Identifying Arrhythmias (Part-2)

Tachyarrhythmia:

Broadly Tachyarrhythmias are classified based on their origin into two main types.

• SUPRA VENTRICULAR
• VENTRICULAR

Supraventricular Tachyarrhythmia:

As the name implies, the impulse originates above the level of AV node.

Sinus Tachycardia:

HR more than 100 with upright P wave followed by QRS complex is termed as Sinus Tachycardia. It has a variety of causes and the most probable cause of  each case should be identified.

Atrial Fibrillation:

Absent P wave with an irregularly irregular rhythm may indicate Atrial fibrillation.

The more specific term is Atrial fibrillation with rapid ventricular response when the HR is more than 100. When the patient is connected to an ECG monitor, You will find the heart rate fluctuating to a wide range from 100-160.

Atrial Flutter:

Atrial flutter can be easily identified on an ECG from the presence of Flutter waves which gives a saw tooth appearance. The baseline could not be identified.

PSVT:

When the term Paroxysmal Supraventricular Tachycardia or simply SVT is used, It usually indicates AV nodal re-entry tachycardia, a type of SVT.

• HR is usually more than 140bpm
• P wave could not be delineated as it merges with the QRS complex
• QRS complex is narrow (less than 3 small boxes)
• T wave is normal

Wolff-Parkinson-White Syndrome:

The main difference between PSVT and WPW is that the impulse re-enters the atrium through the AV node in case of SVT, whereas in WPW syndrome, it re-enters through a special accessory pathway called "Bundle of Kent". It may lead to Atrial fibrillation, other tachyarrhythmias and cause sudden death and is best diagnosed when in sinus rhythm.

• PR interval less than 120ms (3 small boxes) 
• Delta wave i.e slurring of  initial QRS 
• The above two points indicate that impulse is reaching the ventricle earlier than expected.
• Wide QRS complex more than 120ms (3 small boxes) 

Delta Wave-Slurring initial QRS

What makes WPW syndrome more dangerous is that, In other SVT's the AV node slows down the impulse reaching from the atrium significantly before conducting it to the ventricles. But the presence of accessory bundle in WPW results in bypass of the AV node, and all the impulses reaching the ventricles. For example, If the atrial rate is 300 in case of Atrial fibrillation, all these 300 impulses are transmitted to the ventricles which may result in fatal arrhythmias like VT, Vfib, cardiac failure and death. 

WPW with Paroxysmal Tachycardia

Ventricular Tachyarrhythmia:

As the name implies, the impulse originates from the ventricle i.e, below the level of AV node.

Ventricular Tachycardia:

This is a instant diagnosis, as the pattern will be so obvious for a diagnosis of VT. It is characterised by

• HR more than 100
• Very broad QRS, more than 160ms
• P wave could not be delineated due to Atrio-ventricular dissociation, i.e atrium and ventricle beats independent of each other and so P wave may be embedded within the broad QRS.
• Fusion beat may be seen when the sinus and ventricular beat coincide to form a hybrid complex

• The SA node may at times succeed, capture the ventricle and result in a normal beat called the capture beat.

Based on the duration, It is classified into

• Sustained- Lasting for more than 30 secs.
• Non-Sustained- Lasting for less than 30 secs 

Based on the morphology, It is classified into 

• Monomorphic VT
• Polymorphic VT

Differentiating between VT and SVT with broad complex may be difficult at times.

When in doubt, treat as VT.

Monomorphic VT:

Here the impulse originates from a particular focus in the ventricle. It has a regular rhythm and all the QRS in a particular lead looks uniform.

Polymorphic VT:

Here the impulse originates from many foci in the ventricle and hence each QRS has variable amplitude, axis and duration.

Torsades de Pointes:

This is a type of polymorphic VT that may occur in cases with prolonged QT interval. The ECG appears to be twisting around the baseline i.e, positive beats gradually alternate with negative beats.

Ventricular Fibrillation:

This is one of the important cardiac arrest rhythm which is invariably fatal if ACLS is not instituted immediately and shock is delivered. The ventricles are not contracting, but quivering like a bag of worms, with essentially no cardiac output. It should be readily identified just by looking at the monitor and go for the paddles immediately. The findings are

• Irregular fibrillatory waves
• No identifiable waves P, QRS, T
• No pulse is felt.

Hope I've given some basic insight into identifying some common arrhythmias. Remember "Expertise comes with Practice". Try reading every ECG you get your hands on..Keep Medizening!!!

Dr.Praful JK, MBBS.