Intramyocardial diversion of coronary blood flow: effects of isoproterenol-induced subendocardial ischemia

Direct administration of rutin does not protect against catecholamine cardiotoxicity

High levels of catecholamines are cardiotoxic and may trigger acute myocardial infarction (AMI). Similarly, the synthetic catecholamine isoprenaline (ISO) evokes a pathological state similar to AMI. During AMI there is a marked increase of free iron and copper which are crucial catalysts of reactive oxygen species formation. Rutin, a natural flavonoid glycoside possessing free radical scavenging and iron/copper chelating activity, may therefore be potentially useful in reduction of catecholamine cardiotoxicity as was previously demonstrated after its long-term peroral administration. Male Wistar:Han rats received rutin (46 or 11.5 mg kg(-1) i.v.) alone or with necrogenic dose of ISO (100 mg kg(-1) s.c.). Haemodynamic parameters were measured 24h after drug application together with analysis of blood, myocardial content of elements and histological examination. Results were confirmed by cytotoxicity studies using cardiomyoblast cell line H9c2. Rutin in a dose of 46 mg kg(-1) aggravated ISO-cardiotoxicity while the dose of 11 mg kg(-1) had no effect. These unexpected results were in agreement with in vitro experiments, where co-incubation with larger concentrations of rutin significantly augmented ISO cytotoxicity. Our results, in contrast to previous studies in the literature, suggest that the reported positive effects of peroral administration of rutin were unlikely to have been mediated by rutin per se but probably by its metabolite(s) or by some other, at this moment, unknown adaptive mechanism(s), which merit further investigation.

Left ventricular diastolic dysfunction in patients with bronchial asthma with long-term oral beta2-adrenoceptor agonists

BACKGROUND

Long-term administration of oral beta(2)-adrenergic receptor agonists (beta(2)-AG) in patients with bronchial asthma (BA) causes disastrous events such as sudden death and heart attack. However, long-term effects of beta(2)-AG on cardiac function have not been previously quantified.

METHODS

Seventy-four patients with BA with regular long-term use of oral beta(2)-AG (group A) and 69 patients with BA without beta(2)- AG (group B) were examined in medical records of outpatient clinics from 1985 to 1999. In the prospective study, echocardiography was performed in 48 consecutive patients from January to April 1999. There were 26 patients with regular oral use of beta(2)-AG (group a) and 22 patients without beta(2)-AG (group b). Twenty-one age-matched normal volunteers without heart or pulmonary diseases were used as control subjects (group c). Oral beta(2)-AG was withdrawn from remedies in 11 patients of group a, and echocardiographic studies were repeated 2 weeks after its cessation.

RESULTS

Events related to heart failure were more frequently seen in group A than in group B (14% vs 1%, P <.01). The echocardiographic study showed that indexes of left ventricular diastolic but not systolic function were significantly deteriorated in group a, along with a markedly reduced level of plasma norepinephrine concentration (P <.05 vs groups b and c). When heart rate was adjusted to 90 beats/min during isoproterenol infusion, left ventricular diastolic function remained deteriorated in group a (P <.05 vs groups b and c). In 11 patients of group a, the cessation of beta(2)-AG for 2 weeks resulted in an improvement of left ventricular diastolic function and in an increase of plasma norepinephrine level (P <.01).

CONCLUSIONS

Long-term use of oral beta(2)-AG impaired left ventricular diastolic function in patients with BA, and the cessation of beta(2)-AG reversed diastolic pump performance to the normal level.

Method for non-invasively recording electrocardiograms in conscious mice

BACKGROUND

The rapid increase in the development of mouse models is resulting in a growing demand for non-invasive physiological monitoring of large quantities of mice. Accordingly, we developed a new system for recording electrocardiograms (ECGs) in conscious mice without anesthesia or implants, and created Internet-accessible software for analyzing murine ECG signals. The system includes paw-sized conductive electrodes embedded in a platform configured to record ECGs when 3 single electrodes contact 3 paws.

RESULTS

With this technique we demonstrated significantly reduced heart rate variability in neonates compared to adult mice. We also demonstrated that female mice exhibit significant ECG differences in comparison to age-matched males, both at baseline and in response to beta-adrenergic stimulation.

CONCLUSIONS

The technology we developed enables non-invasive screening of large numbers of mice for ECG changes resulting from genetic, pharmacological, or pathophysiological alterations. Data we obtained non-invasively are not only consistent with what have been reported using invasive and expensive methods, but also demonstrate new findings regarding gender-dependent and age-dependent variations in ECGs in mice.

Non-Q wave acute myocardial infarction in acute meningococcemia in a 10-year-old girl

INTRODUCTION

Children with acute meningococcemia may have impaired myocardial function resulting in low cardiac output despite normal intravascular volume. Severe meningococcal infection has been associated with acute interstitial myocarditis, endocarditis, and pericarditis, but not with myocardial infarction.

CASE

We present the case of a 10-year-old girl with positive family history for premature myocardial infarction who sustained an acute myocardial infarction temporally related to meningococcemia.

DISCUSSION

This is the first pediatric case of non-Q wave acute myocardial infarction associated with purpura fulminans in meningococcemia. Similarly, the association of high troponin I levels and meningococcemia has not been described previously. Although, the patient's genetic predisposition for myocardial infarction might have been a potential contributing factor, there was no angiographic evidence of coronary artery disease in this patient. Thereby, other factors related to shock, endotoxin, microthrombi of meningococcemia, and their treatment might have been also contributing. We propose possible mechanisms for this rare but serious complication of meningococcemia and review the literature.

