Pacemakers Outline Basic Function and Types Associated Morbidity

Pacemakers

Outline • Basic Function and Types • Associated Morbidity • Specific Indications for Use • Follow Up

Basics Pulse Generator

Purpose • Symptomatic bradyarrhythmia o Bradycardia o Block

Pacemaker Codes 1 2 3 4 Chambers Paced Chambers Response to Rate Sensed Modulation? Stimulus 5 Multisite Pacing (ICD) O (none) O O O (non-rate responsive) O A (atrium) A T (triggered) R (rate responsive) A V (ventricle) V I (inhibited) D (both atrium & ventricle) V D

Paced Rhythm • Stimulated P wave nearly normal in appearance • Wide complex QRS o Does not use the normal conduction system o Depolarizes ventricles from right to left and from apex to base o Resembles complete LBBB • Broad T wave and may include sharp inversions that mimic ischemia

Paced Rhythm • Stimulated P wave nearly normal in appearance • Wide complex QRS o Does not use the normal conduction system o Depolarizes ventricles from right to left and from apex to base o Resembles complete LBBB • Broad T wave and may include sharp inversions that mimic ischemia

Paced Rhythm • Stimulated P wave nearly normal in appearance • Wide complex QRS o Does not use the normal conduction system o Depolarizes ventricles from right to left and from apex to base o Resembles complete LBBB • Broad T wave and may include sharp inversions that mimic ischemia

AAI Pacing • Underlying sinus note dysfunction but intact cardiac conduction • Sense atrial activity • Inhibit pacing if the patient’s heart rate remains above prevent target • At lower rates, pacer stimulates atria

Pacemaker Configurations AAI Indications Sick sinus syndrome in the absence of AV node disease or atrial fibrillation.

VVI Pacing • No useful atrial function eg Afib • Tracks ventricular activity • Paces ventricle only if a QRS complex is not sensed within a predefined interval

Pacemaker Configurations VVI Indications The combination of AV block and chronic atrial arrhythmias (particularly atrial fibrillation).

DDD Pacing • Most common form of dual chamber pacing • Atrial impulse generated if native atrial activity fails to occur within a preset time period after the last atrial impulse • If a QRS complex does not occur during a preset interval after the atrial impulse, a ventricular impulse occurs

Pacemaker Configurations DDD Indications 1. The combination of AV block and SSS. 2. Patients with LV dysfunction and LV hypertrophy who need coordination of atrial and ventricular contractions to maintain adequate CO.

Pacemaker Configurations VOO Indications Temporary mode some-times used during surgery to prevent interference from electrocautery

Pacemaker Configurations VDD Indications AV block with intact sinus node function (particularly useful in congenital AV block).

• Basic Function and Types • Associated Morbidity • Specific Indications for Use • Follow Up

Associated Morbidity - Pacemaker Syndrome Dizziness, weakness, dyspnea, presyncope, exertional-fatigue o AV dyssynchrony usu d/t VVI pacing with intact sino-atrial activity o Tx: Dual-chamber pacers which restore atrial kick o Complications: Afib, stroke o

Associated Morbidity - Pacemaker-mediated Tachycardia o Rapid ventricular pacing at max programmed rate caused by an endless loop § PVC conducted retrograde via AV node to atrium § Retrograde signal sensed by atrial channel § Pacing of ventricle § Retrograde conduction to atria o Most pacemakers can recognize and terminate PMT

• Basic Function and Types • Associated Morbidity • Specific Indications for Use • Follow Up

Indications • • Sinus Node Disease AV Conduction Disease and Heart Block Neurocardiogenic Syndrome Chronic Heart Failure

• Class I: Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective. • Class II: Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment. • Class III: Conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful/ /effective and in some cases may be harmful.

Indications • Sinus Node Disease o In general, pacemaker therapy is recommended only when symptoms are present Class I 1. Sinus node dysfunction with documented symptomatic bradycardia 2. Symptomatic chronotropic incompetence (failure to increase HR with exercise or increased metabolic demand)

Indications • Sinus Node Disease Class II - Heart rate <40 beats/min spontaneously or in the presence of essential medical therapy when clinically important symptoms are not correlated with bradycardia - Syncope and abnormal sinus node function documented in electrophysiologic study - Heart rate <40 beats/min and minimal symptoms Class III - Asymptomatic sinus node disease - Clear documentation that symptoms are unrelated to bradycardia - Sinus node disease due to nonessential drug therapy

Pacemaker mode selection in sinus node disease may markedly affect patient outcomes

Indications • • Sinus Node Disease AV Conduction Disease and Heart Block Neurocardiogenic Syndrome Chronic Heart Failure

Common Causes of Acquired Atrioventricular Block • Degenerative disease o Lev disease o Lenègre disease o Secondary degeneration/calcification • Medications o β-Receptor blockers o Calcium channel antagonists o Digoxin o Other antiarrhythmic agents • Atherosclerotic heart disease o Myocardial ischemia o Myocardial infarction • Dilated cardiomyopathy • Infiltrative disease o Sarcoidosis o Amyloidosis o Metastasis • Infections o Endocarditis o Lyme disease o Chagas disease • Iatrogenic causes o After atrioventricular nodal ablation o After cardiac surgery o After radiation therapy • Enhanced parasympathetic activity

Indications • Acquired AVB in adults Class I • Third-degree AVB o Asystole >3 s or escape rate <40 beats/min o Associated neuromuscular disease (eg, Kearns. Sayre, Erb dystrophy) o After atrioventricular node ablation o After cardiac surgery • Symptomatic second-degree AVB • Alternating bundle branch block type II second-degree AVB with underlying bifascicular block

