Electrical Therapies of the Heart

Author: Kathleen Fane, MD, Department of Emergency Medicine, Temple University Hospital
Editor: Julianne Jung, MD, Department of Emergency Medicine, Johns Hopkins University School of Medicine


The Emergency Department (ED) is faced daily with patients with heart rhythm disorders, some of whom require electrical therapies to treat their conditions. This chapter covers the basics of permanent internal pacemakers and defibrillators, as well as electrical therapy that may be required in the emergency department, including emergent external/internal pacing, cardioversion and defibrillation.

Emergent Temporary Pacing

This therapy is indicated in patients with hemodynamically unstable bradycardia. In most cases, this will be related to atrioventricular (AV) blocks, typically either third degree (complete) AV block or a high grade (Mobitz II) second degree AV block. Less frequently, severe sinus bradycardia related to sinus node dysfunction can also require temporary pacing, but these patients are typically less symptomatic than those with AV blocks. Patients who are significantly hypotensive or who present with syncope should be considered for temporary pacing if they have ongoing severe bradycardia.

Some additional diagnostic considerations for patients who may require emergent pacing include:

  1. Acute myocardial infarction (MI) can cause either AV block or severe sinus bradycardia.
  2. Toxicities and drug overdoses can cause suppression of either the sinus node or AV node. In particular, attention should be paid to whether the patient has digoxin, beta-blockers, calcium channel blockers or any anti-arrhythmic medications.
  3. Complete AV block is most commonly seen after long-term progression of conduction system disease (ie prior bundle branch block), but can also be seen more acutely with Lyme disease, MI, toxicities, or after heart surgery.
  4. Persistent ventricular tachycardia can be treated with overdrive pacing.
  5. Failure of a previously implanted internal pacemaker could require emergent pacing.
  6. Electrolyte disturbances: hyperkalemia can lead to AV blocks.

Transcutaneous Pacing

Performed with external pads placed on the chest.

Duration and amplitude of the stimulating impulse are greater compared to internal pacemakers, thus contributing to patient discomfort.  Electrical resistance across the chest wall may contribute to difficulty capturing.  Both of these features can limit the utility of this therapy.

Steps for Transcutaneous Pacing

  1. Place pads on the chest in one of two positions: anterolateral or anteroposterior


















    1. If able, administer pain/sedation medicine (if unstable or unresponsive, sedation may be withheld)
    2. Turn machine on and select the Pacer button. (image: standard buttons on the Defibrillator/Pacer)


    1. Select the rate of the pulses (70 to 80 ppm)


    1. Select a current and adjust gain upward until capture is noted on the monitor.


    Evidence of Capture on the Monitor


    Image above demonstrates sensing arrows that denote a native QRS complex; in between there are pacer spikes which are a straight line followed by a wide QRS complex.

    Red=Captured Beat


    Image above now demonstrates spikes that are now capturing the ventricle more often.


    Image above now demonstrates full capture as each pacer spike is followed by a QRS complex.

    Transvenous Pacing

    • Benefits: Less pain for patient, better ability to .
    • Risks: Myocardial perforation (less likely with balloon tipped catheter), sepsis, endocardidits, and arrhythmias
    • Appropriate placement of the tip of the pacing wire is at the apex of the right ventricle.
    • Right Internal Jugular is the preferred site as it is the straightest route to the right ventricle
    • Can perform under fluoroscopy (usually done by Cardiology), using ECG guidance or using specialized flexible semi-floating catheters with a balloon on the tip

    Steps for Transvenous Pacing

    1. Identify the vessel on ultrasound or via landmarks
    2. Gown and drape patient in sterile fashion
    3. Anesthetize the area
    4. Insert an introducer needle under ultrasound guidance until you are in the internal jugular and see venous blood return
    5. Remove the syringe, insert guidewire through the needle into the vessel
    6. Remove the needle, without EVER letting go of the wire
    7. Incise the skin by the wire with an #11 blade
    8. Advance the sheath over the wire into the vessel lumen with a twisting motion
    9. Remove the guidewire
    10. Verify the sheath is in the vessel lumen using ultrasound.
    11. Insert and advance the pacing catheter approximately 10 cm (to make sure it is past the introducer) and inflate the balloon
    12. Slowly advance the pacing catheter; looking at the ECG tracing that is being run during the procedure. Stop advancing when the complexes show ST- elevation, indicating that the tip is abutting the right ventricle
    13. Connect the pacemaker generator to the catheter
    14. Adjust pacemaker output to minimum amount required to capture
    15. Examine chest x-ray for appropriate catheter placement
    16. Secure the catheter and apply sterile dressing controls


    Cardioversion refers to the synchronized delivery of electrical energy used to depolarize the cardiac cells to stop a tachyarrythmia in a patient with a pulse. The electrical impulse is timed by the machine to the patient’s ECG, and is delivered at the peak of the R wave. This is to prevent the shock from being given during a refractory period, which could lead to ventricular fibrillation.