The pharmacokinetics of isoproterenol in critically ill pediatric patients

The pharmacokinetics of isoproterenol (ISO) in infants and children have never been reported. The authors studied ISO pharmacokinetics in two disparate groups of pediatric intensive care unit patients: postoperative cardiac patients (POC, n = 10), and reactive airway disease patients (RAD, n = 9). In all, 44 blood samples were taken at steady-state from the 19 patients, whereas from 15 patients samples were also taken just before and after discontinuation of ISO infusion. There were 12 male and 7 female patients in the study, and their ages ranged from 2 days to 14 years. The average ISO dosing rate was 0.30 micrograms/kg/minute for the whole study population, ranging from 0.01 to 5.5 micrograms/kg/minute. The POC patients received a significantly lower dosing rate than the RAD patients (0.029 +/- 0.002 vs 0.50 +/- 0.21 micrograms/kg/minute, P < .0001); the average steady-state plasma concentrations of ISO were also lower in the POC patients (1.3 +/- 0.3 versus 13.9 +/- 4.9 ng/mL, P < .0001). The steady-state plasma concentration, normalized to a dosing rate of .05 micrograms/kg/minute, was 1.9 +/- 0.3 ng/mL for all patients, and the clearance was 42.5 +/- 5.0 mg/kg/minute. Postoperative cardiac patients had a significant higher normalized steady-state plasma concentration and moderately significant lower clearance than did RAD patients (2.1 +/- 0.3 versus 1.7 +/- 0.4 ng/mL, P < .05 and 33.2 +/- 4.9 versus 48.4 +/- 7.3, P < .06, respectively). The average plasma half-life of ISO was 4.2 +/- 1.5 minutes, and the volume of distribution was 216 +/- 57 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathomimetics for acute severe asthma: should only beta 2-selective agonists be used?

Sympathomimetics have become a mainstay of the treatment of acute asthma. Aerosolization of sympathomimetics provides as great or greater bronchodilation in acute severe asthma with fewer systemic effects than parenteral therapy. Despite the broncho-selectivity achieved with this route of administration, cardiostimulation remains the major, dose-limiting factor in the safe use of sustained, high-dose therapy with these agents. This article reviews the pharmacology, adverse effects, and toxicities of selected beta agonists, as well as clinical studies relevant to the question posed in the title. Although the ideal study to answer this question has not yet been performed, the authors feel that available evidence supports the preferential use of selective beta 2 agonists in patients with acute, severe asthma who will require high doses of beta agonists.

A canine model of transient myocardial dysfunction regional shortening in the presence of critical stenosis and cardiac stimulation

An experimental model of exercise-induced angina pectoris was developed in anesthetized dogs. Two i.v. bolus injections of isoproterenol (ISO, 0.25 microgram/kg; time interval: 10 min) were administered, followed by constriction of the circumflex coronary artery (LCX; critical stenosis). Further i.v. bolus injections of ISO were administered before and after i.v. infusion of 0.9% NaCl (control infusion). Stenosis of the LCX did not modify regional function at rest as assessed with ultrasonic crystals implanted subendocardially both in the distribution areas of the circumflex coronary artery and of the left anterior descending coronary artery (LAD). In the presence of critical stenosis, ISO induced a reproducible, transient decrease in systolic shortening and percent systolic shortening in the area supplied by the LCX and a marked increase in systolic shortening and percent systolic shortening in the area supplied by the LAD. During a 60-min observation period following control infusion, no further substantial changes in regional dimensions were observed. The ISO-induced hemodynamic changes were reproducible during this period. The experimental model of exercise-induced angina pectoris presented in this study can be assumed to provide a reliable basis for evaluating the efficacy of various therapeutical interventions.

Effects of isoprenaline on functional capillary density in the subendocardial and subepicardial layer of the rat myocardium

The functional capillary density in subepicardial and subendocardial layers of rat heart was measured during rest and during isoprenaline-induced (5.0 microgram X kg-1 X min-1, i.v. over 3 minutes) cardiac stimulation. For determination of the number of perfused capillaries, a fluorescent dye (thioflavine S) was infused into the left atrium; 1, 3, 5 and 10 sec, respectively, after starting dye application, hearts were excised and rapidly cooled down to -50 degrees C. In histological sections capillaries which had been perfused during the dye infusion could be identified and counted. An increase in the number of stained vessels was found in both layers of the myocardium when the time of dye exposure was prolonged. Under these conditions the rise was much smaller in isoprenaline-treated animals, this effect being most marked in the subendocardial layer (3560 +/- 199 cap./mm2, control group; 2190 +/- 30 cap./mm2, isoprenaline-treated group; dye exposure 10 sec). Isoprenaline - at the dose used - induced an increase in total blood flow (3.7 +/- 0.6 ml X min-1 X g-1, control group; 6.8 +/- 0.7 ml X min-1 X g-1, isoprenaline-treated group), however, with a relatively less pronounced increase in the subendocardial blood flow (subendocardial/subepicardial flows: 1.08 +/- 0.13, control group; 0.66 +/- 0.01, isoprenaline-treated group). These results favour the view that isoprenaline-induced relative reduction in the subendocardial blood flow is due to disturbance of perfusion pressure and extravascular compression rather than to exhaustion of the myocardial capillary reserve.

Myocardial infarction association with the Riley-Day syndrome

The "sudden death" of a 23-year-old Ashkenazy Jew, suffering from "familial dysautonomia" was probably caused by an arrhythmia accompanying a myocardial infarction. Such a report is unique. Diffuse coronary atherosclerosis and direct myocardial "catecholamine cardiomyopathy" seem responsible for the myocardial damage. However, diversion of the endocardial blood flow toward dpicardium and a "coronary steal" phenomenon, both the result of a sudden catecholamine discharge, could aggravate the ischemic injury.