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Biomedical subjects

D L Ross

Publications and source records attributed to D L Ross.

At least 91 records · Page 5Linked to original sources
PubMed1988

Quantitation of day to day variability in mode of induction of ventricular tachyarrhythmias by programmed stimulation.

Spontaneous day to day variability in the mode of induction of ventricular tachycardia at programmed stimulation in the drug-free state has been described but not quantitated. To quantitate this variability, this study employed a new protocol of programmed stimulation in which the number of extrastimuli required for tachycardia induction was the only major stimulation variable. This protocol was applied to 18 consecutive patients with previously documented sustained ventricular tachyarrhythmia due to coronary artery disease. One to seven extrastimuli were available for arrhythmia induction if required. Each patient underwent programmed stimulation in the absence of antiarrhythmic drugs on 3 separate days with a mean interval of 5 +/- 2.7 days between studies. A sustained ventricular tachyarrhythmia was inducible in all studies with less than or equal to 4 extrastimuli; the mean number of extrastimuli required was 2.4 +/- 0.8. Day to day variability in the number of extrastimuli required for tachycardia induction was observed in the majority of patients (72%). Eleven patients (61%) varied by one extrastimulus over the three control studies, and two patients (11%) varied by two extrastimuli. At analysis of variance, the 95% confidence interval for the degree of day to day variability was +/- 1 extrastimulus from the mean number required in the three studies. Multiple configurations of induced ventricular tachycardia were frequently observed at repeat studies and occurred in 15 patients (83%). In conclusion, spontaneous day to day variability in mode of induction of ventricular tachycardia in the absence of drugs is common.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Arrhythmia Agents↗
PubMed1988

Effect of repetition of extrastimuli on sensitivity and reproducibility of mode of induction of ventricular tachycardia by programmed stimulation.

This study examined the effect of repeating the delivery of a programmed extrastimulus that previously failed to induce ventricular tachycardia, without the usual practice of concurrently altering other stimulation variables such as pacing site or basic cycle length. The impact of such repetition on both sensitivity and day to day variability in mode of arrhythmia induction was assessed in 24 patients with documented sustained ventricular tachycardia or fibrillation. Programmed stimulation in the absence of drugs was performed in each patient on 3 separate days. In the first 12 patients, each extrastimulus was scanned through diastole to refractoriness four times if no ventricular tachyarrhythmia was induced (longitudinal repetition); in the second 12 patients, each extrastimulus was delivered four times at a particular coupling interval before the interval was decreased in 10 ms steps to a closer coupling interval (lateral repetition). Day to day reproducibility of the mode of arrhythmia induction was compared with reproducibility in a control group of 18 similar patients studied previously on 3 separate days without repetition. A sustained ventricular tachyarrhythmia was inducible in all studies with four or fewer extrastimuli. In the group studied with longitudinal repetition, there was a 25% increased yield of induced ventricular tachycardia due solely to repetition of each extrastimulus scan, and the 95% confidence limit for tachycardia induction with any extrastimulus was achieved by delivering that extrastimulus three times. In the group studied with lateral repetition, there was also an increased yield of induced ventricular tachycardia at any extrastimulus coupling interval achieved by repetitive delivery of that coupling interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

Randomized controlled trial of prophylactic antiarrhythmic therapy in patients with inducible ventricular tachyarrhythmias after recent myocardial infarction.

