Characteristics of Sinus Rhythms

Sinus rhythms are those rhythms which are initiated by the sinoatrial node of the heart.    The inherent rate of the SA node is 60-100.    An impulse that is sinus in origin will have an upright P wave in lead II. Sinus rhythms include normal sinus rhythm, sinus bradycardia, sinus tachycardia, sinus arrhythmia, sinus arrest, and sinus pauses.

Normal sinus rhythm

The rhythm is regular with a rate between 60 and 100 beats per minute.   The P waves are upright and precede the QRS complexes. The PR interval is less than .02 seconds and the QRS complex is .06 - .10 sec.  

Sinus tachycardia

The rhythm is regular with a rate between 101 and 170 beats per minute.   The P waves are positive and are associated with a QRS complex.  The PR interval is less than .02 seconds and the QRS complex is .06 - .10 sec.  

Sinus bradycardia

The rhythm is regular with a rate between 40 and 59 beats per minute. The P waves are upright and precede the QRS complexes.  The PR interval is less than .02 seconds and the QRS complex is .06 - .10 sec.   When the rate is less than 40 per minute the rhythm may be referred to as extreme sinus bradycardia

Sinus arrhythmia

The rhythm is irregular with a variation between longest and shortest R-R interval of at least 0.12 sec.  The rate is between 40 and 100 beats per minute. The P waves are upright and precede the QRS complexes. The PR interval is less than .02 seconds and the QRS complex is .06 - .10 sec.   When the rate is between 40-59 beats per minute the rhythm is referred to as sinus bradycardia with sinus arrhythmia. 

Sinus arrest or sinus pause

With sinus arrest and pause there is failure of the SA node to discharge leading to an interruption in the hearts usual rhythm.  The rhythm is irregular with a rate between 40 and 100 beats per minute. The P waves are upright and precede the QRS complexes.  The PR interval is less than .02 seconds and the QRS complex is .06 - .08 sec.   When the rate is between 40-59 beats per minute the rhythm is referred to as sinus bradycardia with sinus arrest or pause.   When the rate is between 101- 160 beats per minute the rhythm is referred to as sinus tachycardia with sinus arrest or pause.  A sinus pause will resume on time after the pause.   A sinus arrest will not resume on time after the pause.

Summary of Sinus Rhythms

	Rhythm	Rate (bpm)	PR interval	QRS complex
Sinus Rhythm	Regular	60 - 100	< .20 sec	.06 - .10 sec
Sinus tachycardia	Regular	101-170	< .20 sec	.06 - .10 sec
Sinus bradycardia	Regular	40 -59	< .20 sec	.06 - .10 sec
Sinus arrhythmia	Irregular	40 -100	< .20 sec	.06 - .10 sec
Sinus arrest and pauses	Irregular	40 - 100	< .20 sec	.06 - .10 sec

Examples of Sinus rhythms

Normal sinus rhythm

Normal sinus rhythm

The rhythm is regular with a rate of 68 beats per minute.    The P waves are uniform and upright and are associated with a QRS complex.   No ectopic beats are present.   PR:  .16 sec,   QRS:  .08 sec,  QT:  .48 sec.

Sinus tachycardia

Sinus tachycardia

The rhythm is regular with a heart rate of 107 beats per minute.    The P waves are upright and have a corresponding QRS complex.    No ectopic beats are noted.   PR:  .12 sec,  QRS:  .08 sec,  QT:  .36 sec. 

Sinus bradycardia

Sinus bradycardia

The rhythm is regular.   The heart rate is 48 beats per minute.    The P waves precede the QRS complex and are uniform and upright.   No ectopic beats are seen.   PR:  .16 sec,  QRS:  .08 sec,  QT:  .48 sec.

Sinus arrhythmia

Sinus arrhythmia

The cardiac rhythm is irregular with a heart rate of 60/min.   The P waves are upright and are paired with a QRS complex.   No ectopic beats are noted.   PR:  .16 sec,  QRS:  .08 sec,  QT:  .40 sec.  

Sinus arrest and sinus pause

Sinus arrest

The heart rhythm is irregular with a rate of 50 beats per minute.  A period of sinus arrest follows the 1st complex.  As the sinus rhythm resumes the rhythm is slightly irregular as the SA node resets the rhythm.  The P waves are positive, uniform, and associated with a QRS complex.   No ectopic beats are noted.   PR:  .20 sec,  QRS:  .08 sec,  QT:  .48 sec.

Sinus Rhythm Practice

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Answers


1.     Normal sinus rhythm
2.     Normal sinus rhythm with a pause
3.     Sinus arrhythmia
4.     Sinus bradycardia
5.     Sinus bradycardia with sinus arrest
6.     Sinus bradycardia
7.     Sinus tachycardia
8.     Normal sinus rhythm
9.     Sinus bradycardia with sinus arrest
10.   Sinus tachycardia
11.   Sinus arrhythmia
12.   Sinus bradycardia
13.   Sinus bradycardia with a pause
14.   Sinus tachycardia
15.   Sinus tachycardia with a pause