Article Content

Determine the following:

Figure. No caption a... - Click to enlarge in new windowFigure. No caption available.

Rhythm: _______________________________________


Rate: ___________________________________________


P waves: _______________________________________


PR interval: ____________________________________


QRS complex: __________________________________


What's your interpretation?


(Answers on next page)


Name that strip: Answers

Rhythm: Basic rhythm regular; irregular with premature atrial contraction (PAC) and burst of paroxysmal atrial tachycardia (PAT)


Rate: Basic rhythm rate 94 beats/minute; PAT rate 167 beats/minute


P waves: Sinus P waves with basic rhythm; premature, pointed P waves with PAC and PAT (P waves are superimposed on preceding T waves)


PR interval: 0.16 second (basic rhythm)


QRS complex: 0.08 second (basic rhythm, PAC, and PAT)


Interpretation: Normal sinus rhythm with PAC and burst of PAT


PAT originates in an ectopic pacemaker site in the atria, producing a rapid, regular atrial rhythm of between 140 and 250 beats/minute. PAT is usually precipitated by a PAC and starts and stops abruptly, occurring in bursts or paroxysms (thus the name paroxysmal atrial tachycardia). By definition, three or more consecutive PACs at a rate of 140 to 250 beats/minute are considered PAT.


The P waves associated with PAT are abnormal (often pointed) but may be difficult to identify because they are usually hidden in the preceding T wave; the T and P wave appear as one deflection called the T-P wave. One P wave precedes each QRS complex, unless an AV block is present. The PR interval is usually not measurable. The duration of the QRS complex is usually normal.


This rhythm is usually caused by a single ectopic focus in the atria. The underlying mechanism of this rhythm can involve enhanced automaticity of atrial pacemaker cells, resulting in rapid firing of an ectopic atrial focus; an atrial reentry circuit in which an impulse travels rapidly and repeatedly around a circular pathway in the atria; or triggered activity during repolarization when ectopic atrial impulses fire more than once in response to a single electrical stimulus. PAT may occur in people with healthy hearts as well as those with heart disease. It is more common in women but may occur in men as well. It is the most common dysrhythmia in children. PAT has been associated with ingestion of substances such as caffeine, alcohol, and tobacco; anxiety; fatigue; electrolyte imbalances; lung disease; congenital heart disease; digitalis toxicity; atrial scarring following heart surgery; hyperthyroidism; and unknown causes.


During an episode of PAT, many individuals can feel palpitations, and this can be a source of anxiety. When the ventricular rate is rapid, the ventricles are unable to fill completely during diastole, resulting in a significant reduction in cardiac output. In addition, a rapid heart rate increases myocardial oxygen requirements and myocardial workload. Because PAT is transient, treatment is generally not necessary. Priorities of treatment depend on the patient's clinical status.


Paroxysmal atrial tachycardia: Identifying ECG features

Rhythm: Basic rhythm regular; irregular with PAC and burst of PAT


Rate: Basic rhythm rate 60 to 100 beats/minute; PAT rate 140 to 250 beats/minute


P waves: Sinus P waves with basic rhythm; PAT P waves abnormal (commonly pointed); usually hidden in preceding T wave, making T wave and P wave appear as one wave deflection (T-P wave); one P wave to each QRS complex unless an AV block is present.


PR interval: Basic rhythm usually normal; usually not measurable in PAT


QRS complex: Normal (0.10 second or less) in basic rhythm and PAT


Comment: A run of three or more consecutive PACs is considered PAT; PAT begins and ends abruptly.