Survivors of acute myocardial infarction who had inducible sustained ventricular tachyarrhythmias at programmed stimulation 1-4 weeks after infarction were recruited to a randomized pilot trial of Class I antiarrhythmic drugs, in an attempt to determine whether their mortality and risk of spontaneous ventricular tachycardia and fibrillation could be reduced by treatment. Of 136 eligible patients, 96 (71%) joined the trial and 47 were randomized to 'no treatment' and 49 were randomized to 'treatment' (quinidine, disopyramide or mexiletine given to attain 'therapeutic' serum levels). During follow-up, the two groups fared similarly. For the 'treatment' and 'no treatment' groups, the respective 3-year probabilities of remaining incident-free were:cardiac death, 0.91 vs 0.89; instantaneous death + non-fatal ventricular tachyarrhythmias, 0.87 vs 0.87; cardiac death + non-fatal ventricular tachyarrhythmias, 0.83 vs 0.85. The highest risk patients with inducible ventricular tachycardia fared similarly in the 'treatment' and 'no treatment' groups. The respective probabilities of remaining incident-free were: cardiac death, 0.89 vs 0.88; instantaneous death + non-fatal ventricular tachyarrhythmias, 0.79 vs 0.84; cardiac death + non-fatal ventricular tachyarrhythmias, 0.76 vs 0.77. We conclude that prophylactic Class I antiarrhythmic drug therapy with quinidine, disopyramide or mexiletine given to achieve a 'therapeutic' serum level does not appear to alter the prognosis of patients with inducible ventricular tachyarrhythmias after myocardial infarction.

Actuarial Analysis↗
PubMed1988

Reassessment of AV and VA conduction and AV junctional reentry in the normal dog heart: the role of altered autonomic tone.

The effects of isoproterenol, atropine, and metoprolol on atrioventricular (AV) and ventriculoatrial (VA) conduction were studied in 30 normal dogs under pentobarbital anesthesia using percutaneously introduced catheters. The inducibility of AV junctional reentry was also assessed before and after drug administration. Resting AV conduction was normal in all dogs, but VA conduction was present in only 57%. Isoproterenol facilitated both antegrade and retrograde conduction, with a preferential effect on retrograde conduction. VA conduction was demonstrated after isoproterenol in 91% of dogs. After testing all drugs, VA conduction was demonstrable in at least one study in 97% of dogs. Atropine had less effect than isoproterenol, suggesting that basal vagal tone was not high in this model. Dual AV nodal pathways were detectable in the antegrade direction in four (13%) dogs, and in the retrograde direction in an additional four (13%) dogs. Single AV junctional echoes were inducible with atrial stimulation in one dog with dual antegrade pathways, but were inducible with ventricular stimulation in at least one study in 83% of dogs with intact retrograde conduction. Sustained AV junctional reentry was never induced before or after drug administration. In conclusion, VA electrical continuity is almost always intact in the normal dog, but its demonstration is significantly modified by the autonomic nervous system. Isoproterenol has preferential effects on retrograde conduction and may have selective influence on distal AV nodal conduction. Twenty-six percent of normal dogs have evidence of dual AV nodal pathways. Single AV junctional echoes are inducible with ventricular stimulation in the majority of dogs and are a normal finding. Sustained AV junctional reentry is not inducible in the normal intact dog heart.

Animals↗
PubMed1988

Comparison of effects of three anesthetic agents on induction of ventricular tachycardia in a canine model of myocardial infarction.

The effects of three anesthetic agents on the inducibility of ventricular tachycardia by programmed stimulation were investigated in dogs with a surgically induced left ventricular infarct. Endocardial catheter electrodes were placed at the right ventricular apex under general anesthesia at least 2 weeks after infarction, and the dogs were allowed to recover for 24 hours before undergoing programmed stimulation in the conscious state on two occasions 2 hours apart. A protocol of programmed stimulation with up to seven ventricular extrastimuli was used. In 15 animals, ventricular tachycardia was inducible on both occasions with 3.4 +/- 0.4 (mean +/- SEM; range, 1-5) extrastimuli. Two hours after baseline conscious induction, the dogs were anesthetized with either halothane, pentobarbital, or a fixed combination of fentanyl-droperidol plus nitrous oxide. Halothane prolonged the PR interval from 99 +/- 4 to 117 +/- 6 msec (p = 0.001) and the ventricular effective refractory period from 140 +/- 4 to 157 +/- 6 msec (p = 0.008). The ability to induce ventricular tachycardia was abolished in five of 10 animals (p less than 0.05). In the animals that remained inducible, the cycle length of tachycardia increased from 153 +/- 10 to 168 +/- 10 msec (p = 0.015), while the number of extrastimuli required was unaltered. Pentobarbital prolonged the PR interval from 104 +/- 6 to 124 +/- 6 msec (p = 0.004) and the QTc interval from 270 +/- 10 to 310 +/- 6 msec (p = 0.006). Ventricular tachycardia remained inducible in only six of 10 dogs (p less than 0.05) with no change in cycle length or the number of extrastimuli required. Ventricular fibrillation was inducible in an additional three dogs with a number of extrastimuli similar to that required to induce ventricular tachycardia before anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Features of cardiac arrest episodes with and without acute myocardial infarction in the Coronary Artery Surgery Study (CASS).

