Ineffective or inappropriate ICD shocks – Part 1

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.

(For additional reading I recommend Are ICDs overused? by John Mandrola, M.D. @DrJohnM).

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.

Vital signs

  • RR: 18
  • HR: 100 and irregular
  • NIBP: 139/79
  • SpO2: 98% on room air

The cardiac monitor is attached.

We see a borderline wide complex tachycardia at a rate of 100 (presumed paced) with a rhythm change at the end of the strip.

A 12 lead ECG is acquired.

The 12 lead ECG shows a paced rhythm with concordant ST segment depression in leads V4 and V5 although we need to remember that ICD shocks can cause transient ST/T wave abnormalities.

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.

It shows a vertical takeoff that goes straight off the paper and comes back down to baseline after about 200 ms (also generally associated with a Yelp! in a conscious patient).

Here’s the post-shock rhythm.

How would you proceed?

See also:

Inappropriate or ineffective ICD shocks Part 1

Inappropriate or ineffective ICD shocks Part 2

Inappropriate or ineffective ICD shocks Part 3

Updated 12/13/2015


  • SoCal Medic says:

    Is the Pacemaker a Demand or Non-Demand Device? What were the physical findings regarding the patient? Skins signs? Edema? Do we know the reason or underlying rhythm the patient had that warranted the device?

  • Tom B says:

    Christopher – We know that it’s a demand pacemaker because it inhibits itself when the competing rhythm shows up.I’m afraid I don’t know any details about the physical exam, but let us assume for the sake of discussion that he’s conscious and hemodynamically stable during the ICD shocks.Let us also assume that he received the device for congestive heart failure and low ejection fractions.Tom

  • SoCal Medic says:

    Part of me says treat heart intitiated rhythm that is causing the shocks chemically, but… Wow.. this one is a pain to figure out. Going through it Tom, and by all means correct me if I am wrong, but in the 12 Lead missing V2, I dont see any axis deviation of significant value (still new at that) in the heart intiated complexes, and I am seeing a P Wave in V5,V6 possibly not related to the QRS Complex, at least not continuously, because of the irregular PR interval, so I think he got the Pacer because he was going into a block affecting is ventricular rate, hence the CHF. We do see a PVC so we know the ventricle is irritated, possibly from the shock.However from the strips capture, it looks like the wide non-paced QRS complex, does not appear to be related to what I think are PWaves in Lead 2 of the strip, again because of the irregular PR Interval, which at that rate, would present a wide complex tachycardia until proven otherwise. Before doing anything (other than oxygen, iv, defib pads), I would call a base and talk to a physician before I do something that may “stablize” the patient terminally. But with the pacer firing fast, potentially the heart doing the same itself when it wants to, I would try Overdrive Pacing after looking through everything, and run a lot of 12 Leads to see if that Concordant T Waves changed, or multiplied. If I was really, close to the hospital, I would run and let the physician see him. Am I close, or really far off?

  • Shaggy says:

    Well, I think the first thing to do is determine if the post shock rythm is recurrent or refractory v-tach. I admit I am having difficulty with it as there seems to be a change in morphology in the rythm, at least the amplitude of the complexes. Yet, it still looks like a paced rythm and the rate is not that fast.Though the patient is stable, recurrent shocks are painful, if not, very uncomfortable and can cause anxiety. One shock causes anxiety, prompting unnecessary calls to 911, the ED or their cardiologist late at night, imagine the anxiety of multiple shocks. I can only imagine the detrimental physiological effects on the heart muscle and/or it’s conduction system these shocks give. So my concern would be if I do suspect a ventricular arrythmia, I would consider amiodarone. Since I am not sure, I may consult medical command, and even send a strip, but I am inclined to believe it is not V-tach.Either way, the patient needs sedated with a benzo. Though almost all the recalled devices have been replaced, I do know that there are times the leads come loose or break, prompting another trip to the EP lab. I heard there is some kind of device that can be used if this is the case that you can apply externally until the patient gets in the EP lab to prevent further shocks, but I am not sure about that.Feel free to bash me about my indecisiveness about the post shock rythm. Again, I think it is just a paced rythm, but I am not an EKG guru.

  • Shaggy says:

    I used to pre and post EP lab patients when I worked Same Day, but the cath lab holding area took over that task and I moved on anyway. What I meant about the leads is sometimes they can cause the devise to recurrently misfire. That is uncommon though, I believe.

  • Tom B says:

    Shaggy – The device in question is a ring magnet. If a device-specific programmer is not available (as it surely would not be in the back of an ambulance or even in the ED) most ICDs will inhibit antitachydysrhythmia functions with application of the magnet. This should not affect antibradycardia therapies (i.e., pacing).Tom

  • Anonymous says:

    Ring magnet to disable the ICD, amiodarone for the wide-complex tachycardia and apply pads to prepare for synchronised cardioversion.

  • Tom B says:

    Anonymous – That's pretty much what ended up happening in the ED! Tom

  • Mike says:

    We’ve got ring magnets in the back of ours haha…haven’t used it!

  • Julie P says:

    I was transporting a pt. on a transfer who had presented himself to the ER because his ICD had fired at home. He was stable in the ER without anymore firing. Before we were even out of town, his ICD fired 5 times for a total of 7 times (accompanied by a lot of cussing and screaming) before we made it back to the ER. The ER staff decided it would be better to fly him.

  • Ricky says:

    I have a question as to why the monitoring strips are leads I,!!, !!!, when it has been determined many years ago by Dr. Marriott that the preferred monitoring lead is never lead II…. It should be lead MCLI or V1 lead if possible.  It would make that diagnosis of a nonspecific intraventricular block nonspecific.

  • Paul says:

    Agree with Ricky. Leads I, II, and III are unhelpful. I set my 3 channels on the monitor up for V1, V6, and AVL. Then I have a whole world of information. It also appears in at least 1 of the later strips that pacing is being sensed when there is in fact no ventricular pacing present. Due to the morphologies on these strips(particularly the later ones), part of the apparently problem is oversensing and double counting the rate, because no ICD is set to fire at a HR of 120-ish. Another strong possibility is dislodgement of one of the cardioversion wires from the ventricle. This was a serious problem that resulted in a class action suit due to the number of ICD patients with frayed/broken/dislodged cardioversion wires that resulted in a large number of inappropriate shocks either from artifact from the frayed/dislodged sensing wire, or lethal tachyarrhythmias caused by these frayed/dislodged wires free-floating around in the ventricle, and making the myocardium irritable. Something to consider, as most people don’t heed recalls or don’t want to participate in a class action suit.

    • Gwen says:

      Pt looks like he’s getting shocked for atrial tach. Treat with Adenosine and turn on the atrial tach response on the ICD which will mode switch to DDI mode.

9 Trackbacks

Leave a Reply

Your email address will not be published. Required fields are marked *