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Biomedical subjects

B Lown

Publications and source records attributed to B Lown.

At least 19 recordsLinked to original sources
PubMed1992

Results of a second-opinion trial among patients recommended for coronary angiography.

OBJECTIVE: To assess the feasibility of carrying out a second-opinion trial for patients urged to undergo coronary angiography and to assess the long-range outcome of such patients denied that procedure, and the criteria evolved for reaching such a conclusion. DESIGN: A case series of patients referred for a second opinion as to the need for coronary angiography. Patients were followed up by questionnaire, telephone call, and center visits. SETTING: Cardiovascular referral center and teaching hospital in Boston, Mass. PATIENTS: One hundred seventy-one patients with coronary artery disease (144 men, average age 60 years; range, 36 to 88 years). Three patients became unavailable for follow-up during a mean of 46.5 months. OUTCOME MEASURES: Concordant-discordant outcome as to the second opinion, cardiac events, invasive interventions, quality of life questionnaire, and level of symptoms. RESULTS: One hundred thirty-four (80%) of the 168 patients were judged not to require angiography; it was recommended in six. In 28 (16%) recommendation was deferred pending further studies. At a mean follow-up of 46.5 months among the 168 patients, there were seven cardiac deaths (annualized cardiac mortality of 1.1%); 19 patients experienced a new myocardial infarction (2.7% annualized rate), while 27 patients (4.3%) were judged to have developed unstable angina. Twenty-six patients (15.4%) ultimately underwent either coronary bypass or angioplasty. CONCLUSIONS: In a large fraction of medically stable patients with coronary disease who are urged to undergo coronary angiography, the procedure can be safely deferred. While there may be a limitation in terms of generalizing this experience to all patients with coronary disease, we reasonably conclude that an estimated 50% of coronary angiography currently being undertaken in the United States is unnecessary, or at least could be postponed.

Adult↗
PubMed1992

Transient coronary stenosis associated with arrhythmia and ischemia 24 hours after reperfusion.

We examined the electrophysiologic sequelae of transient reductions in coronary blood flow (CBF) in conscious dogs. Animals were instrumented to measure arterial pressure, heart rate, repetitive extrasystole threshold (RET), and CBF before coronary stenosis, during 90 minutes of a 50% reduction in CBF, and at 1, 24, 48, and 72 hours after reperfusion. RET was decreased at 24 and 48 hours but returned to baseline by 72 hours after reperfusion. Frequent ventricular ectopic activity (VEA), absent during the control period, was noted during stenosis and at 1, 24, and 48 hours after reperfusion. beta-Adrenergic blockade (metoprolol) normalized the decreased RET at 24 hours. Addition of alpha 1-adrenergic blockade (prazosin) abolished VEA. Endocardial blood flow in the posterior papillary muscle of the left ventricle was reduced by 52 +/- 9% during stenosis, was similar to baseline levels by 1 hour after reperfusion, and decreased by 39 +/- 5% at 24 hours. We conclude that episodes of modest coronary artery stenosis may be followed by electrophysiologic changes indicative of increased vulnerability to malignant ventricular arrhythmias.

Animals↗
PubMed1979

Digitalis drugs and vulnerability to ventricular fibrillation.

The effect of acetylstrophanthidine (AS), a rapid-acting digitalis-like agent, on the ventricular fibrillation (VF) threshold was examined in normal and denervated chloralose-anesthetized dogs. In neurally intact dogs an intravenous bolus of AS (0.075 mg/kg) increased the VF threshold up to a maximum 50% (P less than 0.01) within 30 min after injection. The augmented VF threshold following intravenous administration of AS was not altered by vagotomy. Bilateral stellectomy in vagotomized dogs, as well as carotid sinus and aortic arch denervations, however, prevented the AS induced increase in VF threshold. In neurally intact dogs beta-adrenergic blockade with propranolol (0.25 mg/kg) precluded AS effects. These data suggest that the increase in the VF threshold resulting from AS administration in the normal canine ventricle is due to withdrawal of sympathetic tone mediated via the baroreceptor reflex. The direct effect of AS on the myocardium is to decrease the VF threshold.

Adrenergic beta-Antagonists↗
PubMed1979

Continuous monitoring for ventricular arrhythmias during exercise tests.

Exercise stress testing is being increasingly used to verify exercise-induced arrhythmia and to aid in assessing antiarrhythmic drug efficacy. The true prevalence of ventricular arrhythmia during exercise testing is underestimated by means other than continuous monitoring. We compared the yield of ventricular premature beats (VPBs) between a continuous recording system ("trendscription") and intermittent monitoring among 39 patients undergoing a total of 50 consecutive exercise studies. By intermittent monitoring, 22 (44%) of 50 of the exercise tests demonstrated VPBs; with trendscription, 31 (62%) exhibited such arrhythmia. Most striking, however, was a sixfold increase in the disclosure of complex and repetitive forms of VPBs (56 vs nine episodes). Thus, this form of monitoring presents a cost-efficient, on-line method that allows concentration on the patient during exercise as well as clear recording of all arrhythmic events.

