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Biomedical subjects

D A Richards

Publications and source records attributed to D A Richards.

At least 19 recordsLinked to original sources
PubMed1992

Lack of effect of midazolam on inducibility of arrhythmias at electrophysiologic study.

Midazolam has several advantages over diazepam as a sedative agent in electrophysiologic studies, but its electrophysiologic effects in humans are unknown. Therefore, its effects were studied in 20 patients undergoing electrophysiologic studies. Electrophysiologic variables were measured before and after administration of intravenous midazolam (5 mg). There were no significant changes in the electrophysiologic variables, apart from a minor decrease in sinus cycle length (711 +/- 124 vs 647 +/- 91 ms; p = 0.005). Ease of inducibility of reentrant tachycardia was not significantly altered by midazolam, and tachycardia remained inducible in all patients. The drug was well-tolerated with no significant side effects, apart from a minor reduction (mean 18 mm Hg) in blood pressure (p less than 0.001). Good amnesic effect was achieved in 16 patients, and most patients preferred it to oral diazepam for sedation during the procedure. It is concluded that midazolam can be used safely in patients undergoing electrophysiologic studies without significantly interfering with electrophysiologic variables or the inducibility of reentrant tachycardias.

Adolescent↗
PubMed1992

Accuracy of various methods of localization of the orifice of the coronary sinus at electrophysiologic study.

The coronary sinus (CS) orifice is an important reference point for determining electrode and, thereby, accessory pathway location at electrophysiologic study. The reliability of fluoroscopic landmarks used to identify the CS orifice is not known. This study compared the accuracy of several fluoroscopic landmarks for identifying the CS orifice with the location defined by radiopaque contrast injection of the CS. Forty patients were studied. Radiographic markers of the CS orifice that were examined included: (1) the point at which the CS catheter prolapsed during advancement, (2) the point of maximum convexity of the CS catheter when a superior vena caval approach was used, (3) the right side of the ventricular septum, and (4) the relation to the underlying vertebrae. The least-significant difference method of multiple comparisons was used for statistical analysis. The point at which the CS catheter prolapsed was the most accurate noncontrast method for determining the location of the CS orifice (p less than 0.05), but was possible without the use of excessive force in only 48% of patients. The point of catheter prolapse was a median of 1 mm (range 0 to 11) from the true location of the os. Errors with other examined landmarks ranged up to 3 cm. Identification of the CS orifice is best performed by radiopaque contrast injection. The point of prolapse during catheter advancement in the CS is an accurate alternative when contrast injection is not feasible. Other noncontrast fluoroscopic landmarks are less reliable and are best avoided.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Electrophysiologic studies in patients with unexplained syncope.

This study examined the role of electrophysiologic study in the evaluation of patients with unexplained syncope. The incidence of abnormalities (conduction disease, supraventricular tachycardia, ventricular tachycardia) was compared in patient groups with and without heart disease, and the effect of treatment of these abnormalities on recurrence of syncope was examined. Electrophysiologic study was performed in 111 consecutive patients with syncope, with antiarrhythmic medications being discontinued 1 week prior to study. There was no mortality associated with the procedure and only 9 patients (8%) had complications (groin haematoma, atrial fibrillation or brady-arrhythmias persisting after the procedure). Abnormalities were detected in 31 of 73 patients with heart disease (42%) but in only 6 of 38 patients with no heart disease (16%, P less than 0.01). During follow-up, syncope recurred in 2 of 37 patients (5%) treated because of abnormal findings, compared with a recurrence rate of 24% (18 of 74 patients) in the untreated group (P less than 0.05). Probability of remaining free from syncope at 2 years was 0.94 in the treated group and 0.72 in the untreated group (P less than 0.05). Mortality during follow-up was confined to the heart disease group with 5 of 30 treated patients in this group dying (17%) compared with 3 of 43 untreated patients (7%, P = not significant). Syncope patients with heart disease were thus more likely to have a diagnostically useful study than patients with normal hearts. Treatment directed at correction of abnormalities detected at electrophysiologic study reduced recurrence of syncope but did not significantly affect mortality. Syncope did not appear to be a prelude for sudden death in patients with normal hearts. Electrophysiologic study had no mortality and low morbidity.

Adolescent↗
PubMed1991

Dimensions of the human posterior septal space and coronary sinus.

