INTERPRETING THE ECG IN PATIENTS WITH PACEMAKERS BEFORE INTERPRETING THE ECG: Nora Goldschlager, M.D. MACP, FACC, FAHA, FHRS. Cardiology – San Francisco General Hospital UCSF Disclosures: None 1 2 QUESTIONS FOR THE PATIENT EXAMINATION OF THE PATIENT WITH A PACEMAKER WITH A PACEMAKER • When was the original implant? • Superior vena caval syndrome? • Why was it done? • Fever? (Pacing systems are a • Who did it AND WHERE? source of endocarditis) • How many leads (wires)? • Pericardial rub? • Was there a generator change? Why? • What is the device? • Evidence of pericardial effusion? • Is there a defibrillator in also? • Pneumothorax? • Do you have your ID card? • Diaphragmatic stimulation with pacing? - Get the original records! • Pocket stimulation with pacing? - Call the 800 manufacturers’ numbers for • Hematoma? patient ID from their data base • Ecchymosis? - Call the rep! 3 4 INTERPRETING THE PACEMAKER ECG - GANZ 2017 1
SUPERIOR VENA CAVAL SYNDROME EXAMINATION OF THE PACEMAKER POCKET • Clean? • Intact? • Red? • Swollen? • Large hematoma? • Draining? • Extruded device 5 6 HEMATOMA FORMATION AT PULSE GENERATOR/ DUE TO ANTICOAGULANTS 7 8 INTERPRETING THE PACEMAKER ECG - GANZ 2017 2
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MAGNET FUNCTION We perform all ECGs as simultaneously • Eliminates sensing of the electrical signal recorded 12-leads as rhythm strips, both • Non-programmable without and with magnet, so as to see • May have a constant and short AV interval spontaneous morphology and paced • May have changing rates and AV intervals morphology in all 12 leads. This method can (e.g., 3 AV outputs at 100 with short AVI, followed by outputs at 85 with also identify fusion and pseudofusion programmed AVI) complexes, as well as functional • MRI conditional pacemakers have different noncapture. AV rates and intervals KNOW THE MAGNET RESPONSES 13 14 DEFINITIONS DEFINITIONS SENSING: Sensing of an electrical signal CAPTURE: Depolarization of myocardium by from the lead in that chamber a pacing stimulus - Normal intracardiac signal - Muscle potentials PACEMAKER NONCAPTURE: Failure of a - Far-field signals pacing stimulus to depolarize myocardial - Electromagnetic interference tissue, provided that temporal opportunity (e.g., Bovie, MRI) is present FUNCTIONAL NONCAPTURE: Failure of a INHIBITION OF OUTPUT: Inhibition of pacing pacing stimulus to depolarize myocardial stimulus delivery on sensing an intracardiac tissue due to lack of temporal opportunity, signal e.g., when the tissue is refractory from a TRIGGERED OUTPUT: A sensed signal prior depolarization causes a pacing stimulus output to occur 15 16 INTERPRETING THE PACEMAKER ECG - GANZ 2017 4
ELECTROCARDIOGRAM - WHAT TO IDENTIFY AND RECOGNIZE DEFINITIONS • Perform with and without magnet (to assess magnet rate and to verify capture) UNDERSENSING: Sensing of electrical • Identify: intracardiac signals does not occur - Intrinsic atrial and ventricular rhythm, OVERSENSING: Sensing of unwanted signals rate and QRS complex morphology - Paced P wave and QRS complex morphology - Fusion complexes - Pseudofusion complexes (superposition of pacing stimulus on intrinsic complex without contributing to depolarization) 17 18 ELECTROCARDIOGRAM - STATES OF DDD PACING WHAT TO IDENTIFY AND RECOGNIZE • Spontaneous sinus rhythm – atrial and • Pauses in paced rhythm (oversensing in ventricular sensing confirmed; single-chamber systems) capture not seen • Inappropriately early ventricular paced • AV sequential pacing – sensing not seen events (undersensing in single-chamber • ApVs - atrial pacing (confirmed) with intact ventricular systems, inappropriate triggering AV conduction and spontaneous QRS of ventricular-paced events in dual-chamber complexes (ventricular sensing confirmed; systems due to oversensing in atrial channel) atrial sensing not seen, ventricular • Appropriate early paced ventricular event capture not seen) due to APCs • AsVp – Atrial sensing confirmed, ventricular • Changing paced rates due to rate response capture confirmed (atrial pacing not seen, feature ventricular sensing not seen) • Rapid paced ventricular paced rates (triggered by AT, AF/FL/PMT) 19 20 INTERPRETING THE PACEMAKER ECG - GANZ 2017 5
