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CP1218213-1
Interpreting Pacemaker ECGs: Pearls & Pitfalls
K.L.Venkatachalam MD Division of Cardiovascular Diseases
Mayo Clinic Jacksonville, FL
November 3 2011
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Disclosures
None
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Objectives
• Understand pacing vectors on standard ECGs
• Appreciate some pacemaker “enhancements”
• Review common findings on pacemaker ECGs
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1 2
3
4 5 6
I
II III aVF
aVL aVR
III
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Where is the ventricular lead?
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Where is the ventricular lead?
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Pacemaker Operation (Dual)
• ASENSE - VSENSE (Intrinsic rhythm)
• ASENSE - VPACE (p-synchronous pacing)
• APACE - VSENSE (Intrinsic conduction)
• APACE - VPACE (AV sequential pacing)
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Bernstein et. al. PACE 2002
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Pacemaker Modes
• VVI
• DDD
• VOO
• DDI
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Pacing mode?
DDD or VDD
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Pacing mode?
VOO or VVI
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Programmed Settings
• Lower rate limit
• Upper rate limit
• A-V Interval
• Output Voltage
• Output Pulse Width
• Input sensitivity
• Refractory Periods
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Programming Outputs
• Conserving energy
• Preserving safety margin
• Managing acute threshold rise (usually for first 4-6 weeks)
• Chronic thresholds 2-3 X energy 2-3 X pulse width
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Factors in Programming Outputs
• Pacemaker dependency
• Greater safety margin on RV channel
• History of high thresholds
• History of fluctuating thresholds
• Lower safety margin for LV channel
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Pacer Spike Rejection
2 mV 700 mV
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Simplified ECG Front-end
P
Amp BPF Slew Limiter Amp
dV/dT
ECG Leads
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Pacemaker Timing
• Ventricle Based
• Atrial Based
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Ventricle Based Timing I
• LRL = 60 BPM = 1000 msec CL
• AV delay = 200 msec
• Calculated VA interval (Atrial Escape Interval) = 1000 – 200 = 800 msec
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Ventricle Based Timing II
• For each Ventricular sensed or paced beat, the atrial escape timer will time out after 800 msec
A
V
As
Vs
800
Ap
Vs Vs
200
600
As
75 BPM
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Ventricle Based Timing III
• If the physiologic AV delay is only 150 msec ….
A
V
As
600
As
Vs
800
Ap
Vs Vs
150
80 BPM
800
Ap
800
Ap
63 BPM 63 BPM
Vs
150 150
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Atrial Based Timing
• The A-A interval tries to remain at the programmed LRL and the AEI is allowed to vary
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Managed Ventricular Pacing®
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Medtronic
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Ventricular Safety Pacing®
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DDDR 60-140, AV delay 220 msec
V-A interval (AEI): 780 msec
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Atrial Escape Interval AV
Post-atrial V-blanking
Pseudo-pseudofusion
Usually due to atrial undersensing
Occurs when intrinsic ventricular rate is
calculated V-A interval { for ventricle-based
timing }
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Rhythm?
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76 year old male with dyspnea and palpitations
19 AF
55 Lateral MI, acute
53 Anterior MI, acute
94 PM malfunction, not sensing
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What is the mechanism of tachycardia during atrial threshold testing at setting of DDD 90?
Pacemaker Mediated Tachycardia
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Bradycardia with Pacemaker
• Hysteresis
• Sleep Mode
• Ventricular Ectopy
• Malfunction
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DDD 60-120, PAV 200, , PVARP 275
240
1. Atrial undersensing
800
2. Appropriate ventricular sensing
Kenny 2009.The nuts and bolts of paced ECG interpretation
SAV 150
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Acknowledgements
Samuel Asirvatham MD
Stephen Hammill MD
David Hayes MD
Brian Powell MD
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CP1218213-1
Interpreting Pacemaker ECGs: Pearls & Pitfalls
K.L.Venkatachalam MD Division of Cardiovascular Diseases
Mayo Clinic Jacksonville, FL
November 3 2011