bradycardia

徐脈 　

WordNet

1. abnormally slow heartbeat

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/02/19 01:23:03」(JST)

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Bradycardia
Sinus bradycardia seen in lead II with a heart rate of about 50.
Classification and external resources
Pronunciation	/ˌbrædɪˈkɑːrdiə/
Specialty	Cardiology
ICD-10	R00.1
ICD-9-CM	427.81, 659.7, 785.9, 779.81
Patient UK	Bradycardia
MeSH	D001919

Bradycardia, also known as bradyarrhythmia, is a slow heart rate, defined as a heart rate of under 60 beats per minute (BPM) in adults. Bradycardia typically does not cause symptoms until the rate drops below 50 BPM. When symptomatic, it may cause fatigue, weakness, dizziness, and at very low rates fainting.

During sleep, a slow heartbeat with rates around 40–50 BPM is common, and is considered normal. Highly trained athletes may also have athletic heart syndrome, a very slow resting heart rate that occurs as a sport adaptation and helps prevent tachycardia during training.

The term relative bradycardia is used in explaining a heart rate that, although not actually below 60 BPM, is still considered too slow for the individual's current medical condition.

Definition and etymology

Bradycardia in an adult is any heart rate less than 60 beats per minute (BPM), although symptoms usually manifest only for heart rates less than 50.

The word bradycardia is from the Greek βραδύς, bradys "slow", and καρδία, kardia, "heart".

Classification

Illustration comparing the EKGs of a healthy person (top) and a person with bradycardia (bottom). The points on the heart where the EKG signals are measured are also shown.

Atrial

See also: Sinus bradycardia and Sick sinus syndrome

Atrial bradycardias are divided into three types. The first, respiratory sinus arrhythmia, is usually found in young and healthy adults. Heart rate increases during inhalation and decreases during exhalation. This is thought to be caused by changes in the vagal tone during respiration. If the decrease during exhalation drops the heart rate below 60 bpm on each breath, this type of bradycardia is usually deemed benign and a sign of good autonomic tone.

The second, sinus bradycardia, is a sinus rhythm of less than 60 bpm. It is a common condition found in both healthy individuals and those considered well-conditioned athletes. Studies have found that 50–85% of conditioned athletes have benign sinus bradycardia, as compared to 23% of the general population studied. The heart muscle of athletes has become conditioned to have a higher stroke volume and, so, requires fewer contractions to circulate the same volume of blood.

The third, sick sinus syndrome, covers conditions that include severe sinus bradycardia, sinoatrial block, sinus arrest, and bradycardia-tachycardia syndrome (atrial fibrillation, flutter, and paroxysmal supraventricular tachycardia).

Atrioventricular nodal

See also: Junctional rhythm

An atrioventricular nodal bradycardia or AV junction rhythm is usually caused by the absence of the electrical impulse from the sinus node. This usually appears on an EKG with a normal QRS complex accompanied with an inverted P wave either before, during, or after the QRS complex.

An AV junctional escape is a delayed heartbeat originating from an ectopic focus somewhere in the AV junction. It occurs when the rate of depolarization of the SA node falls below the rate of the AV node. This dysrhythmia also may occur when the electrical impulses from the SA node fail to reach the AV node because of SA or AV block. This is a protective mechanism for the heart, to compensate for an SA node that is no longer handling the pacemaking activity, and is one of a series of backup sites that can take over pacemaker function when the SA node fails to do so. This would present with a longer PR interval. A junctional escape complex is a normal response that may result from excessive vagal tone on the SA node. Pathological causes include sinus bradycardia, sinus arrest, sinus exit block, or AV block.

Ventricular

See also: Atrioventricular block

A ventricular bradycardia, also known as ventricular escape rhythm or idioventricular rhythm, is a heart rate of less than 50 bpm. This is a safety mechanism when there is lack of electrical impulse or stimuli from the atrium. Impulses originating within or below the bundle of His in the atrioventricular node will produce a wide QRS complex with heart rates between 20 and 40 bpm. Those above the bundle of His, also known as junctional, will typically range between 40 and 60 bpm with a narrow QRS complex. In a third-degree heart block, approximately 61% take place at the bundle branch-Purkinje system, 21% at the AV node, and 15% at the bundle of His. AV block may be ruled out with an EKG indicating "a 1:1 relationship between P waves and QRS complexes." Ventricular bradycardias occurs with sinus bradycardia, sinus arrest, and AV block. Treatment often consists of the administration of atropine and cardiac pacing.

