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Cardiac Device Emergencies
Questions and answers
Case: You arrive on scene to find a 69-year-old female with a past medical history of atrial fibrillation, hypertension, and heart failure and an implantable defibrillator with a pacemaker. She called because her defibrillator shocked her.
1
What are the types of implantable devices and their purposes?
An implantable pacemaker is used to ensure that the heart rate is adequate when the native conduction system is not working properly. Indications for pacemakers are provided in Table 16.1 . An implantable cardiac defibrillator (ICD) is an implantable device designed to provide electrical cardioversion to the heart when it goes into a dysrhythmia. Indications for an ICD are also provided in Table 16.1 . All modern ICDs are also capable of acting as pacemakers, but not the reverse.
Table 16.1
Indications for an Implantable Cardiac Defibrillator or Pacemaker
| CARDIAC DEFIBRILLATOR | PACEMAKER |
|---|---|
| Left ventricular function <30%–35% | Third-degree heart block, or high risk or symptomatic second-degree and occasionally first-degree heart block |
| Syncope of presumed cardiac cause (e.g., Brugada, long QT syndrome) | Irreversible symptomatic bradycardia |
| Inducible ventricular tachycardia or ventricular fibrillation | Intermittent asystole or prolonged sinus pause |
| Sustained ventricular tachycardia | Symptomatic sinus node dysfunction |
| Survivors of cardiac arrest from ventricular tachycardia or ventricular fibrillation | Symptomatic carotid dysfunction with prolonged asystole |
2
Your patient says she has a DDD pacemaker mode. What are the different settings for pacemakers?
Pacemakers have a three- (or four-) letter abbreviation. The first letter indicates paced chamber, the second letter indicates the sensed chamber, and the third chamber indicates the response to sensing. Table 16.2 shows the different modes of pacemakers. A DDD pacemaker is what is nearly universally implanted in recent years. These pacemakers sense both chambers, pace both chambers, and have inhibitory and trigger modes for each chamber.
Table 16.2
Types of Pacemaker Settings
| PACING | SENSING | RESPONSE | RATE CONTROL | ||||
|---|---|---|---|---|---|---|---|
| O | None | O | None | O | None | O | None |
| A | Atrial | A | Atrial | I | Inhibit | P | Single programmable |
| V | Ventricular | V | Ventricular | T | Trigger | M | Multiprogrammable |
| D | Dual chamber | D | Dual chamber | D | Dual | R | Rate modulated |
Note that most pacemakers are reported as only their three-letter abbreviation.
3
What are the major types of pacemaker malfunctions?
Oversensing occurs when the pacemaker recognizes native beats that are not present. Output failure occurs when the pacer fails to generate a beat. Failure to capture occurs when the pacer fires, but the heart does not contract. Undersensing is when the pacemaker does not detect native beats and results in asynchronous pacing. Pacemaker associated tachycardia is a re-entrant tachycardia caused by sensing of retrograde p waves. Finally, leads can become dislodged or fractured, causing intermittent or complete failure to capture.
4
What are the treatments for pacemaker malfunction?
This depends on the patient’s heart rate and rhythm. In cases of bradycardia or ventricular tachycardia or fibrillation, the patient should be treated as though the pacemaker were not present. If there is bradycardia, medications may include atropine, epinephrine, dopamine, or isoproterenol. Transcutaneous pacing may also be performed. Patients in ventricular tachycardia or ventricular fibrillation can be defibrillated, but it is ideal to avoid placing the pads directly over the pacemaker. On the other hand, patients experiencing pacemaker-mediated tachycardia may require temporary suspension of pacemaker sensing using a magnet.
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