Heterotopic focus

Japanese: 異所焦点 - いしょしょうてん

…These are caused by degeneration of the conduction system cells (inflammation, impaired blood supply) or partial death of a group of cells. Functionally, they occur when cells in a certain part of the heart become spontaneously excited (ectopic focus), and the excitation propagates retrogradely or forms a spiral circuit. Such abnormalities in the conduction system cause changes in the action potential associated with excitation, so they can be diagnosed from an electrocardiogram. …

From [Electrocardiogram]

…If there is a disturbance in the sinus rhythm or an abnormality in the sinus-atrial conduction, the P-P interval will fluctuate or P will be absent. Also, when rhythmic excitation occurs in the myocardium other than the sinoatrial node (ectopic focus) and the normal sinus rhythm is disturbed by its propagation, P waves appear on the electrocardiogram in addition to the normal P waves (sinus extrasystoles), and then the scheduled normal P waves are absent (compensatory pause). A similar phenomenon is seen when an abnormal focus occurs in the excitation conduction pathway between the atria and ventricles, and abnormal QRS waves (ventricular extrasystoles) and absence of normal QRS waves (compensatory ventricular pause) are observed. …

*Some of the terminology explanations that mention "ectopic focus" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…これらは刺激伝導系細胞の変性(炎症，血液供給障害)，あるいは細胞群の部分的死滅により発生する。また機能的には，心臓内のある部位の細胞が自発興奮を起こし(異所焦点)，その興奮が逆行性に伝播したり，旋回路を形成するために生じる。このような刺激伝導系の異常は，興奮に伴う活動電位に変化をもたらすので，心電図から診断することができる。…

【心電図】より

…洞律動の乱れや洞房間伝導に異常があれば，P―P間隔の変動やPの欠落が起こる。また洞房結節以外の心筋に律動性興奮が起こり(異所焦点)，それが伝播することによって本来の洞性調律を乱すときは，心電図上に本来のP波以外にP波が現れて(洞性期外収縮)，次に予定された正常P波の欠落が起こる(代償性休止)。同様の現象は心房―心室間の興奮伝導路に異常焦点が発生した場合にみられ，異常QRS波(心室性期外収縮)と正常QRS波の欠落(代償性心室性休止)が認められる。…

※「異所焦点」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典第２版について | 情報

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