Indications • Acquired AVB in adults Class II • Third-degree AVB with LV dysfunction • Type II second-degree AVB • Syncope with underlying bifascicular block when VT excluded • Neuromuscular diseases with any AVB or fascicular block Class III - Asymptomatic first-degree or type I second-degree AVB • AVB expected to resolve • Fascicular block with first-degree AVB or no AVB

Indications • • Sinus Node Disease AV Conduction Disease and Heart Block Neurocardiogenic Syndrome Chronic Heart Failure

Neurocardiogenic Syndrome • transient imbalance in the cardiovascular autonomic regulation that results in vasodilation with or without inappropriate bradycardia. • triggered by vasovagal syncope or by compression of the carotid sinus (carotid sinus hypersensitivity)

Neurocardiogenic Syndrome • Substantial bradycardia during tilt-table (not always needed for dx) • If vasodilation cause for hypotension = NOT a candidate for pacing • Ventricular pacing – frequent AV block

Indications • • Sinus Node Disease AV Conduction Disease and Heart Block Neurocardiogenic Syndrome Chronic Heart Failure

Indications • Chronic Heart Failure o Interventricular conduction delay common • poor coordination of ventricular contraction o 3 leads § Right ventricle § Coronary sinus to pace left ventricle § Right atrium to sense intrinsic rhythm to ensure appropriate AV timing interval

Indications • NYHA III – IV on medical therapy • QRS duration > 130 msec (LBBB) • LV enlargement (end-diastolic dimension > 55 mm) • LV Ejection Fraction <35%

Indications

• Basic Function and Types • Associated Morbidity • Specific Indications for Use • Follow Up

Follow Up • Routine visits o Hx: palpitations, light-headedness, syncope, or change in exercise tolerance o 12 -lead EKG o Overpenetrated PA and lat CXR (to check placement of pulse generator and leads)

Pacemaker Failure • Failure to sense • Failure to pace • Internal malfunction of the pacer generator

Failure to Sense • Undersensing o Lead related changes (dislodgement, lead fracture) o Change in lead-myocardium interface (change in activation sequence as in new BBB or PVCs, electrolyte abnormality, new med, lead maturation and fibrosis, infarction at lead tip)

Failure to Sense • Oversensing – sensing of inappropriate signals o Other parts of the normal ECG o Electromagnetic interference when subjected to strong electrical field o Lead or pulse generator malfunction § Lead fracture § Loose set screw

Problems with Pacemakers Failure to Sense Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7 th ed. , 2005. Causes: • Undersensing • Oversensing

Failure to Capture or Pace • Pacer lead (lead dislodgement, fracture) • Pulse generator (battery depletion, loose screw) • Change in interface (fibrosis, electrolyte, meds, infarctions) • Pacemaker-mediated tachycardia

Problems with Pacemakers Failure to Capture Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7 th ed. , 2005. Causes: • • Threshold rise (electrolytes, drugs) Lead dislodgement Lead fracture RV infarct

Problems with Pacemakers Failure to Pace Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7 th ed. , 2005. Causes: • • Oversensing Battery failure Internal insulation failure Conductor coil fracture

Problems with Pacemakers Failure to Pace Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7 th ed. , 2005. Causes: • Crosstalk

Paced Rhythm • Stimulated P wave nearly normal in appearance • Wide complex QRS o Does not use the normal conduction system o Depolarizes ventricles from right to left and from apex to base o Resembles complete LBBB • Broad T wave and may include sharp inversions that mimic ischemia

Acute MI – how to tell? discordant - in the opposite direction of the QRS vector

Perioperative Mgmt • Applicable to neck and chest surgeries o o o o Obtain pacemaker programming info Magnet may be placed over device to inhibit sensing or the pacemaker may be programmed to asynchronous mode before surgery Ensure availability of temporary pacing in case of emergency Use low energy and short bursts of electrocautery Avoid electrocautery near device and place grounding pads away from device Turn off program rate modulation during surgery Interrogate and reprogram pacemaker after surgery

Example 1 The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ Ventricular paced, Ventricular sensed, Consistent with VVI

Example 2 The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ Ventricular paced, Atrial sensed, Consistent with DDD or VDD

Example 3 The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ Atrial paced Consistent with AAI or DDD

Example 4 The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ Failure to Pace

Example 5 The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ Failure to Sense

Key points • Find out pacemaker model, date of implantation, date of last pacemaker check, indication for pacemaker • Modes o VVI: permanent afib o AAI: SSS and normal AV conduction o DDD: Most common Sinus and AV nodal disease

Key points • Modes o VVI: permanent afib o AAI: SSS and normal AV conduction o DDD: Most common Sinus and AV nodal disease

Key points • Permanent pacing for o o symptomatic bradycardia and complete heart block Heart Failure on optimal medical tx for ≥ 3 mo

Key points • Problems o Pacemaker-mediated tachycardia o Pacemaker syndrome o Failure to sense o Failure to pace

Sources • “Contemporary Pacemakers: What the Primary Care Physician Needs to Know” Mayo Clinic Proceedings 2008 • “The Paced Electrocardiogram: Issues for the Emergency Physician” American J of Emergency Med • Dr. Huang’s Cardiology Handout • medresidents. stanford. edu/Teaching. Materials/Pacemak ers/Pacemakers. ppt