Pacemaker diagnostic diagrams

Validation of the EINTHOVEN model-based computerized electrocardiogram rhythm analysis system with three classes of clinical arrhythmias

Rhythm analysis by commercial systems does not meet clinical needs well, because (1) differential diagnosis of complex rhythms is not performed, (2) common rhythms are often misdiagnosed, and (3) transitions between rhythms are not described. We have developed a model-based diagnostic software system named EINTHOVEN that is designed to address the above limitations. A demonstration is available on the World Wide Web at http:@einthoven.uokhsc.edu. The system has been validated using simple rhythms from introductory electrocardiogram (ECG) textbooks. We present here the results of evaluation with more complex rhythm strips taken from clinical records and intermediate-level ECG textbooks. Rhythm strips were described by the onset and offset of each electrical event (P wave, QRS complex, and T wave) and by a morphology classification for each event. The rhythms included a variety of supraventricular and ventricular rhythms. The analysis was considered correct if it named all correct diagnoses in a rhythm strip, incorrect if it completed the analysis and failed to name the correct diagnoses, and indeterminate if it failed to complete the analysis. The system was designed not to complete an analysis if it could not explain an entire rhythm by at least 1 pathophysiological model. The test rhythms were not used to develop the system. Forty-six of 56 test rhythms were diagnosed correctly, and 8 were not analyzed completely. The 2 incorrect diagnoses were atrial tachycardia with variable conduction (diagnosed as intermittent complete heart block) and atrial fibrillation (diagnosed as irregular junctional tachycardia). All 56 rhythms were diagnosed correctly after minor technical improvements to the system. The processing time of the system was 7.6-fold (range 1.5-to 16.9-fold) faster than the elapsed time of the individual records. These preliminary results suggest (1) that computer-based interpretation of complex rhythms is possible, (2) that further software development is necessary to reach a clinical level of accuracy, and (3) that there are no theoretical obstacles to achieving this goal.

A new method for diagramming pacemaker electrocardiograms

Advancements in technology have made paced ECG interpretation increasingly difficult. A new method for depicting the complex pacemaker/heart interactions that eliminates the extensive use of symbols and repetitious use of refractory period and rate limit information of previous methods has been devised. The method uses a framework of parallel horizontal lines drawn on grid paper underneath the ECG. The lines are spaced apart by the actual programmed values (lower rate, AV, VA intervals) of the pacemaker in question. This framework allows the simultaneous use of the horizontal and vertical directions for the diagram of pacemaker timing intervals. Also, a single representation of refractory periods, upper rate intervals, and other variables can be labeled vertically and extrapolated horizontally across the entire diagram. Single chamber, dual chamber, and rate-modulated ECGs are readily represented. The diagram is easily plotted on standard ECG paper and flexible enough to represent complex ECGs.

Computerized interpretation of the paced ECG

Analysis of the paced electrocardiogram (ECG) is important to the follow-up evaluation of patients with implanted pacemakers. Because of the complexity and variability of pacemaker algorithms, diagnosis of paced ECGs is often considerably more difficult than the interpretation of usual ECGs. Automated interpretation of the paced ECG can provide great clinical benefit because few clinicians are adequately trained in the diagnosis of such ECGs for the interpretation of pacemaker functionality. However, comparatively little work has been done in this area, mainly because the diversity and complexity of pacemaker logic makes interpretation, automated or manual, a difficult task. The following paper reviews research in computer interpretation of the pacemaker ECG and presents a new automated method which yields more detailed and accurate results than any previous technique.

Pacemaker syndrome with AAI rate variable pacing: importance of atrioventricular conduction properties, medication, and pacemaker programmability

A patient who received an AAI Activitrax rate variable pacemaker for treatment of symptomatic sinus bradycardia is described. disopyramide prolonged the anterograde effective refractory period of the fast conducting atrioventricular (AV) nodal pathway to such an extent, that conduction switched to the slow AV nodal pathway at low atrial pacing rates. This gave rise to symptoms of the pacemaker syndrome during moderate exercise because the paced atrial event was conducted with a long, spike to Q interval with occurrence of the paced atrial event just after the preceding QRS complex. A change of medication solved this problem. Programming a bipolar electrode configuration avoided sensing of far-field QRS signals with the associated problems of resetting the basic pacing interval as well as the upper rate interval. AAI rate variable pacing requires careful evaluation of AV conduction properties, AV conduction intervals as well as the influence of medication to be given. The use of multiprogrammable pacemakers with marker channel capability will significantly facilitate the understanding and resolution of anomalous behavior.

Computer simulation of cardiac pacing

A mathematical model of the cardiac conduction system, including external pacemakers, has been developed. The heart is modeled as a network in which the impulse propagation is described by differential equations; several arrhythmia-generating mechanisms, such as modulated parasystole, reflection, macro and micro re-entry and block, can be simulated. Different kinds of pacemaker modes have been incorporated in the model, thus making it possible to simulate the interaction between the heart and the pacemaker. The model can be tuned by the user according to electrophysiological data so that pacemaker programs can be tested under different underlying conditions. During a simulation, the program generates ECG signals and pacemaker diagnostic diagrams. This model can be used for training and testing, and also as a support system when searching for the optimal pacing therapy for a particular patient.

Crosstalk due to activation of atrial sense marker function of DDD pulse generators

We studied the occurrence and characteristics of crosstalk related to the atrial sense marker function of the Intermedics Cosmos DDD pulse generator in 29 patients. Upon activation of the atrial sense markers, the pulse generator delivers a series of markers in the form of triggered atrial stimuli at 0.025 ms in duration at the programmed voltage output of the atrial channel. Under certain circumstances, these atrial sense marker stimuli may cause crosstalk when they are sensed by the ventricular sensing amplifier. This form of crosstalk may be eliminated in most cases by decreasing ventricular sensitivity and/or atrial output voltage.