    Lower energy is typically required to restore sinus rhythm when compared to defibrillation (Typically starting with 50-100 Joules when using a biphasic defibrillator)

    Note: When delivering a shock by synchronized cardioversion, the “shock” button may need to be held down until the shock is delivered so that the device can be sure that the charge is delivered in a synchronized manner.  Repeated cardioversion attempts will likely require the operator to repress the sync button after each cardioversion attempt.

    Cardioversion Indications

    -Ventricular Tachycardia with a pulse

    -Supraventricular Tachycardias with hypotension

    -Atrial Fibrillation

    -Atrial Flutter

    -Atrioventricular Nodal Reentrant Tachycardia(AVNRT)/Atrioventricular Reentrant Tachycardia(AVRT)  


    Defibrillation refers to non-synchronized delivery of electrical energy used to depolarize the cardiac cells with the goal of resetting the cardiac threshold and letting the heart restore normal rhythm. This is only used for patients without a pulse. If the patient has a pulse, then synchronized cardioversion should always be used to treat unstable dysrhythmias.  Defibillation machines can be either monophasic or biphasic.  Biphasic sends the electricity in two directions between the pads, whereas  monophasic send electricity in one direction.  In biphasic, a lower level of electricity able to be used (machines max out at 200J).

    Defibrillation Indications

    -Pulseless Ventricular Tachycardia

    -Ventricular Fibrillation

    Pearl: Cardioversion is for the patients who are alive, and Defibrillation is for when they are dead.

    Implanted Permanent Pacemakers 

    Pacemakers are used to treat various bradyarrhythmias and heart failure by providing an appropriate heart rate and heart rate response to other factors (ie exercise).

    Permanent pacemakers Indications

    -Symptomatic bradycardia (rate less than 40 or frequent sinus pauses)

    -Symptomatic chronotropic incompetence (i.e., not having an appropriate heart rate response to exercise)

    -Third degree AV block

    -Advanced (Mobitz II) second degree AV block

    -Symptomatic Mobitz I second degree AV block

    Permanent pacemakers (PPMs) are implanted by cardiac electrophysiologists. The basic components of a PPM are the pulse generator and the leads. The pulse generator is implanted subcutaneously through a small incision under the clavicle and is connected to leads, which are threaded through the subclavian vein into the heart. A basic single-chamber pacemaker will have a lead in the right ventricle, and additional leads can be added to the right atrium and to an epicardial vein on the surface of the left ventricle via the coronary sinus to achieve more sophisticated pacing function. Adding these extra leads allows synchronization of the contraction of the right ventricle with the right atrium and/or the left ventricle, which can be helpful for certain subsets of patients with heart failure. Each lead senses the native electrical activity in that cardiac chamber, and sends these signals back to the pulse generator, which is programmed to evaluate the intrinsic electrical activity of the heart and deliver a pacing impulse when necessary.

    A pacemaker is programmed in one of several modes, which determines its pacing and sensing functions. The mode is identified by a three to five letter coding system:

    1st Letter2nd Letter3rd Letter4th Letter5th Letter
    Chamber PacedChamber SensedResponse to sensingProgram FunctionsAntitachydysrythmias Function
    VentricleVentricleTriggersP: programmable rate, output or bothP:antitachydysrythmia pacing
    AtriumAtriumInhibitsM: multiprogrammability of rate, output, sensitivityS: Shock
    Dual(V+A)Dual(V+A)Dual(V+A)C:communication(telemetry)D: Dual(P+S)
    O: NoneO: NoneO: NoneR: Rate ModulationO: None
    O: None

    The more common programmable functions you will see are and DDD.

    Atrial Pacing


    Blue=Pacer spike; Red=Atrial Beat

    Intermittent Ventricular Pacing


    Blue=Pacer Spike; Red=Ventricular Beat

    AtrioVentricular Sequential Pacing

    You can see here the atrial pacer spike before the atrial beat and then ventricular pacer spike followed by ventricular beat


    Red=Atrial Pacer Spike; Blue-Ventricular Pacer Spike 

    Evaluating Pacemakers

    You will need a few things to evaluate pacemakers:

    -EKG: evaluate sensing and capture as well as ensuring appropriate pacing

    -Chest Xray: Evaluate lead position, lead fracture, evidence of cardiac

    -Device interrogation: Done by cardiology or representative of the company that makes the particular patient’s device. Each company has specific proprietary hardware and software, and requires a specific portable programmer/interrogator to be brought to the patient’s bedside. Through this interrogation process, all stored information about the patient’s intrinsic electrical activity can be obtained, and all programmed settings can be evaluated. If necessary, pacing and sensing parameters can be modified to better suit a patient’s clinical needs.

