How to disable the ICD:
Donut magnet disables ICD but still allows brady pacingBack to top
Amer. J Emerg Med 19:7, Nov 2001 and 18:4, July 2000 are two good review articles.
Sensing what the pacemaker sees when there is a spontaneous event (P wave or QRS)
Pacing sending electrons from the pacemaker pulse generator to the heart via the leads
Capture when pacing causes a cardiac depolarization; you can pace without capture. When analyzing a paced tracing, always look for appropriate capture following pacing.
Lower rate programmed rate below which the rate never gets due to pacing.
Upper rate programmed rate above which pacing does not occur.
AV delay programmed time between atrial events (sensed or paced) and ventricular pacing.
WHAT DO THE LETTERS MEAN? (Mnemonic is PSA R)
First letter chamber(s) paced:
A, for atrium; V, for ventricle; D, for dual or both; O, for neither.
Second letter chamber(s) being sensed:
Same as above.
Third letter What should the pacemaker do with sensed events?
I, for inhibit when you see a spontaneous event, inhibit pacing output in that channel.
T, for trigger or tracking when you see an event, pace either in that chamber or other.
D, for both above.
O, for neither of the above.
Fourth Letter=Program Functions
P-programmable rate, output or both
Fifth Letter=antitachydysrhythmic functions
SOMETIMES THE PACER SPIKES ARE HUGE, SOMETIMES I CANT SEE THEM AT ALL:
Every pacing system has a negative and positive pole. The electrons will flow from the negative to the positive. If both poles are on the lead (negative at the tip and positive in a proximal pole located a few centimeters from the tip) the system is said to be bipolar. If the positive pole is in the pulse generator and the negative at the lead tip, the system is unipolar. In the unipolar configuration, the electrons travel from the lead tip to the far away pulse generator. Because of this, the pacing artifact or spike is large. In the bipolar systems, the electrons only travel a few centimeters and the pacing spike is very tiny and in some leads may not be seen at all. On a 12-lead ECG, at least one of the leads will typically show a small pacing artifact with pacing.
HOW TO TROUBLE-SHOOT A PACED RHYTHM:
Identify atrial and ventricular events (paced and sensed). Is there pacing with capture? This is usually easy in the ventricle, but it can be difficult to ascertain in the atrium. Too many pacing spikes means too little sensing, and vice versa.
When looking at a rhythm strip or ECG of a patient with a pacemaker, start as you would with any ECG. Are there P waves? What is the relationship between Ps and QRSs? This will give you clues as to what kind of pacemaker you have, the programmed mode, lower rate (if the patient is at rest, since the lower rate increases with activities with rate-adaptive pacemakers; which incidentally is the fourth letter, i.e., VVIR, DDDR).
Pacing should be regular. If it isnt, look for atrial arrhythmias that may be present causing tracking to the ventricle. If the pacer is programmed DDD and atrial fibrillation occurs, the atrial events will be sensed and the pacer will track those depolarizations to the ventricle at the upper rate. Most new pacemakers have a programmable feature called automatic mode switch whereby the pacemaker automatically reprograms itself to a non-tracking mode in case of atrial tachyarrhythmias (from DDD to DDI or VVI). Once the atrial arrhythmia resolves, reprogramming to the initial tracking mode is accomplished automatically
The pacing cycle:
2 msec pacer spike (unipolar gives larger spikes)
Ventricular pacing produces LBBB pattern spike as the right venticle is paced first
Minimal pacing rate is known as lower rate limiting interval (LRLI) which is the longest the pacer will wait before firing the ventricle. The ventriculoatrial (VA) interval is the time the pacer will wait after ventricular discharge to fire the atrium.
Undersensing: it is demonstrated by a pacer spike preceded by a normal QRS at a length of time less than the LRLI
Failure to Generate Output: there should be a pacing spike between two native complexes separated by an interval longer than the LRLI. Can be from lead fracture or displacement, battery or component failure, or oversensing. Oversensing is the misinterpretation of extraneous phenomena as ecg activity.
Failure to Capture: pacing spike is seen on the ecg but there is no evidence of resulting depolarization. most common reason is the dislodgement of the pacing wire from the endocardium. Hyperkalemia, ischemia, or myocardial scarring can also lead to failure to capture.
unique to dual chamber pacers. a retrograde conducted PVC or a PAC depolarizing the ventricle will be sensed by the atrial lead and will cause ventricular discharge. This ventricular discharge will also be conducted retrograde causing a circular tachycardia. The maximum rate will be determined by the upper limit of the pacemaker. Place the pacemaker in magnet mode to terminate.
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