Changes in Morphology of the Paced QRS Complex Related to Pacemaker Output

The influence of pacemaker output on the morphology of the paced QRS complex was studied from standard lead electrocardiograms in 69 patients with bipolar pacemakers. In 40 of the 69 patients (58%), there was a significant (P less than 0.001) change in electrical axis, from -75 degrees at the low output setting (2.7 V, 0.15 msec) to -67 degrees at the high output setting (8.1 V, 2.29 msec). In 30 patients, these changes were also associated with changes in the QRS morphology and in the T-wave. This phenomenon may be explained by additional stimulation from the proximal electrode at high output, thus altering the pattern of depolarization.     

Upper Rate Pacing After Radiofrequency Catheter Ablation in a Minute Ventilation Rate Adaptive DDD Pacemaker

A 58-year-old man with an implanted minute ventilation rate adaptive DDD pacemaker underwent RF ablation of the AV junction because of symptomatic supraventricular tachyarrhythmias. Immediately after ablation, while the pacemaker was programmed in the DDDR mode, AV sequential pacing at upper rate was observed. After programming the pacing system to the DDD mode and repeated ablation, no abnormalities were observed. It was concluded that AV sequential upper rate pacing was caused by false interpretation of the RF current by the sensor measuring transthoracic impedance as an indicator for minute ventilation.     

Myopotential Interference Inducing Pacemaker Tachycardia in a DVI Programmed Pacemaker

A 67-year-old male, suffering from ventricular tachycardia unresponsive to drug therapy, received a universal AV sequential pacemaker (DDD,M). Tim pacemaker was programmed in the DVI mode, pacing role 100 bpm, AV interval 250 ms. After implantation, the patient experiences two episodes of tachycardia that proved to be pacemaker tachycardia with a rate of 150 bpm. The first period was self-terminating, and the second had to be stopped by reprogramming the pulse generator. Pacemaker tachycardia could easily be provoked by instructing the patient to contract the pectoral muscle adjacent to the pulse generator. To our knowledge, this is the first report to pacemaker tachycardia provoked by myopotentials in a pulse generator programmed in the DVI mode.     

Fusion or Confusion on Holter Recording

Holter recording of a patient with an implanted dual chamber rate responsive pacemaker revealed an electrocardiogram, where ventricular depolarization seemed to be initiated by the atrial stimulus. In a second patient with a VVI pacemaker, Holter recording showed delay of the pacemaker impulse that was registered after the onset of ventricular depolarization. Misalignment in one of the recorder heads of the display system was responsible for this phenomenon, which in case of dual chamber pacing could have been easily misinterpreted as pacemaker malfunction.     

Programming a Long Paced Atrioventricular Interval May Be Risky in DDDR Pacing

In patients with intermittent AV block and dual chamber pacemakers, a long paced AV interval of 200 msec or more can be selected to prolong pulse generator life (by avoiding the ventricular pace output) and to enable a more physiological and hemodynamically superior activation sequence. This case report describes the potential risks of programming a long paced AV interval in a patient with a DDDR pacemaker. T wave pacing, as described here, can occur if the conducted QRS complex is not sensed because it occurs during the ventricular blanking period (delivery of the atrial stimulus). This can be initiated by the mechanisms that induce apparent and actual P wave undersensing of the conducted QRS complex. In this case report apparent P wave undersensing and subsequent T wave pacing with ventricular capture (in a patient with intermittent AV block) occurred frequently during an exercise test done in the DDDR mode with a paced AV interval of 200 msec, according to the clinical evaluation protocol.     

