1. Pacemakers and Implantable Cardioverter-Defibrillators16
Pacemakers and Implantable Cardioverter-Defibrillators
Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program

2. Artificial Pacemakers
Medical devices used to generate and deliver electrical impulses to the myocardium to stimulate a normal heartbeat
Some are external to the body and provide temporary treatment, others are permanently implanted in the chest

3. Artificial Pacemakers
One type of temporary pacemaker is the transcutaneous pacemaker
It delivers electrical impulses through lead wires to electrode pads that are applied to the surface of the patient’s chest
Permanent pacemakers are implanted in a surgically created pocket beneath the skin in the patient’s chest wall just below the clavicle

4. Permanent Pacemakers Consist of: A generator One or more lead wires
A power source (often a lithium battery)
Logic circuits that detect cardiac electrical activity and determine the appropriate response I

5. Permanent Pacemakers May be used to: Symptomatic bradycardia
Sick sinus syndrome
Atrial fibrillation with bradycardia
3rd-degree (complete) AV heart block
Symptomatic 2nd-degree AV heart block, particularly type II
The sudden development of various combinations of AV heart block and bundle branch block in patients experiencing acute MI
Recurrent tachycardias that can be overdriven and thereby terminated by pacemaker activity
Synchronization of the heart beat in heart failure (cardiac resynchronization therapy)

6. Pacemaker Electrodes
Are either positioned in the atrium or ventricle alone (single-chamber pacemakers) or, more often, in both chambers (dual-chamber pacemakers or AV sequential pacemakers)

7. Permanent Pacemakers Are programmable Adjustments can be made to:
Receive and transmit data/programming instructions through the skin using electromagnetic waves
Adjustments can be made to:
Output
Sensitivity
Refractory period
Rate adaption

8. Pacing Modes Single-chamber Dual-chamber
One pacing lead is inserted into either the right atrium or right ventricle but not both
Dual-chamber
Electrodes are placed into two chambers of the heart
One lead paces the atrium while the other paces the ventricle
By assisting the heart in coordinating the function between the atria and ventricles, this type of pacemaker acts similarly to how the heart naturally paces itself
Also referred to as an AV sequential pacemaker
Most can be programmed to a single chamber mode, which can be useful if the atrial lead wire fails

9. Pacing Modes Fixed-rate Rate-responsive
Paces the heart at a single, preset rate
Rate-responsive
Has sensors that identify increases or decreases in the patient’s physical activity and automatically adjusts base pacing rate to meet the body’s metabolic needs
Can boost the heart rate in response to motion or increased respirations for those patients whose body cannot appropriately increase the heart rate during activity

10. Pacing Modes Demand Most common type used
Fires only when the patient’s intrinsic heart rate falls below a given threshold level
i.e., if the pacemaker is set at 60 beats per minute it remains inactive until there is a pause between beats that translates into a rate below 60, then the pacemaker fires

11. Coding System
Pacemaker mode and function described by a five letter coding system
in practice, only three to four are commonly used

12. Coding System
First letter represents the heart chamber being paced. This letter may be
O = none
A = atrium
V = ventricle
D = dual (ventricle and atrium)
Second letter represents the chamber of the heart being sensed by the pacemaker. This letter may be

13. Coding System
Third letter indicates how the pacemaker generator responds to sensing. This letter may be
O = none
T = triggers pacing
I = inhibits pacing
D = dual (triggers and inhibits pacing)
Fourth letter has to do with adjustment of the pacing rate in response to exercise
If pacemaker is rate responsive, it is denoted with the letter “R”
If there is none, it is denoted as “O”

14. Coding System
The fifth letter indicates multisite pacing. This letter may be
O = none
A = atrium
V = ventricle
D = dual (ventricle and atrium)

15. Coding System Examples
VOO
In this mode, the ventricle is paced and there is no sensing function
AAI
Pacemaker paces and senses in the atrium
When it senses atrial activity, pac­ing is inhibited
VVI
Ventricle is paced and sensed
If spontaneous cardiac output is detected, then the device is inhibited

16. Coding System Examples
VDD
Here the pacemaker paces the ventricle and senses both the atrium and ventricle
On sens­ing intrinsic atrial activity, the pacemaker triggers ventricular pac­ing; on sensing ventricular activity, the pacemaker inhibits pacing
It is also known as a P-synchronous pacer

