Supparerk Prichayudh M.D Pacemaker Supparerk Prichayudh M.D

Normal EKG P wave = atrial depolarization QRS wave = ventricular depolarization T wave = ventricular repolarization

Outline Indications Types Modes of pacemaker Temporary pacemaker Problems with pacemakers Surgical diathermy and pacemakers

Indications

Indication: Symptomatic bradycardia Sinus node dysfunction 3° and advanced 2° AV block Bradycardia associated with AMI

Prophylactic Implant Patients with LBBB requiring Swan-Ganz catheter placement Cardioversion in the setting of SSS New BBB in the setting of acute endocarditis Peri-operatively

Sick Sinus Syndrome

Types Temporary Permanent

Permanent pacemaker Box = pulse generator

Pacemaker Leads Pacemaker leads are the conduits from the generator to the myocardium. Most leads are implanted transvenously.

Wiring systems Unipolar Bipolar One electrode on the heart (-) Signals return through body fluid and tissue to the pacemaker (+) Bipolar Two electrodes on the heart (- & +) Signals return to the ring electrode (+) above the lead (-) tip

UNIPOLAR AND BIPOLAR PACING

Modes of pacemaker

NASPE-BPEG Generic Five-Position Code   Position I II III IV V Parameter measured Chamber(s) paced Chamber(s) sensed Response to sensing Rate modulation Anti-tachyarrhythmia function Possible values O = None A = Atrium I = Inhibited R = Rate modulation on P = Pace V = Ventricle T = Triggered S = Shock D = Dual (A + V) D = Dual (I + T) D = Dual NASPE, North American Society of Pacing and Electrophysiology; BPEG, British Pacing and Electrophysiology Group

First letter: Chamber Paced V- Ventricle A- Atrium D- Dual (A & V) O- None

Second letter: Chamber Sensed V- Ventricle A- Atrium D- Dual (A & V) O- None

Third letter: Sensed Response T- Triggers Pacing I- Inhibits Pacing (demand) D- Dual (synchronous) O- None (asynchronous)

Chamber Paced Atrial pacing Ventricular pacing Intact AV conduction system required Ventricular pacing Loss of atrial kick Atrial/Ventricular pacing Natural pacing Atrial-ventricular synchrony

Commonly used modes AAI - atrial demand pacing VVI - ventricular demand pacing DDD – Dual chamber pacemaker AOO - atrial asynchronous pacing VOO - ventricular asynchronous pacing

ventricular asynchronous pacing VOO Indications Temporary mode some-times used during surgery to prevent interference from electrocautery

ventricular demand pacing VVI Indications The combination of AV block and chronic atrial arrhythmias (particularly atrial fibrillation).

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

atrial synchronous ventricular inhibited pacemaker VDD Indications AV block with intact sinus node function (particularly useful in congenital AV block).

Dual chamber pacemaker 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.

Temporary pacemaker

Types Transvenous- pacing wire via central line to RV under X ray, usually bipolar i.e., with 2 electrodes at the end of wire Transthoracic (epicardial lead)  post op pacer wires. Transcutaneous  one electrode over cardiac apex, other over right scapula or clavicle. Transesophageal

Transcutaneous pacemaker Posterior  Lt side of the spine, behind the scapula, directly behind the anterior electrode. Avoid placement over bone. Anterior  Upper = below nipple, center =V2, V3 position, Female= under the breast, above diaphragm. Output  Increase gradually until captures, then increase 10% more. Require sedation and analgesia.

Transvenous pacemaker

Medtronic 5388 Dual Chamber

Setting Atrial and ventricular output (lowest possible) Milliamperes (mA) Typical atrial mA 5 Typical ventricular mA 8-10 Atrial/ventricular rate Set at physiologic rate for individual patient Post open heart sugery  90/min AV Interval, upper rate, & PVARP automatically adjust with set rate changes Atrial and ventricular sensitivity Millivolts (mV) Typical atrial: 0.4 mV Typical ventricular: 2.0mV

Setting (cont.) AV Interval Milliseconds (msec) Upper rate Time from atrial sense/pace to ventricular pace Synonymous with “PR” interval Upper rate Automatically adjusts to 30 bpm higher than set rate Prevents pacemaker mediated tachycardia from unusually high atrial rates Wenckebach-type rhythm results when atrial rates are sensed faster than the set rate Refractory period PVARP: Post Ventricular Atrial Refractory Period Time after ventricular sensing/pacing when atrial events are ignored

Normal Pacing Atrial Pacing Atrial pacing spikes followed by P waves

Normal Pacing Ventricular pacing Ventricular pacing spikes followed by wide, bizarre QRS complexes