Infantile

For infants, bradycardia is defined as a heart rate of less than 100 bpm (normal is around 120–160). Premature babies are more likely than full-term babies to have apnea and bradycardia spells; their cause is not clearly understood. Some researchers think the spells are related to centers inside the brain that regulate breathing that may not be fully developed. Touching the baby gently or rocking the incubator slightly will almost always get the baby to start breathing again, which increases the heart rate. Medications (theophylline or caffeine) can be used to treat these spells in babies if necessary. Neonatal intensive-care unit (NICU) standard practice is to electronically monitor the heart and lungs for this reason.

Causes

This cardiac arrhythmia can be underlain by several causes, which are best divided into cardiac and noncardiac causes. Noncardiac causes are usually secondary, and can involve recreational drug use or abuse; metabolic or endocrine issues, especially in the thyroid; an electrolyte imbalance; neurologic factors; autonomic reflexes; situational factors such as prolonged bed rest; and autoimmunity. Cardiac causes include acute or chronic ischemic heart disease, vascular heart disease, valvular heart disease, or degenerative primary electrical disease. Ultimately, the causes act by three mechanisms: depressed automaticity of the heart, conduction block, or escape pacemakers and rhythms.

In general, two types of problems result in bradycardias: disorders of the sinoatrial node (SA node), and disorders of the atrioventricular node (AV node).

With sinus node dysfunction (sometimes called sick sinus syndrome), there may be disordered automaticity or impaired conduction of the impulse from the sinus node into the surrounding atrial tissue (an "exit block"). Second-degree sinoatrial blocks can be detected only by use of a 12-lead EKG. It is difficult and sometimes impossible to assign a mechanism to any particular bradycardia, but the underlying mechanism is not clinically relevant to treatment, which is the same in both cases of sick sinus syndrome: a permanent pacemaker.

Atrioventricular conduction disturbances (a.k.a.: AV block; 1^o AV block, 2^o type I AV block, 2^o type II AV block, 3^o AV block) may result from impaired conduction in the AV node, or anywhere below it, such as in the Bundle of His. The clinical relevance pertaining to AV blocks is greater than that of sinoatrial blocks.

Patients with bradycardia have likely acquired it, as opposed to having it congenitally. Bradycardia is more common in older patients.

Beta-blocker medicines also can slow the heart rate and decrease how forcefully the heart contracts. Beta blockers may slow the heart rate to a dangerous level if prescribed together with calcium channel blocker-type medications.

Bradycardia is also part of the mammalian diving reflex.

Diagnosis

A diagnosis of bradycardia in adults is based on a heart rate less than 60 bpm. This is determined usually either via palpation or via an ECG.

If symptoms occur, a determination of electrolytes may be helpful in determining the underlying cause.

Management

The treatment of bradycardia is dependent on whether or not the person is stable or unstable. If oxygen saturations are low, supplemental oxygen should be provided.

Stable

Emergent treatment is not needed if the person is asymptomatic or minimally symptomatic.

Unstable

If a person is unstable, the initial recommended treatment is intravenous atropine. Doses less than 0.5 mg should not be used, as this may further decrease the rate. If this is not effective, intravenous inotrope infusion (dopamine, epinephrine) or transcutaneous pacing should be used. Transvenous pacing may be required if the cause of the bradycardia is not rapidly reversible.

In children giving oxygen, supporting their breathing, and chest compressions are recommended.

Society and culture

Daniel Green holds the world record for the slowest heartbeat in a healthy human, with a heart rate measured in 2014 of 26 bpm. Martin Brady holds the Guinness world record for the slowest heart rate with a certified rate over a minute duration of 27 BPM. Professional cyclist Miguel Indurain had a resting heart rate of 28 BPM.

References

UpToDate Contents

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• 1. 洞徐脈 sinus bradycardia
• 2. 麻酔後回復室（PACU）における心血管の障害 cardiovascular problems in the post anesthesia care unit pacu
• 3. 小児における徐脈 bradycardia in children
• 4. 永久的心臓ペーシング：デバイスおよび適応の概要 permanent cardiac pacing overview of devices and indications
• 5. 洞不全症候群：臨床症状、診断および評価 sick sinus syndrome clinical manifestations diagnosis and evaluation

English Journal

• An update on risk factors for drug-induced arrhythmias.

