허혈성 심전도 변화, ECG of myocardial ischemia

허혈성 ECG의 완전한 spectrum은 ST segment 변화, T wave 변화, U wave 변화이지만 운동 중에 가장 중요한 허혈성 심전도 변화는 ST segment와 관련이 있습니다. 

[Spectrum of electrocardiographic changes during exercise testing] A: Normal resting electrocardiogram (lead V5) before exercise; B: Normal J point depression during exercise; C: Upsloping ST depression of subendocardial ischemia; D: Horizontal ST depression of subendocardial ischemia; E: Downsloping ST depression of subendocardial ischemia; F: ST elevation caused by transmural ischemia; G: U wave inversion.

QRS complex는 심실 탈분극의 time sequence를 반영합니다. ST segment는 plateau 또는 phase 2와 일치하며 T wave는 phase 3를 반영합니다. Phase 4는 resting membrane potential(TQ segment)이며 보통 중요하지 않지만, 실질적으로 허혈성 심전도 변화에서 두드러진 역할을 합니다. 

[Relationship between myocardial action potential and surface electrocardiogram] Each phase of the myocardial action potential (numbers, upper panel) corresponds to a deflection or interval on the surface ECG (lower panel). Phase 4, the resting membrane potential, is responsible for the TQ segment; this segment has a prominent role in the ECG manifestations of ischemia during exercise testing.

Action potentials은 국소적 심근 허혈 동안 현저하게 변합니다. 다음 그림은 exercise-induced ischemia에서 일반적인 임상 상황을 나타내는데 그 이유는 critical coronary lesions에 의해 공급받는  subendocardial regions이 가장 vulnerable하기 때문입니다. Panel A는 안정 시 심전도이며 subendocardial(Endo)과 subepicardial(Epi) muscle cells의 action potential을 나타냅니다. 손상된 subendocardial cells의 diastolic injury current는 TQ segment elevation(또는 "pseudo" ST depression)을 만듭니다(Panel B). 손상된 subendocardial cells의  systolic & diastolic injury currents는 TQ elevation과 "true" ST depression을 만듭니다(Panel C).

[Subendocardial ischemia during exercise testing as viewed from a V5 electrode] Panel A: At rest, a normal ECG results from the firing of hypothetical action potentials from subendocardial (Endo) and subepicardial (Epi) muscle cells. Panel B: A diastolic injury current from injured subendocardial cells causes TQ segment elevation (or "pseudo" ST depression). Panel C: Systolic and diastolic injury currents from injured subendocardial cells (panel C) causes TQ elevation and "true" ST depression.

REF. UpToDate 2018.08.26