Basic Concepts about Rhythm and Conduction

Rhythm and conduction disorders are commonly encountered abnormalities with interpreting ECGs. 

The Rhythm and Conduction section of the website:

• serves as a comprehensive collection of diverse rhythms and conduction anomalies, grouped into major anatomical or functional categories. 

• examines the pathobiology underlying the disorders and discuss how that relates to their respective ECG manifestations.

• explores the standard ECG presentations of these disorders, as well as any variations or deviations from the norm, with many examples.

• describes useful ways to identify these conditions in a clinical setting and tell them apart, giving valuable and practical tips.

• offers a list of possible differential diagnoses for many of the disorders to help with thorough interpretation.

This section will cover the Basic Concepts necessary to better understand arrhythmias and conduction disorders covered in this section. Such concepts include:

• Understanding how cardiac tissue normally tends to depolarize, and how specialized conduction fibres can speed up or bias those depolarization wavefronts in a specific direction.

• Understanding normal automaticity in the heart, and phenomena that can happen as a result of subsidiary or ectopic pacemakers, such as: overdrive suppression, escape rhythms, capture, displacement/resetting, and more.

• Understanding how the heart normally repolarizes, and an introduction to the concept that abnormal depolarization tends to cause abnormal depolarization, accounting for the appropriate discordance seen in wide-complex rhythms.

• An introduction to blocks as interruptions or delays in the normal conduction of the heart, which can manifest in different ways (i.e. exit blocks, entrance blocks, unidirectional blocks, etc.). We will discuss how the AV node exhibits a physiologic block as a protective mechanism. We discuss the grading of blocks, from first to third degree, and then delve into a concept known as concealed conduction, which can simulate different types of blocks.

• An introduction to the mechanisms of arrhythmogenesis, including increased automaticity, triggered activity, and re-entry. We touch on more nuanced details, such as the warm up and cool down phenomena, and phase 2 reentry.

• An introduction to laddergrams, which are graphical representations of rhythms that can enhance your comprehension of otherwise complicated concepts.