13 Pacemakers and Implantable Cardioverter Defibrillators

Pacemakers are electronic devices designed to regulate the heart’s rhythm by delivering electrical impulses to the myocardium. These devices are typically implanted in the chest and consist of a pulse generator and one or more leads with electrodes that connect to directly to a chamber of the heart. Pacemakers are used to ensure the heart beats at a normal rate and rhythm, especially in cases where the natural electrical conduction system is compromised, leading to slow or irregular rhythms.

 

A person holding a St. Jude Medical pacemaker with attached leads in the palm of their hand.
Figure 13.1  Handheld view of a pacemaker. The main body of the pacemaker houses the electronic components and battery, along with the attached leads that would be inserted into the heart to deliver electrical impulses. The owner of this image removed this pacemaker from a deceased patient before cremation.

 

A chest X-ray showing a pacemaker implanted in the left upper chest area with leads extending into the heart.
Figure 13.2  Chest X-ray depicting a pacemaker implanted in the left upper chest with the leads clearly visible extending into the heart to provide electrical impulses for regulating the cardiac rhythm.

 

A medical diagram illustrating the placement of a pacemaker and its leads within the heart, showing the routes and locations of the right atrium lead, right ventricle lead, and coronary sinus lead, along with the generator placed between the skin and pectoralis major.
Figure 13.3  Diagram of pacemaker placement and lead configuration. The pacemaker generator is shown positioned between the skin and the pectoralis major muscle. Leads are routed through the subclavian vein into the heart. The RA lead (red), used in dual-chamber devices, is inserted into the right atrium. The RV lead (blue) is placed in the right ventricle and is common in most pacemaker devices. Additionally, a coronary sinus lead (green), used in biventricular devices, is placed in the coronary sinus to help synchronize the ventricles.

 

Indications for Pacemaker Implantation

Pacemakers are implanted to manage various cardiac conditions that cause abnormal cardiac rhythms. Common indications include symptomatic bradycardia and certain heart blocks. Pacemakers are also used in some cases of heart failure and certain types of tachyarrhythmias to maintain a regular heart rhythm and improve cardiac function.

 

Types of Pacemakers

  • Permanent Pacemakers

    • Implanted under the skin, usually near the collarbone, for long-term management of chronic arrhythmias
    • Used to treat conditions like chronic AV block and sick sinus syndrome

  • Temporary Pacemakers

    • Used for short-term pacing needs, often in hospital settings
    • Indicated for acute conditions like post-surgical heart block or drug-induced bradycardia

 

Pacemaker Classification

  • Synchronous (Demand) Pacemakers

    • Activate only when the heart’s natural rhythm falls below a preset rate
    • Helps conserve battery life and maintain natural heart function when possible

  • Asynchronous (Fixed-Rate) Pacemakers

    • Deliver impulses at a constant rate, regardless of the heart’s intrinsic activity
    • Typically used in situations where the heart’s natural rhythm is unreliable or absent

 

Pacemaker Codes

  • AAI

    • Atrial pacing, atrial sensing, inhibits artificial impulses if intrinsic atrial activity is detected

  • VVI

    • Ventricular pacing, ventricular sensing, inhibits artificial impulses if intrinsic ventricular activity is detected

  • DVI

    • Dual-chamber pacing, ventricular sensing, inhibits artificial impulses if intrinsic ventricular activity is detected

  • VDD

    • Ventricular pacing, dual-chamber sensing, allows for atrioventricular synchrony without directly pacing the atrium

  • DDD

    • Dual-chamber pacing and sensing, can both inhibit and trigger pacing based on intrinsic atrial and ventricular activity

  • DDDR

    • Dual-chamber pacing and sensing, also includes rate modulation to adjust pacing rate based on physical activity

 

EKG Changes with Pacemakers

On the EKG, pacemaker activity is characterized by distinct vertical spikes, known as pacemaker spikes or pacing spikes, which precede the paced chamber’s depolarization. In ventricular pacing, a pacemaker spike is followed by a wide QRS complex, indicating artificial ventricular depolarization. Atrial pacing shows a spike before the P wave. Dual-chamber pacemakers, which involves leads placed in the right atrium and right ventricle, produce spikes before both the P wave and QRS complex. These changes help identify the type of pacemaker and its functioning.

