Heart Block Made Easy (feat Taylor Swift)

Struggling with heart block? Look no further – today we cover how to identify atrioventricular block on an ECG with the help of pop superstar Taylor Swift. Who better to teach us about broken hearts and break ups?

Heart block can be divided into three types – first, second and third degree.

First degree heart block is where the electrical impulse is delayed at the level of the AV node, leading to a longer period between atrial systole and ventricular systole. This manifests on the ECG as a prolonged PR interval – the time between the p wave and QRS complex.

A normal PR interval is between 0.12 and 0.20 seconds – or three to five small ECG squares. If there is more than one large square between the p wave and the QRS complex, first degree heart block is present.

Second degree heart block is where some of the impulses don’t make it through the AV node – not every p wave is followed by a QRS complex. It can be separated into Mobitz Type I and Type II, and 2:1 heart block. Mobitz Type I is also known as the Wenckebach rhythm.

Mobitz Type I is where there is progressive lengthening of the PR interval, before a QRS complex is dropped. By contrast, the PR interval in Mobitz Type II is stable in between the dropped beats. In 2:1 heart block, a QRS complex appears after every other p wave – only half of the impulses are being conducted.

In complete heart block, none of the impulses are making it through. However, an accessory pacemaker fires off the ventricles – this is known as an escape rhythm. The escape rhythm isn’t co-ordinated with the sinus rhythm however – there is no relationship between p waves and QRS complexes on the ECG. The ventricular rate is typically much slower than the atrial rate.

Spotting heart block is difficult, but will improve with practice. The best way to learn is to look at real life ECGs.

REFERENCES:
1. Longmore M, Wilkinson IB, Davidson EH Foulkes A, Mafi AR (2010). Cardiovascular medicine. In: Oxford Handbook of Clinical Medicine (Eight Edition). Oxford Press. pp 86 – 153
2. Ballinger A (2012). Cardiovascular disease. In: Essentials of Kumar & Clark's Clinical Medicine (Fifth Edition). Saunders Elsevier. pp 407 – 504
3. Davies JER, Nijjer S (2014). Cardiology. In: Kalra, PA. Essential Revision Notes for MRCP (Fourth Edition). PasTest. pp 1 - 64

MUSIC:
Super Cool Power Dude

All courtesy of Kevin Mcleod at Incompetech.com