Pacemakers and Implantable Cardioverter Defibrillators





A pacemaker is a device that delivers battery-supplied electrical stimuli over leads to electrodes that are in contact with the heart. It primarily treats bradycardia. An implantable cardioverter defibrillator (ICD) is a multiprogrammable antiarrhythmic device for treating ventricular tachycardia and ventricular fibrillation. ICDs also possess pacemaking capability to treat bradycardia.


I. Pacemakers in Children


For pacemakers, the electrical leads are inserted either directly over the epicardium or transvenously; the latter is the method of choice. Electronic circuitry regulates the timing and characteristics of the stimuli. The power source usually is a lithium-iodine battery. Battery life varies from 3 years to 15 years depending on the type of the device, which determines the amount of battery use. New pacemakers are capable of closely mimicking normal cardiac rhythm (physiologic pacemakers), and most of them are small enough to be implanted in an infant.


Physicians encounter an increasing number of children with either temporary or permanent pacemakers. Basic knowledge about the pacemaker and the pacemaker rhythm strip is essential in taking care of these children.


A. ECGs of Artificial Cardiac Pacemakers




  • 1.

    Rhythm strips of artificial pacemakers: The need to recognize rhythm strips of artificial pacemakers has increased in recent years, especially in intensive care and emergency room settings. The position and number of the pacemaker spikes on the electrocardiogram (ECG) rhythm strip are used to recognize different types of pacemakers.



    • a.

      When the pacemaker stimulates the atrium, a P wave follows an electronic spike. The resulting P wave demonstrates an abnormal P axis.


    • b.

      When the pacemaker stimulates the ventricle, a wide QRS complex appears after the electronic spike.


    • c.

      The ventricle that is stimulated (or the ventricle on which the pacemaker electrode is placed) can be identified by the morphology of the QRS complexes. With the pacing electrode on the RV, the QRS complex resembles an LBBB pattern; with the pacemaker placed on the LV, an RBBB pattern results.



  • 2.

    Examples of pacemaker ECGs: Three examples of pacemaker ECGs are shown in Fig. 18.1 .



    • a.

      Ventricular pacemaker (ventricular sensing and pacing). This mode of pacing is recognized by vertical pacemaker spikes that initiate ventricular depolarization with wide QRS complexes ( Fig. 18.1A ). The electronic spike has no fixed relationship with atrial activity (P wave). The pacemaker rate may be fixed as in the figure, or it may be on a demand (or standby) mode in which the pacemaker fires only after a long pause between the patient’s own ventricular beats.


    • b.

      Atrial pacemaker (atrial sensing and pacing). The atrial pacemaker is recognized by a pacemaker spike followed by an atrial complex. When AV conduction is normal, a QRS complex of normal duration follows (see Fig. 18.1B ). This type of pacemaker is indicated in patients with sinus node dysfunction with bradycardia. When the patient has high-degree or complete AV block in addition to sinus node dysfunction, an additional ventricular pacemaker may be required (AV sequential pacemaker, not illustrated in the figure). The AV sequential pacemaker is recognized by two sets of electronic spikes, one before the P wave and another before the wide QRS complex.


    • c.

      P-wave–triggered ventricular pacemaker (atrial sensing, ventricular pacing). This type of pacemaker can be recognized by pacemaker spikes that follow the patient’s own P waves at regular PR intervals and with wide QRS complexes (see Fig. 18.1C ). The patient’s own P waves are sensed and trigger a ventricular pacemaker after an electronically preset PR interval. This type of pacemaker is the most physiologic and is indicated when the patient has advanced AV block but a normal sinus mechanism. Advantages of this type of pacemaker are that the heart rate varies with physiologic need and the atrial contraction contributes to ventricular filling and improves cardiac output.




    Fig. 18.1


    Examples of some artificial pacemakers. (A) Fixed-rate ventricular pacemaker. The tall spikes (~20 mm) are pacemaker firings and they are followed by low-voltage, wide QRS complexes with predominantly S wave (as seen in BBB). Note the regular rate of the electronic spikes with no relationship to the P waves, which are indicated by arrows . (B) Atrial pacemaker. This tracing is from a 2-year-old child in whom extreme symptomatic bradycardia developed after the Mustard operation. Pacemaker spikes (~10 mm) are followed by nearly flat atrial activities and by QRS complexes of normal duration. (C) P-wave–triggered pacemaker. This tracing is from a child in whom complete heart block developed after surgical repair of tetralogy of Fallot.

    From Park, M. K., & Guntheroth, W. G. (2006). How to read pediatric ECGs (4th ed.). Philadelphia: Mosby.



