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Biomedical subjects

W M Smith

Publications and source records attributed to W M Smith.

At least 181 records · Page 10Linked to original sources
PubMed1986

Determination of effects of internal countershock by direct cardiac recordings during normal rhythm.

Recording cardiac electrical activity after a countershock has been limited by amplifier saturation. Modifications to our computer-assisted mapping system allowed us to record electrical activity from 56 epicardial electrodes within 5 ms of the end of a countershock. Modifications included the use of solid-state switches to disconnect the filter section of the amplifiers during the shock and changing the low-frequency response of the amplifiers from 0.1 to 10 Hz to filter out large, low-frequency potentials after the shock. Six-millisecond truncated exponential shocks were delivered between the superior vena cava and right ventricular apex through a quadripolar catheter during normal rhythm in seven dogs. As shocks of increasing voltage were delivered during the T-Q interval, progressively more of the epicardium was directly depolarized. A shock of 109 +/- 17 (SD) V directly depolarized the entire epicardium. Shocks of constant voltage were then delivered with increasing prematurity during diastole. As the ventricles became more refractory with increasing shock prematurity, the amount of epicardium depolarized became progressively less. Thus computer-assisted mapping techniques are capable of measuring the area depolarized by a shock during normal rhythm and may be useful during arrhythmias to improve our understanding of defibrillation and cardioversion.

Animals↗
PubMed1986

Activation during ventricular defibrillation in open-chest dogs. Evidence of complete cessation and regeneration of ventricular fibrillation after unsuccessful shocks.

To test the hypothesis that a defibrillation shock is unsuccessful because it fails to annihilate activation fronts within a critical mass of myocardium, we recorded epicardial and transmural activation in 11 open-chest dogs during electrically induced ventricular fibrillation (VF). Shocks of 1-30 J were delivered through defibrillation electrodes on the left ventricular apex and right atrium. Simultaneous recordings were made from septal, intramural, and epicardial electrodes in various combinations. Immediately after all 104 unsuccessful and 116 successful defibrillation shocks, an isoelectric interval much longer than that observed during preshock VF occurred. During this time no epicardial, septal, or intramural activations were observed. This isoelectric window averaged 64 +/- 22 ms after unsuccessful defibrillation and 339 +/- 292 ms after successful defibrillation (P less than 0.02). After the isoelectric window of unsuccessful shocks, earliest activation was recorded from the base of the ventricles, which was the area farthest from the apical defibrillation electrode. Activation was synchronized for one or two cycles following unsuccessful shocks, after which VF regenerated. Thus, after both successful and unsuccessful defibrillation with epicardial shocks of greater than or equal to 1 J, an isoelectric window occurs during which no activation fronts are present; the postshock isoelectric window is shorter for unsuccessful than for successful defibrillation; unsuccessful shocks transiently synchronize activation before fibrillation regenerates; activation leading to the regeneration of VF after the isoelectric window for unsuccessful shocks originates in areas away from the defibrillation electrodes. The isoelectric window does not support the hypothesis that defibrillation fails solely because activation fronts are not halted within a critical mass of myocardium. Rather, unsuccessful epicardial shocks of greater than or equal to 1 J halt all activation fronts after which VF regenerates.

Animals↗
PubMed1986

Use of diuretics in treatment of hypertension in the elderly.

Men and women with isolated systolic hypertension who were at least 60 years of age were treated for 1 year with chlorthalidone (25-50 mg daily) or matching placebo as the step I drug. Most patients reached goal blood pressure without requiring a step II drug. The blood pressure response was similar in all age, sex and race subgroups, with an overall difference between the randomised groups of 17 mm Hg for systolic blood pressure (p less than 0.001) and 6mm Hg for diastolic blood pressure (p less than 0.001). The only common adverse effects were asymptomatic changes in the serum concentrations of potassium (0.5 mmol/L lower in the chlorthalidone group, p less than 0.001), uric acid (0.9 mg/dl higher, p less than 0.001), and creatinine (0.08 mg/dl higher, p = 0.02). Compliance was good, and more than 80% of participants were still taking the study medications at the end of the year.

Aged↗
PubMed1986

Systolic Hypertension in the Elderly Program, Pilot Study (SHEP-PS): morbidity and mortality experience.