Normal Pacing A-V Pacing Atrial & Ventricular pacing spikes followed by atrial & ventricular complexes

Normal Pacing DDD mode of pacing Ventricle paced at atrial rate

Assessing Underlying Rhythm

Problems with pacemakers

Problems with pacemakers Failure to pace Failure to capture Failure to sense (overpacing) Wenkebach Pacemaker syndrome

1. Failure to Pace Causes: Oversensing Battery failure Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7th 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, 7th ed., 2005. Causes: Crosstalk (V oversensing when A paced)

Oversensing Pacing does not occur when intrinsic rhythm is inadequate

Oversensing Causes Danger - heart block, asystole Pacemaker inhibited due to sensing of “P” waves & “QRS” complexes that do not exist Pacemaker too sensitive Possible wire fracture, loose contact Pacemaker failure Danger - heart block, asystole

Oversensing Solution View rhythm in different leads Change electrodes Check connections Decrease pacemaker sensitivity (↑mV) Change cables, battery, pacemaker Reverse polarity Check electrolytes Unipolar pacing with subcutaneous “ground wire”

Reversing polarity Changing polarity Requires bipolar wiring system Reverses current flow Switch wires at pacing wire/bridging cable interface

2. Failure to Capture Atrial non-capture Atrial pacing spikes are not followed by P waves

Failure to Capture Ventricular non-capture Ventricular pacing spikes are not followed by QRS complexes

Failure to Capture Causes Danger - poor cardiac output Insufficient energy delivered by pacer Low pacemaker battery Dislodged, loose, fibrotic, or fractured electrode Electrolyte abnormalities Acidosis Hypoxemia Hypokalemia Danger - poor cardiac output

Failure to Capture Solutions View rhythm in different leads Change electrodes Check connections Increase pacer output (↑mA) Change battery, cables, pacer Reverse polarity

3. Failure to Sense (overpacing) Atrial undersensing Atrial pacing spikes occur regardless of P waves Pacemaker is not “seeing” intrinsic activity

Failure to Sense Ventricular undersensing Ventricular pacing spikes occur regardless of QRS complexes Pacemaker is not “seeing” intrinsic activity

Competition Pacemaker & patient’s intrinsic rate are similar Unrelated pacer spikes to P wave, QRS complex Fusion beats

Failure to Sense Causes Pacemaker not sensitive enough to patient’s intrinsic electrical activity (mV) Insufficient myocardial voltage Dislodged, loose, fibrotic, or fractured electrode Electrolyte abnormalities Low battery Malfunction of pacemaker or bridging cable

Failure to Sense Danger – potential (low) for paced ventricular beat to land on T wave (R on T)  VF!!

Failure to Sense Solution View rhythm in different leads Change electrodes Check connections Increase pacemaker’s sensitivity (↓mV) Change cables, battery, pacemaker Reverse polarity Check electrolytes Unipolar pacing with subcutaneous “ground wire”

4. Wenckebach Assessment Appears similar to 2nd degree heart block Occurs with intrinsic tachycardia

Wenckebach Causes DDD mode safety feature Prevents rapid ventricular pacing impulse in response to rapid atrial rate Sinus tachycardia Atrial fibrillation, flutter Prevents pacer-mediated tachycardia Upper rate limit may be inappropriate

Wenckebach Solution Treat cause of tachycardia Fever: Cooling Atrial tachycardia: Anti-arrhythmic Pain: Analgesic Hypovolemia: Fluid bolus Adjust pacemaker upper rate limit as appropriate

5. Pacemaker syndrome Ventricular pacing  sacrifice the atrial contribution to ventricular output Loss of AV synchrony  Atrium contracts against closed TV,MV  ↓ CO, ↑ JVD Retrograde ventriculoatrial (VA) conduction  inverted P, ↑ PR, AV dissociation Absence of rate response to physiologic need 14-57% in VVI Patients with intact VA conduction are at greater risk

Rx VVI  Add A-lead, ↓ Rate Other  interrogation and reprogramming to fix loss of AV synchrony

Surgical diathermy and pacemakers

Ventricular fibrillation – most common if pacemaker unit is older type Inhibition of demand function- sensing may be triggered, with resultant chamber inhibition or arrhythmias induced Unpredictable setting of programmable types Asystole Unit failure

Recommendations Place indifferent electrode on same side as operation & as far from pacemaker unit as possible Limit use of diathermy Use lowest current setting possible Use bipolar diathermy Careful monitoring of pulse, pulse oximetry & arterial pressure Transcutaneous pacing should be available Isoprenaline should be available Interrogation before Sx Magnet Reset PM to asynchronous Inactivate defribillation feature in AICD

Post operative care Full telemetric check Reprogramming back to original setting

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