Sinus bradycardia
Encyclopedia
Sinus bradycardia
is a heart rhythm that originates from the sinus node and has a rate of under 60 beats per minute.
, dizziness
, hypotension
, vertigo
, and syncope
. The slow heart rate may also lead to atrial, junctional, or ventricular
ectopic rhythms.
Bradycardia is not necessarily problematic. People who regularly practice sports may have sinus bradycardia, because their trained hearts can pump enough blood in each contraction to allow a low resting heart rate.
Sinus Bradycardia can aid in the sport of Freediving, which includes any of various aquatic activities that share the practice of breath-hold underwater diving. Bradycardia aids in this process due to drop in blood rate pulse. These adaptations enable the human body to endure depth and lack of oxygen far beyond what would be possible without the mammalian diving reflex
.
Sinus bradycardia is a sinus rhythm of less than 60 bpm. It is a common condition found in both healthy individuals and those who are considered well conditioned athletes. Studies have found that 50 - 85 percent of conditioned athletes have benign sinus bradycardia, as compared to 23 percent of the general population studied.
Trained athletes or young healthy individuals may also have a slow resting heart rate.
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
is a heart rhythm that originates from the sinus node and has a rate of under 60 beats per minute.
Signs and symptoms
The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as lightheadednessLightheadedness
Light-headedness is a common and often unpleasant sensation of dizziness and/or feeling that one may be about to faint, which may be transient, recurrent, or occasionally chronic. In some cases, the individual may feel as though his or her head is weightless. The individual may also feel as...
, dizziness
Dizziness
Dizziness refers to an impairment in spatial perception and stability. The term is somewhat imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness....
, hypotension
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
, vertigo
Vertigo (medical)
Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear...
, and syncope
Syncope (medicine)
Syncope , the medical term for fainting, is precisely defined as a transient loss of consciousness and postural tone characterized by rapid onset, short duration, and spontaneous recovery due to global cerebral hypoperfusion that most often results from hypotension.Many forms of syncope are...
. The slow heart rate may also lead to atrial, junctional, or ventricular
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
ectopic rhythms.
Bradycardia is not necessarily problematic. People who regularly practice sports may have sinus bradycardia, because their trained hearts can pump enough blood in each contraction to allow a low resting heart rate.
Sinus Bradycardia can aid in the sport of Freediving, which includes any of various aquatic activities that share the practice of breath-hold underwater diving. Bradycardia aids in this process due to drop in blood rate pulse. These adaptations enable the human body to endure depth and lack of oxygen far beyond what would be possible without the mammalian diving reflex
Mammalian diving reflex
The mammalian diving reflex is a reflex in mammals which optimizes respiration to allow staying underwater for extended periods of time. It is exhibited strongly in aquatic mammals , but exists in a weaker version in other mammals, including humans. Diving birds, such as penguins, have a similar...
.
Sinus bradycardia is a sinus rhythm of less than 60 bpm. It is a common condition found in both healthy individuals and those who are considered well conditioned athletes. Studies have found that 50 - 85 percent of conditioned athletes have benign sinus bradycardia, as compared to 23 percent of the general population studied.
Trained athletes or young healthy individuals may also have a slow resting heart rate.
Cause
- This rhythm may be caused by one of the following:
- Increased vagal toneMuscle toneIn physiology, medicine, and anatomy, muscle tone is the continuous and passive partial contraction of the muscles, or the muscle’s resistance to passive stretch during resting state. It helps maintain posture, and it declines during REM sleep.-Purpose:Unconscious nerve impulses maintain the...
. - SleepSleepSleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
- HypothermiaHypothermiaHypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
- HypothyroidismHypothyroidismHypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
- Intrinsic disease of the SA node (Eg. sick sinus syndromeSick sinus syndromeSick sinus syndrome, also called sinus node dysfunction, is a group of abnormal heart rhythms presumably caused by a malfunction of the sinus node, the heart's primary pacemaker...
). - An effect of drugsDRUGSDestroy Rebuild Until God Shows are an American post-hardcore band formed in 2010. They released their debut self-titled album on February 22, 2011.- Formation :...
, such as the use of digitalisDigitalisDigitalis is a genus of about 20 species of herbaceous perennials, shrubs, and biennials that are commonly called foxgloves. This genus was traditionally placed in the figwort family Scrophulariaceae, but recent reviews of phylogenetic research have placed it in the much enlarged family...
, beta-blockers, or quinidineQuinidineQuinidine is a pharmaceutical agent that acts as a class I antiarrhythmic agent in the heart. It is a stereoisomer of quinine, originally derived from the bark of the cinchona tree.-Mechanism:...
. - SeizureSeizureAn epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
. - It could also be a normal finding in a healthy, well-conditioned person.
- It may be secondary to infections like DiphtheriaDiphtheriaDiphtheria is an upper respiratory tract illness caused by Corynebacterium diphtheriae, a facultative anaerobic, Gram-positive bacterium. It is characterized by sore throat, low fever, and an adherent membrane on the tonsils, pharynx, and/or nasal cavity...
, acute rheumatic feverRheumatic feverRheumatic fever is an inflammatory disease that occurs following a Streptococcus pyogenes infection, such as strep throat or scarlet fever. Believed to be caused by antibody cross-reactivity that can involve the heart, joints, skin, and brain, the illness typically develops two to three weeks after...
, viral myocarditisMyocarditisMyocarditis is inflammation of heart muscle . It resembles a heart attack but coronary arteries are not blocked.Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly non-viral pathogens such as Borrelia burgdorferi or Trypanosoma cruzi, or as a...
. It is physiologic in trained athletes. - Increased intracranial pressure.
- Increased vagal tone
Diagnosis
ECG Characteristics- Rate: Less than 60 beats per minute.
- Rhythm: Regular.
- P waves: Upright, consistent, and normal in morphology and duration.
- P-R Interval: Between 0.12-0.20 seconds in duration.
- QRS ComplexQRS complexThe QRS complex is a name for the combination of three of the graphical deflections seen on a typical electrocardiogram . It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the human heart...
: Less than 0.12 seconds in width, and consistent in morphology.
See also
- Sinus tachycardiaSinus tachycardiaSinus tachycardia is a heart rhythm with elevated rate of impulses originating from the sinoatrial node, defined as a rate greater than 100 beats/min in an average adult. The normal heart rate in the average adult ranges from 60–100 beats/min...
- Long QT syndromeLong QT syndromeThe long QT syndrome is a rare inborn heart condition in which delayed repolarization of the heart following a heartbeat increases the risk of episodes of torsade de pointes . These episodes may lead to palpitations, fainting and sudden death due to ventricular fibrillation...