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Biomedical subjects

R T Smith

Publications and source records attributed to R T Smith.

At least 55 records · Page 3Linked to original sources
PubMed1987

Mexiletine: an effective antiarrhythmic drug for treatment of ventricular arrhythmias in congenital heart disease.

The use of antiarrhythmic drugs to suppress ventricular arrhythmias in pediatric patients with a structurally or hemodynamically abnormal heart appears to improve long-term prognosis. The previously successful use of phenytoin to treat serious ventricular arrhythmias led to the investigation for an alternative antiarrhythmic agent, in the same antiarrhythmic drug class, for those patients who develop side effects or become intolerant to phenytoin's antiarrhythmic effect. Forty-two children and young adults (age range 5 months to 34 years, mean 15.5 years) were treated with mexiletine. Arrhythmias treated were ventricular tachycardia (25), ventricular couplets (8), multiform ventricular premature beats (4) and frequent uniform ventricular premature beats (5). Anatomic diagnoses included congenital heart disease (postoperative in 26, unoperated in 2), cardiomyopathy (7), no heart disease (4) and other (3). Thirty-three patients had been previously treated with 1 to 5 (mean 1.6) antiarrhythmic drugs. In the short term, ventricular arrhythmias were effectively suppressed in 30 (71%) of all 42 patients treated. During follow-up (ranging to 42 months, median 10.6), 18 (60%) of the 30 acute responders continued to have excellent control. Early suppression of ventricular arrhythmias was more effective in patients with congenital heart disease (89%) than in those with cardiomyopathy (29%) or no heart disease (43%) (p less than 0.01). Initial complexity of ventricular ectopic activity had no effect on treatment results. Of 25 patients previously treated with phenytoin, in whom alternative antiarrhythmic therapy was required, 40% had long-term arrhythmia control when treated with mexiletine. Mexiletine therapy was terminated for side effects in only five patients (12%). Mexiletine is recommended for young patients with congenital heart disease and serious ventricular arrhythmias.

Adolescent↗
PubMed1987

Quantification of macular ischaemia in sickle cell retinopathy.

Macular ischaemia has a central role in the pathophysiology and prognosis of retinal macular disease. We attempted to quantitate two of its major components as follows: vascular nonperfusion, by measuring the foveal avascular zone (FAZ), using fluorescein angiography; and functional damage, using automated perimetry of the central 30 degrees. Sickle cell disease was chosen for study because it was considered a prototype for a purely ischaemic retinopathy without an exudative component. We found that the FAZ measurement was reproducible and that the patients with maculopathy had statistically larger FAZs than the normal controls (p = 0.016, Wilcoxon rank sum test). In addition, scotomas measured by visual field perimetry were significantly larger in the sickle cell patients with maculopathy than in those without maculopathy. Our results showed that angiography and perimetry of the central 30 degrees were more sensitive tests for the detection of ischaemic macular disease than visual acuity and that macular ischaemia could be quantified by their use.

Adolescent↗
PubMed1987

Differential electrophysiologic properties of decremental retrograde pathways in long RP' tachycardia.

Long RP' supraventricular tachycardias (SVT) often demonstrate both slow and decremental conduction properties in the retrograde pathway of the reentrant circuit. The electrophysiologic properties of these pathways are poorly understood. We studied 10 patients with long RP' SVT (RP'/RR, 0.52 to 0.71); five had the unusual form of atrioventricular nodal reentry (fast-slow) and five patients had accessory AV pathways with slow, decremental retrograde conduction properties. During SVT, the effects of intravenous adenosine (37.5 to 150 micrograms/kg), which increases potassium current (iK) in supraventricular tissue and hyperpolarizes membrane potential toward Ek (-90 mV), and the response to slow-inward channel blockade with verapamil (0.10 to 0.20 mg/kg iv) were evaluated. Adenosine and verapamil has similar effects in the presence of fast-slow AV nodal reentry since both agents terminated SVT by producing block in the retrograde slow AV nodal pathway. In contrast, adenosine and verapamil had differential effects on retrograde conduction in decremental accessory pathways. Adenosine terminated all episodes of SVT in the retrograde decremental pathway, whereas verapamil had a direct effect on this tissue in only two of five patients. Decremental retrograde accessory pathways can therefore demonstrate at least two types of electrophysiologic responses. Pathways that respond only to adenosine-induced hyperpolarizing K+ current likely comprise depressed fast-Na+ channel tissue, i.e., partially depolarized (greater than -60 to -70 mV) atrial tissue. In contrast, decremental accessory pathways that respond to both modulation of the slow-inward calcium current and K+ conductance have pharmacologic properties similar to those of the AV node and may represent more completely depolarized atrial fibers with resting membrane potentials of -60 mV or less.