Six-Month Feeding Study of Fenvalerate in Dogs

Six-Month Feeding Study of Fenvalerate in Dogs. Parker, C. M.,PICORILLO, V. J., KURTZ, S. L., GARNER, F. M., GARDINER, T.H., AND VAN GELDER, G. A. (1984) Fundam. Appl. Toxicol. 4, 577–586.Groups of six male and six female Beagle dogs were fed dietscontaining 0, 250, 500, or 1000 ppm fenvalerate for a periodof 6 months. Prominent in-life observations related to treatmentwere emesis, head shaking, biting of the extremities, ataxia,and tremors. One high-dose male dog was sacrificed in extremisduring the study period. Mean body weights of 1000-ppm femaledogs were significantly lower than those of controls. Red bloodcell counts and hematocrit and hemoglobin values in high-dosemale and female dogs were significantly lower than those ofcontrols at most sampling intervals. Serum cholesterol and alkalinephosphatase levels were also increased primarily in the high-dosegroup. Ophthalmic examination revealed changes in retinal vesseltortuosity in some mid- and high-dose dogs. Hepatic multifocalmicro-granulomata were observed in control and treated dogsmicroscopically. These changes increased in incidence and severitywith dose and were considered to be related to treatment Histiocyticcell infiltrate in mesenteric lymph nodes in some 500- and 1000-ppmfemale and 1000-ppm male dogs was the only other treatment-relatedmicroscopic effect.     

Cardioversion of Atrial Fibrillation and Subsequent Maintenance of Sinus Rbythm

This article gives an overview of electrical cardioversion of AF and includes the discussion of newer strategies. DC external cardioversion is highly effective and carries a low risk of complications. Other approaches, like transesophageal cardioversion and high energy internal cardioversion, may improve the acute success rate but do not enhance long-term maintenance of sinus rhythm compared to external cardioversion. An atrial defibrillator may have important advantages which relate to the fact that the duration and possibly also the number of AF episodes become reduced. Supposedly, shortening the attacks of AF may exert an antiarrhythmic effect by limiting electrical, anatomical, and neurohumoral remodeling. So far. low energy biatrial defibrillation using an atrial defibrillator seems to be effective and safe (i.e., does not induce ventricular arrhythmias). However, discomfort limits its tolerability in clinical practice. Future improvement of leads and light sedation that is easy to administer may overcome this problem. In the second part of this overview, the probability of AF recurrence using a serial cardioversion approach is discussed. In middle-aged patients with a fair exercise tolerance and an arrhythmia duration < than 36 months this approach may be worthwhile. Young patients (age < 57 years) with an arrhythmia duration < 3 months and without hypertension may be cured from the arrhythmia with a single shock and without the institution of antiarrhythmic drugs. However, the serial electrical cardioversion approach is unlikely to succeed in elderly patients with a duration of AF exceeding 36 months and a poor exercise tolerance (NYHA Functional Class III or IV).     

Timing of the Left Ventricular Electrogram and Acute Hemodynamic Changes During Implant of Cardiac Resynchronization Therapy Devices

Study Objective: To examine the relationship between timing of the left ventricular (LV) electrogram (EGM) and its acute hemodynamic effect on instantaneous change in LV pressure (LVdP/dt_MAX).
Patients and Methods: In 30 patients (mean = age 67 ± 7.9 years) who underwent implant of cardiac resynchronization therapy systems, the right ventricular (RV) lead was implanted at the RV apex (n = 23) or RV septum (n = 7). The LV lead was placed in a posterior (n = 14) or posterolateral (n = 16) coronary sinus tributary. QRS duration, interval from Q wave to intrinsic deflection of the LV EGM (Q-LV), and interval between intrinsic deflection of RV EGM and LV EGM (RV-LV interval) were measured. The measurements were correlated with the hemodynamic effects of optimized biventricular (BiV) stimulation, using the Pearson correlation coefficient.
Results: The mean LVdP/dt_MAX at baseline was 734 ± 180 mmHg/s, and increased to 905 ± 165 mmHg/s during simultaneous BiV pacing, and to 933 ± 172 mmHg/s after V-V interval optimization. The Pearson correlation coefficient R between QRS duration, the Q-LV interval, and the RV-LV interval at the respective LVdP/dt_MAX was 0.291 (P = 0.66), 0.348 (P = 0.030), and 0.340 (P = 0.033).
Conclusions: Similar significant correlations were observed between the acute hemodynamic effect of optimized BiV stimulation and the Q-LV and the RV-LV intervals. However, individual measurements showed an 80-ms cut-off for the Q-LV interval, beyond which the increase in LVdP/dt_MAX was <10%._.