Angiographic evidence of coronary artery disease was present in 16,002 patients in the Coronary Artery Surgery Study (CASS) registry. Of these patients, 551 had a history of cardiac arrest before enrollment angiography. Cardiac arrest was a complication of acute myocardial infarction (AMI) in 372 patients (68%). Electrocardiographic documentation of the responsible rhythm was available in 283 patients. Ventricular fibrillation (VF) was present in 112 (60%), ventricular tachycardia (VT) in 41 (22%) and both VT and VF in 26 (14%) patients. Stepwise linear discriminant analysis comparing the 551 cardiac arrest patients with the other 15,451 patients selected left ventricular wall motion score (F = 265), use of digitalis (F = 71), impaired blood supply to any segment (F = 16) and particularly to the anterior wall (F = 11) as discriminating variables associated with cardiac arrest. Patients with cardiac arrest occurring as a complication of AMI were younger (F = 12), had greater impairment of coronary blood supply (F = 7) and were more likely to be on a cholesterol-lowering diet (F = 16) than were patients with arrest remote from infarction. Comparison of patients with VT versus those with VF showed a positive association of VT with age (F = 8), a trend toward worse left ventricular function and presence of a left ventricular aneurysm, but no difference in severity and collateralization of coronary artery disease. It is concluded that cardiac arrest is related to the extent of myocardial damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1987

Changes in ventricular activation time on the signal-averaged electrocardiogram in the first year after acute myocardial infarction.

Repeat signal-averaged electrocardiograms were used in 40 patients to document changes in ventricular activation time and delayed potentials in the first 12 months after acute myocardial infarction. Beta-blocking and antiarrhythmic drug use was stopped for 1 week before each recording. Patients with reinfarction during follow-up were excluded. Signal-averaged electrocardiograms were first performed 1 to 4 weeks after infarction. They were repeated at 6 and 12 months in 31 patients in whom spontaneous ventricular tachycardia (VT) did not develop and were repeated after VT in the other 9 patients. Of the 9 patients in whom VT developed, all had delayed potentials at initial study and 8 (89%) still had delayed potentials at restudy after VT. In the VT patients, mean ventricular activation time was similar before and after VT (178 ms and 174 ms, respectively). In the 11 patients who had delayed potentials initially and in whom VT did not develop, the proportion with delayed potentials was 55% (6 of 11) at 6 months and did not change (55%) at 12 months. Mean ventricular activation time in these patients was 164 ms at initial study, decreasing to 147 ms at 6 months (p less than 0.05) and 148 ms at 12 months. In 20 patients with no delayed potentials initially, none had delayed potentials at 6 months and only 2 (10%) had delayed potentials detectable at 12 months. Mean ventricular activation time in these patients increased slightly, from 120 ms at initial study to 128 ms at 12 months (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

Correlation between signal-averaged electrocardiogram and programmed stimulation in patients with and without spontaneous ventricular tachyarrhythmias.

