What is a pacemaker? 

When the heart rate is irregular or too slow, cardiac output is compromised. A pacemaker may be utilized to support the heart’s electrical system, stabilize arrhythmias, and ensure the heart pumps at a rate that supports tissue perfusion throughout the body. While there are different types of pacemakers, they all have a pulse generator and electrodes. The pulse generator provides electrical impulses, which are transmitted through the electrodes, causing cardiac muscle to contract. Once the pacemaker is placed it is programmed to set the rate and other parameters.

What are some common indications for a pacemaker?

A pacemaker may be indicated in patients with arrhythmias such as sick sinus syndrome (also known as sinus node dysfunction), symptomatic bradycardia, or high-grade heart blocks. Other indications include post myocardial infarction, heart failure, congenital heart defects, and temporarily after some cardiac surgeries.

Key pacemaker terminology

The language of pacemakers can be confusing if you aren’t sure what the various terms mean, so here’s a quick review: 

  • Pacing spikes – When the pacemaker generates an adequate electrical impulse, this shows on the ECG as a pacing spike. 
  • Output – The output is how much electrical current is produced with each pacemaker impulse. It is measured in milliamps (mA). You will increase mA until the pacemaker achieves capture.
  • Capture – This refers to the pacemaker impulse causing electrical activity in the atrium or ventricle (depending on what chamber is being paced). Note that if the pacemaker is only pacing the ventricle, the QRS will be wider than normal. This is because it takes a little bit of time for the electrical activity to spread from the location of the lead to the entirety of the left ventricle. If only the atrium is paced, you’ll see a spike followed by a p-wave. And, if the patient is dual paced, you’ll see a spike followed by a p-wave, and then a spike followed by a QRS complex.
  • Failure to capture – When this occurs, the pacemaker fires, but it doesn’t induce electrical activity in the chamber. This is seen on the ECG as a pacing spike that is not followed by a p-wave or QRS (this depends on which chamber is being paced). This may be due to low output from the pacemaker, inflammation in the cardiac tissue, or lead dislodgement.
  • Mechanical capture – It’s not enough to have electrical capture on the ECG, you must also have mechanical capture which is the heart actually pumping and perusing the tissues. You can correlate electrical capture with mechanical capture by palpating a pulse or observing the pulse rate via pulse oximetry.
  • Sensing – The ability of the pacemaker to sense the heart’s intrinsic activity. Sensitivity is the mV required to detect the patient’s naturally-occurring cardiac activity. The higher we have this setting on the pacemaker, the electrical activity has to be stronger in order for it to be detected by the pacemaker. Think of sensitivity as a fence. If you have a high fence, it’s harder to see over it. So, when this setting is turned up on the pacemaker, you are making the pacemaker LESS sensitive.

    On the other hand, when this mV setting is low, the pacemaker can sense the heart’s natural electrical activity at lower levels. In this case, the fence is lower and it’s easier to see over it. In other words, the pacemaker is MORE sensitive.
  • Failure to sense – The pacemaker does not recognize the heart’s natural electrical activity and mistakenly delivers an electrical impulse. You may see a pacing spike in the middle of a p-wave or QRS complex.
  • Oversensing – The pacemaker senses a signal that doesn’t actually come from the heart and pacing is inhibited even if it is needed. Interfering signals can come from faulty leads, areas of the heart that are not being monitored by the pacemaker, and electromagnetic interference from things like metal detectors, magnetic fields, electric fences, and even some medical alert devices. With oversensing, no pacemaker spikes are seen on the ECG. The patient is at risk for severe bradycardia and even asystole if they are 100% pacemaker dependent.

What are the different types of pacemakers?

There are several types of pacemakers and they can be described based on whether they are temporary or permanent, how they are placed, their design, and their pacing characteristics. 

Temporary pacemakers

Temporary pacemakers are used short-term until definitive treatment can be obtained. They may also be utilized after cardiac surgery while the heart is recovering. There are a few different types of temporary pacemakers: transcutaneous, transvenous, epicardial, and transesophageal.

  • Transcutaneous pacemaker – Patches placed on the skin provide temporary pacing in emergency situations. Transcutaneous pacemakers are typically used by first responders and when responding to codes in the acute care setting. Note that transcutaneous pacing is painful, so consider sedation when appropriate. When using a transcutaneous pacemaker, the rate is initially set at around 80 BPM in an adult at the lowest possible mA (output) setting. Slowly increase the mA and watch for pacer spikes to appear on the ECG screen. Continue to slowly increase the output until a QRS appears after each spike, indicating you have electrical capture. Slowly increase mA by an additional 10% to provide a safety margin (or as indicated by your facility protocol) and verify mechanical capture by either feeling for a pulse or observing the heart rate as obtained by pulse oximetry.
  • Transvenous pacemaker – A transvenous pacemaker is the preferred temporary pacemaker for most situations and may be used for a longer duration than a transcutaneous pacemaker. A common indication for a transvenous pacemaker is in cases of endocarditis who require a long course of antibiotics before surgical implantation of a permanent pacemaker can safely be conducted. Transvenous pacing wires are inserted venously, most commonly through the subclavian, internal jugular or femoral vein. The pacer box is external and houses the generator and controls.
  • Epicardial pacemaker – An epicardial pacemaker is placed during cardiac surgery and used temporarily to prevent postoperative arrhythmias. Leads may be attached to the ventricle, the atrium, or both chambers simultaneously. Note that with epicardial pacemakers, the leads will exit through the skin and the pacer box is external.
  • Transesophageal pacemaker – Leads are inserted through the nose or mouth and utilized for atrial pacing or as a diagnostic tool for atrial arrhythmias. Not commonly used due to discomfort and lack of reliability.
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Permanent pacemakers

