Now, there's a special kind of pacemaker called an ICD pacemaker.
It cannot only pace just like a, you know, the DDD pacemaker cuz that's what it is.
It's a DDD pacemaker but in addition, if the patient goes into a dangerous malignant arrhythmia
and we're gonna talk about those in a subsequent lecture when we talk about ventricular arrhythmias.
They're the cause of cardiac arrest, and the ICD pacemaker shocks the heart back to a normal rhythm
when a dangerous ventricular arrhythmia develops.
So, for example, fast ventricular tachycardia or ventricular fibrillation.
I'm gonna have a lot of time to spend on that when I get to the ventricular arrhythmia lecture.
But those are both malignant arrhythmias that can lead to sudden death.
And the pacing component works just like the other pacemakers described,
but the shock or defibrillation component occurs only
when the pacemaker recognizes a dangerous life-threatening arrhythmia.
And here you see them inserting - you see it's inserted in the same way.
The ICD pacemakers are larger cuz they have to carry a bigger battery
because that battery has to be able to shock a lot more than just the impulse.
The shock for causing a little impulse is tiny.
The shock for defibrillating the heart is substantially larger so it needs a bigger battery.
And here, you see it's in the same position under the skin, the wires are the same way,
the wires are a little heavier as well for the ICD pacemaker.
And here's an example. So here we see an electrocardiogram of a patient in ventricular fibrillation.
This is a cardiac arrest, so this is a regular 12 lead ECG. Notice leads I, II and III, aVR, aVL, aVF
and the precordial leads V1 through 6.
Notice that the patient is continuously in ventricular fibrillation
and if you look down at the bottom line that's a rhythm strip.
You see the patient's in ventricular fibrillation and then there's a big spike there; that's the shock.
And the beat after the shock is a paced QRS. So, the ICD successfully terminated ventricular fibrillation
and then paced the patient until the patient's own rate came - would come back normally.
All pacemakers also contain what I call - they have a little tape recorder and they store any beats that occur.
So actually, if there are arrhythmias, you can actually find that out from the pacemaker.
The pacemakers are usually checked every 3 to 6 months.
And during that time, there's a readout of what has happened in terms of electrical activity in the pacemaker.
So, any arrhythmias that occurred during that time period are identified and the physician is alerted.
For example, there could be short periods of atrial fibrillation.
When that occurs, you know, it's seen and recorded in the little pacemaker recording area.
And the - when the pacemaker is checked, they report to the doctor,
"Oh yes, we saw X number one, two, three episodes of paroxysmal atrial fib and they lasted for so and so long."