An Overview of Pacemakers and Cardiac Devices

Implantable Cardiac Devices

Heart disease remains one of the leading causes of death in the United States but there are a number of different implantable cardiac devices (ICDs) available today, including pacemakers, defibrillators and cardiac resynchronization devices, that can help people with heart disease or failure go on to lead normal lives by regulating their heart beats through a series of electric shocks. To determine the facts about these devices, this paper provides a review of the literature to explain the respective indications for these devices as well as their differences. Finally, a summary of the research and important findings concerning these implantable cardiac devices are provided in the conclusion.

Review and Discussion

Indications for each of the following: Pacemaker, ICD (defibrillator) & Cardiac Resynchronization Devices

Pacemaker. According to Gregoratos et al. (1), this type of ICD is indicated for patients suffering from abnormalities of atrioventricular (AV) conduction which may be asymptomatic; however, in some cases, patients will experience serious symptoms due to ventricular arrhythmias, bradycardia, or both). Consequently, Gregoratos and his associates (1) report that indications for pacemaker implants are related to the presence or absence of bradycardia-attributable symptoms. In addition, Gregoratos et al. (1) note that physician discretion concerning permanent pacing is required in cases of AV block following valve surgery. In sum, the American Heart Association (2) reports that pacemakers are indicated for:

Patients whose hearts beat too slow or fast;

Patients who hearts do not beat regularly; and,

Patients who suffer from a block in the heart’s electrical pathways.

ICD (defibrillator). According to Perry (3), ICDs are the most effective method for preventing sudden cardiac death among high-risk coronary patients that have been identified to date. The 2012 ACCF/AHA/HRS Guidelines for Implantable Defibrillator and Cardiac Resynchronization Therapy for Cardiac Rhythm Abnormalities (4) reports that these devices are indicated for patients in the following circumstances:

Level of Evidence: A With left ventricular ejection fraction (LVEF) ? 35% due to prior myocardial infarction (MI) who are at least 40 days post-MI and are in New York Heart Association (NYHA) Functional Class II or III;

With LV dysfunction due to prior MI who are at least 40 days post-MI, have an LVEF ? 30%, and are in NYHA Functional Class I; and,

Who are survivors of cardiac arrest due to ventricular fibrillation (VF) or hemodynamically unstable sustained ventricular tachycardia (VT) after evaluation to define the cause of the event and to exclude any completely reversible causes.

Level of Evidence: B

With nonischemic dilated cardiomyopathy (DCM) who have an LVEF ? 35% and who are in NYHA Functional Class II or III;

With nonsustained VT due to prior MI, LVEF < 40%, and inducible VF or sustained VT at electrophysiological study;

With structural heart disease and spontaneous sustained VT, whether hemodynamically stable or unstable;

With syncope of undetermined origin with clinically relevant, hemodynamically significant sustained VT or VF induced at electrophysiological study;

Assuming patients are on chronic, optimal medical therapy and have a reasonable expectation of survival with good functional status for > 1 year (4).

Cardiac Resynchronization Devices

According to the American Heart Association (5), cardiac resynchronization therapy (CRT) is used to treat various arrhythmias; in sum, CRT devices are indicated for the following patients:

LVEF ? 35%

Sinus rhythm

Left Bundle Branch Block (LBBB)

Q wave, R wave and S wave duration ? 150 ms

NYHA class II, III, or ambulatory

Guideline-Directed Medical Therapy

Class IV symptoms (Level of Evidence: A for NYHA class III/IV; Level of Evidence: B for NYHA class II) (5).

2. Differences between Pacemaker, ICD (defibrillator) & Cardiac Resynchronization Devices


A. implantation site. The American Heart Association (6) reports that these small devices are implanted under the collarbone.

B. function. According to the American Heart Association (6), pacemakers help patients’ hearts beat in a regular fashion through electrical stimulation that are delivered directly to the heart as needed.

C. Population treated including any restrictions for age groups. According to Lamas and Pashos (7), although pacemakers are used by the elderly, younger adults can also benefit from these devices.