Accurate anatomic localization of accessory pathways during preoperative electrophysiologic study and during operative mapping depends on a knowledge of the dimensions of the posterior septal space and the left free wall. These dimensions were therefore studied in 48 human cadaver hearts. Mean distance from the coronary sinus orifice to the left margin of the posterior septal space was 2.3 +/- 0.4 cm and mean length of the left free wall was 5.0 +/- 1.0 cm. The posterior septal space at the level of the valve anuli extended a mean of 3.4 +/- 0.5 cm around the epicardium. The width of the posterior septum measured in the coronary sinus was related to heart weight and a combination of body weight and patient age (p less than 0.05). The probability of an accessory pathway being located in the left free wall or the posterior septum during catheter mapping was calculated for various distances from the coronary sinus orifice for adults of different ages and body weights. In adults, accessory pathways located in the proximal 1.5 cm of the coronary sinus are almost always in the posterior septum. Those located between 1.5 and 3 cm from the coronary sinus orifice may be in either the left free wall or the posterior septum, and those located greater than 3 cm from the coronary sinus orifice are almost invariably in the left free wall.

Adolescent↗
PubMed1991

Routine programmed electrical stimulation in survivors of acute myocardial infarction for prediction of spontaneous ventricular tachyarrhythmias during follow-up: results, optimal stimulation protocol and cost-effective screening.

Of 3,286 consecutive patients treated for acute myocardial infarction, electrophysiologic testing was performed in 1,209 survivors (37%) free of significant complications at the time of hospital discharge to determine their risk of spontaneous ventricular tachyarrhythmias during follow-up. Sustained monomorphic ventricular tachycardia was inducible by programmed electrical stimulation in 75 (6.2%). Antiarrhythmic therapy was not routinely prescribed regardless of the test results. During the 1st year of follow-up, 14 infarct survivors (19%) with inducible ventricular tachycardia experienced spontaneous ventricular tachycardia or fibrillation in the absence of new ischemia compared with 34 (2.9%) of those without inducible ventricular tachycardia (p less than 0.0005). During the extended follow-up period (median 28 months) of those with inducible ventricular tachycardia, 19 (25%) had a spontaneous electrical event; 37% of these first events were fatal. These results suggest that the most cost-effective strategy for predicting arrhythmia will be obtained by restricting electrophysiologic testing to infarct survivors whose left ventricular ejection fraction is less than 40% and using a stimulation protocol containing four extrastimuli. Electrophysiologic testing is the single best predictor of spontaneous ventricular tachyarrhythmias during follow-up in infarct survivors. The majority (94%) with a negative test benefit from the more reliable reassurance that all is well, whereas the 25% risk of electrical events in those with inducible ventricular tachycardia justifies a prospective trial of effective prophylactic antiarrhythmic interventions.

Anti-Arrhythmia Agents↗
PubMed1991

What is the best method for assessing the long-term outcome of surgery for accessory pathways and atrioventricular junctional reentrant tachycardias?

The success of surgery for supraventricular tachycardia (SVT) is evaluated by a variety of methods in different hospitals. Unfortunately, the predictive values of these methods are not known. We therefore compared the various methods in 261 patients undergoing surgery for SVT at Westmead Hospital since 1981. Surgical outcome was assessed by early tests during the first week after surgery (serial 12-lead electrocardiograms, telemetric monitoring of the electrocardiogram, and electrophysiological study performed using epicardial wires); later tests at 6 months after surgery (12-lead electrocardiograms and electrophysiological study); and symptomatic review done by telephone interview at a median of 34 months after surgery. Early tests were obtained in 97%, later tests were obtained in 76%, and symptomatic review was obtained in 98% of patients. All of the examined tests were inaccurate methods of surgical assessment compared with the late electrophysiological study. A large proportion of the patients proven to be surgical failures at the late electrophysiological study were not detected by early tests (83%), by later electrocardiograms (66%), or by symptomatic assessment (41%). Accurate assessment of surgical outcome requires a late electrophysiological study to permit comparison of surgical techniques. Late electrophysiological study also provides accurate information on the current risks and benefits of proposed surgery for communication to patients to enable them to make an informed decision on future treatment. Most patients are willing to have a late electrophysiological study and usually benefit from clarification of their true surgical outcome.

Cardiac Pacing, Artificial↗
PubMed1991

What is the best predictor of spontaneous ventricular tachycardia and sudden death after myocardial infarction?

BACKGROUND: Death during the first year after myocardial infarction is most commonly due to spontaneous ventricular tachycardia (VT) or fibrillation (VF). The purpose of this study was to compare, in a single cohort of patients, the values of inducible VT, delayed ventricular activation, low left ventricular ejection fraction, high-grade ventricular ectopy, and ST segment displacement on exercise in predicting electrical events (witnessed instantaneous death and spontaneous VT or VF) during the first year after myocardial infarction. METHODS AND RESULTS: Three hundred sixty one patients aged less than 71 years underwent electrophysiological study, signal-averaged electrocardiogram, gated blood-pool scan, 24 hour ambulatory electrocardiographic monitoring, and exercise testing 1-2 weeks after myocardial infarction and were then followed up for at least 1 year. There were 34 deaths (eight witnessed instantaneous, 26 other), and nine patients survived one or more episodes of spontaneous VF or VT. Patients with inducible VT were 15.2 times more likely to suffer electrical events than patients without inducible VT. No proportional-hazards model excluding inducible VT was as good a predictor of electrical events as was inducible VT alone. CONCLUSIONS: Inducible VT at electrophysiological study was the single best predictor of spontaneous VT and sudden death after myocardial infarction.