This study examined the incidence of delayed ventricular activation on signal-averaged electrocardiograms and the incidence of inducible sustained ventricular tachycardia (VT) at programmed stimulation (1 or 2 extrastimuli) in patients with and patients without spontaneous ventricular tachyarrhythmias. The correlation between delayed ventricular activation and inducible VT was investigated in 371 patients with acute myocardial infarction (AMI). In 32 patients with no ventricular disease and no spontaneous arrhythmias (group I), ventricular activation time averaged 115 +/- 2 ms, compared with 166 +/- 3 ms (p less than 0.001) for 65 patients with spontaneous ventricular tachyarrhythmias late after AMI (group II). In AMI patients with no spontaneous arrhythmias, ventricular activation time averaged 133 +/- 2 ms for 306 patients studied 1 to 4 weeks after AMI (group III) and 130 +/- 2 ms for 67 patients studied 3 to 12 months after AMI (group IV). The values for group III and group IV patients were each significantly higher than for group I (p less than 0.001), but lower than that for group II (p less than 0.001). The incidence of delayed ventricular activation was 89% for group II, 26% for group III and 18% for group IV. Sustained VT was not inducible in group I patients, but was inducible in 78% of group II (p less than 0.001 vs group I) and 20% of group III (p less than 0.05 vs group I; p less than 0.001 vs group II) (group IV was not studied).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Effect of excision of ventricular myocardium on delayed potentials detected by the signal-averaged electrocardiogram in patients with ventricular tachycardia.

The ability of surgical excision of electrically abnormal ventricular myocardium to either abolish delayed potentials or modify their timing was investigated in 21 patients with spontaneous ventricular tachycardia (VT) late after myocardial infarction. This study also examined whether modification of delayed potentials after surgery was associated with loss of ability to induce VT or improvement in left ventricular function. Signal averaging of the electrocardiogram (ECG), programmed stimulation and radionuclide ventriculography were performed preoperatively and were repeated 10 to 14 days postoperatively. At preoperative investigation, all patients had delayed potentials on the signal-averaged ECG and inducible VT at programmed stimulation. In 7 patients (33%), delayed potentials were abolished by surgery, exceeding the baseline variability of 8.5% for detection of delayed potentials. VT was no longer inducible postoperatively in 16 patients (76%), including the 7 in whom delayed potentials were no longer detectable. In the patients in whom VT was no longer inducible, mean ventricular activation time decreased from 178 ms preoperatively to 151 ms postoperatively (standard error of the mean difference = 6 ms, p less than 0.001). In the 5 patients with inducible VT postoperatively, no significant change in mean ventricular activation time was seen, 181 vs 171 ms (standard error of mean difference = 9 ms). Reductions in ventricular activation time were not associated with an improvement in left ventricular ejection fraction unless aneurysmectomy was performed in addition to excision of electrically abnormal myocardium. Thus, the signal-averaged ECG may have a role in assessing the efficacy of antiarrhythmic surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Surgical therapy for supraventricular tachycardia, a potentially curable disorder.

One hundred fifty-six patients underwent investigation and operation for supraventricular tachycardia: 145 had attempts at curative operations and 11 had His bundle section. Operative mortality was 0.68% and there were no late deaths among patients having curative operations. One patient died suddenly 1 year after His bundle section. All patients underwent electrophysiologic study before discharge and 6 months postoperatively. A satisfactory result, without supraventricular tachycardia and without medication, was achieved in 96.5% of all patients. Ninety-three percent have no supraventricular tachycardia and no demonstrable reentrant pathway at electrophysiologic study. All free wall accessory atrioventricular connections were divided and 97.7% of the patients were cured. Ninety percent of patients with posterior septal accessory atrioventricular connections had a satisfactory result, with cure demonstrated at late electrophysiologic study in 84%. Fifteen patients with atrioventricular junctional reentrant tachycardia were all cured, with preservation of normal atrioventricular conduction. Eight (88%) of nine patients with right atrial tachycardia were cured, and two patients with nodoventricular fibers and one patient with incessant atrioventricular junctional tachycardia had satisfactory results. Supraventricular tachycardia is now a potentially curable disorder when managed by low risk surgical procedures that offer a high cure rate.

Adolescent↗
PubMed1986

Effect of antiarrhythmic therapy on delayed potentials detected by the signal-averaged electrocardiogram in patients with ventricular tachycardia after acute myocardial infarction.

