-IBIS-1.5.0-
tx
cardiovascular system
arrhythmia
diagnoses

definition and etiology

definition:
Abnormal heart rhythm. Normal sinus rhythm originates within the pacemaker cells of the sinoatrial (SA) node at the junction of the superior vena cava and high right atrium. These cells represent the primary electrical generator (pacemaker) for the normal human heart. The impulse generated here travels to the atrioventricular (AV) node, thence to the rest of the myocardium. Conduction of impulses is a complicated series of events; all of the conductive tissues and nodes of the heart contain cells capable of spontaneous depolarization. Cardiac arrhythmias generally represent other tissues assuming the role of pacemaker. There are often complications.

etiology:
Arrhythmias can be the result of damaged conductive tissue in the heart being placed under stress. Causes of arrhythmias are diverse, and include coronary artery disease, hypertension, drug reactions, endocrine abnormalities, myocardial disease, rheumatic fever, metabolic derangements etc. The type of arrhythmia may point to a particular cause.

signs and symptoms

may include:
• sensation of heart irregularity, skipping, extra beats
• associated dyspnea, anxiety, or other symptoms associated with cardiac insufficiency
• changes in pulse rhythm, rate, heart sounds
• symptoms and signs associated with underlying condition

lab findings:
abnormal EKG is generally definitive, and provides the initial differential

course and prognosis

depends upon the type of arrhythmia; some are normal, some are benign, some are medical emergencies

differential diagnosis

• sinus bradycardia (rate of < 60 bpm)
• sinus tachycardia (rate of > 100 bpm in adult, often from decreased vagal tone)
• sinus arrhythmia (heart rate changes cyclically and regularly, usually increasing on inspiration and decreasing on expiration; normal finding, most common in the young)
• sick sinus syndrome (inadequate sinus node function most commonly associated with cerebral manifestations of lightheadedness, dizziness, and syncope)
• premature depolarization:
» of the atria: sensation of a "skipped beat" or flutter
» of the ventricles: similar sensation; often seen in cardiac failure
• paroxysmal supraventricular tachycardia (heart rate races to 100-200 bpm with 1:1 A-V conduction maintained)
• atrial flutter (continuous electrical activity produces an atrial rate between 240-400 or about 300 bpm)
• atrial fibrillation (continuous and chaotic re-entry of electrical impulses within the atrial myocardium)
• multifocal atrial tachycardia (multiple areas of enhanced automaticity within ordinary atrial myocardium)
• His bundle rhythms (enhanced bundle rhythms)
• ventricular tachycardia (100-200 bpm; succession of premature ventricular contractions; usually associated with arteriosclerotic heart disease, but can occur in many conditions)
• ventricular fibrillation (irregular and chaotic ventricular arrhythmia with a rapid rate and disorganized spread of impulses throughout the ventricular myocardium; ventricular systole becomes an uncoordinated event; mechanical activity cannot occur and cardiac output falls to zero; fatal if not terminated immediately; associated with acute myocardial infarction)
• heart block (spread of cardiac electrical excitation is slowed or interrupted in a portion of the normal conduction pathway)
• ventricular pre-excitation ( a form of accelerated A-V conduction, resulting from two A-V conduction pathways)


footnotes