Permanent pacemakers are utilized for long-term pacing and must be surgically implanted. They come in two general designs – a traditional pacemaker with leads and a smaller version that does not use leads (leadless).

A traditional pacemaker is usually placed under the skin in the upper left chest, but in some cases may be implanted in the upper abdomen. The procedure requires surgery and leaves a scar as well as a visible bulge. A leadless pacemaker is much smaller and attaches directly to the wall of the heart, so it is not visible. Rather than using a traditional surgical incision, it is implanted via a catheter inserted at the femoral vein or jugular vein. In both cases, a small computer called an external programmer communicates with the device so adjustments can be made without the need for additional surgery.

Traditional pacemakers can have one to three wires that attach to the heart and deliver electrical impulses: 

  • One wire – Attaches to a single-chamber, either the atrium or the ventricle (single-chamber pacemaker). 
  • Two wires – Attaches to two chambers, one in the atrium and one in the ventricle (dual-chamber pacemaker)
  • Three wires – Two wires attached to the ventricles and one wire attached to the right atrium (biventricular pacemaker)

What are pacemaker settings?

There are a wide range of pacemaker settings and they are described by using a five-position code. Note that not all five positions will be used and if that is the case, this simply means position IV and V are not utilized.

  • Position I – Tells you which chamber of the heart is being paced
    • A = Atrium
    • V = Ventricle
    • D = Dual
  • Position II – Tells you which chambers are being sensed
    • A = Atrium
    • V = Ventricle
    • D = Dual
    • O = No sensing
    • Note – if you see “S” in this position, this is a designation utilized by the manufacturer to indicate the pacemaker is only able to pace a single chamber. Once inserted, the “S” should be changed to “A” or “V” in the patient’s record.
  • Position III – Tells you how the pacemaker responds when it senses an intrinsic event
    • I = Pacemaker is inhibited
    • T = Pacemaker is triggered to provide stimulation
    • D = Dual modes of response (possible with dual chamber and biventricular pacemakers only.) An event sensed in the atrium will inhibit atrial output and trigger ventricular output. This occurs due to a programmatic delay that is set to mimic a normal PR interval. Note that if the pacemaker senses a ventricular event during that delay, it will inhibit the ventricular event.
    • O = None
  • Position IV – Tells you whether the pacer has rate modulation
    • R = The pacemaker has rate modulation. If this is the case, the rate of the pacemaker adjusts to respond to patient activity.
    • O = Rate modulation is disabled or unavailable.
  • Position V – Tells you the location of multisite pacing and is not often utilized.
    • O = No multisite pacing
    • A = Multisite in one or both atria
    • V = Multisite in one or both ventricles
    • D = Dual in both atrium and ventricles
Chamber PacedChamber SensedResponse to SensingRage ModulationMultisite Pacing
A = AtriumA = AtriumI = InhibitedR = Rate AdaptiveA = Atrium
V = VentricleV = VentricleT = TriggeredO = NoneV = Ventricle
D = DualD = DualD = DualD = Dual
O = NoneO = NoneO = NoneO = None

Another key pacemaker setting is the rate. Pacemakers in use today sense the heart’s intrinsic activity and send a stimulus only when the heart rate follows below the programmed pacing rate, which is often set at 60 bpm. In addition, most (if not all) contemporary pacemakers utilize rate responsiveness, which enables the pacemaker to adjust the rate based on the patient’s activity level or physiologic requirements. Many times, you will see a pacemaker with settings that range from 60 – 100 bpm.

Your patient’s pacemaker settings are DDD…what does this mean?

What does AAI indicate?

What does VVI indicate?

What are pacing modes?

Pacing modes are individualized to each patient and take into account the patient’s underlying arrhythmia, medical history, cardiac function, response to exercise, and their general physical condition or health. Pacing modes utilize the five-position code to describe how the pacemaker works for that individual patient. 

Single-chamber pacing is generally utilized in the ventricles in cases of symptomatic bradycardia. In this mode, the pacemaker can only sense and pace in one chamber. Common single-chamber pacing modes are VOO, VVI and AAI.

