Mechanisms for cardiac arrhythmias

Area of Science:

• Cardiovascular Electrophysiology
• Cardiac Arrhythmia Mechanisms

Background:

• Arrhythmias may arise from focal (abnormal impulse initiation, afterdepolarizations, reflection) or non-focal (reentry) mechanisms.
• Studies on isolated tissues suggest these mechanisms also occur in vivo.
• Direct proof for focal arrhythmia mechanisms in vivo is often lacking, unlike macro-reentry.

Purpose of the Study:

• To explore cellular electrophysiological mechanisms underlying cardiac arrhythmias.
• To highlight the need for in vivo techniques to identify arrhythmogenic foci and their mechanisms.

Main Methods:

• Analysis of electrophysiological records from isolated cardiac tissues using extracellular and intracellular electrodes.
• Discussion of potential in vivo mapping techniques.

Main Results:

• Identified focal mechanisms: abnormal automaticity, triggered activity (early/delayed afterdepolarizations), and reflection.
• Identified non-focal mechanisms: reentry (circus movement).
• Confirmed macro-reentry as a cause for some arrhythmias, but focal mechanisms remain less proven in vivo.

Conclusions:

• Cellular electrophysiology provides a basis for understanding focal and non-focal arrhythmia mechanisms.
• Development of 'on line' in situ activation sequence mapping is crucial.
• Unipolar extracellular recording may help identify specific cellular mechanisms within arrhythmogenic foci in the intact heart.