Palpitations
last authored:
last reviewed:
Introduction
Arrhythmias are disruptions normal electrical rhythm of the heart, resulting from alterations in impulse formation, conduction, or both. Arrhythmias may arise from altered impulse at the SA node, the AV node, Purkinje fibres, or regions of cardiac muscle.
Arrhythmias can be transient or permanent. They are often caused by damage to the heart, as can follow ischemia and acute coronary syndromes. Drug toxicity, electrolyte imbalance, or infection can also cause arrhythmias, while congenital causes are also possible.
Arrhythmias can be normal. Sinus arrhythmia is a phasic change with respiration. It is seen in most children. Sinus tachycardia is seen during exercise or times of stress. Premature atrial contractions (PACs) can be normal or caused by electrolyte imbalance, hyperthyroidism, surgery, or digoxin toxicity.
The Case of...
Differential Diagnosis
History and Physical Exam
- history
- physical exam
History
Physical Exam
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Diagnostic Imaging
Management
Pathophysiology
Escape Rhythms
If the SA node becomes suppressed and fires less frequently than normal, latent pacemakers can escape overdrive suppression and initiate an escape beat. This can occur durng very strong parasympathetic activity.
Ectopic Rhythms
If an area of tissue develops an intrinsic rate of firing faster than that of the SA node, ectopic (premature) beats can occur. They can occur due to high catecholamine concentrations, hypoxemia, ischemia, electrolyte disturbances, and drugs such as digitalis.
Abnormal Automaticity
Injured cardiomyocytes can acquire automaticity and spontaneously depolarize, though means not fully understood, but is likely due to slow calcium current.
Triggered Activity
Under certain conditions, action potentials can trigger abnormal depolarizations that result in extra heart beats or rapid arrhythmias. Afterdepolarizations appear as oscillations and can be early, during repolarization, or delayed. Early afterdepoloarizations are most common during conditions that prolong APs, such as long GT syndrome.
Conduction Blocks
Conduction blocks can be transient or permanent, and can be unidirectional or bidirectional. They typically cause bradyarrhythmias. Various conditions can cause conduction block, including ischemia, fibrosis, inflammation, and certain drugs.
Reentry
Reentry occurs when impulses circuluate around a unidirectional conduction block, recurrently depolarizing a region of cardiac tissue. This can lead to tachyarrhythmias. Reentry around distinct anatomic pathways usually appears as monomorphic tachycardia on an ECG, while fibrillation is likely caused by multiple circulation reentry wave fronts.
The Case of...
Additional Resources
Topic Development
created: DLP, Aug 09
authors: DLP, Aug 09
editors:
reviewers:
 |