Implantable Cardioverter Defibrillators (ICDs)
Once upon a time, to receive an implantable defibrillator required that you survive not one, but two episodes of sudden cardiac death. You had to have ventricular arrhythmias refractory to drug therapy, and you had to be strong enough to undergo a thoracotomy.
It’s astonishing that anyone qualified for the device!
Since then, the technology has come a long way. The device has been miniaturized, allowing a transvenous approach. The devices are also now highly programmable, and usually integrated with a pacemaker.
Thanks to a series of clinical trials (MADIT II, DEFINITE, SCD-HeFT) the number of patients for whom the device is indicated has grown significantly although some of the evidence suggests that ICDs are over-utilized in some sets of patients and under-utilized in others.
If you have Class II or Class III heart failure and impaired left ventricular function there’s a good chance you qualify for an ICD assuming you are able to give consent, have not experienced a recent heart attack, and are not a candidate for revascularization.
This means that paramedics are seeing more of these devices in the field. It also means that more of our heart failure patients are going to contact 9-1-1 when they get shocked inappropriately, a problem that is being addressed with smarter programming (registration required to read Medscape article).
We also may be called to a patient with an ICD who presents with a wide complex tachycardia with a rate too slow to trigger the device’s tachy therapy because the patient takes oral antiarrhythmics. For many, the diagnosis of VT seems less straight forward when the heart rate is in the 130s or 140s.
Here’s a case to illustrate the difficulty in managing these patients.
A 70 year old male contacts 9-1-1 after being shocked by his ICD several times.
EMS arrives on the scene and assesses the patient.
- RR: 18
- HR: 100 and irregular
- NIBP: 139/79
- SpO2: 98% on room air
The cardiac monitor is attached.
A 12 lead ECG is acquired.
This patient was shocked at least 12 more times while he was with EMS. If you don’t think this is traumatizing look at this video that shows climate scientist Henrik Svensmark getting shocked by his ICD at a conference in Copenhagen.
When I asked the treating paramedic if he captured a rhythm strip of the patient being shocked (so we could determine whether or not the device was malfunctioning) the first thing he showed me was the second 12 lead ECG.
What we see in this 12 lead ECG is a loose electrode in the V2 position. Had this been an actual ICD shock, leads V1 and V3 would also have been affected. Also, the duration of the shock would have shorter.
However, the paramedic in question did document a few ICD shocks because he wisely pressed the print button and left the printer running.
Here’s a rhythm strip of the ICD firing.
Here’s the post-shock rhythm.
Inappropriate or ineffective ICD shocks Part 1