The accuracy of information retrievable from the memories of DDDR pacing systems has been limited by the absence of actual electrograms confirming the proper sensing of spontaneous cardiac activity versus that of extraneous signals. This study examined the diagnostic power of a new arrhythmia interpretation scheme, which includes the recording and storage of high resolution endocavitary atrial and ventricular electrograms (HREGM). HREGM stored in the memories of new generation pacemakers (PM) in response to nonsustained ventricular tachycardia (NSVT), sustained VT, and atrial arrhythmias were analyzed in a follow-up registry of 520 patients at 1 month, and 3 to 6 months after implantation of a PM for standard indications. For each sequence of stored HREGM, the accuracy of the PM response was examined, classified as accurate (true positive), versus inaccurate (false positive), versus undetermined, and the relative contribution of the HREGM in verifying the PM diagnosis was measured. During a follow-up of 4.9 +/- 2 months, 256 (49%) of the 520 patients had an event recorded, which was confirmed to be arrhythmic on the basis of HREGM. Overall, approximately 34% of atrialtachy response (ATR) episodes were confirmed to be appropriate. Similar percentages of episodes were prompted by oversensing of signals unrelated to cardiac arrhythmias, while nearly 12% of the episodes could not be clarified because of such brief duration as to preclude recording of their onset. Approximately one-third of NSVT, and one-half of VT detections were false positive. Ventricular oversensing, most often due to myopotential interference in presence of unipolar sensing, and atrial undersensing were both identified as sources of false-positive detections of ventricular events. The proportion of true-positive detections was significantly higher in the bipolar (83%) than unipolar configuration. Among 520 PM recipients, miscellaneous episodes of atrial arrhythmias were confirmed by HREGM in 37% of patients within 3 to 6 months of follow-up. Atrial fibrillation was confirmed in only 6% of patients, of whom over 50% already had histories of atrial fibrillation. The prevalence of unsuspected atrial arrhythmia in this unselected population was lower than previously reported.

Propafenone may aggravate the preexisting arrhythmia or induce another one. Usually, such proarrhythmic effects occur in patients with spontaneous ventricular arrhythmias and/or coronary heart disease with poor left ventricular function. We report the case of a 5-year-old girl with junctional automatic tachycardia and no structural heart disease, in whom malignant ventricular tachycardia occurring during propafenone treatment could be terminated by molar sodium lactate (MSL) infusion. The serum propafenone level obtained before MSL infusion was within the therapeutic range. Two hypothesis could explain the beneficial effects of MSL in our patient: (1) alkalinization facilitates the cell membrane hyperpolarization and thus can decrease the voltage-dependent effect of Class Ic drugs, (2) alkalinization could displace propafenone from its tissue receptor sites by an increase in the nonionized fraction.

This study investigated the ability to minimize pace polarization artefacts (PPA) by adjusting the post-stimulus pulse duration of a tri-phasic stimulation pulse. Adjustment of the stimulation pulse was enabled by downloading special study software into an already implanted pacemaker. Tests were performed in a total of 296 atrial leads and 311 ventricular leads. Both chronic and acute leads were included in the study. Statistically significant differences were found in the initial PPA (without any adjustment of the stimulus pulse) between atrial and ventricular leads. In addition, significant differences were observed among various lead models with respect to changes over time in the initial ventricular PPA. Successful PPA reduction was defined as a reduction of the PPA below 0.5 mV for atrial leads and below 1 mV for ventricular leads. Results show a success rate for ventricular and atrial PPA reduction of 97.8% and 98.7%, respectively. Threshold tests showed that after reduction of the PPA loss of ventricular capture can be reliably detected. However, atrial threshold tests showed many false positive evoked response detections. In addition, unexpectedly high evoked response amplitudes were observed in the atrium after reduction of the PPA. Results from additional measurements suggest that these high atrial evoked response amplitudes come from the influence of the input filter of the pacemaker.

Minute ventilation is a physiological parameter that seems to reflect closely the metabolic demands of exercise. Rate responsive pacemakers adjustirig their pacing rate on minute ventilation (MV] changes (META MV; Telectronics and Cordis Pacing Systems] are now availahle.* However, MV rate response may be inappropriate for certain patients with respiratory disorders. An 83-year-old man with ischemic heart disease and chronic congestive cardiac failure was referred to our institution for atrial fibrillation with slow ventricular response. A META MV VVIR pacemaker was implanted. While still in the VVI fixed rate mode, the patient's condition improved slightly. Before discharge, the generator was programmed to the MV rate responsive mode (slope value: 40; minimuin heart rate: 70 ppm; maximum heart rate: 110 ppm). Three days later, the patient returned with acute heart failure; the ECG showed a permanent paced ventricular rhythm at 110 ppm. Despite intravenous dohutamine, nitroglycerine and furosemide, a good hemodynamic condition could not be restored. Careful clinical examination revealed a typical Cheyne-Stokes dyspnea. After the pacemaker was reprogrammed to the fixed rate VVI mode (rate: 70 ppm), clinical status improved and the patient was discharged. It is likely that the rapid respiratory rate of the initial part of the Cheyne-Stokes dyspnea triggered a rapid ventricular rate due to a too high programmed slope, precipitating heart failure; the duration ofthe second part ofthe dyspnea (i.e., brief respiratory arrest) was not sufficient to allow the rate to fall. So a permanent fixed rate yvas present at the upper rate limit. In patients with Cheyne-Stokes dyspnea, the MV responsive mode may not be appropriate. Reference 1. Mond H, Strathmore N, Kertes P, et al. Rate responsive pacing using a minute ventilation sensor.