    -Pacemaker Magnet: Placing a magnet over the pulse generator allows you to turn off the sensing function of the pacemaker and put it in the VOO fixed rate pacing mode (usually around 70 bpm) 

    Pacemaker Failure

    Caused by:

    1. Failure to pace: absence of pacemaker spikes in a patient whose intrinsic rhythm is slower than the programmed rate. This can be caused by:
      1. Lead fracture or dislodgement.
      2. Battery Depletion
      3. Oversensing: Inappropriate sensing of electrical noise that is mistaken for intrinsic electrical activity, which therefore inhibits pacing. This can be corrected by reprograming the device. *THIS IS THE MOST COMMON CAUSE OF FAILURE TO PACE!
    2. Failure to sense or capture: seen by pacemaker spikes at the wrong time or no QRS after pacer spike.
      1. Lead Malposition: Lead displacement(~first month after placement) or cardiac perforation(~ 4 days)
      2. Wire or Insulation Fracture
      3. Battery Depletion
      4. Elevated Myocardial Threshold
        • Fibrosis at electrode
        • Lead Displacement
        • Metabolic/Physiologic Changes
      5. Undersensing: Failure of device to recognize normal intrinsic electrical activity, which therefore results in unnecessary paced beats. This can be corrected by reprogramming the device
      6. Oversensing: (See above)
    3. Pacemaker-Mediated Tachycardia
      1. Reentrant tachycardia triggered by premature beat similar to AVNRT or AVRT, but using pacemaker as part of the reentrant loop
      2. Only seen in dual chamber pacemakers
      3. Modern pacemakers are typically programmed in ways designed to minimize likelihood of this happening and to terminate the circuit if it is detected by the device.

    Internal Cardiac Defibrillators (ICD)

    Devices that can deliver electrical impulses to terminate lethal ventricular dysrhythmias (ventricular tachycardia and ventricular fibrillation).  They consist of a pulse generator (battery and microprocessor) with a capacitor and lead systems containing sensing and shocking electrodes (which are notably different secondary to insulation).  ALL ICDs CAN BE PROGRAMMED TO PACE, but pacemakers cannot defibrillate. In comparison to a PPM, an ICD system requires a specialized right ventricular lead and a different pulse generator. All functions of a standard PPM can be programmed into an ICD. In addition, ICDs are programmed to detect ventricular dysrhythmias and rapidly deliver electrical therapy to treat them.

    Types of Therapy

    1. Defibrillation is a high energy electrical shock that is delivered after detection of VF or fast VT. This is very uncomfortable for patients, but an appropriate shock implies that the patient is likely unconscious and at very high risk of imminent death.
    2. Anti-tachycardia pacing is a therapy to treat slower, and therefore presumably more hemodynamically stable, VT without a shock. When VT is detected, the device delivers an 8-10 beat burst of ventricular pacing at a rate faster than the intrinsic VT in an attempt to capture the ventricle and terminate the intrinsic VT. Most devices will attempt this several times while charging the defibrillator, and then give a shock if the therapy is unsuccessful. Antitachycardia (overdrive) pacing can also degenerate VT into VF, which would then require the device to defibrillate urgently. This is why this pacing feature is not included in PPMs, which could not defibrillate in this scenario.

    Indications for ICD

    1. Patients with prior sudden cardiac death
    2. Brugada Syndrome
    3. Heart Failure patients with EF<35% on maximal medical therapy
    4. Long QT
    5. Hypertropic Cardiomyopathy

    Types of ICD Malfunction

    1. Failure to defibrillate true VT/VF.
      1. Could rarely be due to a malfunction of the device or lead
      2. Most commonly, the device is “working appropriately” but the patient’s arrhythmia does not meet the programmed criteria necessary to initiate treatment. For example, an ICD might be programmed so that it will only defibrillate VT if it is detected at greater than 180 beats per minute for 20 seconds. If the patient has VT at 179 beats per minute or terminates on its own after 19 seconds then the device would not deliver a shock.
    2. Frequent ICD Discharge. Must determine whether shocks were appropriate or inappropriate.
      1. Frequent episodes of VT/VF, which would require further medical workup.
      2. Inappropriate shocks: Device mistakes electrical artifact for VF or misinterprets SVT as VT. This can also occur with lead fracture or picking up muscular contractions or SVT
      3. Ghost shocks: patient feels shocks when there aren’t any
      4. For an awake patient who is obviously getting inappropriate shocks, ICD can be disabled by placing magnet over the device.
    3. Infection: usually with Staphylococcus


    Hayes, D. Temporary Cardiac Pacing. In: UpToDate, Updated: Oct, 2015, UpToDate, Waltham, MA. (Accessed on March 2015.)

    Sullivan B, Bartels K, and Hamilton N. Insertion and Management of Temporary Pacemakers. SEMIN CARDIOTHORAC VASC ANESTH March 2016 20: 52-62.

    Knight, B. Basic Principles and Techniques of Cardioversion and Defibrillation. In: UpToDate, Updated: August, 2014, Waltham, MA.(Accessed on March 2015)

    Ekg strips from Life in the Fast Lane http://lifeinthefastlane.com/; reproduced with permission

    Tintinalli JE, Kelen GD, Stapczynski JS, Ma, OJ, Cline DM, editors. Tintinalli’s Emergency Medicine. 7th ed. New York: McGraw Hill; 2011.  Cardiac Pacing and Defibrillation and Carioversion; pgs 240-250.

    Transvenous picture use with permission courtesy of James P Sarwark, MD and Andrew Pirotte, MD