If ventricular tachycardia occurs in an Implantable Cardioverter Defibrillator (ICD) wearer, the ICD can combat this with 2 different forms of therapy, provided these are activated (which can be done using a programming device). First, the ICD attempts to override the tachycardia. The fastest pacemaker gets control of the heart. If this is not successful, the defibrillator function is used. Here you can see the limb leads. Initially there is a relatively slow ventricular tachycardia.

A sustained VT is a ventricular rhythm with a frequency of more than 100 beats per minute that usually lasts at least 30 seconds or must be terminated earlier due to hemodynamic instability.
We see here a wide complex tachycardia with a frequency of approx. 105-110 beats per minute that lasts for a good minute. It begins with a premature QRS complex without a premature P wave. The short VT after the end of the sustained ventricular tachycardia with the same QRS morphology also indicates a ventricular origin of this arrhythmia.

In this tracing, we see the limb leads + V1/V2. The first two beats are sinus node beats, there is a sinus bradycardia with approx. 55 bpm. Then there is a sinus arrest with a pause of 3000 ms, which is interrupted by a junctional escape beat. After this, the sinus bradycardia is re-established.

If a wide complex tachycardia occurs, the probability is very high that it is a ventricular tachycardia (approx. 80%, in patients with a previous myocardial infarction (...) approx. 90%). Here we see a broad complex tachycardia that looks like an RBBB + LAFB, which is regular. In this constellation, 3 causes must be considered:
1. fascicular tachycardia from the left posterior fascicle of the left tawara fascicle (QRS width usually only around 130 ms, but sometimes significantly longer).
2. AT/AFL with 2:1 conduction in the case of pre-existing bifascicular block

If ventricular tachycardia occurs in an Implantable Cardioverter Defibrillator (ICD) wearer, the ICD can combat this with 2 different forms of therapy, provided these are activated (which can be done using a programming device). First, the ICD attempts to override the tachycardia. The fastest pacemaker gets control of the heart. If this is not successful, the defibrillator function is used. Here you can see the limb leads. Initially there is a relatively slow ventricular tachycardia with a heart rate of approx. 125 bpm.

Why is this a high-grade AV block? If at least 3 P-waves are not conduced and there is normal AV conduction before and after, this can be considered a high-grade AV block. In this Holter strip, P1, P2 and all P-waves from P6 onwards are conducted, albeit with a prolonged PR interval (first-degree AV block). P3, P4, P5 are not conducted. A junctional escape beat is seen before P5. P5 can also not be conducted because the specific conduction system is still refractory at this time due to the junctional escape beat.

Furthermore, a long QT time is observed!

Atrial flutter and atrial fibrillation are two different cardiac arrhythmias, but occur frequently side by side in the same patient. Here is an example of how atrial flutter degenerataes into atrial fibrillation. The initially ordered atrial activity (left in the picture) with 2 flutter waves/1 QRS complex changes into irregular atrial activity (right in the picture) and the RR intervals become completely irregular.

Let's analyze the ECG. It comes from a pacemaker patient whose pacemaker was briefly switched to VVI at 30 bpm due to a stimulation threshold test. The first 3 beats show a sinus rhythm with a frequency of approx. 40 bpm. This is followed by a premature ventricular contraction (PVC). The P wave of the next sinus node beat lands exactly on the T of the PVC. This cannot be conducted to the ventricles, either because the ventricular myocardium is still unexcitable or the PVC has conducted retrogradely into the AV node and this is therefore still refractory.