1. Cardiac Pacing for the Surgeons
Dr. Rezwanul Hoque
MBBS, MS, FCPS, FRCSG, FRCSEd
Associate Professor
Department of Cardiac surgery
BSMMU, Dhaka, Bangladesh

2.             
Pacemaker
A pacemaker or artificial pacemaker is a medical device designed to regulate the beating of the Heart.
The purpose of an artificial pacemaker is to stimulate the heart when either the heart's native pacemaker is not fast enough or if there are blocks in the heart's electrical conduction system preventing the propagation of electrical impulses from the native pacemaker to the lower chambers of the heart, known as the ventricles.

3. ICD
An ICD(Implantable cardioverter & defibrillator) is a specialized device designed to directly treat a cardiac tachydysrhythmia.
If a patient has a ventricular ICD and the device senses a ventricular rate that exceeds the programmed cut-off rate of the ICD, the device performs cardioversion/defibrillation.
Alternatively, the device, if so programmed, may attempt to pace rapidly for a number of pulses to attempt pace-termination of the ventricular tachycardia.
The newer devices are a combination of ICD and pacemaker in one unit. These combination ICD/pacemakers are implanted in patients who require both devices.

4. Temporary Cardiac Pacing
Transvenous
Transcutaneous
Epicardial
Transesophageal

5. Indications for Temporary Pacing
Acute myocardial infarction with:
CHB, Mobitz type 2 AV block, medically refractory symptomatic bradycardia,
alternating BBB, new bifascicular block, new BBB with anterior MI
In absence of acute MI : SSS, CHB, Mobitz type 2 AV block
Treatment of tachyarrhythmias : VT

6. Transcutaneous pacing
Transcutaneous pacing (TCP), also called external pacing, is recommended for the initial stabilization of hemodynamically significant bradycardia of all types.
The procedure is performed by placing two pacing pads on the patient's chest, either in the anterior/lateral position or the anterior/posterior position.
The rescuer selects the pacing rate, and gradually increases the pacing current (measured in ma) until electrical capture (characterized by a wide QRS complex with a tall, broad T wave on the ECG) is achieved, with a corresponding pulse.
Pacing artifact on the ECG and severe muscle twitching may make this determination difficult.
External pacing should not be relied upon for an extended period of time. It is an emergency procedure that acts as a bridge until transvenous pacing or other therapies can be applied.

7. Transvenous pacing
Transvenous pacing, or temporary internal pacing, is an alternative to transcutaneous pacing.
A wire is placed under sterile conditions via a central venous catheter. The distal tip of the wire is placed into either the right atrium or right ventricle. The proximal tip of the wire is attached to the pacemaker generator, outside of the body.
Transvenous pacing is often used as a bridge to permanent pacemaker placement.
Under certain conditions, a person may require temporary pacing but would not require permanent pacing. In this case, a temporary pacing wire may be the optimal treatment option.

8. Epicardial pacing
Epicardial pacing wires are routine leads used for temporary cardiac pacing after open heart surgery.
During surgery the heart is subjected to stress which can lead to myocardial ischemia and cardiac depression.
Temporary pacing may be necessary to re-establish electrical conduction.
Atrial wires (a wires) are positioned on the right atrial surface and exit the chest wall to the right of the sternum. Atrial wires are attached via a connecting cable to “A” marked terminals on the pacemaker box.
Ventricular wires (v wires) are positioned on the right ventricular surface and exit the chest wall to the left of the sternum. Ventricular wires are attached via connecting cable to “V” marked terminals on the pacemaker box.
If a skin wire is used it is attached to positive pole and the ventricular wire is attached to negative pole of the generator.
Epicardial pacing after open heart surgery allows for the treatment of dysrhythmias, the improvement of hemodynamic functioning, and to maintain backup rate with maze procedure.
The patient should remain on a cardiac monitor 2-hours after the removal of epicardial wires. The patient cannot have an MRI while pacing wires are in place.

