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Biomedical subjects

W R Dassen

Publications and source records attributed to W R Dassen.

18 recordsLinked to original sources
PubMed1991

The value of an expert system in performing clinical drug trials.

An expert system has been designed to assist the cardiologist in determining whether patients can be included in clinical trials. This system contains knowledge on inclusion and exclusion criteria for six drug trials, and has been validated in 100 randomly selected patients. In 97 cases, the expert system and the cardiologist made an identical classification; in the remaining three cases, the patient was incorrectly classified by the physician. The system will also optimize the order in which questions are asked in order to minimize the time required to decide on inclusion or exclusion.

Angina, Unstable↗
PubMed1991

Did prognosis after acute myocardial infarction change during the past 30 years? A meta-analysis.

Much effort has been spent to improve survival after acute myocardial infarction. To investigate how effective this effort has been, a meta-analysis was performed of studies published between 1960 and 1987 concerning mortality after acute myocardial infarction. Thirty-six studies were analyzed. They were classified with respect to deaths in the hospital and at 1 month and the 5-year mortality rate starting at hospital discharge. Mortality was assessed from all studies by comparing studies from different institutions with use of identical inclusion criteria (externally controlled studies) and by analyzing studies reporting on changes in mortality in two or more comparable patient cohorts admitted to the same institution at different time periods (internally controlled studies). Reports on clinical trials (for example, thrombolytic therapy, beta-adrenergic blockade) in acute myocardial infarction were excluded. Average overall in-hospital mortality decreased from 29% during the 1960s to 21% during the 1970s and to 16% during the 1980s. The externally controlled studies also showed a declining trend: from 1960 to 1969, 32%, from 1970 to 1979, 19% and from 1980 to 1987, 15%. The 1-month overall mortality rate decreased from 31% during the 1960s to 25% during the 1970s and 18% during the 1980s externally controlled studies. Most internally controlled studies also showed significant improvement in in-hospital and 1-month survival. In contrast, 5-year mortality after hospital discharge did not significantly decrease (33% from 1960 to 1969 and 33% from 1970 to 1979). It is concluded that in the prethrombolytic era, short-term prognosis after acute myocardial infarction has improved since 1960.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1990

An artificial neural network to localize atrioventricular accessory pathways in patients suffering from the Wolff-Parkinson-White syndrome.

UNLABELLED: The electrocardiographic localization of atrioventricular accessory pathways has been extensively described in the literature by a number of well-known electrophysiologists and surgeons. These descriptions, often represented as decision trees, are useful, but do not apply in all cases. To formalize the process of determining the proper localization, this expert human knowledge could be represented in an expert system. But since reasoning is partly based on the use of heuristic knowledge, and are often not represented in the written description of the human expert, the results will be suboptimal. On the other hand, by using a self-learning neural network approach, the causal relations between input (polarity of the delta waves) and output (the correct localization) do not have to be defined by the expert. It is derived by the neural network, by analyzing a learning set of cases consisting of the ECG plus the corresponding correct localization. In our set of 60 cases, 2 hours of training were required to learn how to localize all cases correctly. From a control set of 25 cases, 23 were interpreted by the system satisfactorily. CONCLUSION: the neural network approach can be useful in situations where causal relations between the electrocardiogram and underlying mechanism are partly undefined.

Artificial Intelligence↗
PubMed1989

Angiographic and clinical characteristics of patients with unstable angina showing an ECG pattern indicating critical narrowing of the proximal LAD coronary artery.

