Normal sinus rhythm and sinus arrhythmia
- William H Sauer, MD
William H Sauer, MD
- Associate Professor of Medicine
- University of Colorado School of Medicine
Normal sinus rhythm (NSR) is the characteristic rhythm of the healthy human heart. NSR is the rhythm that originates from the sinus node. The rate in NSR is generally regular but will vary depending on autonomic inputs into the sinus node. There can be an irregularity in the sinus rate and, when this occurs, it is termed "sinus arrhythmia". A sinus rhythm faster than the normal range is called a sinus tachycardia, while a slower rate is called a sinus bradycardia. (See "Sinus tachycardia" and "Sinus bradycardia".)
The sinoatrial (SA) node, due to its small mass, does not have a visible manifestation on the ECG. The behavior of the SA node, therefore, must be inferred from the atrial response. The upper right atrium is depolarized first, followed by the simultaneous depolarization of the remainder of the right and some of the left atrium, and finally by depolarization of the left atrial appendage. The blood supply and anatomy of the SA node along with the ECG characteristics of NSR and sinus arrhythmia will be discussed here. Abnormalities of SA nodal function are considered elsewhere. (See "Manifestations and causes of the sick sinus syndrome" and "Sinoatrial nodal pause, arrest, and exit block".)
NORMAL SINUS HEART RATE
The normal heart rate has been considered to be between 60 and 100 beats per minute, although there is some disagreement with regard to the normal rate in adults. The range (defined by 1st and 99th percentiles) is between 43 and 102 beats per minute in men and between 47 and 103 beats per minute in women (table 1) [1-3]. There is also important variability in age in young children. The normal heart rate is 110 to 150 beats per minute in infants, with gradual slowing over the first six years of life.
A variety of pharmacologic agents and physiologic conditions can result in changes to the normal sinus heart rate. These conditions are discussed in greater detail separately. (See "Sinus tachycardia", section on 'Etiology' and "Sinus bradycardia", section on 'Pathophysiologic sinus bradycardia'.)
The normal heart rate increases with exertion and decreases following the cessation of activity. The rate at which the heart rate returns to baseline following exercise can have prognostic importance, a concept which is discussed in greater detail elsewhere. (See "Exercise ECG testing to determine prognosis of coronary heart disease", section on 'Heart rate response to exercise' and "Exercise ECG testing to determine prognosis of coronary heart disease", section on 'Heart rate recovery after exercise'.)
- Spodick DH. Normal sinus heart rate: sinus tachycardia and sinus bradycardia redefined. Am Heart J 1992; 124:1119.
- Spodick DH, Raju P, Bishop RL, Rifkin RD. Operational definition of normal sinus heart rate. Am J Cardiol 1992; 69:1245.
- Mason JW, Ramseth DJ, Chanter DO, et al. Electrocardiographic reference ranges derived from 79,743 ambulatory subjects. J Electrocardiol 2007; 40:228.
- Sánchez-Quintana D, Cabrera JA, Farré J, et al. Sinus node revisited in the era of electroanatomical mapping and catheter ablation. Heart 2005; 91:189.
- Chandler NJ, Greener ID, Tellez JO, et al. Molecular architecture of the human sinus node: insights into the function of the cardiac pacemaker. Circulation 2009; 119:1562.
- Stiles MK, Brooks AG, Roberts-Thomson KC, et al. High-density mapping of the sinus node in humans: role of preferential pathways and the effect of remodeling. J Cardiovasc Electrophysiol 2010; 21:532.
- Boyett MR, Honjo H, Kodama I. The sinoatrial node, a heterogeneous pacemaker structure. Cardiovasc Res 2000; 47:658.
- Kawashima T, Sasaki H. The morphological significance of the human sinuatrial nodal branch (artery). Heart Vessels 2003; 18:213.
- Hancock EW, Deal BJ, Mirvis DM, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part V: electrocardiogram changes associated with cardiac chamber hypertrophy: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol 2009; 53:992.
- MACRUZ R, PERLOFF JK, CASE RB. A method for the electrocardiographic recognition of atrial enlargement. Circulation 1958; 17:882.
- MORRIS JJ Jr, ESTES EH Jr, WHALEN RE, et al. P-WAVE ANALYSIS IN VALVULAR HEART DISEASE. Circulation 1964; 29:242.
- Coker R, Koziell A, Oliver C, Smith SE. Does the sympathetic nervous system influence sinus arrhythmia in man? Evidence from combined autonomic blockade. J Physiol 1984; 356:459.
- Piepoli M, Sleight P, Leuzzi S, et al. Origin of respiratory sinus arrhythmia in conscious humans. An important role for arterial carotid baroreceptors. Circulation 1997; 95:1813.
- Kaushal P, Taylor JA. Inter-relations among declines in arterial distensibility, baroreflex function and respiratory sinus arrhythmia. J Am Coll Cardiol 2002; 39:1524.
- Taylor JA, Myers CW, Halliwill JR, et al. Sympathetic restraint of respiratory sinus arrhythmia: implications for vagal-cardiac tone assessment in humans. Am J Physiol Heart Circ Physiol 2001; 280:H2804.
- Sasano N, Vesely AE, Hayano J, et al. Direct effect of Pa(CO2) on respiratory sinus arrhythmia in conscious humans. Am J Physiol Heart Circ Physiol 2002; 282:H973.
- Al-Ani M, Forkins AS, Townend JN, Coote JH. Respiratory sinus arrhythmia and central respiratory drive in humans. Clin Sci (Lond) 1996; 90:235.
- Hrushesky WJ, Fader D, Schmitt O, Gilbertsen V. The respiratory sinus arrhythmia: a measure of cardiac age. Science 1984; 224:1001.
- Smith SA. Reduced sinus arrhythmia in diabetic autonomic neuropathy: diagnostic value of an age-related normal range. Br Med J (Clin Res Ed) 1982; 285:1599.
- de Marchena E, Colvin-Adams M, Esnard J, et al. Ventriculophasic sinus arrhythmia in the orthotopic transplanted heart: mechanism of disease revisited. Int J Cardiol 2003; 91:71.
- NORMAL SINUS HEART RATE
- BLOOD SUPPLY
- ELECTROCARDIOGRAPHIC CHARACTERISTICS OF NSR
- P wave duration and amplitude
- P wave axis and morphology
- - Left atrial enlargement
- - Right atrial enlargement
- - Biatrial enlargement
- The PR interval
- SINUS ARRHYTHMIA
- Respiratory type
- Nonrespiratory type
- - Ventriculophasic type
- SUMMARY AND RECOMMENDATIONS