was a significant benefit of lignocaine treatment in preventing VF. However, the trials had widely differing treatment schedules, modes of drug administration, and doses of lignocaine; to decrease the clinical heterogenity, minimum criteria for adequacy of treatment were established and the data from six trials which fulfilled these requirements were pooled. The summary relative risk estimate calculated from the pooled data of these six trials also demonstrated a significant prophylactic effect of lignocaine that was even greater when the two trials which treated patients with left ventricular failure and shock were excluded. From these analyses, it is concluded that lignocaine treatment provides prophylaxis against VF in acute MI. The failure of most trials to demonstrate such a prophylactic effect is due to small sample sizes and inadequate treatment protocols.

Clinical Trials as Topic↗
PubMed1981

Acute psychological disturbances preceding life-threatening ventricular arrhythmias.

To investigate the prevalence of acute psychological disturbances during the 24 hours preceding life-threatening ventricular arrhythmias, we studied the mental states and psychological experiences preceding arrhythmic episodes in 117 patients who were referred for antiarrhythmic management. Sixty-two had survived cardiac arrest and 55 suffered symptomatic ventricular tachycardia. Twenty-five patients were experiencing acute emotional disturbances during the 24 hours preceding the arrhythmias. Eighteen had two or more episodes associated with psychological disturbances. These 25 patients were distinguished from the rest of the series in having generally less severe structural heart disease.

Acute Disease↗
PubMed1981

Tyrosine administration decreases vulnerability to ventricular fibrillation in the normal canine heart.

Intravenous infusion of tyrosine (1, 2, or 4 milligrams per kilogram) for 20 to 30 minutes caused dose-dependent increases in the ventricular fibrillation threshold in normal dogs. Administration of valine, a neutral amino acid that competes with tyrosine for uptake at the blood-brain barrier, in a dose equimolar to the most effective dose of tyrosine, slightly decreased the ventricular fibrillation threshold when given alone and significantly blocked elevation of the ventricular fibrillation threshold after tyrosine infusion. Hence, tyrosine, presumably acting in the central nervous system, can protect against certain ventricular arrhythmias.

Animals↗
PubMed1981

Amiodarone therapy in symptomatic, sustained refractory atrial and ventricular tachyarrhythmias.

Amiodarone was utilized in 70 patients with symptomatic, sustained refractory tachyarrhythmias. Of these, 29 had atrial arrhythmia (20 recurrent atrial fibrillation and nine sustained supraventricular tachycardia). Control was achieved in eight with supraventricular tachycardia and in 16 with atrial fibrillation. Recurrence has been prevented in these 24 patients (83%) during an average follow-up of 13.4 months. An additional 41 patients had recurrent ventricular tachycardia. In 19 with symptoms consisting of dizziness of lightheadedness without syncope or clinically apparent hemodynamic compromise, treatment was limited to amiodarone. Of these, 14 responded (74%) and have been free of arrhythmia during an average follow-up of 13 months. In 22 who had experienced either syncope or life-threatening hemodynamic impairment, amiodarone was added to those agents which had only partially suppressed advanced grades of ventricular premature beats. Fourteen of these patients (64%) have remained free pf recurrent ventricular arrhythmia during an average follow-up of 12 months. After drug loading, maintenance therapy consisted of a daily dose ranging from 200 to 600 mg. Only mild side effects have been encountered in the 17 patients (23%) with any untoward responses. This experience confirms that oral amiodarone is an effective and safely applied agent against recurrent refractory atrial tachyarrhythmia and sustained intractable ventricular tachycardia with moderate symptoms. While also efficacious in refractory sustained life-threatening ventricular tachyarrhythmia, usage of the agent is often difficult in this condition owing in part to insufficient information concerning amiodarone pharmacokinetics.

Adolescent↗
PubMed1981

Extra-adrenergic mechanisms responsible for the effects of glucose-insulin-potassium solution on vulnerability to ventricular fibrillation.

