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INTRODUCTION

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  • Arrhythmia is loss of cardiac rhythm, especially irregularity of heartbeat.

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PATHOPHYSIOLOGY

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SUPRAVENTRICULAR ARRHYTHMIAS

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  • Common supraventricular tachycardias requiring drug treatment are atrial fibrillation (AF), atrial flutter, and paroxysmal supraventricular tachycardia (PSVT). Other arrhythmias that usually do not require drug therapy are not discussed here (eg, premature atrial complexes, sinus arrhythmia, and sinus tachycardia).

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Atrial Fibrillation and Atrial Flutter
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  • AF has extremely rapid (400–600 atrial beats/min) and disorganized atrial activation. There is loss of atrial contraction (atrial kick), and supraventricular impulses penetrate the atrioventricular (AV) conduction system to variable degrees, resulting in irregular ventricular activation and irregularly irregular pulse (120–180 beats/min).

  • Atrial flutter has rapid (270–330 atrial beats/min) but regular atrial activation. Ventricular response usually has a regular pattern and a pulse of 300 beats/min. This arrhythmia occurs less frequently than AF but has similar precipitating factors, consequences, and drug therapy.

  • The predominant mechanism of AF and atrial flutter is reentry, which is usually associated with organic heart disease that causes left atrial distention (eg, ischemia or infarction, hypertensive heart disease, and valvular disorders). Additional associated disorders include acute pulmonary embolus and chronic lung disease, resulting in pulmonary hypertension and cor pulmonale, and states of high adrenergic tone such as thyrotoxicosis, alcohol withdrawal, sepsis, and excessive physical exertion.

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Paroxysmal Supraventricular Tachycardia Caused by Reentry
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  • PSVT arising by reentrant mechanisms includes arrhythmias caused by AV nodal reentry, AV reentry incorporating an anomalous AV pathway, sinoatrial (SA) nodal reentry, and intraatrial reentry.

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VENTRICULAR ARRHYTHMIAS

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Premature Ventricular Complexes
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  • Premature ventricular complexes (PVCs) can occur in patients with or without heart disease.

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Ventricular Tachycardia
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  • Ventricular tachycardia (VT) is defined by three or more repetitive PVCs occurring at a rate greater than 100 beats/min. It is a wide QRS tachycardia that may result acutely from severe electrolyte abnormalities (hypokalemia or hypomagnesemia), hypoxia, drug toxicity (eg, digoxin), or (most commonly) during an acute myocardial infarction (MI) or ischemia complicated by heart failure (HF). The chronic recurrent form is almost always associated with organic heart disease (eg, idiopathic dilated cardiomyopathy or remote MI with left ventricular [LV] aneurysm).

  • Sustained VT is that which requires intervention to restore a stable rhythm or persists a relatively long time (usually >30 s). Nonsustained VT self-terminates after a brief duration (usually <30 s). Incessant VT refers to VT occurring more frequently than sinus rhythm, so that VT becomes the dominant rhythm. Monomorphic VT has a consistent QRS configuration, whereas polymorphic VT has varying QRS complexes. TdP is a polymorphic VT in which the QRS complexes appear to undulate around a central axis.

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Ventricular Proarrhythmia
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  • Proarrhythmia refers to the development of a significant new arrhythmia, such as VT, ventricular fibrillation (VF), or TdP, or worsening of an existing ...

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