Adenosine↗
PubMed1987

Factors influencing return to work following hospitalization for traumatic injury.

This paper describes the employment experience of 266 individuals one year after traumatic injury severe enough to require hospitalization. Of those working full-time prior to their injury, 56 per cent were employed full-time at one year; an additional 5 per cent were working part-time. Those sustaining a severe head or spinal cord injury were at highest risk of not returning to work (only 43 per cent and 21 per cent, respectively, had returned within the year). Low one-year employment rates (58 per cent) were also noted for individuals whose most severe injury was to one or more extremities. The extent and rate of return to work was examined in relation to selected socioeconomic and personal characteristics. Findings indicate that after controlling for type and severity of injury, personal income, and educational level of the injured person, as well as the identification of a strong social network as defined by the presence of one or more confidants, were important correlates of post-injury employment status.

Adolescent↗
PubMed1987

Retinal toxicity of combination antiviral drugs in an animal model.

We investigated the retinal toxicity of various combinations of four antiviral agents in intravitreal injection and vitrectomy infusion solutions in the rabbit. The nontoxic concentration of each individual agent for intravitreal injection and for vitrectomy infusion has previously been described. Our results support the concept that concentrations of 200 micrograms/0.1 mL of trifluridine, 400 micrograms/0.1 mL of hydroxyacyclovir, 200 micrograms/0.1 mL of acyclovir and 30 micrograms/0.1 mL of vidarabine can be combined for intravitreal injection without toxic retinal effects. Moreover, 60 micrograms/mL of trifluridine, 20 micrograms/mL of hydroxyacyclovir, 40 micrograms/mL of acyclovir and 8 micrograms/mL of vidarabine can be combined in vitrectomy infusion solutions without retinal damage. Further study is needed to determine the full potential of such combinations.

Acyclovir↗
PubMed1987

A clinicopathologic study of dye laser photocoagulation on primate retina.

Chorioretinal lesions produced by dye laser photocoagulation were examined on normal monkey retinas, using angiographic and histopathologic techniques. Retinal burns produced by green (514 nm), yellow (577 nm), orange (600 nm), and red (630 nm) laser lights were placed in the posterior pole between the fovea and the major vascular arcades. When examined histopathologically 24 hours after treatment, greater damage to the inner retina and deep choroid was noted with the red laser light than with the green, yellow and orange laser lights. These differences were not detectable 31 days after treatment. There were no appreciable acute differences among the lesions caused by green, yellow and orange irradiation. Laser light at four wavelengths of the orange spectrum (590, 595, 600, and 605 nm) produced comparable chorioretinal destruction in the juxtafoveal zone when examined 24 hours and 31 days after treatment. Retinal arterioles and venules treated with yellow (577 nm) and orange (600 nm) laser light demonstrated endothelial and pericytic cell damage. Changes in the outer retina, pigment epithelium, and choriocapillaris were also present beneath the photocoagulated vessels.

Animals↗
PubMed1986

Encainide for refractory supraventricular tachycardia in children.

Fifteen children, aged 5 days to 19 years (mean 4.7 years), with medically refractory supraventricular tachycardia were given oral encainide. In 10 of 15 children with "incessant" tachycardia (greater than 10% of the day), encainide alone controlled supraventricular tachycardia in 5 children; in combination with other antiarrhythmic agents, it partially controlled supraventricular tachycardia in 4 and was ineffective in 1. In 5 children with accessory atrioventricular connections, encainide eliminated supraventricular tachycardia in 3 and was ineffective in 2. Therapeutic encainide dosages ranged from 60 to 120 mg/m2/day (mean 90) (2.0 to 5.7 mg/kg/day). Encainide caused prolongation of the PR interval by 35%, RP interval by 17%, QRS interval by 44% and corrected QT interval by 10%. In 5 children with depressed left ventricular function administration of encainide, by controlling the arrhythmia, increased echocardiographic left ventricular shortening fraction from a mean of 24% to a mean of 36%. Three patients developed excessive QRS aberrancy, which was associated with wide QRS tachycardia in 2. No adverse reactions were noted in the absence of QRS aberration. Side effects were minor and noted in only 1 of 9 patients continuing to take the drug in 9 months of follow-up. Encainide was effective, or partially effective, in the control of resistant or incessant supraventricular tachycardia in 80% of children treated. Encainide allowed rapid resolution of arrhythmia-induced cardiomyopathy by controlling chronic supraventricular tachycardia.