In 53 chloralose-anesthetized dogs, the actions of glucose (10 mg/kg per min), insulin (0.025 U/kg per min) and potassium (0.025 mEq/kg per min) on the ventricular fibrillation and repetitive extrasystole thresholds were examined. Measurements were initially made in the control state and then repeated at 30, 60 and 120 minutes of infusion of glucose-insulin-potassium solution at a constant rate of 1.23 ml/min. The dogs received on the average 36 g of glucose, 44 U of insulin and 44 mEq of potassium over a 2 hour period. In the nonischemic myocardium, the infusion raised the threshold for ventricular fibrillation and repetitive extrasystole to a peak of 94 and 61 percent, respectively, without significantly changing serum potassium or circulating catecholamine concentration. In the ischemic myocardium, the incidence of spontaneous ventricular fibrillation during 10 minutes of coronary occlusion was reduced from 83 percent in the control state to 17 percent with glucose-insulin-potassium infusion. However, the infusion did not alter the incidence of ventricular fibrillation associated with reperfusion. Because cardio-cardiac sympathetic reflexes are elicited in response to coronary occlusion, the effect of glucose-insulin-potassium infusion on ventricular vulnerability during left stellate ganglion stimulation and norepinephrine infusion was investigated. The infusion completely prevented the reduction in the vulnerable period threshold during stellate stimulation and norepinephrine infusion. Furthermore, the peak protection afforded by the infusion was greater than that achieved with beta adrenergic blockade and was still present in catecholamine-depleted hearts. It is concluded that infusion of glucose-insulin-potassium solution protects against ventricular fibrillation in the normal and ischemic canine heart but not during reperfusion. This protection may be due in part to antagonism of adrenergic activity; however, the primary influence of the solution is mediated by extra-adrenergic mechanism.

Animals↗
PubMed1981

Influence of autonomic nervous system stimulation on the protective zone.

The effect of sympathetic and parasympathetic stimulation on the vulnerable period threshold and the protective zone was studied in chloralose-anaesthetised dogs. Sympathetic stimulation substantially decreased the repetitive extrasystole threshold and shifted the timing of the protective zone earlier into diastole. Vagus nerve excitation exerted the opposite effect on both electrophysiological properties. During concurrent sympathetic nerve stimulation, the changes produced by vagal activation were accentuated. These findings suggest that parasympathetic influences on the protective zone are due, in part, to an antagonism of adrenergic effects on ventricular electrical properties.

Animals↗
PubMed1981

Reduction in vulnerability to ventricular fibrillation by bromocriptine, a dopamine agonist.

The effect of a dopamine agonist, bromocriptine, on ventricular fibrillation (VF) threshold was studied in anaesthetised dogs. Bromocriptine produced an increase of 50% in VFT. Pretreatment with the dopamine antagonist haloperidol abolished the effects of bromocriptine on VF threshold as did pretreatment with the peripheral dopamine antagonist, domperidone. It is concluded that bromocriptine reduces vulnerability of the nonischaemic canine ventricle to fibrillation. This effect is most probably mediated by peripheral presynaptic stimulation of dopaminergic receptors, thereby inhibiting noradrenaline release.

Animals↗
PubMed1980

Retirement and coronary mortality.

Information on several variables, including occupational history and various coronary risk factors, was collected from the wives of 568 married men who died of coronary heart-disease (CHD) and an equal number of matched control subjects. The crude matched-pair relative risk of fatal CHD among men who retired compared with non-retirees was 2.9 (95% confidence limits from 1.9 to 4.9). After adjustment for age and history of hospitalisation for myocardial infarction by means of a paired multiple-logistic regression analysis the relative risk was reduced to 1.8 (range 1.0 to 3.3). These data suggest that retirement and subsequent coronary mortality may be linked.

Adult↗
PubMed1980

Cardioversion and defibrillation.

The use of electrical energy for the immediate treatment of atrial and ventricular arrhythmias is practical and easily applied. The method, though simple, is the most effective method for terminating cardiac arrhythmias and is associated with only a low risk if properly employed. In symptomatic patients, the utilization of cardioversion reduces patient discomfort and complications which may occur while awaiting pharmacologic reversion of arrhythmia. At present, transthoracic defibrillation is the only practical method for terminating VF. Despite the safety of electrical reversion, proper precautions are necessary to prevent complications. In particular, the discharge of excessive energies, especially in the presence of digitalis toxicity, promises grave and life-threatening consequences. The use of antiarrhythmic medications is not supplanted by cardioversion and defibrillation. Rather, ongoing drug therapy is frequently necessary to prevent recurrence of arrhythmia.

Animals↗