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Heart & Pacemaker Basics
Zhihao Jiang
mLab@University of Pennsylvania
1
Heart Anatomy
• 4 heart chambers
Right
Atria
Left
Ventricles
Courtesy of Medtronic
Medical Systems
2
Impulse Formation
• Natural pacemaker: Periodic electrical impulses
SA node
Medical Systems
3
Atrial Contraction
• Activation  Muscle contraction
Atria
Medical Systems
4
Delay At AV Node
• Allows the ventricles to fill fully
AV node
Medical Systems
5
Ventricular Contraction
• Pump blood out of the heart
Ventricles
Medical Systems
6
Bradycardia
• Slow heart rate
Formation
Conduction
Medical Systems
7
Dual Chamber Pacemaker
• Two leads implanted in right atrium and ventricle
Pacemaker
Medical Systems
8
Electrogram (EGM) signals
• Voltage change due to activation
A
V
Pacemaker
Medical Systems
9
Atrial Sensing (AS)
• Generate sensed event when signal above threshold
Threshold
A
V
AS
Pace
Pacemaker
Medical Systems
10
Ventricular Sense (VS)
• Same for ventricular channel
A
V
AS
Pace
Pacemaker
VS
Medical Systems
11
V-A deadline & Atrial Pacing (AP)
• Pace atrium when no AS within deadline
A
V
AS
AP
Pace
V-A
Pacemaker
VS
Medical Systems
12
A-V deadline and Ventricular
Pacing (VP)
• Pace ventricle if no VS happen within deadline
A
V
AS
AP
Pace
A-V
V-A
Pacemaker
VS
Medical Systems
VP
13
V-V deadline
• Minimum ventricular rate allowed
A
V
AS
AP
Pace
A-V
V-A
Pacemaker
V-V
VS
Medical Systems
VP
14
Minimum Ventricular Pacing
Interval
• Scheduled VP delayed if time since last ventricular
event (VS, VP) is less than threshold
A
V
AS
AS
Pace
A-V
V-A
Pacemaker
V-V
VS
Medical Systems
VP
15
Minimum interval between Sensed
events
• Mimic refractory property of heart tissue
Noise
A
V
AS
Pace
Pacemaker
ARP
VRP
VS
Medical Systems
16
Post-Ventricular Atrial Blocking
period (PVAB)
• Preventing crosstalk between A and V channels
Threshold
A
V
AS
AP
Pace
Pacemaker
PVAB
VS
Medical Systems
VP
17
Single Chamber Mode
• Maintain ventricular rate
V
Pace
Pacemaker
V-V
VRP
VS
Medical Systems
VP
18
Pacemaker Mediated Tachycardia
(PMT)
• Pacemaker inappropriately increases ventricular rate
– Normal ventricular rate without pacemaker
– Ventricular Tachycardia with pacemaker
• Two cases
– Atrial Tachycardia Response
– Endless Loop Tachycardia (ELT)
Medical CPS
19
Atrial Tachycardia Response:
Open-loop
• Atrial Tachycardia: Abnormally fast atrial rate
A
V
Medical Systems
20
Atrial Tachycardia Response:
Open-loop
• AV node enters Refractory period
A
V
AV node
Refractory
Medical Systems
21
Atrial Tachycardia Response:
Open-loop
• Another early atrial contraction
A
V
AV node
Refractory
Medical Systems
22
Atrial Tachycardia Response:
Open-loop
• Blocked by AV node during refractory
A
V
AV node
Refractory
Medical Systems
23
Atrial Tachycardia Response:
Open-loop
• Third atrial contraction
A
V
AV node
Refractory
Medical Systems
24
Atrial Tachycardia Response:
Open-loop
• Blocked by AV node again
A
V
AV node
Refractory
Medical Systems
25
Atrial Tachycardia Response:
Open-loop
• AV node refractory finished
A
V
AV node
Refractory
Finished
Medical Systems
26
Atrial Tachycardia Response:
Open-loop
• 3:1 A-V conduction
A
V
Medical Systems
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Atrial Tachycardia Response:
Open-loop
• Normal Ventricular rate in contrast to fast atrial rate
A
V
Within safe region
Medical Systems
28
Atrial Tachycardia Response:
Closed-loop
• Inappropriately increase ventricular rate
A
V
AS
Pace
Pacemaker
Medical Systems
29
Atrial Tachycardia Response:
Closed-loop
• Mimic refractory property of heart tissue
A
V
AS
Pace
Pacemaker
AV node
Refractory
Medical Systems
30
Atrial Tachycardia Response:
Closed-loop
• Some of the fast atrial events are filtered
A
V
AS [AR]
Pace
Pacemaker
AV node
Refractory
ARP
Medical Systems
31
Atrial Tachycardia Response:
Closed-loop
• VP when AV node in Refractory
• AV node function bypassed
A
V
AS [AR]
Pace
A-V
Pacemaker
AV node
Refractory
VP
Medical Systems
32
Atrial Tachycardia Response:
Closed-loop
• Ventricular rate at Upper Rate Limit
A
V
AS [AR] AS[AR]
Pace
A-V
A-V
At URL
Pacemaker
VP
VP
Medical Systems
33
Endless Loop Tachycardia (ELT):
Closed-loop
• Pre-mature Ventricular Contraction (PVC)
A
V
AS
PVC
Pace
A-V
Pacemaker
VP
Medical Systems
VS
34
Endless Loop Tachycardia (ELT):
Closed-loop
• Retrograde conduction causing atrial contraction
A
V
AS
AS
V-A
Pace
A-V
Pacemaker
Retrograde conduction
VP
Medical Systems
VS
35
Endless Loop Tachycardia (ELT):
Closed-loop
• VP after A-V deadline
A
V
AS
AS
V-A
Pace
A-V
A-V
VP
VS VP
Pacemaker
Medical Systems
36
Endless Loop Tachycardia (ELT):
Closed-loop
• The VP-AS-VP pattern persists, causing ELT
A
V
AS
AS
V-A
Pace
AS
V-A
A-V
A-V
A-V
VP
VS VP
VP
Pacemaker
Medical Systems
37