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Name That Strip

doi: 10.1097/01.CCN.0000534925.78300.e2
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In Brief

FU1-6
Figure

Determine the following:

Rhythm: _______________________________________

Rate: ___________________________________________

P waves: _______________________________________

PR interval: ____________________________________

QRS complex: __________________________________

What's your interpretation?

(Answers on next page)

Name that strip: Answers

Rhythm: Regular

Rate:

Atrial: 272 beats/minute; Ventricular: 68 beats/minute

Note: If the ventricular rhythm is regular, multiply the number of flutter waves before each QRS by the ventricular rate to determine the atrial rate.

P waves: Four flutter waves before each QRS (marked in the “V” of the sawtooth waves)

PR interval: Not measurable

QRS complex: 0.08 to 0.10 second

Interpretation: Atrial flutter with 4:1 atrioventricular (AV) conduction

Atrial flutter originates in an ectopic pacemaker in the atria, typically depolarizing at a rate between 250 and 400 beats/minute (the average rate is approximately 300 beats/minute). The atria respond to this rapid stimulation by producing V-shaped waveforms resembling the teeth of a saw. The sawtooth waveforms are called flutter waves (F waves). It is easier to count the number of F waves between QRS complexes if you put the tip of a pencil at the end of a QRS and count each downward “V” as an F wave, including the “V” going into the QRS complex. The F waves affect the entire baseline to such a degree that there is no isoelectric line between the F waves, and the T wave is partially or completely obscured by the F waves. Atrial flutter is primarily recognized by this sawtooth baseline. The PR interval is not measurable. The QRS complexes are usually normal.

Although the atria can tolerate the extremely high heart rate reasonably well, the ventricles cannot. Fortunately, the AV node is present to slow down and decrease the number of impulses that pass through to the ventricles. The AV node conducts the impulses in various ratios. For example, the AV node might allow every second impulse to travel through the AV junction to the ventricles; resulting in a 2:1 AV conduction ratio (a 2:1 conduction ratio indicates that for every two flutter waves, only one is followed by a QRS complex). Even ratios (2:1, 4:1) are more common than odd ratios (3:1, 5:1). If the conduction ratio remains constant (for example, 2:1), the ventricular rhythm will be regular and the rhythm is described as atrial flutter with 2:1 AV conduction. If the conduction ratio varies (for example, from 4:1 to 3:1 to 5:1), the ventricular rhythm will be irregular, and the rhythm is described as atrial flutter with variable AV conduction. In atrial flutter, the ventricular rate is slower than the atrial rate, with the rate depending on the number of impulses conducted through the AV node to the ventricles.

Because atrial flutter usually occurs at a rate of 300 beats/minute and the AV node usually blocks at least half of these impulses, a ventricular rate of 150 beats/minute is common (a 2:1 AV conduction ratio). Atrial flutter with 2:1 AV conduction may be difficult to differentiate from atrial tachycardia, especially if the heart rate in both rhythms is around 150 beats/minute. These two dysrhythmias can be differentiated by closely examining the baseline. In atrial tachycardia, an isoelectric line can usually be seen, whereas in atrial flutter the isoelectric line is absent.

Atrial flutter typically originates from the right atrium and most often involves a large reentry circuit that travels around the area of the tricuspid valve. This type of atrial flutter is referred to as typical atrial flutter. Less commonly, atrial flutter can result from circuits in other areas of the right or left atrium (atypical atrial flutter). Atrial flutter is more common in men than women.

Atrial flutter is rarely seen in patients with normal hearts. This dysrhythmia may be seen in patients with heart failure; ischemic heart disease; cardiomyopathy; valvular heart disease, especially the mitral and tricuspid valves; septal defects; and following heart surgery. It is also seen in hypertension, hyperthyroidism, pulmonary embolism, older age, and chronic lung disease, such as chronic obstructive pulmonary disease. Substances that may contribute to development of atrial flutter include alcohol (especially binge drinking) and stimulants such as cocaine, amphetamines, diet pills, cold medicines, and caffeine. In some people, no underlying cause is ever found.

Like paroxysmal atrial tachycardia, the ventricular rate in atrial flutter may be rapid, increasing myocardial oxygen requirements and cardiac workload and decreasing cardiac output. In addition, the atria do not contract strongly enough to empty all the blood from the atrial chambers into the ventricles. This results in a loss of the atrial kick, which further decreases cardiac output. Over time, some blood in the atria may stagnate and mural thrombi may form. Pieces of the thrombus may break off, leading to a risk of systemic or pulmonary emboli.

Atrial flutter: Identifying ECG features

Rhythm: Regular to irregular (depends on AV conduction ratios)

Rate:

  • Atrial rate: 250 to 400 beats/minute
  • Ventricular rate: Varies with number of impulses conducted through the AV node (will be less than the atrial rate)

P waves: Sawtooth deflections called flutter waves (F waves) affecting entire baseline

PR interval: Not measurable

QRS complex: Usually normal (0.10 second or less)

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