B. Indications


Box 18.1 lists conditions for which pacemaker therapy is or is not indicated, based on the 2012 American College of Cardiology Foundation/American Heart Association/Heart Rhythm Society (ACCF/AHA/HRS) focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities (Epstein et al., 2013).



  • 1.

    In general, the most common indications for permanent pacemaker implantation in children, adolescents, and patients with CHD fit into one of three categories:



    • a.

      Symptomatic bradycardia (with symptoms of syncope, dizziness, exercise intolerance, or congestive heart failure). In children, significant bradycardia with syncope or near syncope results most commonly from extensive surgery involving the atria (such as the Fontan operation).


    • b.

      The bradycardia-tachycardia syndrome (due to overdrive suppression after a period of tachycardia).


    • c.

      Advanced second- or third-degree AV block, either congenital or postsurgical.



  • 2.

    Another noncontroversial indication is surgically acquired heart block that lasts more than 7 days after surgery.


  • 3.

    Temporary pacing is indicated for (a) patients with advanced second-degree or complete heart block secondary to overdose of certain drugs, myocarditis, or myocardial infarction and (b) certain patients immediately after cardiac surgery.



Box 18.1

Recommendations for Permanent Pacing in Children, Adolescents, and Patients with Congenital Heart Disease

Adapted from Epstein, A. E., DiMario, J. P., Ellenbogen, K. A., et al. (2013) 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: a report of American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. Journal of the American College of Cardiology, 61 (3)e6-e75.


Class I (Is Indicated)




  • 1.

    For advanced second- or third-degree AV block associated with symptomatic bradycardia, ventricular dysfunction, or low cardiac output. (Level of Evidence: C)


  • 2.

    For sinus node dysfunction with correlation of symptoms during age-inappropriate bradycardia. The definition of bradycardia varies with the patient’s age and expected heart rate. (Level of Evidence: B)


  • 3.

    For postoperative advanced second- or third-degree AV block that is not expected to resolve or that persists at least 7 days after cardiac surgery. (Level of Evidence: B)


  • 4.

    For congenital third-degree AV block with a wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction. (Level of Evidence: B)


  • 5.

    For congenital third-degree AV block in the infant with a ventricular rate less than 55 beats/min or with congenital heart disease and a ventricular rate less than 70 beats/min (Level of Evidence: C)



Class IIA (Is Reasonable)




  • 1.

    For patients with congenital heart disease and sinus bradycardia for the prevention of recurrent episodes of intraatrial reentrant tachycardia; sinus node dysfunction may be intrinsic or secondary to antiarrhythmic treatment. (Level of Evidence: C)


  • 2.

    For congenital third-degree AV block beyond the first year of life with an average heart rate less than 50 beats/min, abrupt pauses in ventricular rate that are two or three times the basic cycle length, or associated with symptoms due to chronotropic incompetence. (Level of Evidence: B)


  • 3.

    For sinus bradycardia with complex congenital heart disease with a resting heart rate less than 40 beats/min or pauses in ventricular rate longer than 3 seconds. (Level of Evidence: C)


  • 4.

    For patients with congenital heart disease and impaired hemodynamics due to sinus bradycardia or loss of AV synchrony. (Level of Evidence: C)


  • 5.

    For unexplained syncope in the patient with prior congenital heart surgery complicated by transient complete heart block with residual fascicular block after a careful evaluation to exclude other causes of syncope. (Level of Evidence: B)



Class IIB (May Be Reasonable)




  • 1.

    For transient postoperative third-degree AV block that reverts to sinus rhythm with residual bifascicular block. (Level of Evidence: C)


  • 2.

    For congenital third-degree AV block in asymptomatic children or adolescents with an acceptable rate, a narrow QRS complex, and normal ventricular function. (Level of Evidence: B)


  • 3.

    For asymptomatic sinus bradycardia after biventricular repair of congenital heart disease with a resting heart rate less than 40 beats/min or pauses in ventricular rate longer than 3 seconds. (Level of Evidence: C)



Class III (Is Not Indicated)




  • 1.

    For transient postoperative AV block with return of normal AV conduction in the otherwise asymptomatic patient. (Level of Evidence: B)


  • 2.

    For asymptomatic bifascicular block with or without first-degree AV block after surgery for congenital heart disease in the absence of prior transient complete AV block. (Level of Evidence: C)


  • 3.

    For asymptomatic type I second-degree AV block. (Level of Evidence: C)


  • 4.

    For asymptomatic sinus bradycardia with the longest relative risk interval less than 3 seconds and a minimum heart rate more than 40 beats/min. (Level of Evidence: C)


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Apr 11, 2021 | Posted by in CARDIOLOGY | Comments Off on Pacemakers and Implantable Cardioverter Defibrillators
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