Pacemakers and AICD’s

Pacemaker Basics Provides electrical stimuli to cause cardiac contraction when intrinsic cardiac activity is inappropriately slow or absent Sense intrinsic cardiac electric potentials

ICD Basics Designed to treat a cardiac tachydysrythmia Performs cardioversion/defibrillation Ventricular rate exceeds programmed cut-off rate ATP (antitachycardia pacing) Overdrive pacing in an attempt to terminate ventricular tachycardias Some have pacemaker function (combo devices)

Pacemaker and ICD Basics Pulse Generators Placed subcutaneously or submuscularly Connected to leads Battery Most commonly lithium-iodide type Life span 5 to 8 years Output voltage decreases gradually Makes sudden battery failure unlikely

Pacemaker and ICD Basics Asynchronous Fixed rate Impulse produced at a set rate No relation to patients intrinsic cardiac activity Susceptible to Torsades if impulse coincides with t wave

Pacemaker and ICD Basics Synchronous Demand mode Sensing circuit searches for intrinsic depolarization potential If absent, a pacing response is generated Can mimic intrinsic electrical activity pattern of the heart

Pacemaker Nomenclature I II III IV V Chamber Paced Chamber Sensed Response to Sensing Rate Modulation, Programmability Anti-tachycardia Features A=Atrium T=Triggered P=Simple P=Pacing V=Ventricle I=Inhibited M=Multi-programmable S=Shock D=Dual R=Rate Adaptive O=None C=Communicating

Examples VVI Paces ventricle Senses ventricle Inhibited by a sensed ventricular event

Pacing Nomenclature Examples AAT Paces atria Senses atria Triggers generator to fire if atria sensed DDD Paces atria and ventricle Senses atria and ventricle Atrial triggered and ventricular inhibited EKG – 2 spikes

DDD Atrial Spike Ventricular Spike

Pacemaker Lead System Endocardial leads placed via central access Placed in right ventricle and/or atria Fixed to the endocardium via screws or tines Experimental pacing systems 2 atrial leads (minimize afib) Biventricular pacing

Magnet Inhibition Closes an internal reed switch Causes sensing to be inhibited Temporarily turns pacemaker into “asynchronous” mode (set rate) Does NOT turn pacemaker off Rate can confer info regarding battery life Distinct rates for BOL, ERI, EOL

Pacemaker Indications Absolute indications Sick sinus syndrome Symptomatic sinus bradycardia Tachy-brady syndrome Afib with slow ventricular response 3rd degree heart block Chronotropic incompetence Inability to increase heart rate to match exercise Prolonged QT syndrome

Pacemaker Indications 3rd Degree heart block

Pacemaker Indications Relative indications Cardiomyopathy Dilated Hypertrophic Severe refractory neurocardiogenic syncope Paroxysmal atrial fibrillation

ICD Indications Generally Used in cases where there was a previous cardiac arrest Or, patients with undetermined origin or continued VT or VF despite medical interventions

Pacemaker Complications EKG abnormalities due to Failure to output Failure to capture Sensing abnormalities Operative failures

Pacemaker Failure to Output Definition No pacing spike present despite indication to pace Etiology Battery failure, lead fracture, break in lead insulation, oversensing, poor lead connection, “cross-talk” Atrial output is sensed by ventricular lead

Pacemaker Failure to Capture Definition Pacing spike is not followed by either an atrial or ventricular complex Etiology Lead fracture or dislodgement, break in lead insulation, elevated pacing threshold, MI at lead tip, drugs, metabolic abnormalities, cardiac perforation, poor lead connection

Pacemaker Sensing Abnormalities Oversensing Senses noncardiac electrical activity and is inhibited from correctly pacing Etiology Muscular activity (diaphragm or pecs), EMI, cell phone held within 10cm of pulse generator Undersensing Incorrectly misses intrinsic depolarization and paces Poor lead positioning, lead dislodgement, magnet application, low battery states, MI

Pacemaker Operative Failures Due to pacemaker placement Pneumothorax Pericarditis Perforated atrium or ventricle Dislodgement of leads Infection or erosion of pacemaker pocket Infective endocarditis (rare) Venous thrombosis

Pacemaker Complications Pacemaker syndrome Patient feels worse after pacemaker placement Presents with progressive worsening of CHF symptoms Due to loss of atrioventricular synchrony, pathway now reversed and ventricular origin of beat

ICD Complications Similar to pacemaker complications Operative failures Same as pacemakers Sensing and pacing failures Inappropriate cardioversion Ineffective cardioversion/defibrillation Device deactivation

ICD Sensing failures Similar to pacmakers Appropriate failure to treat Oversensing Undersensing Appropriate failure to treat Programmed cut off at 180 bpm If V Tach occurs at 160 bpms, appropriately fails to cardiovert

ICD Inappropriate Cardioversion Most frequent complications Provokes pain and anxiety in pts Consider when Pt is in afib With ventricular response > programmed cut off Received multiple shocks in rapid succession Etiology Afib, T-wave oversensing, lead fracture, insulation breakage, MRI, EMI

ICD Inappropriate Cardioversion Treatment Magnet over ICD inhibits further shocks Does NOT inhibit bradycardiac pacing Note Some older devices produce beep with each QRS If left on for >30 seconds, ICD disabled and continous beep To reactivate, lift off magnet and then replace for > 30 seconds, beep will return with each QRS

ICD Failure to Deliver Cardioversion Etiology Failure to sense, lead fracture, EMI, inadvertent ICD deactivation Management External defibrillation and cardioversion Do not withhold therapy for fear of damaging ICD If pt’s internal defibrillator activates during chest compressions, you may feel a mild shock (no reports of deaths related to this) Antidysrhymthic medications

ICD Ineffective Cardioversion Etiology Inadequate energy output Rise in the defibrillation threshold MI at the lead site Lead fracture Insulation breakage Pre-programmed set of therapies per dysrythmia Manufacturer specific Once number of attempts reached, will not deliver further shocks until new episode is declared

Electromagnetic Interference Can interfere with function of pacemaker or ICD Device misinterprets the EMI causing Rate alteration Sensing abnormalities Asynchronous pacing Noise reversion Reprogramming

Electromagnetic Interference Examples Metal detectors Cell phones High voltage power lines Some home appliances (microwave)

Electromagnetic Interference Intensity of electromagnetic field decreases inversely with the square of the distance from the source Newer pacemakers and ICDs are being built with increased internal shielding