Epicardial Pacing

The Epicardial Pacing Workshop is required education to enable RNs  to care for patients requiring temporary epicardial pacing after open heart surgery. 

Through this education you will :
All education is  based on caring for the patient as per  NCS6347 – Epicardial Pacing and Pacing Wires.

Please familiarize yourself with the information on this site in preparation for the classroom portion of the workshop.

Pacing Basics


A pacemaker is an artificial pulse generator that delivers an electrical current to the heart muscle when the heart fails to deliver this impulse on its own. Pacemakers may be permanent (implanted) or temporary (external).

Pacing is used to initiate myocardial contractions when the heart’s intrinsic stimulation is:

  • insufficient,
  • the native impulses are not being conducted, 
  • the heart rate is too slow to maintain an adequate cardiac output. 

As per ACLS guidelines, when available, pacing is a first line, and the most likely beneficial, treatment for bradycardiac arrhythmias.

Key Pacing Terms and Concepts

Asynchronous (fixed-rate): a pacing mode that paces the heart at a programmed rate regardless of intrinsic cardiac activity.  This may result in competition between the pacemaker and the heart’s own electrical activity.  Asynchronous pacing of the ventricle is dangerous.  If the pacing stimulus occurred during the vulnerable period of repolarization, ventricular fibrillation may result.  Asynchronous pacing of the right ventricle is less dangerous but may cause atrial fibrillation.

Atrial pacing:  Pacing from a lead attached to the right atrium; designed to correct abnormalities in the SA node.

Atrial tracking:  A state of pacing in which sensed atrial activity triggers a ventricular pacing output at the end of the programmed atrioventricular interval. In other words, when the pacemaker senses an intrinsic P wave it will start counting (tracking) the AV interval. If the set time passes without the ventricle depolarizing, the pacemaker will deliver the electrical stimuli to the ventricles.

AV interval:  In dual-chamber pacing, the length of time between an atrial sensed/paced event and the delivery of a ventricular paced event; equivalent to the PR interval of an intrinsic rhythm.  If no intrinsic QRS occurs within the AV interval the pacemaker is triggered to pace the ventricle.  However, if an intrinsic QRS wave occurs within the AV interval the pacemaker will be inhibited from firing.

AV (sequential) pacing:  Occurs when the pacemaker stimulates the atrium and then the ventricle, mimicking normal cardiac physiology.

Base Rate: Rate at which the pulse generator is set to pace when no intrinsic activity is detected.  Determines the minimum rate at which the pacemaker paces in the absence of intrinsic activity.

Bipolar lead:  Pacing lead with two electrical poles that are external from the pulse generator; bipolar pacing is used in transvenous or permanent pacing systems.

Capture: This is both an electrical and a mechanical event. A pacing spike followed by a corresponding P wave/QRS complex indicates electrical capture.

Cardiac Resynchronization Therapy (CRT): Also called a biventricular pacemaker, or dual chamber pacemaker, CRT is used to treat the delay in ventricle contractions that occur in some people with advanced heart failure. An implanted pacemaker sends electrical signals to the chambers on both sides of the heart, making sure they contract at the same time. The device has 2 or 3 leads which are implanted through a vein in the right atrium and right ventricle and into the coronary sinus vein to pace the left ventricle. CRT defibrillators (CRT-D) incorporates defibrillating therapy to quickly terminate  life-threatening dysrhythmias.

Demand Pacing: A pacing stimulus is delivered to the myocardium if the intrinsic rate falls below the base  rate on the pacemaker.

Epicardial Pacing: Type of temporary pacing where epicardial pacing wires are fixed directly to the myocardium (ventricular and often atrial) and are exposed through the skin on the chest wall. 

Fixed Rate Pacing: A pacing stimulus is delivered to the myocardium at a programmed fixed rate regardless of the underlying rate and rhythm. This is also known as asynchronous ventricular pacing.

Fusion beat: the ECG waveform that results when an intrinsic depolarization and a pacing stimulus occur at the same time, both contributing to depolarization of the chamber.

                                                                 P = paced   F = fusion

Inhibited:  When an intrinsic cardiac event is sensed, the pacemaker suppresses electrical output and resets the timing cycle of the pacemaker.

Interval (automatic, demand or paced):  The period, measured in milliseconds, between two consecutive events in the same chamber without an intervening sensed event (A-A or V-V); in pacing, intervals are more useful than rate because pacemaker timing is based on intervals.

Intrinsic:  Naturally occurring, native. 

Microshocks: Low voltage electrical current from ungrounded equipment or static electricity that may pass through to the patient, with as little as 0.1 mA causing ventricular fibrillation. 