One hundred eighty of 1260 patients consecutively admitted to the hospital because of unstable angina pectoris had the typical ST-T segment changes suggestive of a critical stenosis in the proximal LAD. In 108 patients the ECG abnormalities were present at the time of admission. In the remaining 72 patients they developed shortly thereafter. The difference between these two groups was a longer duration of anginal complaints in the former (mean 2.3 days). Results of coronary angiography, performed a mean of 4.6 days after the last attack of chest pain, showed 50% or more narrowing in the proximal LAD in all patients. Thirty-three patients had complete occlusion of the LAD and 75 had collateral circulation to the LAD. Results of left ventricular angiography showed abnormal systolic left ventricular wall motion in 137 patients and normal systolic motion in the remaining 43 patients. The difference between these two groups was a shorter mean time interval between the last attack of chest pain and angiography in the former group (p less than 0.001). Twenty-four patients had only abnormal diastolic wall motion. Twenty-one patients had a small increase in the creatine kinase level at the time of admission. Fifteen patients (nine before and six during early revascularization) had an anterior wall myocardial infarction in the hospital; these patients had a patent but severely narrowed LAD and a low incidence of collateral circulation to the LAD.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina Pectoris↗
PubMed1988

Modern pacemakers: implantable artificial intelligence?

For over twenty years computer programs have been written for applications in cardiology. Approximately one decade ago the first Expert Systems using knowledge on cardiology were built. The use of Expert System shells enabled a breakthrough. Many systems were developed, each covering a small part of cardiology. In the pacing environment Expert Systems can be used to select the optimal pacemaker therapy or to analyze complex pacemaker electrocardiograms. With the help of these artificial intelligence techniques pacemakers can be designed, that behave in an intelligent way. Finally this knowledge representation enables the reproducible simulation of the heart-pacemaker interaction.

Artificial Intelligence↗
PubMed1987

Triggered activity induced by pacing during digitalis intoxication: observations during programmed electrical stimulation in the conscious dog with chronic complete atrioventricular block.

In isolated Purkinje fibers, digitalis intoxication induces triggered activity, which is based upon delayed afterdepolarizations. The characteristics of delayed afterdepolarizations have been studied systematically by programmed electrical stimulation. The present investigations were done to study the role of triggered activity during digitalis intoxication in the intact heart. For this purpose, a pacing protocol, similar to that used in experiments of isolated Purkinje fibers, was used. The experiments were done on conscious dogs with chronic complete atrioventricular block. Ventricular tachycardia was induced with digoxin IV 0.1 mg/kg/1-1 1/2 hr. The effect of programmed electrical stimulation on the first post-pacing interval was determined during sustained ventricular tachycardia and, following its spontaneous termination during an episode when ectopic activity could only be induced by pacing. During sustained ventricular tachycardia there was a direct linear relation between the interstimulus interval of regular pacing and the first post-pacing interval. During the episode when ectopic activity could only be induced by pacing, shortening of the post-pacing interval resulted in biphasic behavior of the first post-pacing interval. Pacing with interstimulus intervals of more than 400 ms induced a first post-pacing interval equal to the interstimulus interval, whereas shorter interstimulus intervals induced a first post-pacing interval twice the interstimulus interval. When during regular pacing only the last pacing interval was changed, a similar biphasic response resulted. When toxicity had almost subsided, ectopic activity could only be induced following short pacing intervals (200-320 ms). Again, a direct linear relation was found between the pacing interval and the first post-pacing interval. Our findings strongly suggest that at different levels of digitalis intoxication triggered activity is the underlying mechanism for the first post-pacing QRS complex.

Animals↗
PubMed1986

Effects of different modes of stimulation on the morphology of the first QRS complex following pacing during digitalis-induced ventricular tachycardia: observations in the conscious dog with chronic complete atrioventricular block.

