see also: [[ICD]], [[Cardiac Resynchronization Therapy|CRT]] - [Rosen - pacemaker issues](x-devonthink-item://D1C9BB26-7BC6-4984-8F43-910B743D0001?page=4) > [!Key Points] > - batteries should last 5-10 years. in last 3 months of battery life, pacing may slow down. unpredictable pacing as battery dies > - **hyperkalemia** and **ischemia** can be causes of [[#Failure to capture]] > - atrial [[#Oversensing]] can cause tachycardia, but ventricular oversensing will cause bradycardia > - a ==magnet turns off sensing==; therefore, if pacemaker is working, it should default into its default pacing mode, should correct oversensing issues. > - note: with ICDs, a magnet can turn off to inactivate defibrillator if pt getting inappropriate shocks > > **5 causes of pacemaker failure to capture** > - pacemaker lead displacement (most common cause, often in first month) > - acute infarct in contact with pacemaker lead (exit block --> failure to pace) > - hyperkalemia > - amiodarone > - pacemaker battery failure > > **categories:** > - Box issues - battery failure. Inappropriate settings. > - Cable issues - lead fracture, lead displacement (eg twiddler-in-the-chest syndrome) > - Interface issues - focal necrosis/fibrosis/oedema > - More global patient issues - eg medication/electrolytes. ![[Pasted image 20240309234057.png]] # Oversensing - intrinsic waves or crosstalk from PPM signal are misinterpreted as ventricular depolarisation --> inhibits PPM - results in **bradycardia** - Tall T waves due to [[hyperkalemia]] or LV hypertrophy are a common cause of oversensing failure - oversensing the **atria** can cause inappropriate **tachycardia** when false atrial signals trigger the pacing of the ventricle - can place a magnet to turn off sensing, this SHOULD cause pacing to resume at 60-100 BPM ![[Pasted image 20230614231250.png]] Note the artifact is being oversensed and the PPM is not appropriately firing ## magnet test ![[Pasted image 20230614231043.png]] note that after magnet placed, no sensing at PPM starts AV sequental pacing with 100% capture at 100 BPM ## failure to pace - **failure to pace** if PPM fails to deliver a pacing stimulus after a pause that exceeds programmed AV delay - magnet can differentiate whether failure to pace is caused by oversensing or failure of output - if it is caused by oversensing, can leave the magnet on - if it is caused by failure of output, patient may need transcutaneous or transvenous pacing # failure of output - can be caused by any part of the pacemaker hardware or a disconnected lead # pseudomalfunctions - some programing may have reduced rates at certain times of day, for example # Failure to capture > Any critically ill patient with a pacemaker can develop failure to capture - pacemaker artifact is visible but there is no **capture** (depolarization of myocardium) - ==pacemaker spikes +/- p waves, but no QRS comples== - can be caused by inadequate output delivered to the myocardium, or conditions that **increase the threshold for capture** (see below list) - can also be caused by battery depletion, lead breaks/fracture, dislodgement, etc - “Failure to capture may range from the complete absence of pacemaker spikes to spikes not followed by a stimulus-induced complex” **Factors that can increase the threshold to capture** - flecanide - mineralocorticoids - sotalol - ?lignocaine - metabolic factors: - acidosis - alkalosis - [[hyperkalemia]] - hypoxia - severe hyperglycemia threshold is decreased by: - atropine - adrenaline - glucocorticoids - isoprenaline ![[Pasted image 20230614205119.png]] ^ Failure to capture. paced impulse fails to capture (star) **causes:** - pacemaker lead displacement (most common cause, often in first month) - acute infarct in contact with pacemaker lead (exit block --> failure to pace) - hyperkalemia  - amiodarone  - pacemaker battery failure **Box issues** - battery failure. Inappropriate settings. **Cable issues** - lead fracture, lead displacement (eg twiddler-in-the-chest syndrome) **Interface issues** - focal necrosis/fibrosis/oedema More global **patient issues** - eg medication/electrolytes. # Undersensing - PPm fails to sense intrinsic pacemaker activity and attempts to pace ![[Pasted image 20230614205635.png]] this shows PPM impulses fired at 60 BPM, in spite of intrinsic ventricular activity