  • VOO – In this mode, the ventricle is paced, there’s no sensing, and there’s no response to the sensed event (which makes sense, because sensing is set to “off”). With this mode, the pacemaker is going to stimulate cardiac contraction at a programmed rate no matter what the heart is intrinsically doing. This is an asynchronous mode and is not generally used long-term. An example might be a patient who is pacemaker dependent who is undergoing an MRI. Signals in the MRI could confuse the pacemaker, making it think the heart has activity when it does not. By placing the pacemaker in VOO mode, the patient’s heart will continue to beat at a programmed rate throughout the procedure.
  • VVI – In this mode, the pacemaker is pacing the ventricle, sensing the ventricle, and it will not fire if it senses a ventricular event. Essentially, it senses a heartbeat and withholds pacing when it is not needed.
  • AAI – In this mode, the pacemaker is pacing the atrium, sensing the atrium, and it will not fire if it senses an atrial beat. In other words, it senses the atrial activity only paces when needed.

Dual-chamber pacing modes most closely resemble the heart’s normal physiologic activity and maintain atrial/ventricular synchrony. Common dual-chamber pacing modes are DDD and DDI.

  • DDD – In this mode, the pacemaker is able to pace both the atrium and the ventricle, it senses atrial activity and ventricular activity, and it has dual modes of response so it inhibits or triggers based on what the patient needs.
  • DDI – In this mode, the pacemaker is able to pace both the atrium and the ventricle, it senses atrial activity and ventricular activity, and when atrial activity is sensed the pacemaker is inhibited and will not fire. Ideally, the atrial activity is followed by normal conduction to the ventricle and ventricular contraction. However, if there is an AV block, the pacemaker will sense that the ventricle did not have activity and this will trigger an impulse to the ventricle at a programmed rate.

How do I troubleshoot common temporary pacemaker problems?

The key problems with pacemakers are issues with sensing, output and capture. If the patient has a permanent pacemaker, the settings will need to be adjusted using the programmer that communicates with the device. This is typically done by the cardiologist. However, if the patient has a temporary pacemaker,  you have a bit more control over troubleshooting, provided it is covered by your scope of practice, the training you have received, and hospital policy.

  • Failure to pace – If the patient’s heart rate is lower than the programmed rate of the pacemaker and you don’t see any pacing spikes on the ECG, you may have a problem with the device’s output. Common causes include:
    • Loose connections (or disconnection) – Check all connections to ensure they are secure.
    • Battery failure or low battery – Make sure the device is on and that the indicator lights are flashing. If they are not, this may mean the battery is low and the battery needs to be changed. Note that most pacemaker generators will continue to work for a few seconds when you remove the old battery, but you have to be quick!
    • Oversensing – If the pacemaker is oversensing, it is too sensitive, meaning the fence is too low. Increase the mV on the sensitivity setting to make the device less sensitive.
    • Lead failure – The patient may need a chest x-ray to ensure the leads are in the correct position. If the leads are damaged, new leads may need to be inserted (which is a job for the cardiologist).
  • Failure to capture – If the ECG shows pacing spikes that are not followed by a p-wave or QRS (depending on which chamber is being paced), you may have a problem with capture. This occurs when the pacemaker impulse does not cause the cardiac muscle to depolarize. If your patient has no underlying rhythm (or a very slow underlying rhythm), be prepared to provide transcutaneous pacing or CPR if needed. Common causes of failure to capture include:
    • Loose connections – Check all connections to ensure they are secure.
    • Low output – Ensure the pacemaker is set at the prescribed settings as someone may have inadvertently changed them, especially if there is no plastic cover or it is loose. If that is not the case, increase the mA setting slowly (and according to orders or protocol) until capture is obtained.
    • Elevated myocardial pacing threshold  – Factors that influence the pacing threshold include the patient’s level of activity and the use of antiarrhythmic medications such as procainamide. Let the MD know as output may need to be increased.
    • Wire migration or lead failure – A chest x-ray can help the cardiologist see if the leads have migrated or are damaged and need to be replaced.
  • Failure to sense – When the pacemaker does not sense the heart’s intrinsic electrical activity it delivers impulses when they’re not actually needed. A quick way to remember this is undersensing leads to overpacing. And, if the electrical impulse falls on the T-wave, this can cause “R on T phenomenon” which can lead to ventricular fibrillation. Failure to sense can occur due to:
    • Low sensitivity – To combat this, we want to increase the sensitivity by lowering the fence. We do this by turning the mV setting down.
    • Low battery – The device may need a battery change.
    • Interfering factors – Remove items from the vicinity that could be interfering with pacemaker function, including cell phones. If safe to do so, unplug items in the vicinity one-by-one to see if any are causing the interference.

As will all of these troubleshooting steps, if your interventions are not successful let the cardiologist know immediately.

What is an ICD?

An ICD is an implantable cardioverter defibrillator which is a device that detects lethal arrhythmias and delivers a high-energy shock to stop the arrhythmia and prevent death. Generally, ICDs just perform this one function, though some newer models can also provide lower-energy pacing impulses if that’s what the patient needs.

Review the ins and outs of pacemakers for your exams, clinicals, and NCLEX while you’re on the go by tuning in to episode 335 of the Straight A Nursing podcast. Tune in wherever you get your podcast fix, or straight from the website here.


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