Pacer Problem
Answer: B
The indications for permanent pacemaker placement are many, but in general they depend on two main principles: an arrhythmia with symptoms and the location of the lesion. This man likely had a high-grade AV block post-MI. On review of his medications, he also likely has advanced heart failure, as the typical sequence of medical management for systolic heart failure begins with a diuretic, then addition of an ACE inhibitor or ARB, then titration of a beta-blocking agent, then possibly addition of hydralazine plus a nitrate.
His differential diagnosis initially is broad to explain his non-specific symptoms. However, his electrocardiogram helps to make the diagnosis. To understand what is occurring in his ECG, a review of pacemaker settings may be helpful.
The first three positions are the most important for emergency physicians to know. A useful mnemonic is “PaSeR” (chamber Paced, chamber Sensed, Response to sensing) to know what the pacemaker should be doing.
In this case, this man’s pacer is programmed at DDD. When all is working well, his ECG would look like this:
The indications for permanent pacemaker placement are many, but in general they depend on two main principles: an arrhythmia with symptoms and the location of the lesion. This man likely had a high-grade AV block post-MI. On review of his medications, he also likely has advanced heart failure, as the typical sequence of medical management for systolic heart failure begins with a diuretic, then addition of an ACE inhibitor or ARB, then titration of a beta-blocking agent, then possibly addition of hydralazine plus a nitrate.
His differential diagnosis initially is broad to explain his non-specific symptoms. However, his electrocardiogram helps to make the diagnosis. To understand what is occurring in his ECG, a review of pacemaker settings may be helpful.
The first three positions are the most important for emergency physicians to know. A useful mnemonic is “PaSeR” (chamber Paced, chamber Sensed, Response to sensing) to know what the pacemaker should be doing.
In this case, this man’s pacer is programmed at DDD. When all is working well, his ECG would look like this:
He presents today with failure to capture (B):
Here the atrial and ventricular spikes appear at appropriate intervals, but the myocardium fails to respond to the pacemaker stimulus. The effect is a slower pulse and subsequent decreased cardiac output (CO=Stroke Volume x Heart Rate). This likely explains his presentation (given an otherwise negative work-up). The pacemaker battery typically lasts 5-7 years; a common cause of failure to capture is insufficient voltage from a failing battery. Other causes include exit block, which results from a chronic fibrosis around the electrode lead, or a damage to the surrounding tissue after external cardiac defibrillation (the external impulse in conducted down the internal electrode and may cause local damage).
Failure to sense (D) occurs when the pacemaker does not detect native cardiac activity. For example, the ECG may show normal P waves then atrial pacing spikes, demonstrating that the pacer did not register the patient’s native P wave. In this case, the cardiologist may simply program the pacemaker for a higher sensitivity.
Pacemaker syndrome (C) occurs when there is loss of AV synchrony (loss of atrial “kick”) and the pacemaker fails to provide a physiologic rate. Heart failure symptoms and signs predominate, but patients may also present with headache, dizziness, right upper quadrant pain, dysrhythmias, and hypotension. These patients may present with chronic or acute-on-chronic complaints. They need the pacemaker interrogated (and likely re-programmed).
Runaway pacemaker (A) is a malfunction of the pacemaker causing ventricular rates of 280 bpm and above. It is most commonly caused by sudden failure of the circuits or battery depletion. Clinically, this may induce tachycardia, ventricular tachycardia, or ventricular fibrillation. Paradoxically, runaway pacemaker may result in bradycardia, because although the pacer is firing at a high rate (case reports of 1000-2000 bpm!), due to low voltage, there may be failure to capture, resulting in a de facto lack of pacing. Reportedly the incidence is decreasing with newer models and more fail-safe features. Immediate treatment includes a magnet over the generator; some cases need emergency surgery to cut the pacer wires.
References
Chan TC, Cardall TY. Electronic pacemakers. Emerg Med Clin North Am. 2006 Feb;24(1):179-94.
Kusumoto FM, Goldschlager N. Device therapy for cardiac arrhythmias. JAMA. 2002 Apr 10;287(14):1848-52
Failure to sense (D) occurs when the pacemaker does not detect native cardiac activity. For example, the ECG may show normal P waves then atrial pacing spikes, demonstrating that the pacer did not register the patient’s native P wave. In this case, the cardiologist may simply program the pacemaker for a higher sensitivity.
Pacemaker syndrome (C) occurs when there is loss of AV synchrony (loss of atrial “kick”) and the pacemaker fails to provide a physiologic rate. Heart failure symptoms and signs predominate, but patients may also present with headache, dizziness, right upper quadrant pain, dysrhythmias, and hypotension. These patients may present with chronic or acute-on-chronic complaints. They need the pacemaker interrogated (and likely re-programmed).
Runaway pacemaker (A) is a malfunction of the pacemaker causing ventricular rates of 280 bpm and above. It is most commonly caused by sudden failure of the circuits or battery depletion. Clinically, this may induce tachycardia, ventricular tachycardia, or ventricular fibrillation. Paradoxically, runaway pacemaker may result in bradycardia, because although the pacer is firing at a high rate (case reports of 1000-2000 bpm!), due to low voltage, there may be failure to capture, resulting in a de facto lack of pacing. Reportedly the incidence is decreasing with newer models and more fail-safe features. Immediate treatment includes a magnet over the generator; some cases need emergency surgery to cut the pacer wires.
References
Chan TC, Cardall TY. Electronic pacemakers. Emerg Med Clin North Am. 2006 Feb;24(1):179-94.
Kusumoto FM, Goldschlager N. Device therapy for cardiac arrhythmias. JAMA. 2002 Apr 10;287(14):1848-52