9. MEASURES: FAILURE TO CAPTURE/PACE: Secure connections
Replace battery/pacemaker as needed
Increase ma
Reduce sensitivity (turn mv dial counter clockwise or to a higher numerical
setting).
Reverse polarity
Check stimulation threshold
Monitor electrolytes and ABG
Obtain EKG to check for ischemia (ST depression)

10. FAILURE TO SENSE (OVERSENSING OR UNDERSENSING):
Eliminate any electrical interference.
Note: check to ensure that all electrical equipment attached to the patient is grounded
Replace battery/pacemaker as needed
If undersensing [not recognizing patients' own rhythm]increase sensitivity (turn mv dial clockwise to lower mv numerical value)
Note: this will make the pacemaker more sensitive to patient’s own rate
If oversensing [when A-V pacing, the pacemaker may sense the atrial pacing spike as the qrs complex and not fire (cross talk) or the patient is having breakthrough rate and pacemaker does not fire] decrease sensitivity (turn mv dial counter clockwise to raise the numerical mv value)
Note: this will make the pacemaker less sensitive to the patient's rate.
If patient has an adequate underlying rhythm, turn off the pacemaker

11. When to consider PPM
Patients with symptoms directly attributable to bradycardia (even SB)
Disease within AV node as manifest by extreme PR prolongation, normal QRS
Disease below AV node as manifest by normal or mildly prolonged PR and wide QRS
Disease in His – purkinje system (less stable than above)

12. Indications for Pacing for AV Block
Degree
Pacemaker necessary
Pacemaker probably necessary
Pacemaker not necessary
Third
Symptomatic congenital complete heart block
Aquired symptomatic complete heart block
Atrial fibrillation with complete heart block
Acquired asymptomatic complete heart block
Second
Symptomatic type I
Symptomatic type II
Asymptomatic type II
Asymptomatic type I at intra-His or infra-His levels
Asymptomatic type I at supra-His (AV nodal) block
First
Asymptomatic or symptomatic

13. Indications for Pacing for Sinus Node Dysfunction
Pacemaker
Pacemaker probably necessary
Pacemaker not necessary
Symptomatic bradycardia
Symptomatic patients with sinus node dysfunction with documented rates of <40 bpm without a clear-cut association between significant symptoms and the bradycardia
Asymptomatic sinus node dysfunction
Symptomatic sinus bradycardia due to long-term drug therapy of a type and dose for which there is no accepted alternative

14. Where pacing may be helpful
Evolving Indications for Pacing
Pacing for Hemodynamic Improvement
Hypertrophic Obstructive Cardiomyopathy
Cardiac Resynchronization Therapy
Long QT syndromes
Sleep apnea
Neurally mediated syncope

15. The Pacemaker System
Patient
Lead
Lead
Pacemaker
Programmer
Pacemaker

16. Basic pacemaker function
Modern pacemakers usually have multiple functions.
The most basic form listens to the heart's native electrical rhythm, and if the device doesn't sense any electrical activity within a certain time period, the device will stimulate the vetricles of heart with a set amount of energy, measured in joules.
The more complex forms include the ability to sense and/or stimulate both the atrial and ventricular chambers.

17. Permanent pacing
Permanent pacing with an implantable pacemaker involves placement of one or more pacing wires within the chambers of the heart. One end of each wire is attached to the muscle of the heart. The other end is screwed into the pacemaker generator.
The pacemaker generator is a hermetically sealed device containing a power source and the computer logic for the pacemaker.
Most commonly, the generator is placed below the subcutaneous fat of the chest wall, above the muscles and bones of the chest.
The outer casing of pacemakers is so designed that it will rarely be rejected by the body's immune system. It is usually made of titanium, which is very inert in the body.