During digitalis-induced, sustained, monomorphic ventricular tachycardia, programmed electrical stimulation was performed and the effect on the first post-pacing QRS morphology was determined. Ventricular tachycardia was induced in nine conscious dogs with chronic complete atrioventricular block by administering digoxin i.v. 0.1 mg/kg given in 1-1 1/2 hour. Spontaneous ventricular tachycardia most frequently had a right bundle branch block morphology and an extreme left axis suggesting an origin in the apex of the left ventricle. Less frequently, a left bundle branch block-like configuration with an intermediate axis was observed, compatible with an origin in the basal part of the right ventricle. Following pacing close to one of these predilection sites, the first post-pacing QRS morphology suggested an origin close to the site of stimulation. Pacing distant from these predilection sites resulted in fusion complexes between electrical activation from these predilection sites and the stimulation site. The amount of fusion depended on interstimulus interval and the number of stimuli. Long interstimulus intervals and few stimuli induced a QRS complex similar to that of the spontaneous tachycardia. The faster and longer the stimulation train, the more the QRS complex became similar to the paced QRS complex. Similar findings were also observed on decreasing the last paced interval only. Our findings suggest that triggered activity is the underlying mechanism for the first post-pacing QRS complex. QRS configuration and the relation between the R-R interval and QRS configuration during tachycardia suggest that triggered activity is also the mechanism for the spontaneously occurring ventricular tachycardia during digitalis intoxication. These observations may have important clinical implications.

Animals↗
PubMed1985

PACTOT: a reprogrammable software pacing system.

The long battery life in modern pacemakers has created the need for pacemakers in which all the parameters can be changed and updated. The availability of such a system has potential advantages: new pacing techniques can be programmed without reoperation; the number of different pacemaker systems in stock in a hospital can be reduced to this reprogrammable unit; and, finally, this system can be of great help in designing and evaluating new pacing strategies.

Computers↗
PubMed1985

Evaluation of pacemaker performance using computer simulation.

A description is given of a mathematical model of impulse conduction through the heart. The model can be used to evaluate the best pacing mode for the individual patient and to develop new pacemakers. This allows study of the influence of different parameters related to the behavior of the heart or pacemaker. Two examples using a model of a DDD pacemaker and two examples describing simulation of an antitachycardia pacing system are given to illustrate how the performance of pacemakers under different conditions can be simulated.

Electrophysiology↗
PubMed1984

Differential diagnosis of tachycardia with narrow QRS complex (shorter than 0.12 second).

One hundred eighty-seven patients with clinically documented supraventricular tachycardia with a narrow QRS complex were admitted for electrophysiologic study. The diagnoses after this study were circus movement tachycardia using an accessory pathway in 50 patients, atrioventricular nodal tachycardia in 50 patients, atrial flutter in 50 patients, atrial tachycardia in 27 patients and an incessant tachycardia retrogradely using a slowly conducting accessory pathway in 10 patients. On retrospective analysis, 5 criteria on the 12-lead electrocardiogram during tachycardia were analyzed for their value in making the diagnosis of site of origin. These criteria were P-wave location, axis of the P wave, atrial rate, alternation of the QRS complex and atrioventricular relation. Fifty-seven patients with a narrow QRS tachycardia were prospectively studied using the 5 criteria. A correct diagnosis was made in 48 of the 57 patients (84%). Thus, in most patients with a narrow QRS tachycardia, information from the 12-lead electrocardiogram is adequate for diagnosis.

Adolescent↗
PubMed1984

Prognostic value of Q waves, R/S ratio, loss of R wave voltage, ST-T segment abnormalities, electrical axis, low voltage and notching: correlation of electrocardiogram and left ventriculogram.

Data on the correlation of left ventricular segmental wall motion and electrocardiographic findings are, except for Q waves and ST segment elevation, still controversial. Therefore, in addition to Q waves and ST segment elevation, eight features of the electrocardiogram were studied in 265 patients, 61 with normal coronary arteries and 204 with coronary artery disease. Patients with a QRS duration of 0.12 second or greater were excluded. Left ventricular wall motion was assessed in the 30 degrees right anterior oblique and the 60 degrees left anterior oblique projections and analyzed by the Stanford method and a modification of that method, respectively. Asynergy of a particular segment correlated well with the presence of Q waves in the corresponding electrocardiographic lead or leads, but was also found in other segments. There was a significant (p less than 0.001) correlation between the number of leads with Q waves and the degree of extension of asynergy. The R/S ratio in lead V1 and Q waves in lead V6 appeared to be the most informative about the posterior wall. Loss of R wave voltage had a lower predictive value for segmental asynergy than did Q waves in the same lead. Among patients with electrocardiographic findings of an infarct, asynergy was found in 83 to 94%. Patients having Q waves in combination with ST segment elevation manifested more severe asynergy than did patients whose Q waves were not associated with ST elevation. New data are presented for lateral and posterior infarction. Patients having left-axis deviation, low voltage and QRS notching had severe asynergy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Dual atrio-ventricular nodal pathways and atrial fibrillation.

