Nodal tachycardia, which is the most common cause of paroxysmal supraventricular tachyarrhythmia, usually occurs at rates of 100 to 180 beats/min. Although it is usually seen in young patients who have no cardiac disease, it may occur at any age and be associated with digitalis toxicity, pulmonary embolus, myocardial infarction, rheumatic heart disease, and chronic obstructive pulmonary disease. The sequence is usually initiated by a premature atrial beat which enters the re-entry loop in the atrioventricular node, activating both atrium and ventricle ( Fig, 1). The P wave is not usually visible, and the QRS complex is identical to that occurring during normal sinus rhythm. The rhythm is also regular, which helps to differentiate it from atrial fibrillation or atrial flutter with varying atrioventricular block ( Fig..2). It is important to distinguish this rhythm from sinus tachycardia, which can be more difficult. Increasing vagal activity by carotid sinus massage may be helpful ( Table 1).
Fig. 2 Atrioventricular nodal tachycardia (rate, 130 beats/min). P waves are not visualized.
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