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Biomedical subjects

N A Estes

Publications and source records attributed to N A Estes.

117 records · Page 7Linked to original sources
PubMed1985

Laser photoablation of pathological endocardium: in vitro findings suggesting a new approach to the surgical treatment of refractory arrhythmias and restrictive cardiomyopathy.

In selected patients, malignant ventricular tachyarrhythmias have been successfully abolished by excision of subendocardial arrhythmogenic foci. Likewise, in certain patients in whom restrictive cardiomyopathy is due to endocardial thickening, endocardial resection has resulted in hemodynamic improvement. The present study was designed to explore the utility, in vitro, of laser photoablation of pathologically thickened endocardium. Endocardial photoablation was easily accomplished regardless of etiological or anatomical variations using either the focused beam of a carbon dioxide laser or argon laser light delivered through a 200-microns optical fiber. Photoablation of areas as large as 3.9 X 1.3 cm was performed within 40 seconds. The extent or depth of endocardial photoablation could be limited to 2 mm2 in area or 1 mm in depth using either form of laser therapy. These in vitro results suggest that either carbon dioxide or argon laser phototherapy can be successfully applied to the surgical treatment of refractory arrhythmias and restrictive cardiomyopathy. Advantages of laser photoablation include speed and precision. Furthermore, laser photoablation obviates the difficulty associated with conventional techniques in establishing tissue planes.

Argon↗
PubMed1984

Electrophysiologic properties of flecainide acetate.

Preliminary clinical experience indicates that flecainide is a useful antiarrhythmic agent for the suppression of spontaneous ventricular arrhythmias. The drug also exerts marked effects on accessory atrioventricular (AV) pathway and retrograde fast AV nodal pathway refractoriness, and therefore may be effective in treatment and prevention of reentrant supraventricular tachycardias. Electrophysiologic studies indicate that flecainide slows atrial, AV nodal, His-Purkinje and intraventricular conduction and, to a far lesser degree, prolongs refractory periods in these tissues. The effect of the drug in slowing conduction within the His-Purkinje system is particularly marked and is commonly associated with prolongation of the HV interval beyond the normal range. Flecainide causes a small but significant increase in the QT interval duration, which results largely from prolongation of the QRS interval. Significant prolongation of the sinus node recovery time has been observed in patients with preexisting sinus node dysfunction. Available electrophysiologic data suggest that flecainide should not be administered to patients with advanced disease of the His-Purkinje system or sinus node. The safety of the drug in patients with mild to moderate abnormalities of His-Purkinje conduction or sinus node function awaits further study.

Anti-Arrhythmia Agents↗
PubMed1983

Permanent pacemaker therapy in corrected transposition of the great arteries: analysis of site of lead placement in 40 patients.

A retrospective analysis of 58 pacemaker leads in 40 patients with corrected transposition of the great arteries (CTGA) was made to compare the function of endocardial and epicardial leads. Extensive trabeculations of the normal right ventricle are generally thought to be essential for endocardial pacemaker lead stability. Because the systemic venous ventricle in CTGA lacks an extensive trabecular network, there has been concern that transvenous lead placement may result in a high rate of dislodgement. Epicardial leads have been assumed to be more reliable in these patients. Forty-seven epicardial and 11 endocardial leads were placed in 40 patients with CTGA who required permanent pacemaker therapy for symptomatic bradycardia. Of 13 episodes of epicardial lead malfunction in 158 patient-years, 3 were due to lead fracture and 10 to high thresholds. Surgery was required to correct the lead malfunction in 12 instances and thoracotomy was necessary for new lead placement in 6 patients. During 26.2 patient-years, there were 2 episodes of endocardial lead failure due to a high acute threshold and perforation. There were no instances of endocardial lead dislodgement. No association between type of failure and lead design was noted for either endocardial or epicardial leads. Actuarial analysis of survival revealed no significant differences in reliability between endocardial and epicardial leads. Endocardial lead fixation in the systemic venous ventricle in patients with CTGA is adequate to prevent lead dislodgement and preferable to epicardial lead placement because thoracotomy is avoided.

Adolescent↗
PubMed1983

Disseminated varicella-zoster virus infection with the syndrome of inappropriate antidiuretic hormone.

A patient with non-Hodgkin's lymphoma who was previously treated with chemotherapy and radiotherapy was seen with intestinal pseudoobstruction due to paralytic ileus associated with herpes zoster (varicella zoster) infection. The infection was accompanied by a polydermatomal rash with typical morphologic characteristics, followed by cutaneous dissemination and the syndrome of inappropriate antidiuretic hormone (SIADH), as well as myotomal paresis. The diagnosis was supported by cytology and by culture of the virus from the CSF. The isolation of the virus from the CSF, coupled with abnormalities of the patient's mental status and CSF, indicate that meningoencephalitis occurred and probably accounted for the SIADH. The patient had a spontaneous and complete recovery. To our knowledge, this is the first report of SIADH associated with herpes zoster infection.