18. Code Combinations Codes are combined to describe: Mode of pacing
Mode of sensing
How the pacemaker will respond to the
presence or absence of intrinsic beats

19. NASPE / BPEG Generic (NBG) Code
September 11, 2018
NASPE / BPEG Generic (NBG) Code
Position: I II
III IV V
Category:
Chamber(s) Paced
Chamber(s)
Sensed
Response
to Sensing
Rate
Modulation
Multisite
Pacing
Letters Used: O R
None
Atrium
Ventricle
Dual A+V A T
Triggered
Rate
Modulation V I
Inhibited D
Dual T+I
Single A or V S
Manufacturers’ Designation Only:
Bernstein, A.D., et al. PACE 2002; 25: 19

20. Physics of pacing
Pacemaker energy output is dependent upon the signal amplitude and pulse width. Signal amplitude is measured in electrical units of volts or milliamperes. Pulse width is a measure of output duration and is measured in milliseconds. For proper permanent pacer operation, signal amplitude and width are set high enough to reliably achieve capture of the myocardium, yet low enough to prolong battery life.
Pulse generators can be set to a fixed-rate (asynchronous) or demand (synchronous) mode. In the fixed-rate mode, an impulse is produced at a set rate and has no relationship to the patient's intrinsic cardiac activity. This mode carries a small but inherent danger of producing lethal dysrhythmias should the impulse coincide with the vulnerable period of the T wave. In the demand mode, the sensing circuit searches for an intrinsic depolarization potential. If this is absent, a pacing response is generated. This mode can closely mimic the intrinsic electric activity pattern of the heart.

21. Single-chamber Modes VOO Ventricular lead Ventricular pacing
September 11, 2018
Single-chamber Modes
VOO
Ventricular lead
Ventricular pacing
No sensing
Ventricular asynchronous pacing at lower programmed pacing rate 21

22. Single-chamber Modes VVI Ventricular Lead (I) Ventricular pacing
September 11, 2018
Single-chamber Modes
VVI
Ventricular Lead (I)
Ventricular pacing
Ventricular sensing
Sensed intrinsic QRS inhibits ventricular pacing 22

23. Single-chamber Modes AOO Atrial Lead Atrial pacing No sensing
September 11, 2018
Single-chamber Modes
AOO
Atrial Lead
Atrial pacing
No sensing
Atrial asynchronous pacing at lower programmed pacing rate 23

24. Single-chamber Modes AAI Atrial Lead (I) Atrial pacing Atrial sensing
September 11, 2018
Single-chamber Modes
AAI
Atrial Lead (I)
Atrial pacing
Atrial sensing
Intrinsic P-wave inhibits atrial pacing 24

25. Dual-chamber Modes Tracking Modes
September 11, 2018
Dual-chamber Modes Tracking Modes
DDD Pacing
Atrial Lead (T/I)
Ventricular Lead (I)
Pacing in atrium and ventricle
Sensing in atrium and ventricle
Intrinsic P-wave and intrinsic QRS can inhibit pacing
Intrinsic P-wave can “trigger” a paced QRS 25

26. Dual-chamber Modes Tracking Modes
September 11, 2018
Dual-chamber Modes Tracking Modes
DDD Pacing
Dual-chamber pacing capable of pacing and sensing in both the atrial and ventricular chambers of the heart
Four distinct patterns can be observed with DDD pacing
Sensing in the atrium and sensing in the ventricle (AsVs)
Sensing in the atrium and pacing in the ventricle (P wave tracking) (AsVp)
Pacing in the atrium and sensing in the ventricle (ApVs)
Pacing in the atrium and pacing in the ventricle (ApVp) Adapts to changes post-implant
May resemble AAI, VAT, VDD, DVI modes
Will strive to maintain AV synchrony with variable atrial rates and AV conduction 26

27. Rate Response Adaptive-rate Pacing
September 11, 2018
Rate Response Adaptive-rate Pacing
In rate-responsive pacing (modes ending with “R”), sensor(s) in the pacemaker are used to detect changes in physiologic needs and increase the pacing rate accordingly
Sensors
Detect changes in metabolic demand
Sense motion or physiologic indicator
accelerometer or minute ventilation
Definition: Chronotropic Incompetence
“inability to increase and maintain heart rate appropriately with exercise…”*
*Ellenbogen, Kenneth A. Cardiac Pacing and ICDs. Malden, Mass.: Blackwell Pub.,2005. 27

28. Rate Response Rate-responsive Pacing: DDDR
September 11, 2018
Rate Response Rate-responsive Pacing: DDDR
Example of dual-chamber, rate-responsive pacing 28

