Effects of anisotropic myocardial conductivity in model of defibrillation current density distribution.
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Anisotropy↗
Biomedical subjects
F W Lindemans
Publications and source records attributed to F W Lindemans.
Holter documented sudden death in a patient with an implanted defibrillator.
A 68-year-old man with recurrent attacks of monomorphic ventricular tachycardia (VT) received a pacer cardioverter defibrillator featuring antitachycardia pacing and cardioversion/defibrillation. Over 300 episodes of VT were successfully terminated by antitachycardia pacing. During Holter monitoring the patient experienced supraventricular tachycardia with delivery of multiple antitachycardia pacing, cardioversion, and defibrillation therapies ending with the death of the patient. The following factors played a role in the unfortunate outcome of this patient: 1. triggering of VT therapy by an unexpected high sinus rate; 2. atrial fibrillation induced by cardioversion therapy; 3. a gradual and continuous increase in rate during atrial fibrillation possibly caused by repeated VT and ventricular fibrillation therapies and/or by a thrombus, found at autopsy, in a bypass graft; and 4. the limited ability of presently available defibrillators to distinguish between ventricular and supraventricular arrhythmias.
Aged↗
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.
Aged↗
Detection of insulation failure by gradual reduction in noninvasively measured electrogram amplitudes.
Insulation failure of pacemaker leads may give rise to functional defects such as under- or oversensing, loss of capture or muscle stimulation. An increased incidence of such failures has been reported for the bipolar polyurethane-insulated Medtronic model 6972 pacing lead. It is therefore important to identify techniques that will detect such insulation defects early. A case report is presented in which diminishing electrogram amplitude at follow-up predicted lead failure several months before becoming clinically manifest. This finding suggests that routine measurement of such an electrogram may be a useful tool in predicting impending lead malfunction.
Aged↗
Clinical experience with an activity sensing pacemaker.
During clinical evaluation of the Medtronic Activitrax pacemaker in a worldwide multicenter study, implant and follow-up data were provided by 61 investigators on 222 patients. Pacing indications included two- and three-degree AV block in 149 and atrial arrhythmias in 174 patients; 16 patients received atrial pacing. Average and longest documented follow-up periods were 7.5 and 16 months respectively. Paired treadmill tests, one in Activity mode and one in VVI/AAI mode, were performed by 120 patients. At peak exercise, average heart rate was 95 bpm in VVI/AAI mode and 118 bpm in Activity mode (p less than 0.0001). Average exercise time was 9.4 minutes in VVI/AAI mode and 10.8 minutes in Activity mode (p less than 0.0001). In 54 patients who exclusively had paced rhythm during both treadmill tests, average heart rates and exercise times were 70 ppm and 8.1 minutes in VVI/AAI mode and 111 ppm and 10.3 minutes in Activity mode respectively (p less than 0.0001). 24-hour Holter recordings typically demonstrated pacing at or near basic rate during periods of rest and appropriate increase in pacing rate during daily activities. Patients had significantly fewer problems with physical effort in daily life during a week of Activity mode pacing than during a week of VVI/AAI mode pacing (p less than 0.05) as assessed from the symptom scores recorded by 62 patients in special diaries.
Clinical Trials as Topic↗
Merits of various antipacemaker circus movement tachycardia features.
Pacemaker circus movement tachycardia (PCMT) was a significant problem in first generations of DDD pacemakers. Programmability of the atrial refractory period proved to be an effective tool to prevent PCMT except in patients with very long ventriculoatrial (V-A) conduction intervals, because a long atrial refractory period severely limits the maximum tracking rate. In these patients, extension of the atrial refractory period after a VPB, bipolar atrial sensing, adaptation of atrial refractory period to atrial rate, and VPB synchronous atrial stimulation helped limit the incidence of PCMT. Rate smoothing and fallback behavior have given rise to other forms of PCMT. Once initiated, PCMT can be terminated by a single P wave or by means of an appropriately timed atrial stimulus. Recognition by means of continued upper rate pacing may not be helpful in patients with a long V-A conduction interval because their PCMT rate will be low, thus requiring a low upper rate to trigger. Therefore, absolute prevention of PCMT has not yet been achieved, but PCMT is no longer a significant problem in DDD pacing; recognition of PCMT should not be related to the ventricular upper rate limit.
Atrioventricular Node↗
Noninvasive evaluation of pacemaker circus movement tachycardias.