SHEP-Pilot Study, a randomized, double-blind, placebo-controlled trial of drug therapy for isolated systolic hypertension, followed 551 participants aged 60 years or more with untreated blood pressures of greater than or equal to 160/less than 90 mmHg for an average of 34 months. Mean age was 72 years, 63% were female and 82% white. Pretreatment blood pressures averaged 172/75 mmHg. As their Step I drug, 443 participants were assigned chlorthalidone and 108 placebo. Of 512 surviving participants, 80% and 84% of the chlorthalidone and placebo groups, respectively, attended their last clinic visit; 71% and 60% were still taking blinded drug; and 60% and 33% had systolic blood pressures less than 160 mmHg. Final blood pressures averaged 140/67 and 154/72 mmHg for the chlorthalidone and placebo groups, respectively. All-cause mortality rates were 25 and 23 deaths per 1000 participant-years of risk, respectively; rates for 'definite' first strokes were 8.3 and 13 deaths. Differences between chlorthalidone and placebo groups were significant for blood pressure but not for event rates.

Aged↗
PubMed1985

Systolic Hypertension in the Elderly Program (SHEP): antihypertensive efficacy of chlorthalidone.

The Systolic Hypertension in the Elderly Program (SHEP) is a randomized, blinded test of the efficacy of antihypertensive drug treatment. In a large feasibility trial, 551 men and women who had isolated systolic hypertension and were at least 60 years old received chlorthalidone (25 to 50 mg/day) or matching placebo as the step I drug. After 1 year, 83% of the chlorthalidone group and 80% of the placebo group were still taking SHEP medications. Of those still taking chlorthalidone, 88% had reached goal blood pressure (BP) without requiring a step II drug, and most had responded to the lower dose (25 mg/day). The BP response was similar in all age, sex and race subgroups, with an overall mean difference between randomized groups of 17 mm Hg for systolic BP (p less than 0.001) and 6 mm Hg for diastolic BP (p less than 0.001). The only common adverse effects were asymptomatic changes in the serum levels of potassium (0.5 mEq/liter lower in the chlorthalidone group, p less than 0.001), uric acid (0.9 mg/dl higher, p less than 0.001) and creatinine (0.08 mg/dl higher, p = 0.02). This study indicates that chlorthalidone is effective for lowering BP in elderly patients with systolic hypertension and sets the stage for a larger trial of the effects of such treatment on the incidence of cardiovascular disease.

Aged↗
PubMed1985

Development of an endocardial-epicardial gradient of activation rate during electrically induced, sustained ventricular fibrillation in dogs.

Electrograms recorded with currently available electrodes become indistinct soon after the onset of ventricular fibrillation (VF), thus, little is known about transmural myocardial depolarization during VF. A plunge electrode system (plunge) was developed that registers discrete deflections during VF. These plunges were used to record for 20 minutes after inducing VF with a single premature shock in 20 open-chest dogs. In the first 6 dogs the epicardium was exposed to room temperature and in 14 dogs transmural temperature was maintained at 38 degrees C. Electrograms recorded with the transmural plunges contained sharp, discrete deflections during early VF in all dogs. Over the next 20 minutes of VF, the rate, regularity of cycle length and discreteness of the deflections in the electrograms decreased with time, first at the epicardial level, then deeper toward the endocardium. In all dogs, however, discrete, regular, rapid deflections persisted in the most subendocardial electrogram throughout the recording period. In 8 dogs, transmural myocardial biopsy samples were taken before fibrillation, and at intervals after the onset of fibrillation. The high-energy phosphate content of the myocardium decreased during VF, with comparable decreases in the epicardial and endocardial halves. Coronary perfusion was maintained during the first 20 minutes of VF in 6 additional dogs by cardiopulmonary bypass. A gradient of activation rates did not develop on bypass, but did develop within 1 minute of halting bypass. Thus, the endocardial-epicardial gradient of activation rates during VF is caused by ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1985

Epidemiology of congestive heart failure.

Despite the paucity of epidemiologic work on congestive heart failure (CHF), the salient features of the natural course of cardiac failure are understood. The estimated 1983 incidence of CHF in the United States was 214,000 men and 184,000 women. The estimate of prevalence was 2.3 million persons, with a remarkable increase with advancing age and higher rates in men than women at all ages. Overt heart disease plus age are the principal determinants of the incidence of CHF. Nearly 90% of patients with CHF have systemic hypertension or coronary heart disease, or both, as the antecedent underlying condition. Diabetes mellitus increases the risk of CHF at all ages, particularly in women and those treated with insulin. The prognosis after diagnosis of CHF is grim and is related to the degree of myocardial dysfunction. The challenge is to develop more effective drugs not only for the management of overt CHF, but also for the prevention of its progression.