Milliampere (mA):  Unit of measure of the pulse generator's electrical current output.  

Output: The energy from pulse generator supplied to the heart muscle sufficient to stimulate a contraction. It is determined by three components:

  • Rate: the setting that provides a pacing rate (bpm) to the myocardium.
  • Amount: level of energy delivered from the pulse generator to the heart to initiate depolarization and is measured in  mA.
  • Chamber: the atria, the ventricles, or both chambers can be paced. If both the atria and ventricles are paced, a separate output setting is required for each chamber.  

Pacemaker spike:  Vertical line on the ECG that indicates the pacemaker has discharged. Note: a pacing spike does not indicate perfusion, merely the delivery of eletrical current. 

Pacing Wires: Atrial pacing wires are sutured to the right atrial appendage, or the body, of the right atrium.  Ventricle pacing wires are placed on the anterior or diaphragmatic surface of the right ventricle. 

Polarity: Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow. Unlike other temporary pacing leads, epicardial pacing wires are unipolar - having no designation of positive or negative because  polarity is assigned once the lead is attached to the pacemaker generator. The negative electrode is in contact with the myocardium with the pulse generator acting as the positive pole.

Phrenic Nerve Stimulation: The proximity of the right and left branches of the phrenic nerves to the epicardium makes it possible for impulses from pacing leads to produce inadvertent phrenic nerve stimulation. The rate of diaphragmatic stimulation is typically much greater than that of normal respiration, contributing to symptoms including dyspnea, uncomfortable muscle twitching, hiccups, and general malaise.

Pulse generator:  The power source that houses the battery and controls for regulating a pacemaker. 

Sensing: Ability of a pacemaker to recognize and respond to an intrinsic electrical activity; the pacemaker’s response to sensed activity depends on its programmed mode and parameters.  Occurs only in synchronous mode.

Stimulation Threshold:  The minimum energy (output) from the pacemaker required to maintain consistent capture.

Synchronous (demand): Paces only when the heart fails to depolarize on its own; the pacemaker fires on demand only.  With synchronous pacing, the pacemaker’s sensing circuit is capable of sensing intrinsic cardiac activity and then inhibiting pacer output when intrinsic activity is present.

Temporary Epicardial Pacing: Method of stimulating through the use of Teflon-coated unipolar, stainless steel wires that are inserted loosely to the epicardium after cardiac surgery. The epicardial wires may be attached to the right atrium for atrial pacing, the right ventricle for ventricular pacing or both for atrioventricular (AV) pacing. Temporary epicardial pacing may be especially helpful after valvular surgery where the incidence of heart block or arrhythmia is increased.

Transvenous Pacing: Type of temporary pacing where pacing wires are inserted into the veins via an introducer sheath and passed through the venous system to the heart.

Transthoracic Pacing: Technique of electrically stimulating the heart by use of a set of pads placed externally on the torso. ECG electrodes are placed on the patient to sense ventricular events (spontaneous or paced), and the pulse generator delivers a wave pulse when a predetermined escape interval has elapsed. 

Ventricular pacing:  Pacing system with a lead attached to the right ventricle.

Indications for Pacing

Pacing can sustain a heart rate to provide sufficient filling and emptying of the heart’s chambers and maintaining cardiac output when abnormalities occur in the conduction system.The following cardiac rhythms may require temporary pacing IF hemodynamically unstable:

  • Asystole  of greater than 3 seconds
  • Sinus Arrest/Sinus Block
  • Sinus bradycardia
  • Second degree AV block, Type II
  • Third degree AV block
  • Junctional bradycardia

Physicians may use the pacemaker to overdrive tachyarrhythmias (supraventricular or ventricular) refractory to pharmacological therapy in an attempt to restore normal conduction. 

Please note, however, this is not the purpose of pacing on our unit and is not a nursing responsibility.


Pacing Equipment

This video provides a good review of epicardial pacing. Some of the practices noted in the video do not apply to our site.

Pacing Wires 

The exposed metal ends of the epicardial pacing wires (EPWs) form a pathway for current to the heart muscle, therefore, wires must be insulated to prevent micro-shocks. Gloves should always be worn when handling EPWs to minimize the risk of electrical current transmission. 

The EPWs form a pathway to the heart and the wire exit site is a potential avenue for bacteria to enter.  The wire exit site should be covered with a transparent dressing or sterile, non-adherent, adhesive bordered dressing (Mepore) to prevent infection. 

The site(s) must be checked daily for signs of infection, such as redness or purulent discharge. Notify the NP or MRP immediately. A swab for Culture & Sensitivity may be required. 