Adolescent↗
PubMed1986

Transcatheter ablative techniques for treatment of the permanent form of junctional reciprocating tachycardia in young patients.

Five patients with medically refractory incessant supraventricular tachycardia due to a posterior septal, slowly conducting accessory connection underwent transcatheter closed chest ablative treatment. The tachycardia characteristics were consistent with the permanent form of junctional reciprocating tachycardia. In each patient the ablative attempts resulted in independent interruption of either the anterograde limb (atrioventricular node-His bundle conduction) or the retrograde limb (accessory connection) of the tachycardia circuit. Permanent retrograde pathway ablation was achieved in only one patient and followed separate permanent transcatheter His bundle ablation. In three of the other four patients the ablation attempt caused temporary interruption of retrograde conduction. Each patient had improved control of tachycardia related to the ablation attempt. Of the five patients, four required pacemaker implantation. With further refinements, selective ablation of the retrograde limb of the tachycardia circuit may be possible. This experience confirms the anatomic independence of the anterograde and retrograde limbs of the tachycardia circuit.

Adult↗
PubMed1986

Fetal ventricular pacing for hydrops secondary to complete atrioventricular block.

The advent of ultrasound recording has expanded the capabilities for treatment of the fetus in utero. The diagnosis of specific disease processes has allowed for prenatal intervention by new techniques designed to improve fetal survival. The application of ventricular pacing in a hydropic fetus with complete atrioventricular (AV) block is reported. Complete AV block resulted from maternal collagen vascular disease. The application of ventricular pacing was to allow for further in utero development and for reversal of hydrops fetalis after improvement in cardiac output. Despite fetal death 4 hours after placement of the ventricular pacing lead, this procedure when applied earlier in the development of hydrops may allow for fetal survival. Ventricular pacing was accomplished without apparent trauma to mother or fetus and no evidence of fetal injury was seen at necropsy. Therefore, in the fetus who would otherwise die in utero before the point of viability ex utero, fetal ventricular pacing may be a rational alternative to current observation.

Adult↗
PubMed1986

Predicting posttrauma functional disability for individuals without severe brain injury.

The utility of the Abbreviated Injury Scale (AIS), the most widely used anatomic scale for rating severity of injuries, and its derivative for assessing the combined effect of multiple injuries, the Injury Severity Score (ISS), were tested for their ability to predict functional disability at time of discharge from the hospital and 6 months after discharge. The ISS has been shown to correlate well with mortality and length of stay, but the relationship to levels of subsequent disability has not been examined. Five hundred and ninety-seven patients (aged 16-45 years) were interviewed at time of discharge and 6 months after discharge to ascertain functional disability along three dimensions: activities of daily living (ADL), instrumental activities of daily living (IADL), and mobility. The authors report on the relationship between severity and functional disability at time of discharge and 6 months after discharge for a subset of 473 patients who did not suffer a severe brain injury. The results show that the relationship between ISS and status at discharge and 6 months after discharge is not monotonically increasing, as it is with mortality and length of stay (LOS). Rather, the proportion of people with severe injuries who report limitations is lower than for those with moderately severe injuries as defined by the ISS. Further, it is shown that the AIS of the most severe extremity and spinal cord injury carry considerably more weight when predicting functional status at discharge and 6 months after discharge than do the AIS scores of injuries to any other body region, although the relative explanatory power of each type of injury varies with the nature of the functional disability and the time interval between the initial insult and assessment.

Activities of Daily Living↗
PubMed1986

Invasive electrophysiologic studies in children.

