Paroxysmal junctional tachycardia

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This may occur and is identical to paroxysmal supraventricular tachyarrhythmia in rate and configuration. Ventricular tachyarrhythmias Ventricular premature complexes

Ventricular premature complexes arise below the bundle of His, prematurely depolarizing the ventricular myocardium and resulting in wide complexes with no preceding P wave. These beats are usually blocked in the atrioventricular node and there is no retrograde depolarization of the atrium. The sinus node continues to fire at its normal rate, thereby resulting in a fully compensatory pause (twice the normal RR interval). This pause does not occur with atrial premature contractions and, when present, helps to establish the diagnosis of ventricular premature complex. Occasionally, however, the ventricular premature complex does penetrate the atrioventricular node in a retrograde fashion and may reset the sinus node, resulting in a pause that is less than fully compensatory. Ventricular premature complexes may be monomorphic or polymorphic, and there is usually a constant interval between the sinus complex and the ventricular premature complex. This is referred to as fixed coupling and supports the concept that most are due to re-entry. If the re-entry circuit continues, more complexes may occur with pairs known as ventricular couplets and three or more sequential ventricular premature complexes resulting in ventricular tachycardia. When every other complex is a ventricular premature complex, the pattern is known as ventricular bigeminy; with every third it is known as trigeminy, and with every fourth it is known as quadrigeminy.

Ventricular premature complexes may occur in patients without cardiac or pulmonary disease and do not need to be treated. However, the detection of frequent ventricular premature complexes in an individual may warrant a thorough cardiovascular evaluation. If myocardial infarction has occurred, the tolerance for ventricular ectopy is decreased. Other causes include digitalis toxicity, cardiomyopathy, valvular heart disease, myocarditis, congenital heart disease, long QT syndrome, hypoxemia, hypokalemia, hypomagnesemia, tricyclic antidepressants, antiarrhythmic medication, theophylline toxicity, and other drugs.

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