LETTERS TO THE EDITOR To the Editor: We read with great interest the article by L. Kritharides and J. Vohra on "Late development of conduction block over the Mahaim fibers after electrical atrioventricular junction ablation for Mahaim fiber tachycardia" (PACE, 1992; 15:256-261). However, their Figure 2 may be interpretable in a different way. In their interpretation, an RV extrastimulus advanced QRS by only 10 msec but prolonged VA conduction by 35 msec (60 msec —» 95 msec). If this were true, atrial cycle length encompassing the RV extrastimulus should have been lengthened from 300 msec to 325 msec by 25 msec (35 msec - 10 msec = 25 msec). But the atrial cycle length on HRA and PCS encompassing the RV extrastimulus is 300 msec (according to our measurement), indicating that the RV

To the Editor: We thank Drs. Suzuki and Hiejima for their comments on Figure 2 in our article. They are quite correct in their observation that the atrial cycle length encompassing the right ventricular extrastimulus (RVES) is not lengthened by 25 msec and their suggestion that the RVES did not penetrate the tachycardia circuit is certainly a valid one. The diagnosis of Mahaim fiber tachycardia in this patient is beyond doubt. Our inference that RVES penetrated the tachycardia circuit is based

To the Editor: The article "Activity-based pacing: Comparison of a device using an accelerometer versus a piezoelectric crystal" by Bacharach, et al, PACE 1992; 15:188-196, presents very disturbing aspects of clinical pacemaker research. The article compares two single chamber rate adaptive pacemakers that depend on activity in order to stimu-

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extrastimulus most probably did not penetrate the tachycardia circuit. If one were to assume that the RV extrastimulus delayed the activation of the low septal right atrium on HBE alone by 25 msec, shortening by 25 msec in intraatrial conduction time between the low septal right atrium to HRA and PCS would have to occur, which would be unlikely. It seems to us that exact measurement of VA conduction time on HBE in Figure 2 is very difficult in consideration of the very sinall atrial deflection on HBE during sinus beat (last beat in Fig. 2). Fumio Suzuki Kazumasa Hiejima Tokyo Medical and Dental University Tokyo,Japan

on prolongation of the tachycardia cycle length (by 20 msec in the surface ECC and 35 msec in RV electrogram) and consistent termination of tachycardia by only slightly premature right ventricular extrastimuli. It would have, of course, been ideal to measure the VH interval in the HBE tracing for confirmation of retrograde delay by RVES; however, that was not possible here. Jitu K. Vohra Royal Melbourne Hospital Melbourne, Australia

late the sensor. One model uses an accelerometer (EXCEL™, Cardiac Pacemakers, Inc., St. Paul, MN, USA) and the other a piezoelectric crystal (Legend*^, Medtronic, Inc., Minneapolis, MN, USA). The study was funded by one of the companies and its employees were included in the authorship. Comparative studies with commercial involvement are suspect because of potential bias, are therefore open to criticism and should not be

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accepted for publication. This bias is further highlighted in the article where only one of the product trade names is published in full upper case. The study is based on previous wdrk comparing the rate response of piezoelectric activitybased pulse generators strapped to the anterior chest wall with identical pacemakers implanted in the same patients. Two references for this work are cited, both from the same major authors. The first by Mianulli (PACE 1991; 14:732) is an abstract and the wrong page reference is given. Incorrect information makes references hard to find and reviewers or readers may not attempt to read the original data. In both references there was a damped response by the external pulse generator compared with the implanted model. This can be overcome using more sensitive settings for the external piezoelectric-based rate adaptive pulse gen-

erator. The authors should have been aware of this fact as a reference for this was quoted in their article (Mond et al., PACE 1990; 13:514). The authors assume that with the accelerometer-based rate adaptive pacing system, the external strap-on system would also provide comparable data to the implanted system. Without the necessary studies to prove this, the clinical application of this study is limited. The only conclusion that can be drawn from this study is that when these two systems are compared using external pulse generators at nominal settings [the actual settings are not quoted], differences exist that may or may not be relevant to implanted pacing systems.

To the Editor:

did base itself on the ability to achieve valid and reliable data from a strapped-on system. The degree of damping that takes place between implanted pacemakers and strapped-on pacemakers is far from perfect, but we, as do others, believe it to be within an acceptable range for studies of this nature. The strap-on procedure may not have been ideal as with the selection of nominal settings versus optimized settings; however, with counterbalancing placement and equating response settings, we felt we could make an interpretation about the effectiveness of each pacemaker with regard to the activities selected for this study. It was also our intent not to begin a debate of which specific manufacturer may be better, but rather draw issue with the frequency of each pacemaker as the main focus and the response to that signal that is generated. An engineer could easily explain how a piezoelectric crystal can be much more responsive to distortion than a bridge circuit strain gauge. The difficult part is how one harnesses the sensitivity of such a system to match biomechanical responses of the human body. I spoke of this same issue at length with an engineer from Medtronic, Inc. in the fall of 1991. They too are exploring the use of accelerometers for application to the arena of electrophysiology, which leads me to believe that our study is noteworthy.

This is in response to the letter of concern from Drs. Mond and Strathmore regarding our article "Activity-based pacing: Comparison of a device using an accelerometer versus a piezoelectric crystal" PACE 1992; 15:188-196. My interpretation of the statement in the "Instructions For Authors" was that only our university research group made any evaluation and/or comment regarding both products such that it was not in violation of manuscript preparation. Inclusion of employees as co-authors was done out of courtesy for their assistance in the study, but they did not bias us in the study design. Nor did they in any way, shape, or form influence the procedures or interpretation of these data. I too recognize the need to separate oneself from a funding agency as to prevent potential bias as suggested. But, when a company has an official registered trademark with all upper case letters, namely, "EXCEL™," it ought to be used without implications of bias. My apologies to the readers of PACE. The correct page from NASPE Abstract #459 of PACE 1991, volume 14 is page 732, not page 742.1 hope this error hasn't caused readers much additional time in locating the correct abstract. This study

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Harry Mond Neil Strathmore The Royal Melbourne Hospital Victoria, Australia

August 1992

PACE, Vol. 15

Activity-based pacing: comparison of a device using an accelerometer versus a piezoelectric crystal.

LETTERS TO THE EDITOR To the Editor: We read with great interest the article by L. Kritharides and J. Vohra on "Late development of conduction block o...
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