Electrocardiogram (EKG)
Whats with the K
Some say because the German translation is electrokardiogram
But the dude who invented it was Dutch. The Dutch translation is elektrocardiogram (that works too)
P-wave
Represents atrial depolarization
➔ atrial contraction
Q-wave
Septal depolarization
R&S-waves
Ventricular depolarization
➔ ventricular contraction
T-wave
Ventricular repolarization
Determine Rate and rhythm
EKG Leads
Which 3 limb leads “look down” (inferiorly)?
______________ = inferior leads
Which 2 limb leads (ignoring aVR) “look up”.
One looks at “upper” heart
______________ = reciprocal of inferior leads
Those 2 leads “look right ➔ left”
Which 2 precordial leads “look right ➔ left”? (Pt’s right and left)
_____________
So, those 4 leads “looking right ➔ left” are looking laterally
_____________ = lateral leads
And the reciprocal leads for those lateral leads are inferior leads
Which 4 precordial leads “look at the front” (anterior)
____________ = anterior leads
V1 & V2 “look” at the septum
Which way does aVR “look”?
___________
V1 kinda looks that way too…
Heart's electrical vector (normal axis) is toward LV
Leads looking in the direction of vector are positive
Note the R-wave progression from V1 to V6
Leads looking away from vector are negative
aVR and V1 have a negative inflection
Modified from: https://commons.wikimedia.org/wiki/File:Nsr_(CardioNetworks_ECGpedia).jpg CardioNetworks: Drj, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
4 electrodes ➔ 3 limb leads AND 3 augmented limb leads
5 electrodes (tele monitor)➔ all limb leads AND 1 precordial lead (usually V1)
10 electrodes ➔ all limb leads AND 6 precordial leads
Myocardial Infarction
A partial occlusion of a coronary artery (or one that doesn't last long) ➔ ischemic changes ➔ ST depression or T-wave inversions
A complete occlusion of a coronary artery causes ST-elevation ± deep Q-waves (usually develop later)
STEMI (ST elevation myocardial infarction)
>0.1mV (1 small box) in limb leads
>0.2mV (2 small boxes) in precordial leads
In anatomically contiguous leads (supplied by same artery)
Reciprocal changes (ST-depression) in opposing leads
Where is the MI (which artery is affected)
Modified from: https://commons.wikimedia.org/wiki/File:Nsr_(CardioNetworks_ECGpedia).jpg CardioNetworks: Drj, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Random EKG tidbits
Posterior EKG
Because MI ➔ ST elevation in affected leads and ST depression is in reciprocal leads...
If you had leads that “looked at the posterior”… the anterior leads would be reciprocal. So, anterior leads can tell you there is a posterior MI
If you see ST depression in anterior leads - think posterior MI
Do a posterior EKG: V4 becomes V7 (left posterior axillary line), V5 becomes V8 (bottom of mid-scapula), V6 becomes V9 (left paraspinal)
Left Main Coronary Artery Occlusion
STE in aVR > STE in V1 and Horizontal ST depression in leads I, II, V4-6
Subendocardial ischemia ➔ ST depression, and because aVR is the electrical opposite of left leads (I, II, V4-6)... ST depression in left leads ➔ STE in aVR
I am no expert and I understand that this EKG pattern is classically taught for LMCA occlusion
But this pattern can be present with sub-occlusion of LMCA and is most commonly seen in subendocardial ischemia
Also, a true left main occlusion is likely fatal because it supplies so much of the heart...
"STE-aVR with multilead ST depression was associated with acutely thrombotic coronary occlusion in only 10% of patients. Routine STEMI activation in STE-aVR for emergent revascularization is not warranted, although urgent, rather than emergent, catheterization appears to be important." https://pubmed.ncbi.nlm.nih.gov/30639554/