Aged↗
PubMed1985

Hypertension management in the Multiple Risk Factor Intervention Trial (MRFIT). Six-year intervention results for men in special intervention and usual care groups.

The Multiple Risk Factor Intervention Trial was a large collaborative primary prevention trial designed to test the effects of lowering cardiovascular risk factors (ie, diastolic blood pressure [DBP], serum cholesterol, and cigarette smoking) on mortality rate from coronary heart disease in 12,866 high-risk men aged 35 to 57 years. Men were randomly assigned to either special intervention (SI) or usual care (UC) groups. Usual care men were referred to their regular source of medical care. Special intervention men were seen frequently and underwent intensive intervention initially followed by maintenance intervention in 22 different clinical centers. Hypertension intervention in SI men primarily consisted of a stepped-care pharmacologic approach designed to lower blood pressure (BP). After six years, 58.2% of SI men and 47.0% of UC men were given antihypertensive medication. In both study groups, mean systolic and diastolic BPs decreased from baseline; after six years, overall DBP was 3.2 mm Hg lower in SI men compared with UC men. In hypertensive men (DBP greater than or equal to 90 mm Hg or those taking antihypertensive medication at baseline), after six years, DBP was 4.4 mm Hg lower in the SI group compared with the UC group. Use of specific antihypertensive agents differed substantially between the two groups. Self-reported complaints while taking antihypertensive drugs were minimal in both groups. Weight loss was associated with BP lowering in both study groups, regardless of treatment status.

Adult↗
PubMed1984

Identification of reproducible ventricular tachycardia in a canine model.

Epicardial mapping was used as a standard to investigate how well the limb leads, both alone and in conjunction with 5 select epicardial electrodes, can verify reproducibility in a common, open-chest canine model of ventricular tachycardia (VT). Reproducible VT was defined as 2 or more episodes of monomorphic VT with similar rates, limb lead tracings and epicardial maps. In this study, 21 dogs underwent 2-hour occlusion of the left anterior descending coronary artery followed by reperfusion. Three days later, programmed stimulation was used to induce VT that was analyzed with limb leads I, II and III and 27 simultaneously recorded, bipolar epicardial electrodes. Thirteen dogs had VT of which 11 had polymorphic VT (varying QRS morphology). Twelve dogs yielded at least 1 form of monomorphic VT. Eight had 2 or more distinct forms of monomorphic VT (pleomorphism). Four of these 8 dogs had pleomorphic VT that was not apparent from the limb lead tracings, but was recognized from the epicardial activation maps constructed from the 27 epicardial recordings. To provide a method of distinguishing various VTs without the need of full epicardial mapping, 5 of the 27 epicardial electrodes were selected. These were positioned over the midanterior and midposterior right and left ventricles, and the left ventricular apex. By analyzing electrogram morphology and activation time, VT reproducibility could be as accurately identified with these 5 electrodes as with epicardial mapping derived from 27 electrodes. In conclusion, multiple VT morphologies are common in this open-chest canine model. Limb lead recordings alone are inadequate for analysis of VT reproducibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Percutaneous absorption of corticosteroids: age, site, and skin-sectioning influences on rates of permeation of hairless mouse skin by hydrocortisone.

As part of a long-range plan to decipher the mechanism of mass transfer of corticosteroids across skin, the permeation of [3H]hydrocortisone through hairless mouse skin was characterized by in vitro diffusion cell techniques. Age and anatomical site-related behaviors were explored mainly with whole skin but also with skin stripped of its horny layer. Permeability of the mouse skin was low shortly after birth and increased during the singular normal hair cycle exhibited by the SKH-hr-1 mouse strain. The return to a hairless state over a period of 20-35 d was accompanied by decreased permeability of hydrocortisone. A permeability coefficient of approximately 2 X 10(-4) cm/h was found for the mature mouse. For whole skin, there was no difference in the permeabilities of dorsal and abdominal skin sections, but for stratum corneum-free membranes and dermal membranes, the abdominal site appeared to be more permeable, which is consistent with its thinner dimensions. Totally stripped skin and isolated dermis are approximately 500 and approximately 1000 times more permeable than intact skin, respectively; the unaltered stratum corneum of the hairless mouse is thus shown to be the major barrier to the mass transfer of hydrocortisone.

