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[Pathophysiology of cardiac arrhythmias]
1Physiologisches Institut der Universität Freiburg.
Insights
Cardiac arrhythmias stem from issues with impulse formation or conduction. Understanding these mechanisms, including cellular changes and re-entry pathways, is key to diagnosing and treating irregular heart rhythms.
Area of Science:
- Cardiology
- Electrophysiology
- Molecular Biology
Context:
- Cardiac arrhythmias present ambiguous symptoms with limited direct ECG insights.
- Both intracardiac and extracardiac factors contribute to arrhythmias.
- Distinguishing between impulse formation and conduction disturbances is crucial.
Purpose:
- To elucidate the pathophysiological mechanisms underlying bradycardic and tachycardic arrhythmias.
- To detail the cellular and molecular basis of altered impulse formation and conduction.
- To highlight factors influencing cardiac electrical activity, including electrolytes, metabolites, and drugs.
Summary:
- Arrhythmias arise from disturbances in impulse formation (automaticity, triggered activity) or conduction (re-entry).
- Tachycardias involve enhanced pacemaker firing, abnormal automaticity, triggered activity, or re-entry.
- Bradycardias primarily relate to sino-atrial node dysfunction or conduction blocks.
Impact:
- Provides a foundational understanding of arrhythmia generation.
- Informs diagnostic strategies by clarifying ECG limitations.
- Offers insights into cellular mechanisms, aiding therapeutic development for irregular heart rhythms.
Abstract:
Cardiac arrhythmias are ambiguous symptoms. Intracardiac as well as extracardiac alterations may be responsible. There is little direct information from the ECG concerning their pathophysiological mechanism. Bradycardic as well as tachycardic arrhythmias can be the result of two different fundamental disturbances: alterations of impulse formation (automaticity) or alterations of impulse conduction. Either one of these, or both of them acting together, may be responsible for the arrhythmia. Tachycardias due to disturbances of impulse formation may be brought about by enhanced firing of regular pacemakers (sino-atrial node, av-node, ventricular conduction system), by abnormal automaticity occurring in ordinary atrial or ventricular myocardium, or by triggered activity due to early or delayed afterdepolarizations. Bradycardic disturbances of impulse formation are primarily concerned with sino-atrial nodal function. Bradycardic conduction disturbances mainly impair sinoatrial or atrioventricular propagation causing partial or total conduction block. Tachyarrhythmias due to disturbances of conduction are generated by re-entry of excitatory waves either along anatomically preformed pathways or around functional obstacles (refractory zones) with excitable gaps being more or less pronounced. On the cellular level, altered activities of ionic channels or transport systems play a significant part. Such changes are caused by: alterations of electrolyte composition (potassium, sodium, calcium), acidosis or alkalosis, autonomic and hormonal influences, membrane active metabolites (long-chain acylcarnitine, lysophosphatidylcholine), drugs (class I and III antiarrhythmics, cardiac glycosides) and poisons. In disturbances of conduction other aspects like geometry of pathways or cable properties (anisotropic conduction, coupling resistances between cells) are of particular significance.(ABSTRACT TRUNCATED AT 250 WORDS)