D. Rhythms treated. The Heart Rhythm Society (8) reports that pacemakers are typically used to treat the following conditions: bradycardia, atrial fibrillation, heart failure and syncope.

E. Complications. Caution should be exercised when operating large industrial microwave devices and batteries must be replaced every 5 to 8 years (8).


A. implantation site. According to the American Heart Association (9), these devices can be implanted in the chest or abdomen, but they are usually placed just below the collarbone.

B. function. These devices stimulate the heart when it detects the heart slowing beyond a certain point (ICD, 2016).

C. Population treated including any restrictions for age groups. Although typically used in adults, ICDs can also be used for children (9).

D. Rhythms treated. ICDs are used to treat patients who suffer from known, sustained ventricular tachycardia or fibrillation (9).

E. Complications. Strong magnetic fields can interfere with ICD functioning (9).

Cardiac Resynchronization Devices

A. implantation site. These devices are usually implanted in the upper chest (10).

B. function. These devices deliver an electric shock if the heart is detected beating too fast (10).

C. Population treated including any restrictions for age groups. There are no specified age restrictions for this device (10).

D. Rhythms treated. CRD devices are used to treat heart failure, ventricular tachycardia and ventricular fibrillation (10).

E. Complications. Any complications such as infection or drug reactions related to the implant of these devices are usually related to the surgical implantation procedure and are regarded as minimal (11).


Although heart disease remains a leading cause of death in the United States, the introduction of various implantable cardiac devices in recent years has provided a growing number of patients with the ability to lead relatively normal lives by regulating their heart beats. Although the research showed that pacemakers, ICD defibrillators and cardiac resynchronization devices differ in their specific functioning and purposes, they all shared the common feature of moderating the heart beat in order to maintain its regularity by delivering electrical shocks. All of these devices also shared a common feature of being surgically implanted, a procedure that also carries some risks. Finally, while all of these devices were shown to be effective in regulating heart beats, they all still rely on battery power which means that batteries must be replaced periodically.


1. Gregoratos, G et al. American Heart Association [Internet] ACC/AHA Practice Guidelines 2016 [cited 2016 April 26] Available from

2. American Heart Association. [Internet] What is a pacemaker. 2016 [cited 2016 April 26] Available from / downloadable/ucm_300451.pdf.

3. Perry, P ICD — The Beat Goes On: Experts Call for Expanded Coverage of ICDs, the Most Effective Method to Date for Preventing Sudden Cardiac Death in High-Risk Coronary Patients. The Saturday Evening Post 2004, March-April 276(2): 28-29.

4. Medtronic [Internet] 2012 ACCF/AHA/HRS Guidelines for Implantable Defibrillator and Cardiac Resynchronization Therapy for Cardiac Rhythm Abnormalities. 2012. [cited 2016 April 26] Available from / documents/2012-accf-aha-hrs-guidelines.pdf.

5. American Heart Association [Internet] Cardiac Resynchronization Therapy (CRT) 2016. [cited 2016 April 26] Available from: / Cardiac-Resynchronization-Therapy_UCM_452920_Article.jsp#.VyDjgfkrK1s.

6. American Heart Association. [Internet] What is a pacemaker. 2016 [cited 2016 April 26] Available from / downloadable/ucm_300451.pdf.

7. Lamas, GA & Pashos, CL Permanent pacemaker selection and subsequent survival in elderly Medicare pacemaker recipients. 1995. Circulation 91(4): 1063-1069.

8. Heart Rhythm Society [Internet] Pacemaker 2016. [cited 2016 April 26] Available from: Rhythm Society

9. American Heart Association [Internet] ICD. 2016. [cited 2016 April 26] Available from:

10. St. Jude Medical [Internet]. CRD. c2016 [cited 2016 April 26] Available from:

11. Medtronic. [Internet] Resynchronization Therapy for Cardiac Rhythm Abnormalities. 2016 [cited 2016 April 26] Available from:

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