![]() R atrial lead J shaped(tip medially on AP) entering right atrial appendage.Obtain PA/Lateral Films to confirm pulse generator, manufacturer, lead placement/number/integrity.Simultaneous depolarization of ventricles produces dominant R wave in V1.Bi-ventricular devices can produce paced QRS complexes that are either narrow or wide and bizarre, depending on device programming.New RBBB pattern may indicate lead in LV.Leads in RV apex produce LBBB pattern with appropriate discordance.Pacing artifacts preceding depolarizations indicate successful pacing and capture.With newer pacemakers, pacer spikes may not appear on some or all paced beats, depending on EKG machine.Absence of pacer artifact indicates intrinsic depolarization.Most cath labs will have machines capable of interrogating each brand.Each company has on-call representatives who will come interrogate a device 24/7 (phone numbers above).Tachycardia does not exceed programmed upper limit rate on pacemaker.Most commonly: paced ventricular beat -> retrograde AV node conduction -> intrinsic P wave -> device reacts to intrinsic P wave by looking for intrinsic QRS, but since AV node is now refractory it delivers a paced beat at the programmed P-R interval (typically ~200-250ms), starting the process anew.Formation of a re-entrant circuit causing inappropriate tachycardia.Potentially life-threatening as it can cause V-Fib or (paradoxically) bradycardia due to failure to capture.Signals generated by interaction of different portions of the pacing system.Physiologic electrical activity (T waves, muscle potentials).New intrinsic arrhythmia (AF has a smaller depolarization than sinus beat), AMI, electrolyte abnormalities, lead separation, battery depletion.Voltages of patient's intrinsic QRS complex is too low to be detected.Failure to sense results in a paced beat on top of an intrinsic beat (as the device is "unaware" of the intrinsic beat").Normal function: a sensed myocardial depolarization greater than the programmed threshold causes inhibition of pacing.Crosstalk - type of oversensing where the ventricular lead senses atrial pacing stimulus, and ventilator output inhibited. ![]()
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