7. Atrial Arrhythmias

Sinus tachycardia is a regular rhythm, with a rate greater than 100 bpm. The maximum rate of sinus tachycardia depends on a person’s age and can be estimated by the formula (Max HR = 220 – person’s age). A QRS follows each P wave at a constant interval. The heart rate in Figure 7.2 is 107 bpm. Sinus tachycardia always has an underlying cause. The pathophysiology is most commonly sympathetic over activity, but it can be parasympathetic block.

Sinus arrhythmia is a rhythm characterized by a gradually increasing, then decreasing heart rate, over a period of seconds. The variation between the maximum (88 bpm) and minimum (75 bpm) heart rates in Figure 7.3 is greater than 10%. A QRS follows each P wave. When marked, it can be a sign of further conduction disease called sick sinus syndrome.

Sinus bradycardia (SB) is a regular rhythm, with a rate of less than 60 bpm. A QRS follows each P wave at a constant interval, and the interval between P waves is constant. The heart rate in Figure 7.4 goes down to 45 bpm. Sinus bradycardia is the result of decreased sympathetic or increased parasympathetic activity. The class of medications called beta blockers commonly cause sinus bradycardia.

Atrial tachycardia (AT) or supraventricular tachycardia (SVT) is a regular rhythm at a rate of 160 to 260. A P wave, if present (P’), appears differently from the normal P wave (P). The heart rate in Figure 7.5 increases from 91 to more than 160 bpm. Atrial tachycardia is usually associated with increased sympathetic activity. It can be seen in normal and abnormal hearts.

Atrial flutter is a regular atrial rhythm characterized by atrial flutter waves. Lead II frequently demonstrates the classic sawtooth appearance of the flutter waves, some of which are hidden in the ST segment. Atrial flutter usually is a regular rhythm at a rate of 240 to 340 with flutter waves, but not every flutter wave produces a QRS. The number of flutter waves to QRS complex in Figure 7.6 is described as flutter with varying 3 to 1 and 2 to 1 conduction. The atrial rate (230) and ventricular rate (88 to 115) should be described separately. Atrial flutter frequently is associated with underlying heart or lung disease.

A premature atrial contraction (PAC) is a premature (too early) ectopic (not from the expected place) beat. A PAC typically throws the rhythm off step, with a slight pause after it. Also, there is a visible P wave right before the PAC. This is called a P’ (P prime) to distinguish it from a normal sinus P wave. PACs can be associated with increased sympathetic activity.

A sinus pause is a period of electrical silence with no activity after a period of sinus rhythm. It is measured in duration from the QRS before the pause to the QRS after the pause, 1.5 seconds in Figure 7.8. Sinus pauses are a sign of underlying disease in the conduction system or a complication of medication such as digitalis, calcium channel blocker, or beta blocker. The most common cause of a sinus pause is a PAC that was nonconducted.

Atrial fibrillation (AF) is an irregularly irregular rhythm. The atrial rhythm may be coarse and visible, or not apparent at all. The ventricular rate is calculated by measuring a 6 second interval, and multiplying the number of QRS complexes by 10. The ventricular rate in Figure 7.9 is 130 bpm. Atrial fibrillation increases in incidence with advancing age. It can be associated with underlying heart diseases such as hypertension, coronary disease, valvular heart disease, and heart failure. It can be associated with acute lung disease such as pulmonary embolism, or chronic lung disease such as COPD. It can be associated with systemic diseases such as hyperthyroidism. It puts the patient at risk for systemic embolism. c4