8/19/2019 Physiological Basis of Arrhythmias(Missing Objective We Did Not Get)

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Physiological Basis of Arrhythmias

An arrhythmia is a disorder of the heart rate (pulse) or heart rhythm, such as beating too fast(tachycardia), too slow (bradycardia), or irregularly. The rhythm of the heart is normallygenerated and regulated by pacemaker cells within the sinoatrial ( SA) node, which is located

within the wall of the right atrium. SA nodal pacemaker activity normally governs the rhythm of the atria and ventricles. Normal rhythm is very regular, with minimal cyclical fluctuation.

urthermore, atrial contraction is always followed by ventricular contraction in the normal heart.!hen this rhythm becomes irregular, too fast ( tachycardia ) or too slow ( bradycardia ), or thefre"uency of the atrial and ventricular beats are different, this is called an arrhythmia. The term#dysrhythmia# is sometimes used and has a similar meaning.

$atients may describe an arrhythmia as a palpitation or fluttering sensation in the chest. orsome types of arrhythmias, a skipped beat might be sensed because the subse"uent beat producesa more forceful contraction and a thumping sensation in the chest. A #racing# heart is another

description. $roper diagnosis of arrhythmias re"uires an electrocardiogram, which is used toevaluate the electrical activity of the heart.

%epending on the severity of the arrhythmia, patients may e&perience dyspnea (shortness of breath), syncope (fainting), fatigue, heart failure symptoms, chest pain or cardiac arrest.

What causes arrhythmias?

A fre"uent cause of arrhythmia is coronary artery disease because this condition results inmyocardial ischemia or infarction. !hen cardiac cells lack o&ygen, they become depolari'ed,which leads to altered impulse formation and or altered impulse conduction . The formerconcerns changes in rhythm that are caused by changes in the automaticity (spontaneous activity)of pacemaker cells or by abnormal generation of action potentials at sites other than the SAnode (termed ectopic foci ). Altered impulse conduction is usually associated with complete or

partial block of electrical conduction within the heart. Altered impulse conduction commonlyresults in reentry , which can lead to tachyarrhythmias. hanges in cardiac structure thataccompany heart failure (e.g., dilated or hypertrophied cardiac chambers), can also precipitatearrhythmias. inally, many different types of drugs (including antiarrhythmic drugs ) as well aselectrolyte disturbances (primarily * + and a ++) can precipitate arrhythmias.

What are the consequences of arrhythmias?

Arrhythmias can be either benign or more serious in nature depending on the hemodynamic

conse"uence of the arrhythmia and the possibility of evolving into a lethal arrhythmia.ccasional premature ventricular comple&es ($- s), while annoying to a patient, are generally

considered benign because they have little hemodynamic effect. onse"uently, $- s if not toofre"uent, are generally not treated. n contrast, ventricular tachycardia is a serious condition thatcan lead to heart failure, or evolve into ventricular fibrillation and cause death.

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8/19/2019 Physiological Basis of Arrhythmias(Missing Objective We Did Not Get)

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