The determinants of the ventricular rate during atrial fibrillation were studied in a group of eleven patients demonstrating dual A-V nodal pathways during atrial stimulation. The shortest R-R interval and the mean ventricular cycle length during at least 1 min of pacing-induced atrial fibrillation were compared: a) to the effective and functional refractory period of the fast pathway; b) to the effective refractory period of the slow pathway determined during atrial stimulation, at two or more different basic cycle lengths of pacing; and c) to the shortest cycle length during atrial stimulation followed by 1:1 A-V conduction. A group of 8 patients not demonstrating dual A-V nodal pathway-curves during atrial stimulation was used as a control. In both groups the shortest R-R interval during atrial fibrillation was best predicted by the shortest cycle length followed by 1:1 A-V conduction during atrial stimulation. The mean ventricular cycle length during atrial fibrillation was not accurately predicted by any of the variables studied. The similar results in patients with and without dual A-V nodal pathways suggest that concealed conduction from one to another A-V nodal pathway does not play a role in determining the ventricular response during atrial fibrillation in patients with dual A-V nodal pathways.

Adolescent↗
PubMed1984

A comparison of the electrophysiologic effects of intravenous and oral amiodarone in the same patient.

In 12 patients (nine with Wolff-Parkinson-White syndrome and three with ventricular tachycardia) the electrophysiologic effects of intravenous (5 mg/kg body weight in 1 min) and oral (total dose 9800 to 11,200 mg) amiodarone were studied with programmed stimulation of the heart. Intravenous and oral amiodarone had a similar (p less than .05) effect of lengthening on the effective refractory period of the atrioventricular node. Only intravenous amiodarone prolonged (p less than .05) the AH interval. Oral amiodarone was more effective than intravenous amiodarone in lengthening the anterograde effective refractory period of the accessory atrioventricular pathway. Only oral amiodarone prolonged the effective refractory period of atrium and ventricle and the HV interval, all significantly (p less than .05). Intravenous amiodarone slowed (p less than .05) the rate of circus-movement tachycardia in patients with Wolff-Parkinson-White syndrome, and further slowing was observed after oral amiodarone. Termination of tachycardia by intravenous amiodarone predicted prevention of reinitiation of tachycardia during oral amiodarone. These data indicate that intravenous and oral amiodarone do not have the same electrophysiologic effects. It is not clear whether cumulative effects, active metabolites, or both are responsible for these differences.

Administration, Oral↗
PubMed1983

Value of the ajmaline-procainamide test to predict the effect of long-term oral amiodarone on the anterograde effective refractory period of the accessory pathway in the Wolff-Parkinson-White syndrome.