Ventriculoatrial (VA) conduction was studied in 11 patients before DDD pacemaker implantation by incremental right ventricular pacing while recording right atrial endocavitary signals. After implantation and at 3-month outpatient visits, VA conduction and ability to initiate and sustain pacemaker circus movement tachycardia (PCMT) were systematically assessed noninvasively by testing the response of the pacemaker to asynchronous and single synchronized chest wall stimuli, muscle signals, and programmer pertubations. VA conduction was demonstrated in 3 of 11 patients before implantation as well as by noninvasive techniques after implantation with induction of PCMT. VA conduction became apparent in 2 additional patients after implantation. One of the 2 patients presented clinically with PCMT. In both patients, PCMT could be induced noninvasively. The presence or absence of VA conduction was variable, as was the rate of right ventricular pacing at which VA block occurred. In conclusion, (1) noninvasive testing techniques were effective in inducing PCMT in all patients with VA conduction and helpful in determining control of PCMTs, and (2) thorough preimplantation and repeated postimplantation assessment is needed to control and prevent PCMT.
Adult↗
A versatile pacemaker system for termination of tachycardias.
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Adolescent↗
Pacemaker related tachycardias.
Three cases of pacemaker interactive tachycardia are presented. The first two are [artificial] circus movement tachycardias. In the first one the retrograde arm of the tachycardia circuit was provided by the A-V node and the antegrade arm by an atrial synchronous pulse generator. In the second case, the A-V node and, coincidentally, an A-V sequential pulse generator alternately provided the antegrade arm while the retrograde arm was by way of an accessory pathway. In the third case ventricular inhibition during A-V sequential pacing gave the paced atrial events the chance to be conducted to the ventricles with a long A-V interval. This resulted in a tachycardia with a rate of 150 bpm, instead of the programmed rate of 110 bpm.
Adult↗
Acute voltage, charge, and energy thresholds as functions of electrode size for electrical stimulation of the canine heart.
This paper analyses the relationships between electrode size and charge, voltage, and energy thresholds in acute animal experiments. Cathodal stimuli of 1 ms duration are applied to canine hearts by using epicardial disc electrodes. Threshold charge in constant current and in constant voltage stimulation proves to be proportional to the electrode radius (a) to the power 1.5 for a greater than 0.4 mm and to be independent of electrode size for a less than 0.2 mm. Voltage and energy thresholds are proportional to square root a and a2 respectively for a greater than 1 mm. Voltage thresholds show a minimum at a radius of about 0.5 mm, energy thresholds at about 0.3 mm. These results are explained by using two principles. The first is that the charge applied to the heart determines the response of the tissue to a stimulus and the second, that electrode impedance may be described by an RC-series circuit in these experiments. The resistance in this circuit is inversely proportional to electrode radius, in agreement with calculation of the electric field around the electrode. Electrode capacity depends linearly on electrode surface area. Stimulation is most efficient under the circumstances mentioned above for an electrode radius of about 0.3 mm.
Animals↗
Current thresholds and liminal size in excitation of heart muscle.
End-diastolic current thresholds have been measured in 12 open-chested dogs with epicardial disc electrodes ranging in radius from 0.01 to 9.0 mm. The current threshold for cathodal 1 ms impulses proved to be independent of electrode size for radii smaller than 0.2 mm and proportional to the radius to the power 1.5 for radii greater than 0.4 mm. This relationship can be explained on the assumption that excitation occurs if the current passing through a 'liminal area' with dimensions of about 0.3 mm exceeds a critical value. This result is in agreement with the liminal length concept used to describe excitation of cardiac Purkinje fibres. The existance of a liminal area or liminal lenght for excitation implies that there will be a limit to increasing stimulation efficiency by applying smaller stimulation electrodes.
Animals↗
Site of initial excitation and current threshold as a function of electrode radius in heart muscle.
End-diastolic current thresholds have been measured in 13 open chested dogs as a function of electrode radius by stimulating the left ventricle with epicardial disc electrodes ranging in a radius from 0-3 mm to 9 mm. Thresholds for cathodal rectangular short stimuli as well as specifically for cathodal make stimulation, proved to be proportional to the electrode radius to the power 1-5. This relationship between radius and threshold can be explained theoretically, assuming that electrical stimulation results in a propagated depolarization front if a critical current density is reached somewhere in the myocardium. The current distribution measured over the electrode and the site of initial depolarization in the tissue are in accordance with this theoretical explanation.
Animals↗