29. Mode Selection Considerations
Status of Atrial Rhythm - Intrinsic vs. Paced Presence of Atrial Tachyarrhythmias:
Acute/Chronic
Status of AV Conduction
Normal -Slowed-Blocked
Presence of Chronotropic Incompetence

30. Choice of Pacing Mode Mode Representative Indications VVIR
Rare Need for Pacing Simple; System Desirable (Old, Debilitated Patient; Very Young)
VVIR
Chronic AF With Symptomatic Pauses; Inadequate Ventricular Response After AV Nodal Ablation for Rate Control in AF
AAI
Symptomatic Sinus Pauses With Otherwise Normal Sinus Node Function and Intact AV Conduction
AAIR
Sinus Node Dysfunction With Intact AV Conduction and No Atrial Arrhythmias
VDD
AV Block With Normal Sinus Node Function; Uses Single Lead; No Atrial Pacing, Therefore Not Appropriate for Patients With Sinus Bradycardia
DDD
AV Block With Normal Sinus Node Function
DDDR
AV Block With Sinus Node Dysfunction; Mode Switching Feature if Any Paroxysmal Atrial Arrhythmias
DDIR
An Alternate to DDDR for Patients Who Require Dual-Chamber Pacing but Have Paroxysmal Atrial Arrhythmias Does Not Permit Atrial Tracking in Sinus Rhythm

31. Biventricular Pacing (BVP)
   
A biventricular pacemaker, also known as CRT (cardiac resynchronisation therapy) is a type of pacemaker that can pace both ventricles (right and left) of the heart.
By pacing both sides of the heart, the pacemaker can resynchronize a heart that does not beat in synchrony, which is common in heart failure patients.
CRT devices have three leads, one in the atrium, one in the right ventricle, and a final one is inserted through the coronary sinus to pace the left ventricle.
CRT devices are shown to reduce mortality and improve quality of life in groups of heart failure patients.

32. Bi-Ventricular Pacing
Right atrial lead
Coronary sinus lead
Right ventricular lead
N Engl J Med 2003

33. SVC coil
RA lead
LV lead
RV coil

34. Acute Complications of Pacemaker Implantation
Venous access
Pneumothorax, hemothorax
Air embolism
Perforation of central vein
Inadvertent arterial entry
Lead placement
Brady – tachyarrhythmia
Perforation of heart, vein
Damage to heart valve
Generator
Pocket hematoma
Improper or inadequate connection of lead

35. Delayed Complications of Pacemaker Therapy
Lead-related
Thrombosis/embolization
SVC obstruction
Lead dislodgement
Infection
Lead failure
Perforation, pericarditis
Generator-related
Pain
Erosion, infection
Migration
Damage from radiation, electric shock
Patient-related
Twiddler syndrome

36. “Pacemaker Syndrome” Fatigue, dizziness, hypotension
Caused by pacing the ventricle asynchronously, resulting in AV dissociation or VA conduction
Mechanism: atrial contraction against a closed AV valve and release of atrial natriuretic peptide
Worsened by increasing the ventricular pacing rate, relieved by lowering the pacing rate or upgrading to dual chamber system
Therapy with fludrocortisone/volume expansion NOT helpful

37. Failure to output
Failure to output occurs when no pacing spike is present despite an indication to pace. This may be due to battery failure, lead fracture, a break in lead insulation, oversensing (inhibiting pacer output), poor lead connection at the takeoff from the pacer, and "cross-talk" (i.e., a phenomenon seen when atrial output is sensed by a ventricular lead in a dual-chamber pacer).
Management of pacer output complications includes medications to increase the intrinsic heart rate and placement of a temporary pacer. A chest radiograph is warranted to check pacer leads, with close scrutiny to evaluate for possible lead fracture, which occurs most commonly at the clavicle/first rib location. The patient's pacer identification card should be obtained and his/her electrophysiologist/cardiologist consulted.