• Vlachos K1, Georgopoulos S1, Efremidis M1, Sideris A1, Letsas KP1.
• Expert review of clinical pharmacology.Expert Rev Clin Pharmacol.2016 Jan;9(1):117-27. doi: 10.1586/17512433.2016.1100073. Epub 2015 Oct 13.
• A variety of drugs, either anti-arrhythmics or non-antiarrhythmics, have been associated with drug-induced arrhythmias. Drug-induced arrhythmias are usually observed in the presence of long QT interval or Brugada electrocardiographic pattern. Clinical risk factors, such as female gender, structural
• PMID 26460585

• Cisplatin-induced bradycardia: Cardiac toxicity or cardiac hypersensitivity and Kounis syndrome?

• Kounis NG1, Cervellin G2, Lippi G3.
• International journal of cardiology.Int J Cardiol.2016 Jan 1;202:817-8. doi: 10.1016/j.ijcard.2015.10.027. Epub 2015 Oct 9.
• PMID 26476038

• Effect of beta-blocker therapy on heart rate response in patients with hypertension and newly diagnosed untreated obstructive sleep apnea syndrome.

• Wolf J1, Drozdowski J2, Czechowicz K3, Winklewski PJ4, Jassem E2, Kara T5, Somers VK6, Narkiewicz K3.
• International journal of cardiology.Int J Cardiol.2016 Jan 1;202:67-72. doi: 10.1016/j.ijcard.2015.08.139. Epub 2015 Aug 21.
• BACKGROUND: Beta1-receptor antagonists (BBs) are commonly administered in the treatment of cardiovascular disease (CVD). The reported benefits of BB use in CVD patients with concomitant obstructive sleep apnea (OSA) may be limited by their impact on apnea-induced bradycardias. Therefore the aim of t
• PMID 26386925

Japanese Journal

• 症例 超高齢者EML4-ALK肺癌におけるクリゾチニブ奏効例に生じた洞性徐脈

• 林 和菜,山岸 智子,越智 宣昭 [他]
• 日本呼吸器学会誌 = Annals of the Japanese Respiratory Society 4(4), 278-282, 2015-07-10
• NAID 40020538125

• 膀胱穿孔を契機として高度徐脈を来した経尿道的膀胱腫瘍生検術の1症例

• 今城 幸裕,駒澤 伸泰,石尾 純一 [他]
• 麻酔 64(5), 552-554, 2015-05
• NAID 40020470785

• 研究・症例 クリゾチニブ内服中に重度の洞性徐脈を来した92歳のEML4-ALK遺伝子転座陽性例

• 竹村 知容,中川 望,加耒 佐和子 [他]
• 日本胸部臨床 74(4), 478-483, 2015-04
• NAID 40020423452

Related Links

• bradycardiaの意味 - 英和辞書 - goo辞書

bradycardiaとは。意味や和訳。[名][U]医学徐脈，心拍緩徐：通例毎分60以下の脈拍. - goo辞書は国語、英和、和英、中国語、百科事典等からまとめて探せる辞書検索サービスです。

• bradycardiaの意味・用例｜英辞郎 on the WEB：アルク

bradycardia 【名】《医》徐脈 - アルクがお届けする進化するオンライン英和・和英辞書データベース。一般的な単語や連語から、イディオム、専門用語、スラングまで幅広く収録。

• Bradycardia?????

Is bradycardia a constant thing or can it come and go? ... The heart is a hollow muscular organ – approximately the size of your clenched fist – that beats 40 million times per year (between 60 and 100 beats per minute).

Related Pictures

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★リンクテーブル★

リンク元	「徐脈」「徐拍」
拡張検索	「bradycardiac」

「徐脈」

　　[★]

英

bradycardia

関

徐拍

• 脳圧亢進、閉塞性黄疸、甲状腺機能低下症、迷走神経緊張
• 脈拍数が60回/分以下のものを指す。

「徐拍」

　　[★]

英

bradycardia

関

徐脈

• 心拍が緩徐なことであり、徐脈とは厳密には区別されるべき？

「bradycardiac」

　　[★]

• adj.

• 徐脈の、徐脈性の、徐拍の、徐拍性の

関

bradycardia、bradycardic