Replies from. Dr. M. Rosengarten

From: K.M. McGill.ca 20 Nov 1996
We think the pacemaker is in VVI mode. The manufacturer is Medtronic. The frequent spike under the curve we think are markers to signify that the pacer is not in magnet mode.
Reply: The pacemaker is a VVI pacer as as it is sensing the intrinsic beats of the patient (first and third from the left). The pacer with the magnet is pacing at a sustained rate of 100/min. which is unusual for a Medtronic pacer. It is true that the frequent spikes on the left indicate that the pacer is not in its magnet mode, but this is not the purpose of these spikes.


From: Empress Vancouver 20 Nov 1996
The underlying rhythm is either atrial fibrillation with slow ventricular response, or sinus arrest with junctional/hisian escape. There is appropriate capture and sensing. With the magnet there is VOO pacing, the signature of which may be decipherable to give the identity of the pacemaker manufacture and model type if one had the appropriate reference manual. The numerous spikes on the tracing before the magnet application are clearly artifact, but I am unsure by what mechanism. Does this represent break in insulation on the lead with transmission of pectoral myopotentials, or EM interference? Or is it part of the
manufacturer's interrogation setup? Thanks.

Reply: Yes the underlying rhythm is atrial fibrillation and the pacer is sensing and pacing well. The magnet does put the patient into a VOO mode at a rate of about 100/min. The numerous spikes are not pacing spikes but are coming from the pacer. Although this can be seen with communication signals and other causes of artifact this is not the case here. Myopotentials are usually not seen on an ECG trace but rather as inhibition of a pacer that should have paced. The frequent spikes are unlikely to be pacing spikes even if the pacer was in the VVT mode to mark sensed events as it is rate limited and could not pace at this rate, and there are clearly two different types of spikes.


From: S. C. aol.com 22 Nov 1996
Looks like a VVIR pacer, probably a telectronics with minute ventilation activity sensor. It gives the monitor fits at times, with the monitor sensing the pulses that measure the impedance.

Reply: Yes this is a VVI.R pacer which has a minute ventilation sensor. This is an interesting sensor that measures trans-thoracic impedance and varies the paced rate with the respiratory rate. Placing a magnet over the pacer cancels the respiratory spikes and places the pacer in the magnet mode. The spikes can be a real problem on bedside monitors and if you want to check this pacer by telephone, but in the clinic the extra spikes are wiped out on the Telectronics programer's display.


From: J. C. compu.net 24 Nov 1996
It appears to be working correctly. I believe that it is a Telectronic
Reply: It is a Telectronic pacer. It was working correctly but that is a lot to say about a VVI.R. The tracing shows that it does give brady pacing, is sensing and has a normal magnet rate. What we would also like to see is if its rate response worked for this patient. For this we could access the rate histograms stored since the last visit. This is a nice sensor form most but remember in a patient with respiratory disease it is better to consider another type of sensor.


From: G.M. indy.net 24 Nov 1996
I think all the spikes are from some kind of interference, I think the pacer is O.K.
Reply: The pacer is O.K. The extra spikes could be interference but are the respiratory sensor measuring chest impedance.

From: D.T. ipa.net Westark Community College 25 Nov 1996
Four chamber pacer.

Reply: An interesting idea but this was as a ventricular pacer which leaves only 2 ventricular chambers to pace. Biventricular pacing (right and left ventricular pacing) and septal RV pacing may have a role in increasing cardiac output as compared to apical RV pacing.


From: Dr. S.C. 4 Dec 1996 nt.net
Electrical interference caused the results in the first half. Yes, the pacemaker is working, because, there is capture with the magnet applied.
Reply: The pacer senses and captures on the first part and captures on the last part. Yes it is interference but it is coming from the pacer's sensor!

From: F. C. RN(student)worldnet.att.net 5 Dec 1996
In my humble opinion, this rhythm is an example of a Vent pacer that is intermittently failing to capture due to an inadequate amperage with failure to sense. We see pacer spikes marching across the strip until the magnet is applied. The first beat we see is a non-paced vent beat with a rate of aprox. 50 to the next beat. The next 2 beats are paced at a rate 72 with the 4th beat returning to the underlying rate of 50. Also, there is no apparent atrial activity. I believe sensing is Atrial, Pacing is Vent.
Reply: The pacer is sensing well as seen by the first and fourth beats. The rhythm is atrial fibrillation which is slow and can be a good indication for a rate responsive pacer. Yes the spikes on the left first part of the recording are from the pacer but some are pacing and some are used to measure respiration. All pacing spikes capture the ventricle. The pacer rate is about 50/min. which increases to about 100 with the magnet. From what you see here you have to assume the pacemaker is working well.

From: M. Y. M. F. ax.apc.org 23 Dec 1996
Dear Sir, The answers for the ECG puzzler are:
1- The multiples spikes seen in the ECG can be caused by minute ventilation sensing that delivers subthreshold stimuli every 50msec.
2- The manufacturer is Telectronics system and the pacemaker is a VVIR pacing system with minute ventilation sensing (Meta I MV - Telectronics system ).
3- The use of a magnet had changed the pacemaker to VOO with a rate of 100 bat/per minute ( Telectronics behavior ) and the artifacts spikers had disappeared.The pacemaker is working well.

Reply: Very good! This is a Telectronics Meta but not a I but a Meta II.


From: Dr. N. M. paknet1.ptc.pk 01 Jan 1997
Two types of rhythms are seen 1) Intrinsic 2) pacemakers spike. Pacemaker implanted is VOO , Unipolar. Manufacturer ? Pacemaker in not functioning because of improper lead contact. Intrinsic pacemaker function is normal.
Reply: The pacer is only functioning as a VOO when the magnet is over it and it is running at 100/min. on the last part of the strip. The pacer is capturing well and you would have to do a lead threshold measurement to determine if the pacing threshold was acceptable. In this case the lead was just fine.