  • Pacemaker Spikes

    • Vertical spikes on the EKG represent the electrical activity of the artificial pacemaker

  • Atrial Pacing

    • A pacemaker spike precedes the P wave
    • P wave morphology depends on lead placement, as it could appear biphasic, inverted, or have low amplitude, but may appear normal if the pacing lead is positioned appropriately

  • Ventricular Pacing

    • A pacemaker spike precedes the QRS complex
    • Wide QRS complexes
    • Right ventricular pacing typically results in a QRS morphology similar to a LBBB
    • Left ventricular pacing can resemble QRS morphology found in RBBB
    • QRS complexes should be discordant with the following ST segments and T waves

  • Dual-Chamber Pacing

    • Artificial pacing of both the atrium and ventricle results in pacemaker spikes before the P wave and the QRS complex

 

A 12-lead EKG showing atrial paced rhythm with narrow QRS complexes and consistent pacing spikes.
Figure 13.4  Atrial paced rhythm. Pacemaker spikes are visible before each P wave, indicating successful atrial pacing. The QRS complexes are narrow, and there is a regular atrial rate with consistent capture by the pacemaker.

 

Problems with Pacemakers

  • Failure to Capture

    • Occurs when the electrical impulse of the pacemaker fails to depolarize the myocardium
    • May be due to lead displacement, battery depletion, or increased pacing threshold

 

Figure 13.5  An atrial failure to capture in a dual chamber pacemaker. Pacing spikes are clearly visible, however, there are no corresponding P waves generated, indicating the inability of the atrial pacemaker to stimulate atrial depolarization. Whereas, the ventricular pacemaker successfully stimulates the ventricular myocardium to depolarize as there are wide, corresponding QRS complexes thereafter.

 

  • Sensing Malfunction

    • The pacemaker fails to detect intrinsic cardiac activity, leading to inappropriate pacing
    • Can be caused by lead issues, interference, or incorrect sensitivity settings

 

Rhythm strip showing an atrial sensing malfunction, with irregular atrial pacing spikes and variable capture of the atrial signal.
Figure 13.6  Atrial sensing malfunction. Atrial pacing spikes are present right after spontaneous atrial activity. The following QRS complexes are narrow, indicating the impulse did not originate in the ventricles.

 

Rhythm strip showing a ventricular sensing malfunction, characterized by irregular pacing spikes due to oversensing of ventricular activity.
Figure 13.7  Ventricular sensing malfunction. The ventricular pacemaker detects signals incorrectly, leading to irregular pacing spikes and a loss of ventricular contraction.

 

Implantable Cardioverter Defibrillators

A pacemaker and an implantable cardioverter defibrillator (ICD) are both devices used to manage arrhythmias, but they serve different purposes. While both are implanted under the skin to regulate cardiac rhythms, a pacemaker primarily delivers low-energy electrical impulses to maintain a steady rate, addressing issues like bradycardia or irregular rates. In contrast, an ICD monitors the heart for dangerously fast rhythms and can deliver both low-level pacing and high-energy shocks to restore normal rhythm during life-threatening arrhythmias, such as ventricular fibrillation. An ICD is recommended for patients who have experienced cardiac arrest or are at high risk of sudden cardiac death due to cardiac issues. It is important to know that patients with ICDs need to be careful around devices with strong magnets and should consult their doctor about safe exercise and lifestyle choices.

 

Image Attributions:

Fig. 13.1 – “St Jude Medical pacemaker in hand” by Steven Fruitsmaak is licensed under CC BY 3.0

Fig. 13.2 – “Chest xray pacemaker” by Jonas de Jong is licensed under CC BY-NC-SA 4.0

Fig. 13.3 – “PPM” by Nicholas Patchett is licensed under CC BY-SA 4.0

Fig. 13.4 – “DVA0838” by W.G. de Voogt, used under CC BY-NC-SA 3.0 / Cropped from original

Fig. 13.5 – “DVA0856” by W. G. de Voogt, used under CC BY-NC-SA 3.0 / Cropped from original

Fig. 13.6 – “Atrial malsensing” by Jonas de Jong, used under CC BY-NC-SA 4.0 / Cropped from original and grayscaled

Fig. 13.7 – “Ventricular oversensing” by Jonas de Jong, used under CC BY-NC-SA 4.0

License

Icon for the Creative Commons Attribution-NonCommercial 4.0 International License

EKG Essentials: A Student Handbook Copyright © 2024 by Joshua E. McGee, PhD is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

Share This Book