![]() ![]() Variety of clinical symptoms including fatigue, dizziness, palpations, pre-syncope.Caused by improper timing of atrial and ventricular contractions resulting in AV dyssynchrony and loss of atrial “kick”.May result in rate-related ischaemia in the presence of IHD.Newer pacemakers contain programmed algorithms designed to terminate PMT.Results in a paced tachycardia with the maximum rate limited by the pacemaker programming.⇒ adjustable post ventricular (pacing spike) atrial refractory period (PVARP) or slowing AV conduction e.g. (2) retrograde conduction between ventricle and atrium through AV node or accessory pathway -> retrograde p waves being sensed as native atrial activity with subsequent ventricular pacing -> paced ventricular complex results in further retrograde conduction with retrograde p wave generation -> ‘endless’ loop of periodicity -> re-entry tachycardia ⇒ use an atrial blanking period (now preset into box) (1) atrial sensing of a ventricular spike -> interpreted as an endogenous atrial depolarisation -> another ventricular impulse can switch to VVI or DVI (but may lose AV synchrony).Also known as endless-loop tachycardia or pacemaker circus movement tachycardia.⇒ reduce mA delivered to the ventricular or pacing wire ⇒ reduce sensitivity in atrial or ventricular channel > inhibits ventricular pacemaker output (ventricular standstill) in dual chamber pacing it is possible that the atrial pacemaker spike will be sensed by the ventricular wire and is misinterpreted as a ventricular depolarisation.⇒ increase sensitivity threshold or switch to an asynchronous mode (AOO, VOO) in DDD external electrical impulses can also be misinterpreted as atrial activity causing pacemaker mediated tachycardia. ![]() ![]() ⇒ increase absolute value of sensitivity (making it harder to inhibit) usually due to settings on the pacemaker.Reduced pacemaker output / output failure may be seen on ECG monitoring if the patient contracts their rectus or pectoral muscles (due to oversensing of muscle activity).Abnormal signals may not be evident on ECG.These inappropriate signals may be large P or T waves, skeletal muscle activity or lead contact problems.produces inappropriate/excessive inhibition of atrial pacing -> confuses pacemaker into thinking that there has been a return to spontaneous atrial activity.Oversensing occurs when electrical signal are inappropriately recognised as native cardiac activity and pacing is inhibited.⇒ decrease absolute value of sensitivity (making it easier to inhibit) ⇒ same mechanisms as failure to capture and pace due to specific setting of sensitivity (including AOO mode).produces atrial pacing when not appropriate.⇒ in bipolar leads, the negative electrodes develop fibrosis first -> use other electrode and plug into negative terminal and insert return electrode in the subcutaneous tissue (create unipolar circuit) ⇒ bipolar leads may be tried in reverse positions or can try convert to unipolar pacing ![]() ⇒ tight and confirm all external connections
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