17. Coding System Examples
DVI
Pacemaker can pace in the atrium, the ventricle, or both
Sensing takes place only in the ventricle
When the pacemaker senses intrinsic ventricular activity, it inhibits pacing
DDD
Pacemaker paces and senses in the atrium, the ventricle, or both
On sensing ac­tivity in either chamber, the pace­maker inhibits pacing in that chamber
Or, on sensing atrial ac­tivity, the pacemaker may trigger ventricular pacing

18. Cardiac Resynchronization Therapy (CRT)
Used to resynchronize a heart that does not beat in synchrony, a common problem in patients with heart failure
Employs three leads:
one is placed in right atrium
one is located in right ventricle
last one is inserted through the coronary sinus to pace the free wall of the left ventricle
These three wires are connected to a CRT generator and programmed so that the two ventricular wires are activated simultaneously
Instructional Point:
Asynchronous contractions lead to blood being moved within, rather than out of the ventricle. This results in reduced cardiac output. Further, these patients experience greater mitral regurgitation and reduced diastolic filling time. Simultaneous contraction of the right and left ventricles achieved through CRT results in less blood being shunted within the ventricle and more blood being propelled into the aorta. These devices relieve symptoms of heart failure, improve prognosis, and lessen the chance of ventricular dysrhythmias. I

19. Unipolar and Bipolar Systems
positive electrode is positioned in the heart tissue and the negative electrode is connected to the pulse generator
produces tall pacing spikes on the ECG
In a bipolar system,
electrodes are only millimeters apart in the cardiac tissue
produces short pacemaker spikes
In some patients, pacemaker spikes are not easy to see on an ECG because their amplitude is less than 1 mV. If the patient is able to communicate and is appropriately oriented, asking the question “Do you have a pacemaker?” may be of use when broad QRS complexes and left axis deviation are seen on the ECG. I

20. ECG Features of a Pacemaker
Depending on how many chambers are paced, the firing of a pacemaker produces one or two narrow pacemaker spikes on the ECG

21. ECG Features of a Pacemaker
A paced ECG complex shows two features: (a) a narrow “pacing spike,” which reflects the impulse depolarizing the paced chamber and (b) a P wave or QRS complex that immediately follows the pacing spike
Instructional Point:
Two types of electrodes are used. One simply goes into the ventricle and fires off an impulse much like a PVC. Another type, more commonly used today is called an A-V sequential pacemaker. With this device the impulse is sent to an electrode in the right atrium simulating a SA node firing. The impulse then travels to the AV node and the remainder of the impulse conduction occurs normally. If the AV node fails to respond a second electrode in the ventricle fires similar to the old style pacemaker. I

22. Pacemaker Failure
Pacemakers may not work properly for a number of reasons, including a failure to capture, a failure to pace, a failure to sense, oversensing, and pacemaker-mediated tachycardia

23. Pacemaker Failure
Failure to capture is seen as the presence of pacemaker spikes that are not followed by a P wave or broad QRS complex

24. Pacemaker Failure
Failure of the pacemaker to sense is seen as the presence of ECG pacemaker spikes that fall where they shouldn’t

25. Pacemaker Failure
Oversensing is seen as an absence of pacemaker spikes in the presence of a heart rate that is slower than the rate set for the pacemaker

26. Pacemaker Failure
Pacemaker-mediated tachycardia is seen as a fast heart rate with a pacemaker spike preceding each QRS complex on EGG.

27. Implantable Cardioverter-Defibrillator (ICD)
Is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation and ventricular tachycardia

28. Implantable Cardioverter-Defibrillator
Is programmed to detect cardiac dysrhythmias and correct them by delivering paced beats, cardioversion, or defibrillation

29. Therapies Provided by the ICD

30. Practice Makes Perfect
Analyze this ECG tracing
Answer: Ventricular pacemaker I

31. Practice Makes Perfect
Analyze this ECG tracing
Answer: AV sequential pacemaker I

32. Practice Makes Perfect
Analyze this ECG tracing
Answer: Ventricular pacemaker I

33. Practice Makes Perfect
Analyze this ECG tracing
Answer: AV sequential pacemaker I