Although the technique of performing invasive electrophysiologic studies is similar in children and adults, the indications, interpretation, and management based on the studies are different. The major indications in children are determination of the specific diagnosis of an unknown arrhythmia and mapping prior to surgical treatment; chronic drug studies are performed for severely symptomatic patients, but technical considerations in the child limit the routine use of repeated drug trials. The greatest potential indication for invasive studies is in prognostication of symptomatic arrhythmias; this has not been possible in sinus node dysfunction and AV block, and the role in ventricular arrhythmias is under investigation. In the area of therapeutics, although drugs may have a similar effect in adults and children, the mechanism for the underlying arrhythmias may differ. The ventricular arrhythmias after congenital heart disease may have as their underlying cause the hypertrophic ventricle, not the pediatric substrate. Thus, some of the investigations originally performed in children eventually may contribute to a better understanding of arrhythmias in patients of all ages.

Arrhythmias, Cardiac↗
PubMed1986

Vitreous fluorophotometer data analysis by deconvolution.

The measurement process in fluorophotometry inherently involves a loss of information due to the finite sampling volume of the instrument. Mathematically, the effect is expressed as a convolution of the actual fluorescein distribution with the spread function of the instrument. Scattering by the ocular media can increase the spread function over that due to the instrument alone. A method is proposed for deconvolution of vitreous fluorophotometry data. Simulation studies and analyses of patient data demonstrate recovery of information with this method, including enhancement of retinal peaks and resolution of detail in the posterior vitreous which was not apparent from the original scans.

Data Display↗
PubMed1985

Chronic supraventricular tachycardia. A curable cause of congestive cardiomyopathy.

Two cases of congestive cardiomyopathy were proved to be due to chronic atrial automatic-focus tachycardia. Surgical elimination of the tachycardia resulted in normalization of cardiac function in both cases. We suggest that patients with congestive cardiomyopathy be carefully screened for supraventricular tachycardia. Patients with chronic supraventricular tachycardia should be treated aggressively to prevent myocardial dysfunction.

Cardiomyopathy, Dilated↗
PubMed1985

Prevention of sudden death after repair of tetralogy of Fallot: treatment of ventricular arrhythmias.

The majority of sudden deaths after repair of tetralogy of Fallot have been presumed to be due to ventricular arrhythmia; however, it remains to be demonstrated that antiarrhythmic medication reduces the incidence of sudden death. Since 1978, ventricular arrhythmias have been treated aggressively; these include any ventricular arrhythmia on routine electrocardiogram and more than 10 uniform premature ventricular complexes per hour on 24 hour electrocardiogram. A review was undertaken of 488 patients followed up for more than 1 month after repair of tetralogy of Fallot (mean follow-up time 6.1 years); 13.5% had ventricular arrhythmia on routine electrocardiogram. Ventricular arrhythmia appeared from 2 months to 21 years postoperatively (mean 7.3 years). Ventricular arrhythmias were significantly (p less than 0.01) related to: longer follow-up duration, older age at follow-up, older age at operation and higher postoperative right ventricular systolic and end-diastolic pressures. Ventricular arrhythmia on routine electrocardiogram occurred in 100% of those who later died suddenly compared with 12% of those who did not die (p less than 0.01). Treatment for ventricular arrhythmia was given to 46 patients and considered "successful" if there were fewer than 10 uniform premature ventricular complexes per hour on 24 hour electrocardiogram. A successful drug was found in 44 of the 46: 30 of 34 given phenytoin, 6 of 9 given propranolol, 1 of 7 given quinidine, 1 of 2 given disopyramide, 8 of 9 given mexiletine and 4 of 5 given amiodarone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Ventricular arrhythmias and sudden death in children.

In children, sudden death related to ventricular arrhythmias occurs virtually always in a patient with an abnormal heart. Therefore, children with ventricular tachycardia should be thoroughly investigated by anatomic cardiac catheterization and possibly electrophysiologic study. Sudden death may occur in a patient who had been relatively asymptomatic. This especially occurs in patients after repair of congenital heart disease. The patient may also never have had documented ventricular tachycardia, although most have had at least premature ventricular complexes on a Holter monitor recording. Finally, sudden death related to ventricular arrhythmias can often be prevented with vigorous medical and surgical therapy.

Adolescent↗