Aged↗
PubMed1991

Patients with two types of atrioventricular junctional (AV nodal) reentrant tachycardia. Evidence that a common pathway of nodal tissue is not present above the reentrant circuit.

BACKGROUND: The site of the reentrant circuit in atrioventricular (AV) junctional reentrant tachycardia has not been defined; in particular, the existence of a common pathway of AV nodal tissue above the reentrant circuit is controversial. METHODS AND RESULTS: Two types of AV junctional reentrant tachycardia were induced in each of three patients at electrophysiological study. In one type of tachycardia (anterior), the onset of atrial activity occurred from 0 to 12 msec before the onset of ventricular activation, and earliest atrial activity was recorded near the His bundle. In the second type of tachycardia (posterior), the ventriculoatrial intervals were longer (76-168 msec), and earliest atrial activity was recorded near the mouth of the coronary sinus. In individual patients, the two types of tachycardia had different cycle lengths. Posterior AV junctional reentrant tachycardia was not a fast-slow form of AV junctional reentry in at least two of the three patients. Surgical cure was attempted in two patients. In one patient, anterior AV junctional reentrant tachycardia was abolished by dissection of the anterior perinodal atrium, but posterior AV junctional reentrant tachycardia could still be induced. At reoperation 4 months later, dissection of the posterior perinodal atrium abolished posterior AV junctional reentrant tachycardia while preserving AV conduction. CONCLUSION: Differences in ventriculoatrial intervals and cycle lengths and the results of selective surgery suggest that the two types of AV junctional reentrant tachycardia used different reentrant circuits. These observations imply that a common pathway of AV nodal tissue is not present above the reentrant circuit and suggest that perinodal atrium is part of these circuits.

Adolescent↗
PubMed1991

Exposure therapy for post-traumatic stress disorder. Four case studies.

Four cases of PTSD, and their treatment, are described. Symptoms responded differently to two behavioural approaches. In-vivo exposure was effective for phobic anxiety while imaginal exposure improved dysphoria and some phobic symptoms. Audio-taped imaginal exposure may be important as part of treatment.

Accidents, Occupational↗
PubMed1979

Electrochemical detection of tryptophan metabolites following high-performance liquid chromatography.

Electrochemical detection of tryptophan metabolites following separation on a reversed-phase high-performance liquid chromatography column was compared with other means of detection. Of 29 compounds studied, 26 could be detected at a sensitivity comparable to that of fluorescence derivatisation procedures. Response was linear over a wide range of concentrations and selectivity was shown to be superior to ultraviolet detection when analysing urine. Additionally, it was possible to control selectivity so that only those tryptophan metabolites from the tryptophan hydroxylase pathway were detected. This is of particular value in the study of distrubances of serotonin metabolism and is unique to this type of detector.

Chromatography, High Pressure Liquid↗
PubMed1979

Effects of H1- and H2-receptor blocking agents on histamine-induced bronchoconstriction in non-asthmatic subjects.

1 Two studies have been carried out to investigate the effect of H1- and H2-receptor blocking agents on histamine-induced bronchoconstriction in non-asthmatic subjects. 2 The H2-receptor blocker cimetidine administered orally had no effect on histamine-induced bronchoconstriction on any of the subjects tested. In three of four subjects, the H1-receptor blocker, chlorpheniramine given orally, inhibited the effect of the histamine in the lung. 3 The effects of intravenous chlorpheniramine and cimetidine, both alone and in combination, upon histamine-induced bronchoconstriction, were also studied. Chlorpheniramine inhibited the effect of the histamine and this was significantly dose related. This was not so with cimetidine and there was no evidence that the dose response curve to chlorpheniramine was affected by the additional administration of cimetidine. 4 The results show that histamine-induced bronchoconstriction in non-asthmatic subjects is not mediated by H2-receptors, but it is likely that H1-receptors are involved.

Administration, Oral↗
PubMed1979

Blood pressure reduction by incremental infusion of labetalol in patients with severe hypertension.

1. Labetalol was given by incremental intravenous infusion to nineteen severely hypertensive patients, of whom nine were refractory to previous oral antihypertensive therapy. 2. Smooth reduction of arterial pressure was achieved in twelve subjects; one remained resistant to labetalol up to 160 mg/h; a sudden fall in pressure occurred in the remaining six. No serious complications were encountered. Blood pressure control was accompanied by slight byt significant reduction in heart rate and in plasma angiotensin II and aldosterone concentrations. 3. The administration of labetalol in this way appears to be a useful technique in patients requiring rapid reduction of arterial pressure, although close and continuous supervision is necessary.

Adolescent↗