Aged↗
PubMed1973

The distinction between gamma-glutamylhydroxamate synthetase and L-glutamine-hydroxylamine glutamyltransferase activities in rat tissues.

The formation of gamma-glutamylhydroxamate by homogenates under optimum assay condition showed an inconstancy in the ratios of the enzyme activities utilizing l-glutamate and ATP (gamma-glutamylhydroxamate synthetase) and l-glutamine and ADP (l-glutamine-hydroxylamine glutamyltransferase) in a number of normal and neoplastic rat tissues. Although gamma-glutamylhydroxamate synthetase activities in adult livers and kidneys were identical in males and females, l-glutamine-hydroxylamine glutamyltransferase activities in the organs of females were significantly lower. The developmental formations of the two activities in liver, kidney, brain and muscle were not simultaneous. The l-glutamine-hydroxylamine glutamyltransferase activity in foetal liver or neonatal kidney could be prematurely evoked by thyroxine, but the gamma-glutamylhydroxamate synthetase activity remained unchanged. Injections of cortisol also had dissimilar effects on the two activities in thymus and hepatomas. The discrepant tissue distribution, asynchronous developmental formation and differential response to several hormonal stimuli provide evidence in vivo that the two activities are not catalysed by the same protein.

Acyltransferases↗
PubMedDate not supplied

Cardiac electrophysiologic testing: its role in the selection of antiarrhythmic drug regimens for supraventricular and ventricular arrhythmias.

Cardiac electrophysiology studies use intracardiac recording and programmed stimulation to define the mechanisms and most appropriate therapy for supraventricular and ventricular arrhythmias. Using these techniques, the majority of clinical tachycardias can be reproducibly initiated and terminated in the electrophysiology laboratory, thereby allowing the most appropriate therapy to be selected. With this approach, antiarrhythmic agents can be tested in a systematic, serialized fashion for efficacy, safety and patient tolerance. With both supraventricular and ventricular tachycardias, suppression of arrhythmia induction predicts freedom from recurrence, whereas inducibility carries a poor prognosis in clinical follow-up. Electrophysiology studies provide a safe and effective approach to the treatment of selected patients with cardiac arrhythmias.

Anti-Arrhythmia Agents↗
PubMedDate not supplied

What is commotio cordis?

Although thought to be rare, sudden deaths caused by nonpenetrating chest wall impact in the absence of structural injury to the ribs, sternum, and heart (commotio cordis) are reported with increasing frequency. This phenomenon is described in individuals when they are struck by relatively innocent blows to the chest wall. Young male athletes aged 5 to 18 years are particularly at risk for this catastrophe. It has been described after blows to the chest from baseballs, softballs, hockey pucks, and other objects. Death is usually instantaneous, and successful resuscitation is uncommon. A recently reported experimental model provides clues to the mechanisms and inferences for the prevention and treatment of this devastating condition. This swine model shows that a) ventricular fibrillation results from low-energy chest wall impacts during a vulnerable period of repolarization, b) the risk of this event can be decreased with softer-than-standard baseballs, and c) prompt defibrillation is crucial for resuscitation to be successful.

Animals↗
PubMedDate not supplied

Cardiac arrhythmias in the athlete.

Cardiac arrhythmias in the athlete are a frequent cause for concern. Some arrhythmias may be benign and asymptomatic, but others may be life threatening and a sign that serious cardiovascular disease is present. Physicians often are consulted with regard to arrhythmias, or symptoms consistent with arrhythmias, in athletes. Sinus bradyarrhythmias are common and even expected in athletes. These bradyarrhythmias are rarely a cause for concern. Heart block is unusual and merits a thorough workup. Atrial fibrillation may be more common in the athlete. Supraventricular tachycardias other than atrial fibrillation generally warrant consideration of radiofrequency ablation for cure of the tachyarrhythmia. Ventricular arrhythmias in the athlete generally occur in the setting of structural heart disease that is genetically determined (hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, anomalous coronary arteries) or acquired (coronary artery disease, myocarditis, idiopathic dilated cardiomyopathies). In these conditions, the arrhythmia generally is life threatening. Ventricular arrhythmias that occur in the athlete without structural heart disease are not thought to be life threatening. Athletes with structural heart disease and syncope and those with exertional syncope merit a complete evaluation.

Arrhythmias, Cardiac↗