Anti-Arrhythmia Agents↗
PubMed1979

Effect of nitroglycerin on vulnerability to ventricular fibrillation during myocardial ischemia and reperfusion.

The effect of nitroglycerin on vulnerability to ventricular fibrillation was examined in 44 chloralose-anesthetized dogs. In 19 animals ventricular fibrillation threshold was measured before and during a 10 minute period of occlusion of the left anterior descending coronary artery followed by abrupt release of occlusion. Fibrillation threshold was determined using the single stimulus and train of stimuli methods. The influence of nitroglycerin on vulnerability was assessed with and without prevention of the drug's hypotensive effect by intravenous injection of phenylephrine. In the nonischemic myocardium, infusion of nitroglycerin alone or in combination with phenylephrine did not alter the ventricular fibrillation threshold. However, during both coronary occlusion and reperfusion, administration of nitroglycerin alone afforded partial protection against vulnerability to ventricular fibrillation. Nearly complete protection was imparted by combined administration of nitroglycerin and phenylephrine. The incidence of spontaneous ventricular fibrillation during reperfusion was significantly reduced by combined administration of nitroglycerin and phenylephrine. It is concluded that infusion of nitroglycerin decreases susceptibility to ventricular fibrillation during both acute myocardial ischemia and reperfusion and that this beneficial action is substantially enhanced when the drug's hypotensive effect is prevented.

Animals↗
PubMed1979

Central serotonergic agents raise the repetitive extrasystole threshold of the vulnerable period of the canine ventricular myocardium.

Systemic administration of three central serotonergic agents, melatonin, 5-methoxytryptophol, and 6-chloro-2-(1-piperazinyl)-pyrazine (MK-212), produced significant increases in the threshold of the vulnerable period for repetitive electrical activity in the canine cardiac ventricle. MK-212 was effective despite bilateral vagotomy. The specific serotonin antagonist, metergoline, blocked the effect of MK-212 on the threshold. An increase in central serotonergic activity may inhibit the flow of arrhythmogenic sympathetic nerve traffic from the brain to the heart.

Animals↗
PubMed1978

Roles of psychologic stress and autonomic nervous system changes in provocation of ventricular premature complexes.

Neural and psychologic factors have been implicated as risk factors for ventricular arrhythmias and sudden death in man. However, the relation between these factors and arrhythmia has hitherto not been systematically explored. We examined the effect of psychologic stress testing in 19 patients with advanced grades of ventricular arrhythmias. Psychologic stress consisted of mental arithmetic, reading from colored cards and recounting emotionally charged experiences. Such testing induced a significant increase in ventricular premature beat frequency in 11 of 19 patients (P less than 0.05). One patient experienced paroxysms of ventricular tachycardia. In 14 of these 19 patients elicitation of vagal or sympathetic autonomic reflexes failed to induce significant arrhythmia in all but one patient. It is concluded that (1) objective psychologic tests may precipitate ventricular arrhythmia in susceptible patients, and (2) evocation of peripheral autonomic reflexes is an insufficient trigger for enhanced ventricular ectopic activity.

Adolescent↗
PubMed1978

Effects of clonidine on vulnerability to fibrillation in the normal and ischemic canine ventricle.

Clonidine infusion (10 microgram/kg, i.v.) elicited a 30% increase in repetitive extrasystole (RE) threshold in 6 chloralose-anesthetized dogs. A reduction in heart rate and arterial blood pressure accompanied the increased threshold. Intracisternal injection of clonidine (2 microgram/kg) in 6 dogs caused similar alterations in these parameters. Bilateral vagotomy, performed in 6 dogs prior to intravenous clonidine, prevented the increase in RE threshold but did not prevent the drug-induced bradycardia. Atropine (0.2 and 0.6 mg/kg), however, did not attenuate the effect of clonidine on RE threshold. Clonidine administration did not prevent the reduction in ventricular fibrillation threshold associated with a 10 min occlusion of the left anterior descending coronary artery or following reperfusion. We conclude that: (1) clonidine reduces ventricular vulnerability in the normal but not the ischemic heart, and (2) its protective effect is mediated by enhanced afferent vagal input to midbrain cardiovascular regulatory centers. This central nervous system action causes a reduction in sympathetic tone to the heart.

Animals↗