Supraventricular Rhythms

Narrow complex tachycardias

Atrial flutter

Atrial flutter
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Atrial rate	250-350 bpm
Ventricular rate	75-150bpm (3:1 of 2:1 block)
Regularity	regular (sometimes changing block)
Origin	atrial (SVT)
P-wave	negative sawtooth in lead II
Effect of adenosine	temporary reduced AV conduction (eg 4:1)
Example ECG: The arrows mark the flutter waves. This is an example of an alternating 2:1 and 3:1 block.
Example ECG2: Atrial flutter with 2:1 conduction.

During atrial flutter the atria depolarize in an organized circular movement. This is caused by re-entry. The atria contract typically at around 300 bpm, which results in a fast sequence of p-waves in a sawtooth pattern on the ECG. For most AV-nodes this is way to fast to be able to conduct the signal to the ventricles, so typically there is a 2:1, 3:1 or 4:1 block, resulting in a ventricular frequency of 150, 100 or 75 bpm respectively. Often the grade of block changes every couple of beats, resulting in e.g. 2:1, or 3:1 blocks and a somewhat irregular ventricular heart rate. The saw-tooth is especially prominent in lead II, this lead normally shows constant electrical activity: it is never horizontal. Causes and risk of atrial flutter are comparable to atrial fibrillation.

Atrial fibrillation

Main article: Atrial Fibrillation

Atrial fibrillation
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Atrial rate	400-600 bpm
Ventricular rate	75-175 bpm
Regularity	irregular
Origin	atria (SVT)
P-wave	absebt
Effect of adenosine	reduces heart rate
Example ECG:
Example ECG2: {{{example2}}}

During atrial fibrillation the atria show chaotic depolarisation with multiple foci. Mechanically the atria stop contracting after several days to weeks of atrial fibrillation, the result of the ultra-rapid depolarisations that occur in the atria, typically around 400 bpm, but up to 600 bpm. At the AV node 'every now and then' a beat is conducted to the ventricles, resulting in an irregular ventricular rate, which is the typical ECG characteristic of atrial fibrillation. Sometimes atrial fibrillation results in a course atrial flutter wave on the ECG, but the baseline can also be flat. A flat baseline is more often seen in long standing atrial fibrillation. The cardiac stroke volume is reduced by 10-20% during atrial fibrillation, as the 'atrial kick' is missing and because the heart does not have time to fill at the often higher ventricular rate. Causes; age (+- 10% of 70+ year olds and 15% of 90+ year olds have AFIB [1]), ischemia, hyperthyreoidism, alcohol abuse. Risc: thrombo-embolisation of thrombi that form in the atrial caverns as a result of the reduced atrial motion. These thrombi can emblise to the brain and cause strokes.

Atrial flutter can be catechorized as follows:

First documented episode:
Recurrent atrial fibrillation: after two or more episodes.
Paroxysmal atrial fibrillation: if recurrent atrial fibrillation spontaneously converts to sinus rhythm.
Persisting atrial fibrillation: if an episode of atrial fibrillation persists more than 7 days.
Permanent atrial fibrillation: if atrial fibrillation persists after an effort of electrical or chemical cardioversion

Lone AF is atrial fibrillation in patients younger than 60 years in whom no clinical or electrocardiographic signs of heart or lung disease are present. These patiens have a favourable prognosis regarding thrombo-embolic events.

Non-valvular atrial fibrillation is atrial fibrillation in patients without heart valve disease or heart valve replacement or repair. [2]

Atrial Tachycardia

Atrial tachcyardia is a more or less regular heart rate > 100 bpm that does not origin from the sinus node. The p-waves therefore have a different configuration and easily be recognized if the are negative in AVF.

AVNRT

AV Nodal Re-entry Tachycardia (AVNRT)
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Atrial rate	180-250 bpm
Ventricular rate	180-250 bpm
Regularity	regular
Origin	AV node
P-wave	inside or right after the QRS complex
Effect of adenosine	terminates the arrhythmia(!)
Example ECG: The first part of this example shows AVNRT. After injection of adenosine, the arrhythmia terminates.
Example ECG2:

An AV Nodal Re-entry Tachycardia (AVNRT) is a rapid tachycardia with a typical frequency around 200 bpm. The tachycardia origin is the AV node. A prerequisite for AVNRT is a slow and fast pathway in the AV node, most often caused by degradation of the AV nodular tissue. The dual pathways facilitate re-entry.

Two sensitive characteristics to identify AVNRT on the ECG are:

R'. This is a small secondary R wave. It resembles a right bundel branch block, but the QRS width stays < 120ms.
RP << 100ms. The distance between the R and P waves is less than 100ms.

Atrio-ventricular Reentry Tachycardia AVRT

Atrio-ventricular Re-entry Tachycardias are somewhat similar to AVNRT. An important diffence however is that an accessory bundle is present in AVRT. This accessory bundle connects the atria and ventricles, thereby bypassing the AV node. The most common type of accessory bundle is a bundle of Kent. AVRTs can result from abnormal retrograde conduction (from ventricles to the atria) and anterorade conduction (from atria to ventricles). This results in two type of circular tachycardias:

Orthodrome AV Re-entry Tachcardia (conduction retrogarde through the accessory bundle). Usually a narrow QRS complex preceded by a p-wave.
Antidrome Atrioventricular Re-entry Tachcardia (anterogarde conduction through the abnormal accessory bundle). The ECG shows wide QRS complexes followed by retrograde P-waves. The RP-time is >> 100ms.
Concealed Bypass Tract

AV junctional tachycardia

AV junctional tachycardia / Junctional Ectopic Tachycardia (JET)
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Atrial rate	60-100 bpm
Ventricular rate	70-130 bpm
Regularity	regular
Origin	AV node
P-wave	RP > RP
Effect of adenosine	slows down heartrate
Example ECG: Lead II shows competition between the sinus rate and the nodal tachycardia. After around the third beat, some sinus beats are conducted and followed by QRS complexes. Thereafter the nodal tachycardia takes over resulting in a negative p-wave around the 8th beat, the proof of a junctional rhythm.
Example ECG2: {{{example2}}}