                                                                                   Position of wires              

Pacing Cables

The Medtronic® cables (blue or beige coloured cables) with the round insertion holes that are re-processed from SPD are used for epicardial pacing. For dual-chamber pacing use 2 cables. 

The EPWs have small posts (pins) that will fit into the electrode connection sites (holes) of this Medtronic adapter. The adapter holes are labelled “+” and “-”. It does not matter which epicardial wire is placed in the “+” or “-”.

Pulse generator

The pulse generator is the power source that contains the battery and the electronic circuitry that controls the pulse generator's functions. The function of the generator is to supply sufficient electrical energy to the heart muscle to stimulate depolarization, contraction and produce cardiac output. A dual chamber pacemaker can be used for single or dual chamber pacing. 

The pulse generator is powered by a standard 9-volt battery*. The battery life is approximately 7 days but the battery is changed every 5 days. The pulse generator has a plastic cover that should be in place after adjustments to the generator are made. The image on the left is the older pulse generator (model 5388) that we primarily use. The image on the right is the newer version (model 5392) that you may encounter. Both are operated in a similar manner. 

*Note - model 5392 requires AA batteries


          Model 5338                                                                       Model 5392


Pacing Parameters

Pacing Parameters

It is the 5B RN's responsibility to set the parameters on a pacemaker  in an emergency only. RNs may adjust pacemaker settings with orders if no NP /MRP is available to do so. If the NP/MRP is present they should be making the adjustments. 

When  setting the parameters of the pacemaker the NP/MRP considers 4 aspects:

  • Rate - determines the number of stimulations to be delivered per minute
  • Output - controls the amount or level of energy/electrical charge delivered to the myocardium 
  • Chamber - defines the location in the heart to which the energy is delivered
  • Sensitivity - the ability of the pacemaker to detect intrinsic myocardial electrical activity 

Rate - Patient condition and the reason for pacing determine the rate of pacing.  The rate is the base pacing rate at which pacing pulses are delivered. For example, if the rate is set at 70 bpm, the heart rate will not go below this rate while the pacing is on. The heart rate on a patient’s rhythm strip should never be below the base rate if they are paced. If they are, there's a problem!

Output - The output amount is the level of electricity delivered by the pulse generator to the heart to initiate depolarization.  Output is measured in  milliamperes (mA). 

Chamber - The atrial chambers (single chamber), the ventricular chambers (single chamber) or both chambers (dual chamber) may be paced.  For dual-chamber pacing there is a separate output control for atrial and ventricle output settings.

Sensitivity can be a difficult concept to wrap your head around so don't be worried if you don't understand it right away. Sensitivity involves sensing and capture. The impulses from the pulse generator travel down the lead to the negative pole that is in contact with the myocardium.  The impulses reach the tip of the pole, travel through the myocardium and return to the positive pole of the system completing the circuit.   This process results in a pacing spike on the ECG.  If the stimulus is strong enough to depolarize the myocardium, the pacing spike is immediately followed by a P wave, if the wire is in the atrium, or a wide QRS complex, if the wire is in the ventricle.  

  • Capture is the level of electrical activity required to capture and depolarize cardiac cells and cause contraction. Capture occurs when the electrical impulse initiates a cardiac response.  Capture is determined by the strength of the stimulus (the mA), the amount of time the stimulus is applied to the heart, and by the contact of the pacing electrode with the myocardium.  Capture requires “live” tissue so myocardial ischemia/necrosis will impair capture. Capture is both an electrical and mechanical event.  Capture is achieved when a pacer spike is followed by a corresponding P wave or QRS complex.  Electrical capture alone is not sufficient evidence of cardiac output.  Ensure perfusion by checking pulse and BP.

                                                Appropriate capture as pacing spike is followed by complex

Note: Because the pacemaker causes the heart to depolarize in an artificial fashion, the result is a widened, abnormal P wave and/or QRS complex. 

  • Sensing refers to the ability of the generator to detect and recognize the impulses the myocardial tissue is generating on its own. The sensing threshold is the level at which the pacemaker can consistently sense intrinsic atrial or ventricular activity.   Sensing is basically the height of the cardiac complex required to inhibit or trigger the pacemaker.
  • Imagine the sensing circuit as an eyeball trying to see over a fence at the intrinsic complex.  If the fence is 5 feet tall (5.0 mV) it will be harder to see the complex compared to a fence that is only 1.5 feet tall (1.5 mV).  Changing the sensitivity from 5.0 to 1.5 mV is like lowering the fence, as the pacemaker becomes more sensitive and is able to “see” intrinsic activity more easily. Therefore, to increase the sensitivity of a pacemakerthe millivolts number (the fence) must be lowered. The example below is in reference to V pacing. 


