Determine the following:
Rhythm: _______________________________________
Rate: ___________________________________________
P waves: _______________________________________
PR interval: ____________________________________
QRS complex: __________________________________
What's your interpretation?
(Answers on next page)
Name that strip: Answers
Rhythm: Irregularly irregular
Rate: Atrial, not measurable; ventricular, 170 beats/minute
P waves: Fibrillatory waves (f waves) present
PR interval: Not measurable
QRS complex: 0.08 second
Interpretation: Atrial fibrillation
Atrial fibrillation is an irregularly irregular dysrhythmia caused by chaotic electrical impulses that arise from multiple ectopic sites in the atria, depolarizing at a rate greater than 400 beats/minute. These impulses are so rapid that they cause the atria to quiver instead of contracting regularly, producing irregular, wavy deflections. These deflections are called fibrillatory waves (f waves). Large waves are described as coarse f waves and small waves are called fine f waves. In atrial fibrillation, an actual atrial rate is not measurable. The PR interval is also not measurable. The QRS complex is usually normal. Because the atrial impulses occur irregularly, the ventricular response is irregular, too. Atrial fibrillation is characterized by indiscernible P waves and an irregularly irregular ventricular rhythm. If the ventricular rate is very rapid, the ventricular rhythm may appear somewhat more regular.
The AV node blocks most of the impulses from entering the ventricles, thus protecting the ventricles from excessive rates. The ventricular rate is slower than the atrial rate and depends on the number of impulses conducted through the AV node to the ventricles. When the ventricular rate is less than 100 beats/minute, the rhythm is called controlled atrial fibrillation. When the ventricular rate is greater than 100 beats/minute, the rhythm is called uncontrolled atrial fibrillation, or atrial fibrillation with a rapid ventricular response.
Atrial fibrillation is the most common dysrhythmia seen in clinical practice. The prevalence of atrial fibrillation increases with age. Atrial fibrillation can occur in healthy individuals or in those with heart disease. In healthy individuals, the dysrhythmia is usually classified as paroxysmal and may be associated with emotional stress or excessive alcohol consumption ("holiday heart syndrome"). In many patients, this type of atrial fibrillation spontaneously converts to sinus rhythm or is easily converted with drug therapy alone. Other disorders commonly associated with atrial fibrillation include coronary artery disease, hypertension, valvular heart disease, heart failure, and pulmonary disease. Atrial fibrillation is also common after cardiac surgery.
The ventricular rate may be rapid, increasing myocardial oxygen demands and cardiac workload, and decreasing cardiac output. Because the atria quiver rather than contract effectively, the atrial kick is lost, which can further reduce cardiac output. Decreased cardiac output is especially marked in patients with underlying cardiac dysfunction and in older adults, who are more dependent on atrial contraction for ventricular filling. The noncontracting atria cause blood to pool in the atrial chambers, increasing the potential for thrombus formation, which may lead to stroke.
Atrial fibrillation: Identifying ECG features
Rhythm: Irregularly irregular (unless the ventricular rate is very rapid, in which case the rhythm appears more regular)
Rate: Atrial rate: 400 beats/minute or more; not measurable on surface ECG
Ventricular rate: Varies with number of impulses conducted through AV node to the ventricles (will be less than the atrial rate)
P waves: Indiscernible; irregular wave deflections (f waves) affecting entire baseline
PR interval: Not measurable
QRS complex: Usually less than 0.12 second