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Pacing Reference Questions included for Critical Care Competency Day 2010 - 2011 Pacemaker • Medtronic 5388 Dual Chamber (DDD) Temporary Pacing Review • The following slides are designed to help you review some aspects of temporary pacing. • Other resources available include – pacing resource book in SICU – medtronic website: temporary pacing powerpoints Indications for Temporary Pacing Placement of Epicardial Wires Transvenous Pacing Insertion Sites Internal Jugular Vein External Jugular Vein Internal Jugular Subclavian Brachial Vein Femoral Femoral Vein Subclavian Vein Transvenous Pacing Wire • Bipolar lead system – Transvenous wire is floated into the right ventricle – The negative and positive electrodes are in contact with the heart Single Chamber Temporary Pacing Pacer Settings: • Pacing rate (heart rate) • Output/stimulation threshold • Sensitivity Model 5388 Dual Chamber Temporary Pacemaker 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. Pace/Sense LEDs Lock/Unlock Key Lock Indicators Rate Dial Atrial Output Dial Ventricular Output Dial Menu Parameter Dial Parameter Selection Key Menu Selection Key Pause Key Power On Key Power Off Key Emergency/Asynchronous Pacing Key Lower Screen Ventricular Output Graphics Atrial Output Graphics Upper Screen Rate Graphics Setup Indicators DDI Indicator Low Battery Indicator Setup Labels Lower Screen Menus Menu 1: Pacing Parameters Menu 2: Rate-Based Pacing Parameters Menu 3: Rapid Atrial Pacing Menu M: Dial-A-Mode NBG Codes 1st Letter Chamber(s) Paced A = atrium V = ventricle D = dual (both atrium and ventricle) Chamber paced 2nd Letter 3rd Letter Chamber(s) Sensed A = atrium V = ventricle D = dual O = none Response to Sensing I = inhibit (Demand mode) T = triggered D = dual O = none (Asynch) Chamber sensed Action or response to a sensed event Set Up Guide Pacemaker EKG Strips • Assessing Paced EKG Strips – – – – – Identify intrinsic rhythm and clinical condition Identify pacer spikes Identify activity following pacer spikes Assess for Failure to capture Assess for Failure to sense • EVERY PACER SPIKE SHOULD HAVE A PWAVE OR QRS COMPLEX FOLLOWING IT. Capture Depolarization of cardiac muscle following an electrical stimulus Sensitivity The degree that the pacing system “sees” or senses signals, controlled by the sensitivity setting which is graduated in millivolts (mV) Sensitivity (mV) 5 (mV) 2.5 (mV) 1.25 (mV) Sensitivity The lower the setting, the more sensitive the pacemaker is to intracardial signals 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 Troubleshooting Pacing • Look for – Failure to Fire (No Output from Pacer) – Failure to Capture (pacer not followed by depolarization) – Failure to Sense • Undersensing: pacer not sensing all intrinsic activity so may misfire at inappropriate times • Oversensing: pacer sensing artifact as well as intrinsic activity so may not fire when necessary Failure to Fire: No Output Possible Causes Corrective Measures •Battery depletion •Pacemaker OFF •Faulty cable connections •Fractured/dislodged lead •Oversensing •Replace battery •Verify pacemaker settings •Check cable connections •Replace/reposition lead •Verify/adjust sensitivity Failure to Fire • Indicated by absence of pacer spikes where they should be • Possible Causes: Solution: – Low battery – Loose connections – Oversensing – Lead dislodged or Fractured Replace battery Check and secure connections Increase mV to lower sensitivity Place skin wire or reposition transvenous wire Factors that Affect Capture and Sensing 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 – – – – Check connections Increase pacer output (↑mA) Change battery, cables, pacer Reverse polarity Atrial/Ventricular Stimulation Thresholds Capture Loss of Ventricular Capture 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 Capture Threshold testing • Capture Stimulation threshold – Definition: Minimum current necessary to capture & stimulate the heart – Testing • • • • Set pacer rate 10 ppm faster than patient’s HR Starting at 0 mA, increase mA until 100% capture is obtained This is your pacing threshold Set mA 2-3x greater than the pacing threshold – Example: Set output at 10-15 mA if 100% capture was at 5mA Failure to Sense : Undersensing • Causes – Pacemaker not sensitive enough to detect patient’s intrinsic electrical activity (mVset too high) – Asynchronous pacing – Insufficient myocardial voltage – Dislodged, loose, fibrotic, or fractured electrode – Mechanical failure: wires, bridging cables, pacemaker – Low battery • Danger – Potential (low) for paced ventricular beat to land on T wave and lead to Vtach Undersensing • Solutions – Check all connections – Make sure pacer is not set for asynchronous pacing – Increase pacemaker sensitivity (↓mV) until pacer spikes move away from intrinsic beats – Change battery Undersensing 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 • Danger – potential for paced ventricular beat to land on T wave Oversensing • Inhibition of the pacemaker by events it should ignore such as: – T waves – Artifact 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 – asystole or heart rate too low to maintain adequate cardiac output – If pacer “thinks” intrinsic heart rate is at or above set rate, then it won’t pace Oversensing • Solution – – – – – Check connections Decrease pacemaker sensitivity (↑mV) Change cables, battery, pacemaker Reverse polarity Check electrolytes Oversensing One Last Thing to Consider: Fusion and Pseudofusion Beats Pseudofusion Beat: Fusion Beat: When Intrinsic Depolarization Initiates at Same Instant as Pacer Fires: Beat is A combination Of a paced and Intrinsic beat This is NOT a problem with The pacemaker Intrinsic Beat Intrinsic Beat Fusion Beat Fusion Beat Paced Beat Paced Beat Pseudofusion Beat Pseudofusion Beat Occurs when pacer fires just after intrinsic depolarization begins. Pacer spike will appear at middle to end of R wave. Beat will be intrinsic. This is also not a malfunctoning pacemaker. The pacemaker has fired too close to time of depolarization to be able to detect it. If this were undersensing the pacer spike would be at the end of QRS or later. Pacing Responsibilities • Check all connections are proper • Assess and troubleshoot pacing problems – Failure to fire – Failure to capture – Under or over sensing • Determine pacing threshold and set mA appropriately – Document threshold and setting Pacing Responsibilities • Determine underlying rhythm and document – This can be done when you are determining pacing threshold – By turning down the mA to below the pacing threshold, the patient’s intrinsic rhythm will become apparent • Document sensitivity settings – Atrial is normally < 1 mV – Ventricular is usually between 2-7 mV • For patient attached to pacemaker but not actively pacing, thresholds still need to be checked and documented – It is important to know that the pacemaker will work if the patient needs it • Additionally for transvenous pacing – Check and document position of pacing wire Pacing Questions • Look at each of the following pacing strips – ?fire – ?capture – ?sensing properly • if not, is it undersensing or oversensing – ?what would you do if you saw this strip Practice Strip #1 Practice Strip #2 Pacing Strip #3 Practice Strip #4 Practice Strip #5 Pacing Strip # 6 Pacing Strip # 7