  • Sensitivity is measured in millivolts (mV). The higher the number, the less intrinsic activity can be sensed (the bigger the number on the generator (the higher the fence) , the less sensitive the pacemaker is to the heart’s intrinsic activity).
  • The weaker the heart's intrinsic activity the more sensitive the generator must be.  For example, if the sensitivity (fence) is set at 5mV, the pacemaker will only sense a QRS greater than 5mV in height, as it cannot see anything less than that.  If the QRS is 7 mV then the pacemaker will 'see' the intrinsic beat and does not fire.  If the QRS is less than 5 mV in height the pacemaker does not see it and fires. 

Intrinsic cardiac activity stimulates a superior contraction with greater forward blood flow from the chambers of the heart so we want the heart to do its own work whenever possible.  However, if the intrinsic rhythm is not sufficient to generate enough cardiac output, the heart will need help. A pacemaker that senses intrinsic beats is able to allow for intrinsic beats to occur and only provide help as needed to keep a rate of 80 bpm.   

Pacing Modes

Pacemaker classification is determined using a "Pacemaker Code" that is divided into five categories as delineated in the table below (note that while all of the variations can seem quite complex, there are a few modes that are most often used):

VOO – asynchronous mode (paces the ventricle despite intrinsic beats)

VVI –  synchronous (senses and paces ventricles). 
Indications for these two modes are afib, heart block; not used with HF patients who require the atrial kick.

AOO – asynchronous
Indications for this mode: sick sinus syndrome, patient requiring atrial kick, NSR with decreased cardiac output, sinus brady, asystole. You can just pace the atria if the rest of the conduction system is normal.  If the rest of the conduction system is not working (AV conduction problems) this is not the mode to choose.This mode cannot be used with afib or aflutter because the atrial spikes will not capture the erratic atria.

DVI – also called AV sequential pacing; paces the atria and ventricle based on what the pacemaker senses in the ventricle. Indications for this mode include AV block with decreased CO, sick sinus syndrome requiring atrial kick. The pacemaker may be inhibited if it senses large P waves as it thinks it is an “R” wave. 

DDD - atria and ventricles are both paced and sensed providing pacing that is very similar to normal cardiac function.

* "Inhibits": the delivery of a pacing pulse is inhibited if a beat is detected from that chamber. If no intrinsic beat is detected within a predetermined time period (AV interval), the pacemaker goes ahead and paces.

** "Triggered": in a dual chamber pacemaker, a normal or paced atrial beat is sensed by the pacemaker and can trigger a paced ventricular beat if the AV node conduction is slow or fails. Upon detecting a spontaneous depolarization or other signal, a triggered mode will deliver an electrical stimulus to the heart. This way atrial and ventricular beats are sequential and at the same rate for optimal cardiac output. (This is more complex than you need to worry about now!). Not normally used with temporary pacemakers except in the DDD mode.

Pacing Complications

Understanding Pacing Complications

 *Rule of Thumb - Assess the patient, not the technology*                   


Failure to Pace 
Failure to pace (failure to fire, failure to output) occurs when the pacemaker fails to deliver an electrical stimulus or the correct number of electrical stimuli per minute.  It is identified by an absence of pacemaker spikes.  The malfunction may be caused by a battery failure, poor connections, broken wires or high sensitivity. If the pacemaker does not pace the patient will usually return to their underlying rhythm .

What to do?

  • Check patient first 
  • Call CODE BLUE if patient is acutely decompensating
  • Call physician/NP
  • Check all connections of pacing system
  • Consider changing battery
  • Consider changing pulse generator
  • Remove source of electromagnetic interference
  • NP/MD may adjust sensitivity (mV) 

Failure to Capture
With a failure to capture the pulse generator sends an impulse to the heart at the right time, but the heart doesn't respond; the pacer spikes are coming at the right time relative to the patient's rate, or lack of a rate – but they’re not capturing. The generator  is sensing that the intrinsic heart rate is too slow, but the output signal isn't making the myocardium respond. On a rhythm strip, you will see  clear pacing spikes generated by the pulse generator – at the right time after either an intrinsic beat or a paced one – but they’re not followed by a QRS response. 

There can be all sorts of reasons for this: broken wires, pulse generator failure, acidosis, alkalosis, bad connection to a pulse generator, battery failure, which can be serious if the patient is depending on the pacemaker to maintain a blood pressure.  Call the team but while you’re waiting, have atropine at the bedside, in case “bad” capture goes to “no” capture. 

What to do?

