ECG Challenge: A 75-year-old man with known chronic obstructive pulmonary disease attributable to a long history of cigarette smoking presents to the emergency department with a 2-day history of worsened shortness of breath and a cough productive of yellowish sputum. He is afebrile. His blood pressure is 120/70 and his pulse rate is 150 bpm. Lung examination is remarkable for diffuse rhonchi and expiratory wheezes. An ECG is obtained. His chest x-ray is consistent with chronic obstructive pulmonary disease, but there are no infiltrates present. It is felt that he has a chronic obstructive pulmonary disease exacerbation and bronchitis and is begun on antibiotics and a steroid taper. ECG A was obtained in the emergency department, and ECG B was obtained 2 days later after there was improvement in his respiratory status.
ECG A: There is a regular rhythm at a rate of 150 bpm. The QRS complex has a normal duration (0.08 s) and a normal morphology. The QRS axis is normal between 0° and +90°(positive QRS complex in leads I and aVF). There is, however, low voltage in the limb leads, defined as a QRS complex amplitude <5 mm in each limb lead. The QT/QTc intervals are normal (280/440 ms). There is a P wave before each QRS complex (+) with a stable PR interval (0.14 s). The P wave appears to be negative-positive in leads II and aVF. Hence, this is not a sinus rhythm. There is a waveform at the very end of the QRS complex, most obviously seen in lead V1 and V2 (▾). It has the same morphology as the P wave that is seen, and there is a constant interval between this waveform and the P wave, with a rate of 300 bpm. This is consistent with atrial flutter with 2:1 atrioventricular (AV) block as the underlying rhythm.
ECG B: The rhythm is now irregular, but there is a pattern to the irregularity (ie, all the short intervals are the same and the long intervals are the same). This is, therefore, regularly irregular. The presence of atrial flutter is confirmed on this ECG. There are 2 longer RR intervals (↔) during which clear atrial activity can be seen at a rate of 300 bpm (+). The atrial waveforms are negative-positive in leads II and aVF and have a continuously undulating appearance, without any isoelectric baseline between them. The atrial waves are uniform in morphology, amplitude, and interval. This waveform morphology is characteristic of typical atrial flutter. In addition, the only atrial arrhythmia with a regular atrial rate >260 bpm is atrial flutter. It can be seen that there is some variability in the relationship between the atrial flutter wave and the QRS complex (ie, the PR interval; ▴). This is the result of antegrade concealed conduction, a property of the AV node that manifests as variable rates of AV nodal conduction because of the variability in AV nodal refractoriness. At rapid atrial rates, some impulses conduct through the AV node, others are completely blocked, whereas some impulses may partially penetrate the node (ie, concealed within the node), rendering it partially refractory and affecting the rate at which the subsequent impulse is conducted through the node. Thus, although the atrial rate is regular, there may be variability of the RR intervals, even if there is a stable pattern of AV block (ie, 2:1, 3:1, 4:1).
- © 2013 American Heart Association, Inc.