The ability of class I and class II antiarrhythmic drugs to either abolish delayed potentials or modify their timing was investigated in 39 patients with spontaneous ventricular tachycardia (VT) after myocardial infarction. Before the study all patients had delayed potentials on the signal-averaged electrocardiogram and inducible VT with programmed stimulation. These investigations were repeated during 67 trials of oral antiarrhythmic therapy (mexiletine 25, quinidine 24, metoprolol 13, disopyramide 2, procainamide 1, drug combinations 2). Delayed potentials were abolished in only 5 trails (7%), which was within the baseline variability of 8.5% for detection of delayed potentials. In the 7 trials in which VT inducibility was suppressed, delayed potentials persisted in 6 and mean ventricular activation time was virtually unchanged (151 ms before drug therapy, 152 ms after). Quinidine, mexiletine and metoprolol caused no consistent change in ventricular activation time. There was also no change in mean ventricular activation time (164 ms before and 163 ms after drug treatment) in patients in whom spontaneous VT did not recur with drug therapy during follow-up. Thus, the tested antiarrhythmic drugs had no consistent effects on presence or timing of delayed potentials on the signal-averaged electrocardiogram, even when VT inducibility was suppressed or recurrence of spontaneous VT was prevented.

Action Potentials↗
PubMed1986

Reproducibility of measurements of ventricular activation time using the signal-averaged Frank vectorcardiogram.

Interobserver and day-to-day variability in detecting delayed potentials and in measuring duration of ventricular depolarization using the signal-averaged Frank vectorcardiogram were investigated in 20 patients, 12 with and 8 without ventricular tachycardia (VT). No patients were taking antiarrhythmic medications, digoxin or beta blockers at the time of study. The presence of delayed potentials and duration of ventricular activation were measured 2 times a mean of 5 days apart by 2 observers. Analysis of variance showed no significant interobserver variability in ventricular activation time. Day-to-day differences in ventricular activation times were small in patients without VT, none of whom had delayed potentials at either study. Delayed potentials were present in all 12 patients with VT at the first recording and in 11 at the repeat recording. However, significant (p less than 0.01) day-to-day variability was found in ventricular activation times, and 3 of the 12 patients had marked (more than 20 ms) day-to-day changes. It is concluded that in the absence of medical or surgical intervention, delayed potentials detected on 1 day have a high chance of being present at a repeat recording. However, the exact timing of these delayed potentials shows marked day-to-day variation in some patients. Interobserver variability is not significant with this method of detecting delayed potentials.

Adult↗
PubMed1986

Technique for maximizing the frequency response of the signal averaged Frank vectorcardiogram.

This system for signal averaging of the Frank vectorcardiogram incorporates several important features: 1, simultaneous analogue to digital conversion of three orthogonal leads; 2, interactive editing of the data; 3, optimization of the fiducial timing point using a template derived from the calculated QRS vector magnitude; and 4, simultaneous display of both the averaged recording and the noise level at high amplification, which facilitates the assessment of low amplitude signals in the ST segment. The effective frequency response of the system approached theoretical expectation and background noise was low. The effect of exclusion versus inclusion of the fiducial timing point optimizing routine in the signal averaging program was examined in 21 patients. Exclusion of the optimizing routine effectively reduced the high frequency response of the system at the -3dB point from 350 Hz to about 60 Hz. The QRS complex was prolonged, and attenuation and spreading of signals in the ST segment occurred so that some delayed potentials merged with background noise and were no longer visible. We conclude that the system has several theoretical and practical advantages when compared with other techniques. A major benefit is the inclusion of a routine to optimize the QRS fiducial timing point. This minimizes distortion and attenuation of signals in the ST segment, thereby enhancing the probability of detecting the signals.

Humans↗
PubMed1986

Orthodontics for the dog. Treatment methods.

This article considers the prevention of orthodontic problems, occlusal adjustments, simple tooth movements, rotational techniques, tipping problems, adjustment of crown height, descriptions of common orthodontic appliances, and problems associated with therapy.

Animals↗
PubMed1986

Oral surgery. Basic techniques.

Some of the clinical problems most frequently seen in veterinary dentistry and their surgical solutions are discussed. Extraction of teeth, surgical repositioning of teeth, tooth transplant, oral abscesses of tooth origin, impaction of teeth, repair of maxillary canine oronasal fistula, and simple techniques for oral wiring are among the issues considered.

Animals↗