to have failed (Figure 11.4). The patient will require hemodynamic support, which may include external cardiac pacing. If external pacing is indicated, care should be taken to not cover the implanted device with the external pads. If the patient is tachycardic, the physician will need to determine if the pacemaker is firing inappropriately or if there is another medical cause. The presence of pacer spikes prior to every tachycardic beat is the best indicator of a pacemaker issue.
Figure 11.4 The first ECG depicts failure of electrical capture with pacer spikes not associated with QRS complexes and a ventricular escape rhythm, while the second ECG shows the same patient with electrical capture with a QRS complex with every pacer spike.
The next step is to determine what therapy is needed. Optimally, the patient can be transported to a facility where the implanted device can be interrogated by an electrophysiologist, preferably at the hospital where the device was implanted. If the patient’s clinical condition requires more emergent intervention, a special magnet can be held over the pacemaker to suspend inappropriate pacing. The magnet will not turn the pacemaker off, but it will trigger the device to pace at an asynchronous (fixed) rate depending on the device and manufacturer [26]. A DDD pacemaker will pace at DOO, a VVI device will pace at VOO, and an AII device will pace as AOO [26]. Magnet therapy is only effective when the magnet is on the skin over the pacemaker. In the event that magnet therapy is ineffective, it is theoretically possible to cut the pacemaker wires. However, this would be difficult in the field, may permanently damage the device, and should not be performed unless as a last resort.
Temporary transvenous pacemakers may also be encountered by the EMS physician during interfacility transports. Transvenous pacemakers are placed in the hospital setting in patients with unstable bradycardic dysrhythmias unresponsive to medical therapy or transcutaneous pacing. The pacer wires are generally placed via the right internal jugular vein or the left subclavian vein and are attached to a pacing generator that generally allows for adjustment of the pacing rate, sensitivity, and energy output. Members of the transport team should be familiar with the specific pacing generator technology and how to troubleshoot it with regard to adjusting those settings. If the sensitivity is too low, the pacer may detect vibrations of transport, interpret them as R waves, and thus will not appropriately pace the patient. Consequently, if the sensitivity is set too high, it may not detect the underlying rhythm and will pace in an asynchronous mode.
Implantable cardioverter defibrillators
ICDs are a first‐line therapy for many patients at risk for sudden cardiac death (SCD). They are usually implanted in the left infraclavicular region and are typically palpable. All patients with these devices get identification cards that note the manufacturer and device model. ICDs have four main functions:1) sensing atrial and ventricular signals, 2) classification of those signals into programmable heart rate zones, 3) administration of electrical therapy to terminate ventricular tachycardia or ventricular fibrillation, and 4) pacing for bradycardia or cardiac resynchronization therapy (equivalent to a standard pacemaker) [27]. If ventricular fibrillation or ventricular tachycardia is detected, shocks of 1 to 40 joules can be delivered [27]. Although this is less energy than external defibrillation or cardioversion, the shock can still be painful to the patient.
The EMS physician will most likely encounter one of three possible scenarios with a patient who is suffering from an ICD‐related cardiac event. The first is device failure in the event of a ventricular arrhythmia. The second is an appropriately functioning device in the setting of a ventricular arrhythmia. The third possibility is the ICD delivering shocks inappropriately in the absence of a ventricular arrhythmia. The first steps in all cases are assessment of mental status, vital signs, and cardiac monitoring. If the patient has an unstable ventricular arrhythmia, and the ICD does not fire, it should be assumed the device is nonfunctional and resuscitation protocols should be followed. If external defibrillation is needed, the defibrillator pads should not be placed over the implanted device. If the patient has a ventricular rhythm and the ICD is giving appropriate shocks, care should be focused on additional treatment of the arrhythmia, as well as rapid transport to the hospital. The patient may benefit from analgesia and possibly sedation in the event of multiple shocks. External electrical therapy should not be needed.
In the third scenario, the ICD is giving inappropriate shocks in the absence of a ventricular arrhythmia. Some ICDs are programmed to simply detect an elevated rate and not specifically detect ventricular arrhythmias. Inappropriate shocks are most often induced by T‐wave oversensing in which the high amplitude T‐wave is interpreted as another QRS complex leading to double counting. This can also occur during CPR when compressions can trigger an inappropriate shock [28]. As with pacemaker malfunctions, ideally the device can be interrogated by an electrophysiologist at the receiving hospital. In the event the patient’s condition requires emergent intervention to stop inappropriate shocks, a special magnet can be placed over the device. The magnet will suspend detection of ventricular fibrillation and ventricular tachycardia and should stop the shocks. The magnet will not stop the pacemaker function of the ICD or place the pacemaker in asynchronous (fixed) mode [27]. In the event a magnet is used, cardiac monitoring is required because the ICD will no longer be able to sense nor shock arrhythmias. Magnet therapy is only effective while the magnet is secured to the skin over the device. It may also be prudent to apply external defibrillator pads during transport. As with a pacemaker, cutting the lead wires of an ICD will most likely permanently damage the device, is difficult to perform in the field, and is not recommended short of a dire last resort.
Wearable cardioverter defibrillator
While ICDs have been shown to improve survival from SCD, placement is not always feasible. Ventricular fibrillation and ventricular tachycardia are the most common arrhythmias associated with SCD. The WCD can be used as a bridge to ICD placement or a bridge for short‐term protection against SCD when cardiac recovery is expected [29].
The WCD is a vest‐type garment with an inner layer containing sensing and energy delivering electrodes in direct contact with the patient’s skin. The holster of the vest contains the monitor, battery packs, and other device contents not in contact with the patient’s skin. The convex, resin‐insulated electrodes sense the patient’s electrical activity and the processor is programmed to detect shockable ventricular arrhythmias and initiate defibrillation if appropriate. The vest alerts the patient to the activation of the shock delivery algorithm via audible alarms and through vibration signals. This gives the patient the opportunity to deactivate the process by pressing two buttons simultaneously if they are alert. If not deactivated, gel is ejected between the electrodes and patient’s skin and a shock between 75 and 150 joules is delivered. The vest contains a lithium‐ion battery pack that provides continuous power for 24 hours [29].
Some of the issues related to the success rate of WCDs in preventing SCD is patient compliance. The device should be worn at all times. It should only be removed when bathing and then only if someone is present to initiate lifesaving measures as appropriate. The device has been redesigned to make it more comfortable and lightweight. The sense of security that the WCD provides also contributes to patient compliance [29].
The trials to date have reported a 75% success rate of WCDs providing appropriate shock therapy. Like ICDs, however, the WCDs also produce inappropriate shocks when ventricular arrhythmia is not present. Although WCDs have built‐in patient response buttons to prevent inappropriate shocks, shocks are still delivered because patients forget how to deactivate the device. Patients also do not receive appropriate shocks due to incorrect positioning of the device or its electrodes [29].
When an EMS clinician encounters a WCD patient, a standard evaluation should be conducted. CPR can be performed with