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Temporary Pacemakers
Electrophysiology Care Coordinator Temporary pacemakers Objectives Explain the situations when temporary pacemakers are indicated. Describe the principles of pacing. Illustrate normal and abnormal pacemaker behavior. Discuss the steps to be taken in troubleshooting a temporary pacemaker. Indications for Temporary Pacing Bradyarrhythmias AV conduction block Congenital complete heart block (CHB)- normal or abnormal heart structure L-Transposition (corrected transposition) Bundle of His long; AV node anterior Prone to CHB Trauma- surgical or other Slow sinus or junctional rhythm Suppression of ectopy Permanent pacer malfunction Drugs, electrolyte imbalances Sick Sinus Syndrome Secondary to pronounced atrial stretch Old TGA s/p Senning or Mustard procedure Indications for Temporary Pacing Sick Sinus Syndrome Principles of Pacing Electrical concepts Electrical circuit Pacemaker to patient, patient to pacemaker Current- the flow of electrons in a completed circuit Measured in milliamperes (mA) Voltage – a unit of electrical pressure or force causing electrons to move through a circuit Measured in millivolts (mV) Impedance- the resistance to the flow of current Principles of Pacing Temporary pacing types Transcutaneous Emergency use with external pacing/defib unit Transvenous Emergency use with external pacemaker Epicardial Wires sutured to right atrium & right ventricle Atrial wires exit on the right of the sternum Ventricular wires exit on the left of the sternum Principles of Pacing Wiring systems Unipolar 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 Principles of Pacing Modes of Pacing Atrial pacing Intact AV conduction system required Ventricular pacing Loss of atrial kick Discordant ventricular contractions Sustains cardiac output Atrial/Ventricular pacing Natural pacing Atrial-ventricular synchrony Principles of Pacing 3-letter NBG Pacemaker Code First letter: Chamber Paced V- Ventricle A- Atrium D- Dual (A & V) O- None Principles of Pacing 3-letter NBG Pacemaker Code Second letter: Chamber Sensed V- Ventricle A- Atrium D- Dual (A & V) O- None Principles of Pacing 3-letter NBG Pacemaker Code Third letter: Sensed Response T- Triggers Pacing I- Inhibits Pacing D- Dual O- None Principles of Pacing Commonly used modes: AAI - atrial demand pacing VVI - ventricular demand pacing DDD – atrial/ventricular demand pacing, senses & paces both chambers; trigger or inhibit AOO - atrial asynchronous pacing Principles of Pacing Atrial and ventricular output Milliamperes (mA) Typical atrial mA 5 Typical ventricular mA 8-10 AV Interval Milliseconds (msec) Time from atrial sense/pace to ventricular pace Synonymous with “PR” interval Atrial and ventricular sensitivity Millivolts (mV) Typical atrial: 0.4 mV Typical ventricular: 2.0mV Principles of Pacing (cont.) Atrial/ventricular rate Set at physiologic rate for individual patient AV Interval, upper rate, & PVARP automatically adjust with set rate changes 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 Principles of Pacing Electrical Safety Microshock Accidental de-wiring Taping wires Securing pacemaker Removal of pacing wires Potential myocardial trauma Bleeding Pericardial effusion/tamponade Hemothorax Ventricular arrhythmias Pacemaker care & cleaning Batteries Bridging cables Pacemakers Pacemaker Medtronic 5388 Dual Chamber (DDD) Pacemaker EKG Strips Assessing Paced EKG Strips Identify intrinsic rhythm and clinical condition Identify pacer spikes Identify activity following pacer spikes Failure to capture Failure to sense EVERY PACER SPIKE SHOULD HAVE A P-WAVE OR QRS COMPLEX FOLLOWING IT. 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 Abnormal Pacing Atrial non-capture Atrial pacing spikes are not followed by P waves Abnormal Pacing Ventricular non-capture Ventricular pacing spikes are not followed by QRS complexes Failure to Capture Causes 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 Reversing polarity Changing polarity Requires bipolar wiring system Reverses current flow Switch wires at pacing wire/bridging cable interface Skin “ground” wire Abnormal Pacing Atrial undersensing Atrial pacing spikes occur irregardless of P waves Pacemaker is not “seeing” intrinsic activity Abnormal Pacing Ventricular undersensing Ventricular pacing spikes occur regardless of QRS complexes Pacemaker is not “seeing” intrinsic activity 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 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” Oversensing Pacing does not occur when intrinsic rhythm is inadequate Oversensing Causes 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” Competition Assessment Pacemaker & patient’s intrinsic rate are similar Unrelated pacer spikes to P wave, QRS complex Fusion beats Competition Causes Asynchronous pacing Failure to sense Mechanical failure: wires, bridging cables, pacemaker Loose connections Danger Impaired cardiac output Potential (low) for paced ventricular beat to land on T wave Competition Solution Assess underlying rhythm Slowly turn pacer rate down Troubleshoot as for failure to sense Increase pacemaker sensitivity (↓mV) Increase pacemaker rate Assessing Underlying Rhythm Carefully assess underlying rhythm Right way: slowly decrease pacemaker rate Assessing Underlying Rhythm Assessing Underlying Rhythm Wrong way: pause pacer or unplug cables 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 Threshold testing Stimulation threshold Definition: Minimum current necessary to capture & stimulate the heart Testing Set pacer rate 10 ppm faster than patient’s HR Decrease mA until capture is lost Increase output until capture is regained (threshold capture) Output setting to be 2x’s threshold capture Example: Set output at 10mA if capture was regained at 5mA Performing an AEG Purpose: Determine existence & location of P waves Direct EKG from atrial pacing wires Bedside EKG from monitor Full EKG Atrial pacing pins to RA & LA EKG lead-wires Interpreting an AEG Sensitivity Threshold Definition: Minimum level of intrinsic electric activity generated by the heart detectable by the pacemaker Sensitivity Threshold Testing Testing Set pacer rate 10 ppm slower than patient’s HR Increase sensitivity to chamber being tested to minimum level (0.4mV) Decrease sensitivity of the pacer (↑mV) to the chamber being tested until pacer stops sensing patient (orange light stops flashing) Increase sensitivity of the pacer (↓mV) until the pacer senses the patient (orange light begins flashing). This is the threshold for sensitivity. Set the sensitivity at ½ the threshold value. Example: Set sensitivity at 1mV if the threshold was 2mV Factors Affecting Stimulation Thresholds Practice Strip#1 Practice Strip #2 Practice Strip #3 Practice Strip #4 Practice Strip #5 Practice Strip #6 Practice Strip #7 Practice Strip #8 Practice Strip #9 Answers Mode of pacing, rhythm/problem, solution AAI: normal atrial pacing Sinus rhythm: no pacing; possible back-up setting AAI, VVI, DDD DDD: failure to sense ventricle; increase ventricular mA VVI: ventricular pacing DDD: failure to capture atria or ventricle; increase atrial & ventricular mA DDD: normal atrial & ventricular pacing DDD: normal atrial sensing, ventricular pacing DDD: failure to capture atria; increase atrial mA DDD: oversensing; decrease ventricular sensitivity |
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http://www.ocaheart.com/patient_services/patient_education/testsandprocedures/Pacemakers/Temporary_Pacemaker.asp
http://www.nhlbi.nih.gov/health/dci/Diseases/pace/pace_whatis.html http://www.medtronic.com/for-healthcare-professionals/products-therapies/cardiac-rhythm/index.htm |