Download Pacemakers and AICDs: The ABCs

Pacemakers and AICDs: The ABCs
Published on Physicians Practice (http://www.physicianspractice.com)
Pacemakers and AICDs: The ABCs
August 25, 2015
By Steven Brent Deutsch, MD [1] and Eric Lawrence Krivitsky, MD [2]
Back to basics here on pacemakers and automated implantable cardioverter defibrillators so that
the next time you place a consult for cardiology, you will know how to best manage the patient and
support your consult decision.
An estimated 4.5 million persons worldwide have cardiac implantable electronic devices (CIEDs).1 In
the United States alone, close to 400,000 CIEDs are placed each year.
In reviewing numerous studies from 1990-2015, we found fundamental facts all hospitalists should
know about pacemakers versus automated implantable cardioverter defibrillators (AICDs). In this
3-part article, we discuss the basics so that the next time you place a consult for cardiology you will
know how to best manage the patient and support your consult decision.2
Here we distinguish between pacemakers and AICDs and offer clues to identifying the implanted
device.
CXR Pacemaker Non ICD vs ICD
Pacemakers and AICDs are somewhat similar in appearance on gross examination, but they have
unique functions and indications. Pacemakers are small devices that, once implanted in the chest,
help control the normal heart rate and treat arrhythmias. They use electrical impulses to maintain a
regular rhythm in instances when the heart’s inherent electrical conduction system is
malfunctioning.
Defibrillators are small implantable devices placed in patients at risk for sudden cardiac death
secondary to certain arrhythmias. They are programmed to deliver an electrical impulse when a
specific arrhythmia is detected. These devices can detect arrhythmias that present from the atria or
ventricles. Like pacemakers, some AICDs also can pace the heart. Even so, providers (and even
patients) may become confused about which device was implanted.3
Clues to Identifying the Device
A few clues may provide the answer. The most striking difference on initial examination is the size.
The average pacemaker weighs about 15 g and is about the size of 2 silver dollars stacked. A
defibrillator typically weighs about 70 g and is 200% to 250% the size of a pacemaker. These devices
are rarely seen ex-vivo, but this difference can be appreciated by palpating the pocket site,
especially on thin patients.
A second clue is the patient history. Most defibrillators in the US are implanted for primary
prevention of sudden cardiac death, meaning implant prior to any event in a patient who is at high
risk for ventricular arrhythmias. Decades of research (MADIT, MADIT II, Dynamite) has shown that
patients with a decreased ejection fraction (under 35%) are the most easily identifiable group with a
proven risk and benefit from primary prevention ICD implantation.4
Consequently, if you encounter a patient with a history of ischemic or nonischemic cardiomyopathy
and an ejection fraction of less than 35% who has a device, it is most likely a defibrillator (or the
patient requires upgrade). However, caution must be exercised because patients with seemingly
normal cardiac function may have an ICD. They may have had a previous cardiomyopathy that has
resolved or a condition that places them at high risk, such as Brugada syndrome, hypertrophic
cardiomyopathy, or prolonged QT interval, or they may have had an idiopathic cardiac arrest and
were implanted for secondary prevention indications.5
Page 1 of 3
Pacemakers and AICDs: The ABCs
Published on Physicians Practice (http://www.physicianspractice.com)
Figure. This EKG demonstrates high degree heart block.
Pacemakers may be implanted in anyone who has symptomatic bradycardia. The typical symptom is
fatigue; however, syncope or presyncope may overlap with symptoms caused by ventricular
arrhythmias leading to ICD implantation. Thus, this strategy may not be as helpful for distinguishing
them.6
A third and telling distinction is the chest x-ray film, which helps differentiate between pacemakers
and AICDs. Imaging of both can offer identifiers of the product manufacturer and device function.
ICD generators traditionally were larger than pacemakers, but current ICDs may be smaller than
older pacemakers. ICDs are best distinguished from pacemakers on CXR by coils that appear as
thickened radio-opaque structures on the lead. There may be just 1 coil, in the RV portion of the
lead, or 2 coils, in the RV and SVC portions of the lead. These coils serve to deliver high-energy
therapy to effect defibrillation.
In contrast, a pacemaker lead does not have coils because the device is incapable of delivering
high-voltage energy. Lead orientation offers insight into device function and capabilities. For
example, a single chamber ventricular pacemaker/defibrillator typically has 1 lead near the RV apex.
A dual chamber device has an additional lead, typically in the RA appendage. A biventricular device
has 3 leads—a third lead is placed in the coronary sinus, which paces the LV for resynchronization.
Companies often place logos on devices to help the physician identify the type of product.7 For
example, St Jude Medical has the descriptor “SJM” on the generator and Medtronic has “M.”
Subcutaneous ICDs—defibrillators that recently gained FDA approval—have a typical pulse
generator, but the lead is implanted subcutaneously and no part of the system is intracardiac or
intravascular. This allows for easier extraction in high-risk patients and reduces some complications
associated with standard leads, such as crush fracture dislodgement. However, these devices
essentially are incapable of pacing function in the current models.8
The EKG in the Figure above shows evidence of high degree heart block. There appears to be
sensing of P waves with subsequent ventricular pacing, suggesting a DDD system.
Next: Nomenclature, Malfunction, and Pseudomalfunction
In part 2 of this article, we will discuss pacemaker nomenclature and device function and address
malfunction and pseudomalfunction.
References:
1. Lanzman RS, Winter J, Blondin D, et al. Where does it lead? Imaging features of cardiovascular
implantable electronic devices on chest radiograph and CT. Korean J Radiol. 2011;12:611-619.
2. Buch E, Boyle NG, Belott PH. Pacemaker and defibrillator lead extraction. Circulation.
2011;123:e378-e380.
Page 2 of 3
Pacemakers and AICDs: The ABCs
Published on Physicians Practice (http://www.physicianspractice.com)
3. Epstein AE, Kay N, Plumb VJ, et al. Combined automatic implantable cardioverter-defibrillator and
pacemaker systems: implantation techniques and follow- up. JACC. 1989;13:121-131.
4. Reynolds MR, Josephson ME. MADIT II (Second Multicenter Automated Defibrillator Implantation
Trial) debate. Circulation.2003;108:1779-1783.
5. Myerburg RJ, Reddy V, Castellanos A. Indications for implantable cardioverter-defibrillators based
on evidence and judgment. J Am Coll Cardiol. 2009;54:747-763.
6. Wood MA, Ellenbogen KA. Cardiac patient pages: cardiac pacemakers from the patient’s
perspective. Circulation. 2002;105:2136-2138.
7. Costelloe CM, Murphy WA Jr, Gladish GW, Rozner MA. Radiography of pacemakers and implantable
cardioverter defibrillators. Am J Roentgenol. 2012;199:1252-1258.
8. Weiss R, Knight BP, Gold MR, et al. Safety and efficacy of a totally subcutaneous
implantable-cardioverter defibrillator. Circulation. 2013;128:944-953.
Source URL:
http://www.physicianspractice.com/cardiovascular-diseases/pacemakers-and-aicds-abcs
Links:
[1] http://www.physicianspractice.com/authors/steven-brent-deutsch-md
[2] http://www.physicianspractice.com/authors/eric-lawrence-krivitsky-md
Page 3 of 3