Pacemakers and Defibrillators

Published on 07/03/2015 by admin

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Chapter 18 Pacemakers and Defibrillators

Scott C. Streckenbach, MD , Kenneth Shelton, MD

1 What are the general principles of cardiovascular implantable electronic device (CIED) management according to the Heart Rhythm Society (HRS)–American Society of Anesthesiologists Consensus Statement published in 2011?

The primary recommendation is that the best prescription for the perioperative care of a patient with a CIED will be realized when that patient’s CIED team (electrophysiologist or cardiologist) is asked for advice and that advice is effectively communicated to the procedural team. Thus the surgical or procedural team should communicate with the CIED team to identify the type of procedure and the likely risk of electromagnetic interference. The CIED team should then communicate with the procedure team to deliver information about the pacer or implantable cardiac defibrillator (ICD) and recommendations for the perioperative management of the patient and the device.

2 How can one differentiate a pacemaker from an ICD?

Occasionally a patient is seen initially without information about his or her CIED. A critical step is to determine whether the device is a pacemaker or an ICD. The patient may be able to tell you why the device was inserted, and this might provide a clue. However, if the patient’s history cannot help, the patient’s chest radiograph can. The ICD leads, unlike pacer leads, have one or two radiodense shocking coils. Because of the shocking coils, the ICD leads (Fig. 18-1) are much larger than the pacer leads (Fig. 18-2), and this can be appreciated radiographically.

Figure 18-1 Chest radiographs (PA and lateral) of an ICD. A, The SVC shocking coil (arrowhead) and the RV shocking coil (arrow) are radiopaque and differentiate the ICD from a pacemaker radiographically. B, An atrial pace/sense lead is also noted in the lateral view.

Figure 18-2 Chest radiographs (A and B, PA and lateral) of a pacemaker. The atrial pacing lead (arrowhead) and the ventricular pacing lead (arrow) are smaller in diameter and less radiopaque than the leads associated with an ICD.

3 Describe the five-letter pacemaker code

• First position of the code reflects the chamber(s) in which stimulation occurs.

Second position refers to the chamber(s) in which sensing occurs.

Third position refers to the mode of setting (or how the pacemaker responds to a sensed event).

Fourth position reflects rate modulation.

Fifth position of the code indicates whether multisite pacing is present.

See Table 18-1.

Table 18-1 The Generic Pacemaker Code

4 What is cardiac resynchronization therapy (CRT)?

CRT is the term applied to reestablishing synchronous contraction between the left ventricular (LV) free wall and the ventricular septum in an attempt to improve LV efficiency and subsequently to improve functional class. The LV pacing lead is usually placed in the posterior lateral LV wall via the coronary sinus circulation. CRT may be used with a pacemaker or with an ICD. Indications typically include a low ejection fraction (< 35%), a prolonged QRS (> 120 ms), and class IV heart failure symptoms.

5 Explain the following pacemaker codes: DOO, VVI, DDD, and DDDRV

DOO = asynchronous atrial-ventricular pacing with a constant A-V interval. Atrial and ventricular pacing pulses are emitted regardless of the underlying cardiac rhythm.

VVI = ventricular-only antibradycardia pacing. Failure of the ventricle to produce an intrinsic event within the appropriate time window results in ventricular pacing. With no atrial sensing, there can be no atrioventricular (AV) synchrony in a patient with any intrinsic atrial activity.

DDD = dual-chamber antibradycardia pacing. In the absence of intrinsic activity in the atrium, it will be paced. After any sensed or paced atrial event, an intrinsic ventricular event must occur before the expiration of the AV timer or the ventricle will be paced.

DDDRV = dual-chamber antibradycardia pacing with rate response mode circuitry (to increase the paced rate in setting of increased metabolic demand) and biventricular pacing capability.

6 What is the effect of placing a magnet on a pacemaker?

Most pacemakers respond to a magnet by converting to an asynchronous pacing mode (e.g., DOO if pacer mode is DDD or VOO if VVI) at a rate dependent on the device manufacturer and the remaining battery life. For adequately charged pacemakers, the following is generally true:

Medtronic pacemakers pace at 85 beats/min

Biotronik, 90 beats/min

St. Jude, 98 beats/min

Boston Scientific, 100 beats/min

See Table 18-2.

Table 18-2 Magnet Effect on Pacemakers

7 What is a rate response mode?

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