Aging↗
PubMed1983

Clinical spectrum of ventricular tachycardia with left bundle branch morphology.

Twenty-nine patients with apparent ventricular tachycardia (VT) of left bundle branch block (LBBB) morphology were evaluated. Tachycardia was associated with an organic basis in 24 of 29 patients: 7 had Mahaim fibers of the nodoventricular type, 7 had arrhythmogenic right ventricular dysplasia, 5 had coronary heart disease, 3 had biventricular cardiomyopathy, and 2 had associated congenital heart disease. In many patients the underlying cardiac disease was not readily apparent. In the patients with a Mahaim fiber, the electrocardiogram taken during sinus rhythm was frequently normal. A reentry tachycardia with anterograde conduction over the nodoventricular fiber could mimic VT as diagnosed by the usual criteria; nodoventricular fibers were, therefore, often unsuspected before electrophysiologic evaluation. In patients with arrhythmogenic right ventricular dysplasia, cineangiography demonstrated abnormalities of the right ventricle, but only minor or no abnormalities of the left ventricle. Clinical and electrocardiographic features were not distinctive. Of the 29 patients, 22 had serious symptoms accompanying the tachyarrhythmia or had required cardioversion. Patients were followed up for an average of 20 months: 4 patients died. Thus, VT exhibiting an LBBB morphology is not uncommon and is frequently associated with organic heart disease, serious symptoms, and significant mortality. Right ventricular angiography and electrophysiologic study may clarify the diagnosis in these patients.

Adolescent↗
PubMed1983

Transvenous ablation of the atrioventricular conduction system in dogs: electrophysiologic and histologic observations.

The correlation of histologic and electrophysiologic findings in dogs undergoing transvenous ablation of atrioventricular (AV) conduction has not been described. The creation of complete AV block in 10 dogs was attempted by delivering a direct-current shock transvenously through a standard tripolar electrode catheter. The catheter was positioned to record the largest unipolar atrial and His bundle electrograms. A 280 J shock was delivered to the recording electrode by a standard cardioversion unit. After 1 shock, all dogs were in complete AV block refractory to isoproterenol (1 to 4 micrograms/min) and atropine (0.5 to 2.0 mg). Four weeks later, 5 dogs remained in complete AV block, 1 had first-degree block, and 4 had resumed normal AV conduction. Each dog with complete heart block had histologic evidence of severe damage to the AV node, His bundle, or both. On gross examination, these dogs were found to have discrete scars at the base of the septal leaflet of the tricuspid valve. Of the 5 dogs that had resumption of AV conduction, only 1 had histologic evidence of significant damage to the AV conduction system. That animal manifested a marked increase in the P-R interval (100 to 210 ms). Although temporary heart block occurred in each animal, chronic interruption of AV conduction was more difficult. Catheter location, atrial and His bundle electrogram relations, and the electrode used for delivery of energy were factors determining the effectiveness of this technique.

Animals↗
PubMed1983

A system for the analysis of long-term electrocardiographic studies in clinical research and training.

A computer system has been developed for the analysis of data from long-term electrocardiographic studies in the context of an institution committed to clinical research and training. The major characteristics required of such a system are intelligence, flexibility, friendliness, and maintainability. These attributes are achieved by a user interface which consists of menus and interactive graphics, and by the use of highly modular software developed in a high-level programming language. The system has been used in studies of the effects of drugs on cardiac arrhythmias and has been easy to learn and convenient to use.

Academies and Institutes↗
PubMed1983

Localization of septal pacing sites in the dog heart by epicardial mapping.

To examine whether different septal pacing sites could be distinguished by their epicardial activation patterns, six to eight stimulating electrodes were placed throughout the septum in seven open chest dogs. Unipolar electrograms were obtained from 52 epicardial electrodes during pacing from each stimulating electrode and isochronous epicardial maps were constructed. The location of each stimulating electrode was found by dissection, and its distance from the overlying epicardium was measured. To allow comparison among epicardial maps, the septum was conceptually subdivided into nine regions to which stimulating electrodes were assigned. Epicardial activation patterns from the same region were similar and these patterns allowed the region containing a stimulating electrode to be identified in many cases. Three other variables were found to have additional localizing value. There were: 1) the time from the stimulus to epicardial breakthrough, 2) the duration of epicardial activation, and 3) the area of epicardium activated in the first 5 ms after epicardial breakthrough. For those stimulating electrodes that could not be localized by their epicardial activation patterns, the distance of the stimulating electrode beneath the epicardium was well fit from these three variables by multiple regression (correlation coefficient [r] = 0.97). Thus, using all the previous factors, localization of septal pacing sites was possible in the noninfarcted dog heart by epicardial mapping.