In patients with the Wolff-Parkinson-White syndrome, intravenous ajmaline (50 mg administered over 3 minutes) or procainamide (10 mg/kg body weight administered over 10 minutes) is helpful in defining the duration of the anterograde effective refractory period of the accessory pathway. In this study the value of the ajmaline-procainamide test to predict the effects on the anterograde effective refractory period of the accessory pathway of long-term oral amiodarone were assessed. Thirty-six patients with the Wolff-Parkinson-White syndrome were studied. Twenty-four (Group A) had a negative result of the ajmaline-procainamide test and a mean duration of the anterograde effective refractory period of the accessory pathway of 237 +/- 24 ms. Twelve (Group B) had a positive result in the ajmaline-procainamide test (disappearance of preexcitation during sinus rhythm after administration of ajmaline and procainamide) and a duration of the anterograde effective refractory period of the accessory pathway of 284 +/- 25 ms (p less than 0.05 versus values in Group A). Amiodarone prolonged the anterograde effective refractory period of the accessory pathway by 53 +/- 35 ms in patients in Group A to 290 +/- 37 ms (p less than 0.001) and by 100 +/- 85 ms in patients in Group B to 384 +/- 94 ms (p less than 0.001). The difference in mean increase between both groups was not significant. In most patients (83%) in Group A amiodarone prolonged the anterograde effective refractory period of the accessory pathway to 260 to 330 ms. However, in most patients (83%) in Group B, amiodarone prolonged the anterograde effective refractory period of the accessory pathway to greater than or equal to 330 ms (p less than 0.01). Thus, an ajmaline-procainamide test is of value in predicting the results of oral amiodarone on the anterograde effective refractory period of the accessory pathway.

Adolescent↗
PubMed1983

Extrastimulus-related shortening of the first postpacing interval in digitalis-induced ventricular tachycardia: observations during programmed electrical stimulation in the conscious dog.

The effect of different modes of pacing on interval and configuration of the first postpacing QRS complex was studied during digitalis-induced ventricular tachycardia in the conscious dog. The effect of overdrive pacing was related to pacing rate; the longest pacing intervals resulted in prolongation of the first postpacing interval, while increasing the rate of overdrive pacing led to a progressive shortening of the first postpacing interval. When extrastimuli were introduced during fixed rate pacing, the duration of the first postpacing interval was found to be predominantly effected by the extrastimulus coupling interval. The importance of the last paced interval to the duration of the first postpacing cycle length was also observed when only a single or two extrastimuli were given. The duration of the first postpacing interval was found to be independent of the site site of stimulation. In contrast, the configuration of the first postpacing QRS complex was found to be related to the site of pacing; the first postpacing QRS complex originated close to the site of stimulation independent of the configuration of the tachycardia. In conclusion, it was found that during digitalis-induced ventricular tachycardia 1) the first postpacing interval is mainly, dependent on the interval of the last paced beat, 2) the length of the first postpacing interval is independent of the site of stimulation, but 3) the configuration of the first postpacing QRS complex is related to the site of stimulation. These findings may facilitate the understanding of complex ventricular arrhythmias observed during severe digitalis intoxication in human beings.

Animals↗
PubMed1980

Comprehensive clinical electrophysiologic studies in the investigation of documented or suspected tachycardias. Time, staff, problems and costs.

To assess time, staff, problems and costs involved in clinical electrophysiologic studies for documented or suspected tachycardia, 33 consecutive cases were analyzed prospectively. At least seven staff members were used for each study. Insertion of catheters required 24--105 minutes (mean 63 +/- 20 minutes). Programmed stimulation required 12--210 minutes (mean 87 +/- 38 minutes). Total fluoroscopy times were 6--67 minutes (mean 22 +/- 15 minutes). Each study used 360--2100 feet (mean 1260 +/- 390 feet) of recording paper. Detailed analysis of tracing took 1--11 hours (mean 5 +/- 2.5 hours). Delays occurred during electrophysiologic study in 25 cases (76%), with multiple causes of delay in 14 cases (42%). These were caused by 1) difficulty in obtaining venous access (five patients); 2) difficult initial catheter placement (15 cases); 3) repositioning of catheters during stimulation (17 cases); 4) sustained atrial fibrillation (four cases). Coronary sinus catheterization was achieved from the groin in 21 of 27 cases (78%) in whom a sustained attempt was made. The approximate cost of each study was greater than $800. Our data show that clinical electrophysiologic studies in the investigation and management of tachycardia are difficult, time-consuming and expensive.

Adolescent↗