  • Check patient first
  • Call CODE BLUE if patient is acutely decompensating
  • Check all connections of pacing system
  • Call physician/NP
  • You may be asked to adjust the output;  to increase output, turn UP to 15-20 mA
  • Check pulse for mechanical capture
  • Consider changing battery
  • Consider changing pulse generator

Failure to Sense and Oversensing
Failure to sense (over or under sensing) occurs when the pacemaker fails to recognize intrinsic electrical activity or inappropriate senses extraneous electrical signals causing the pacemaker to fail to deliver an impulse when one is needed.  For example, atrial sensing may inappropriately sense ventricular activity or ventricular sensing pacemakers may misidentify a tall, peaked intrinsic T wave as a QRS complex. If the pacemaker senses any small amount of electrical activity as intrinsic (the fence is too small to block out all the activity), it fails to deliver an electrical stimulus.   Remember, the pacemaker has both a sensing circuit and an output, or pacing circuit. The pacer has to sense whether or not the patient is generating a rhythm, so it will know when to pace and when not to. In this case, the pacemaker will generate spikes that do capture, but the spikes come at the wrong time, and the box is clearly unable to "see" what the patient’s heart is doing. It is identified when the pacemaker does not recognize intrinsic beats and generates unnecessary pacing spike.  Clearly a bad thing– it can result in the R-on-T situation, producing VT or VF. Failure to sense may be caused by battery failure, dials set incorrectly, poor connections, broken wires or inadequate QRS signal.

The thing to keep in mind: the pacer spikes will be coming but at the  wrong time. 

                      Pacing spikes appear randomly through cyle

What to do?

  • Check patient first
  • Call CODE BLUE if patient is acutely decompensating
  • Call physician/NP
  • You may be asked to adjust sensitivity (mV). To increase sensitivity, turn mV down.
  • Check all connections of pacing system
  • Consider changing battery
  • Consider changing pulse generator

Check Your Knowledge

Why is temporary epicardial pacing used after open heart surgery?

  • Prevents dysrhythmias from occurring in the immediate post-op period
  • Provides backup or 'just in case' protection from bradycardia
  • Sustains a heart rate for sufficient emptying and filling of the chambers
  • Restores normal cardiac conduction that is unresponsive to medications

What action helps prevent a patient with pacing wires from receiving microshocks?

  • Wearing gloves when handling pacing wires
  • Attaching the pulse generator to the patient so it is grounded
  • Not showering the patient while the wires are in-situ
  • Covering each wire with special microshock tape

The plastic cover used with the pulse generator is optional.

  • True
  • False

Asynchronous pacing paces only when the heart fails to depolarize on its own, as the pacemaker’s sensing circuit is capable of sensing intrinsic cardiac activity and then inhibiting pacer output when intrinsic activity is present.

  • True
  • False

What is output amount?

  • The level of energy delivered by the pulse generator to the heart to initiate depolarization
  • The base pacing rate at which pacing pulses are delivered, in pulses per minute
  • The ability of the pacemaker to detect intrinsic myocardial electrical activity
  • Atrial activity triggers a ventricular pacing output at the end of the programmed atrioventricular interval when sensed

A pacing spike followed by the appropriate complex (P wave/QRS complex) indicates capture and adequate cardiac output.

  • True
  • False

Mr. Smith is on a temporary pacemaker for an issue with 2 degree block type I. When the rhythm strip is analyzed it is interpreted to not be capturing. What are three possible interventions?

  • Notify the NP/MD
  • Check all connections on the pacing system
  • Increase the ventricular output
  • Assess your patient for symptoms
  • Order a 12 lead ECG to verify rhythm
  • Increase rate of pulse generator

Mrs. Abudaba is transferred from CSICU on the temporary pacemaker. When the nurse analyzes the telemetry strip she notices there are pacing spikes that are not associated with any complex. What is the problem?

  • Failure to capture
  • Failure to pace
  • Failure to sense
  • Failure to track

What are three possible causes of a temporary pacemaker's failure to capture?

  • Lead is too close to the phrenic nerve
  • Lead is broken or fractured
  • Output amount is too low to achieve depolarization
  • Sensitivity is too high so pulse generator cannot see waveforms
  • Pulse generator malfunction
  • Pulse generator is programmed for VVI instead of DDD

Mr. Lee is post op day 2 after his valve replacement. His EPW are in situ. Mr. Lee becomes very symptomatic and decompensates  when his heart rate dips into the 20s. What three interventions should the nurse perform?

  • Call a code blue
  • Give atropine 0.5 mg IV STAT
  • Connect him to the temporary pacemaker
  • Begin compressions
  • Assess patient's pulse and VS
  • Place patient on his right side