Animals↗
PubMed1983

Late fractionated potentials and continuous electrical activity caused by electrode motion.

Late fractionated potentials, recorded during cardiac mapping to find the source of a ventricular arrhythmia, have been ascribed particular localizing value. Re-entry is assumed when these highly amplified and filtered recordings span diastole during tachycardia. The purpose of this study was to see if such potentials can occur artifactually. A saline soaked 7 X 2 X 3 cm sponge was sewn to the epicardium of the right ventricle in five non-infarcted, open-chest dogs. Two bipolar button electrodes, one with 1 mm and one with 1 cm interelectrode spacing, were attached to the outer surface of the sponge and a bipolar wire hook electrode was placed just under the outer surface of the sponge. Thus all three electrodes were 3 cm from the nearest myocardium yet still subjected to cardiac motion. The electrodes were recorded at gains of 4,000-40,000 and filtered to pass 50-300 hertz. One to three rapid deflections were recorded during the QRS from all electrodes. In seven of the the 15 electrode recordings, two or three additional deflections, 1100-200 microV in amplitude, occurred after the QRS. These late potentials were fractionated and recurred reproducibly from cycle to cycle. In two cases, these late fractionated potentials could be made to span diastole by rapid pacing to simulate tachycardia. Clamping the sponge to sliminate motion between the sponge and electrode caused this late activity to disappear. Thus, in highly amplified and filtered recordings, electrode motion can cause artifacts resembling late fractionated potentials and continuous electrode activity.

Animals↗
PubMed1983

Bystander accessory pathway during AV node re-entrant tachycardia.

Between 1970 and July 1980, wide QRS tachycardia due to re-entry confined to the AV node with bystander involvement of an accessory atrioventricular pathway (AAV) was documented in three of 290 patients with the Wolff-Parkinson-White syndrome studied at Duke Medical Center. In each of the patients, at least one transition between wide and narrow QRS morphology was recorded without change in either the cycle length of tachycardia or the atrial activation sequence. Two of the three patients had a single left-sided AAV (lateral, postero-lateral) showing antegrade conduction only. The third patient had two right-sided AAVs (free wall, septal), each capable of bidirectional conduction. Initiation and termination of repetitive concealed conduction into the ventricular insert of an AAV appeared to be one mechanism determining bystander AAV participation. Documentation of the retrograde sequence of atrial activation during tachycardia, and examination of the effects of interpolated premature depolarizations from both the ventricle and mid-line atrium are the most helpful features in resolving the differential diagnosis of wide QRS tachycardia in patients with W-P-W syndrome.

Adolescent↗
PubMed1983

The induction of atrial flutter and fibrillation and the termination of atrial flutter by esophageal pacing.

In patients with Wolff-Parkinson-White syndrome (WPW), it is important to assess the ventricular response during atrial flutter or fibrillation since conduction across the accessory pathway during these atrial rhythms may cause hemodynamic impairment or life-threatening ventricular arrhythmias. We have recently reported the effective use of an esophageal electrode in pacing the atrium. In this study we prospectively assessed the ability to induce atrial flutter and fibrillation by esophageal pacing in 23 patients with WPW or other electrophysiological abnormalities. An esophageal bipolar electrode with 29 mm interelectrode distance was positioned in the esophagus to record the most rapid and largest esophageal electrogram (mean distance of 36.6 +/- 2.9 cm (SD) from the nares). Pacing was performed at cycle lengths of 40-340 ms (mean 166 +/- 72), pulse durations of 7.0-9.9 ms, and currents of 10-25 mA. Atrial flutter alone was induced in 6 patients, fibrillation alone in 11 patients, and both arrhythmias in 5 patients. In one patient neither flutter nor fibrillation was induced by esophageal pacing, and fibrillation was induced only with difficulty using intracavitary pacing. Of the 11 patients with flutter, the arrhythmia was terminated in 8 by esophageal pacing at cycle lengths of 160-220 ms (mean 176 +/- 18 ms). All patients tolerated the procedure well with only mild to moderate discomfort. Therefore, esophageal pacing appears to offer an effective, well tolerated method of initiating atrial fibrillation and flutter and terminating atrial flutter and offers a potentially useful noninvasive method of following patients serially.

Adolescent↗