38. Failure to capture
Failure to capture occurs when a pacing spike is not followed by either an atrial or a ventricular complex.
This may be due to lead fracture, lead dislodgement, a break in lead insulation, an elevated pacing threshold, myocardial infarction at the lead tip, certain drugs (eg, flecainide), metabolic abnormalities (eg, hyperkalemia, acidosis, alkalosis), cardiac perforation, poor lead connection at the takeoff from the generator, and improper amplitude or pulse width settings.
Management of pacer capture complications is the same as for output complications, with extra consideration given to treating metabolic abnormalities and potential myocardial infarction.

39. Oversensing
Oversensing occurs when a pacer incorrectly senses noncardiac electrical activity and is inhibited from correctly pacing.
This may be due to muscular activity, particularly oversensing of the diaphragm or pectoralis muscles, electromagnetic interference such as MRIs, or lead insulation breakage. More recently, cellular phones held within 10 cm of the pulse generator may elicit this response.
Undersensing
Undersensing occurs when a pacer incorrectly misses intrinsic depolarization and paces despite intrinsic activity.
This may be due to poor lead positioning, lead dislodgment, magnet application, low battery states, or myocardial infarction. Management is similar to that for other types of failures.

40. Operative failures
A final category of pacer failures is termed operative. This includes malfunction due to mechanical factors, such as pneumothorax, pericarditis, infection, skin erosion, hematoma, lead dislodgment, and venous thrombosis.
Treatment depends on the etiology.
Pneumothoraces, being dependent on size, may require chest thoracostomy. Erosion of the pacer through the skin, while rare, requires pacer replacement and systemic antibiotics. Hematomas may require drainage. Lead dislodgment usually occurs within 2 days following implantation of a permanent pacer and may be seen on chest radiography. If the lead is floating freely in the ventricle, malignant arrhythmias may develop. Thrombosis is rare and usually presents as unilateral arm edema. Treatment includes arm elevation and anticoagulation.
Advanced life support protocols, including defibrillation, may safely be executed in patients with pacemakers in place. Sternal paddles are placed at a safe distance (10 cm) from the pulse generator. Temporary transcutaneous pacing may become necessary in cases of myocardial infarction.

41. Sources of Electromagnetic Interference
Nonmedical
Arc welding equipment
Automobile engines
Radar Transmitters
Medical
MRI
Lithotripsy
Electrocautery/cryosurgery
External defibrillators
Therapeutic radiation

42. Devices with pacemaker function
Sometimes devices resembling pacemakers, called ICDs (implantable cardioverter-
defibrillator) are implanted.
These devices are often used in the treatment of patients at risk from sudden cardiac
death.
An ICD has the ability to treat many types of heart rhythm disturbances by means of
pacing, cardioversion, or defibrillation.

43. Indications For ICDs Secondary prevention of SCD:
VF arrest, sustained VT not secondary to reversible
cause
Primary prevention of SCD:
LVEF < 36%, class II-III symptoms of CHF
CAD, h/o MI, LVEF ≤ 40%, inducible sustained VT
Familial or inherited conditions with high risk for SCD:
HCM, long QT syndrome, Brugada syndrome

44. Pacemaker programming
Pacemaker programming can be performed noninvasively by an electrophysiologist or cardiologist. Because of the myriad of pacemaker types, patients should carry a card with them providing information about their particular model.
This information is crucial when communicating with the cardiologist about a pacer problem.
Most pacemaker generators, however, have an x-ray code that can be seen on a standard chest x-ray. The markings, along with the shape of the generator, may assist with deciphering the manufacturer of the generator and pacemaker battery.
This may be helpful in the event a patient neither recalls the company nor has the permanent pacemaker card.

45. FOLLOW UP
Placing a magnet over a permanent pacemaker causes sensing to be inhibited by closing an internal reed switch. This only temporarily "reprograms" the pacer into the asynchronous mode, where pacing is initiated at a set rate. It does not turn the pacemaker off.
Each pacemaker type has a unique asynchronous rate for beginning-of-life (BOL), elective replacement indicator (ERI), and end-of-life (EOL).
Therefore, application of a magnet can determine if the pacer's battery needs to be replaced.
Further interrogation, or manipulating of the device, should be performed by an individual skilled in the technique.
Patients should carry a card that contains information about their particular pacemaker, since these rates are dependent on the manufacturer and the model.