1.
Arrhythmias are usually divided into those that occur in the ventricles and those that occur in the atrium, above the ventricles, also called “supra-ventricular”.

2.
The major supra-ventricular arrhythmias are:
1. Atrial extra-systole
2. Atrial flutter
3. Atrial tachycardia
4. AV-nodal tachycardia
5. Atrial fibrillation
(see previous page).

3.
The major ventricular arrhythmias are:
a. Ventricular extra-systole
b. Ventricular tachycardia
c. Ventricular fibrillation.

4.
There are a few arrhythmias that do not fit into one of these two groups. The most famous one is the WPW syndrome (=Wolf-Parkinson-White).

5.
Also the duration of the arrhythmia is important.

6.
There are three types:
- Paroxysmal: lasts for seconds to a few hours
- Persistent: lasts for days to weeks
- Chronic: lasts months to years.

1.
In this disease, the impulse has difficulty in propagating from the atria, through the AV-node, into the ventricles.

2.
Based on the behaviour of the heart, there are three types of AV-block:

3. First degree AV-block:
This is not really a block but the impulse takes longer than normal to propagate through the AV-node. This is visible on the ECG by a longer PQ-interval.

4. Second degree AV-block:
In this situation, some impulses propagate through the AV-node and some do not. The ratio between those that pass and those that do not pass can be expressed; for example 1:3 second degree AV-block (as in this case).

5. Third degree AV-block:
In this case, there is total block between the atrium and the ventricles. The atrium will continue to function as before, visible by the P waves.

6.
The ventricles will also produce impulses (from the Purkinje system) but at a lower rate than the atrium. Furthermore, there is no relationship any more between the atrial activity (and contraction) and that of the ventricles.

1.
As with the atrial extra systole, the ventricular extra systole is an “extra” beat.

2.
But this time, the extra beat starts somewhere in the ventricles and not in the atria.

1.
A ventricular tachycardia is usually caused by an ectopic focus that induces many impulses at a rapid rate.

2.
This repetitive focus can be located anywhere in the right or left ventricle.

1.
In ventricular fibrillation, there are multiple re-entrant propagations simultaneously present, in the right and in the left ventricles.

2.
Therefore, some parts of the ventricles are constantly excited while others are recovering. All these excited and recovering areas shift all the time throughout the muscle.

1.
In the Wolf-Parkinson-White syndrome, the AV-bundle is not the only connection between the atria and the ventricles.

2.
In this situation, there are other muscle fibres that connect the atria to the ventricles. These fibres are often named as the bundle of Kent (after the first discoverer).

6.
In addition, because this earlier activation is propagating more slowly through the ventricle than through the Purkinje system, the delta wave is a slow wave on the ECG.

7.
However, the impulse also propagates through the AV-node and, after this delay, is conducted rapidly through the Purkinje system. This conduction is much faster than the impulse through the Kent bundle. Therefore the major and second part of the QRS shows a normal configuration

1.
Patients who suffer from the presence of such an abnormal AV-bundle often complain of sudden (paroxysmal) palpitations.

2.
In that situation, the heart is beating much faster than normal. This is therefore a tachycardia.

5.
This abnormal rhythm is often called a “reciprocating rhythm” because the impulse is continuously “reciprocating” or travelling between the atria and the ventricles.

6.
For the ECG, it looks very much like a ventricular tachycardia.

7.
This rhythm is uncomfortable for the patient but does not kill. However, there is now another situation possible that will certainly kill the patient.

8.
If for some reason the atria fibrillate then the situation becomes very dangerous. Then, all the impulses can propagate through the bundle of Kent to the ventricles. All these impulses will then make the ventricles fibrillate, which will immediately kill the patient. This is a typical example of “sudden death”.

9.
Note that this does not happen in a normal heart. There, if the atria fibrillate, most impulses from the fibrillating atria will not reach the ventricles as they are delayed and blocked by the AV-node.

10.
Therefore, in the normal heart, the AV-node protects the ventricles. But in WPW patients, their ventricles are not protected due to the presence of the abnormal AV-bundles.