Ectopic Atrial Rhythm Ectopic Atrial Rhythm In children and young adults, sinus arrhythmia (sinus rates that vary by more than 10% during 10 seconds) due to respiration is frequently observed. During sleep, when parasympathetic tone is high, sinus bradycardia (sinus rates 100 bpm) is common. The normal sinus rate is usually between 60 and 100 bpm but can vary significantly. In lead V I, the P wave is usually biphasic with a small initial positive deflection due to right atrial activation and a terminal negative deflection due to left atrial activation. Because the sinus node is located at the junction of the superior vena cava and the right atrium, in sinus rhythm the atria are activated from “right to left” and “high to low.” The P wave in sinus rhythm is upright in lead II and inverted in lead aVR. The sinus node is the primary pacemaker for the heart. Using the categorization above, refer to Tables 7–1 and 7–2 to select a specific diagnosis for the cardiac rhythm. What is the “rhythmicity” of the QRS complexes (defined as the spacing between QRS complexes)? Regular or irregular? (Any change in the spacing of the R-R intervals defines an irregular rhythm.).Is the duration of the dominant QRS morphology narrow (Fast heart rates have fewer than three large boxes between QRS complexes. What is the mean rate of the QRS complexes? Slow (100 bpm): If there are ≥ 17 complexes in a 10-second period, the rate is fast.This method proceeds in three steps that lead to a diagnosis based on the most likely rhythm producing a particular pattern: A rhythm is defined as three or more successive P waves or QRS complexes.Ĭategorize the patterns seen in the tracing according to a systematic method. Most electrocardiograph machines display 10 seconds of data in a standard tracing. Approach to Diagnosis of the Cardiac Rhythm
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