AV PACING, SENSING NOT SEEN CONSIDERATIONS IN ASSESSING CAPTURE • Is the pacing stimulus clearly visible on the recording equipment ? • Are apparent noncapture episodes confirmed by multiple ECG leads? • Are true fusion and pure paced complexes clearly identified and distinguished from pseudo- and pseudopseudofusion complexes? (True fusion implies capture, whereas pseudofusion does not.) 21 22 AV PACING, VENTRICULAR PSEUDOFUSIONS V noncapture? V capture? Latency? Neither V sensing nor pacing is confirmed 23 24 INTERPRETING THE PACEMAKER ECG - GANZ 2017 6
NOT ALL PACING STIMULI ARE VISIBLE 25 26 ATRIAL PACING, VENTRICULAR FUSIONS 27 28 INTERPRETING THE PACEMAKER ECG - GANZ 2017 7
CONFIRMATION OF VENTRICULAR CAPTURE V Fusions NOT ALL WIDE QRS COMPLEXES CAN BE AVI 200 ms V Fusions ASSUMED TO BE PACED AVI 125 ms Pure V Paced 29 30 CONSIDERATIONS IN ASSESSMENT CAPTURE - 2 • In DDD mode, where the ECG reveals As function, loss of atrial capture is confirmed by the occurrence of ventricular paced events. If AV pacing is occurring but the ventricular complexes are fusions, loss of atrial capture is confirmed at the time of occurrence of pure paced ventricular complexes. • In DDD mode, where AV pacing is occurring, loss of atrial capture can be inferred by the onset of retrograde P-waves 31 32 INTERPRETING THE PACEMAKER ECG - GANZ 2017 8
CONSIDERATIONS “FUNCTIONAL” NONCAPTURE IN ASSESSMENT CAPTURE - 3 Is there temporal opportunity for capture? (Functional noncapture will occur if myocardial tissue is refractory during the stimulus delivery) 33 34 EVALUATION OF SENSING FUNCTION • Rate program to low rate to see spontaneous rhythm • Sensing threshold • Marker channel analysis and telemetered electrograms • Trended information 35 36 INTERPRETING THE PACEMAKER ECG - GANZ 2017 9
EVALUATION OF ATRIAL UNDERSENSING IN DDD SYSTEMS • Program low rate to achieve spontaneous atrial activity. • Program short AVI to ascertain TRACKED ventricular response. If tracking is appropriate, then sensing function is confirmed • Delivery of atrial stimulus output on time (unless VA timing reset by a native or paced QRS) • Event markers with surface ECG and intracardiac Egram • Autothreshold 37 38 39 40 INTERPRETING THE PACEMAKER ECG - GANZ 2017 10
CAUSES OF PACEMAKER OVERSENSING • Physiologic intracardiac signals R waves (atrial channel) T waves (ventricular channel) • Physiologic extracardiac signals Muscle potentials (diaphragm, pectoral, seizure, tremor, shiver) • Environmental signals Pacemaker related (crosstalk, lead fracture, insulation break) Pacemaker unrelated EMI Environmental Hospital 41 42 PACEMAKER – UNRELATED CAUSES HOSPITAL SOURCES OF OF OVERSENSING ELECTROMAGNETIC INTERFERENCE • Electrocautery • Medical equipment • Catheter ablation - Electrocautery • Cardioversion and defibrillation - MRI • Ionizing radiation - Cardioversion, defibrillation • MRI, other than “conditional” - Transcutaneous pacing • Cell phones - Electrotherapy • Antitheft devices - Transcutaneous nerve stimulation • iPhones - Implanted neuromuscular stimulators • Tasers • Transcutaneous or implanted nerve stimulators - Ionizing radiation • Implanted bladder stimulators 43 44 INTERPRETING THE PACEMAKER ECG - GANZ 2017 11
CAUSES OF ABSENCE OF PACEMAKER STIMULUS OUTPUT • Normal inhibition by native atrial and ventricular events, or by oversensed signals, including electromagnetic interference • Loose lead-generator connections (stimulus is generated, but does not reach body tissue) • Low-amplitude stimuli not registered by recording equipment (including telemetry and critical care unit monitors and ECG machines) • Battery end-of-life • Component failure 45 46 DIAGNOSIS OF CONDUCTOR WIRE FRACTURE ECG Differential Dx Absence of stimulus Low amplitude bipolar artifacts stimulus Attenuation of stimulus Low amplitude bipolar artifacts stimulus Reversal of stimulus Artifact of recording artifact polarity equipment Intracardiac Electrogram Voltage transients Actual far field signals sensed as “P” or “R” waves Interrogation High lead impedence 47 48 INTERPRETING THE PACEMAKER ECG - GANZ 2017 12
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