Iâve had countless sessions and lectures on ECGs. I donât know how many websites I have bookmarked, or how many times my eyes glazed over reading Dubin. Iâm also terrible at cardiology. I was on my way to accepting my fate of being horrible at ECGs forever, until I had a life changing session on ECGs taught by a great ER doc. I want to post it here because it was probably the most useful thing I learned in med school, and it will stick with me for the rest of my career.Â
WHEN LOOKING AT ECGs FOR THE FIRST TIME:
1. One ECG is never enough. Always get old ones for comparison. If none available, do another one. Because. One ECG is never enough.Â
2. RATE. Look at the number on top of the printed ECG. Itâs stupid not to use that number. Yes, you should know the rule, 300-150-100-75-60-50. People say you shouldnât trust the machine because⊠well, itâs a machine, and it can make mistakes. This is true. I donât like to look at their âdiagnosisâ until I have gone through it myself. But the rate is just a number. Plus you should be able to eyeball it and be able to tell if itâs tachy, brady, etc. If the machine is telling you itâs 200 and if it looks tachy, then itâs probably the right number.Â
3. RHYTHM. Is there a p-wave for every QRS and a QRS for every p-wave? Is the p-wave upright in lead II and down in aVR? Good. Done. BOOM. Itâs sinus rhythm. ***if you cannot clearly see the p-waves then you cannot call sinus. move on.
4. AXIS. Again, look at the number at the top of the page. If itâs between 0 and +90, then itâs normal axis. If the number isnât provided, or if your preceptor doesnât believe in the convenience of machines/technology, look at the QRS complex of lead I and lead II.Â
up in lead I, up in lead II: normal axis
up in lead I, down in lead II: left axis deviation (most common causes are left anterior hemi block and left ventricular hypertrophy)
down in lead I, up in lead II: right axis deviation (most common causes are right ventricular hypertrophyâŠPE)
5. did someone say HYPERTROPHY?
is the R wave tall? (greater than 7mm?) right ventricular hypertrophy.
is the S wave tall? (greater than 11mm?) left ventricular hypertrophy.
is it wide? left atrial enlargement.
is it tall? right atrial enlargement.
should be between 0.12 sec and 0.2 sec (3-5 small boxes). I used to always get this interval and QRS complex (less than 0.12 sec) mixed up. Think: atria depolarizing + shit getting to ventricles is gonna take longer than ventricles depolarizing. [2 things happening] versus [1 thing happening]. [0.12 sec-0.2 sec] versus [<0.12 sec].
long PR interval means thereâs some sort of block at the AV node.Â
1st deg block. PR interval is long. everything else is normal. cool.Â
type I: PR interval progressively gets long. eventually a dropped QRS.
type II: PR interval is constant, but randomly dropped QRS.Â
3rd deg block âcomplete blockâ
there is no association between P waves and QRS. they run separately. **QRS does NOT have to be wide. Just look for P wave/QRS complex disassociation. I sometimes get this and 2nd deg type II mixed up. The only difference I try to remember is that PR interval is constant in 2nd deg type II, but is variable in 3rd deg.Â
narrow: good. signal coming from somewhere above ventricles.Â
wide: think BBB (bundle branch block)
if the last deflection of QRS is DOWN, then itâs a left BBB
if the last deflection of QRS is UP, then itâs a right BBB. super easy. no more of this bunny ears crap.Â
always look from J point, and compare with the isoelectric line of T-P segment (NOT PR interval).Â
elevated/depressed⊠STEMI⊠duh. indicates ACUTE ischemic changes.Â
look for reciprocal changes of the heart. if ST elevation in lateral leads, could see ST depression in the septal leads. PAILS:
posterior up, anterior down
anterior up, inferior down
inferior up, lateral down
lateral up, septal down. Â
LBBB can look like STEMI. How to tell?
disconcordant changes is normal. (QRS and STEMI on opposite sides of the isoelectric line.)
concordant changes is abnormal.Â
massive discordance is abnormal. (STEMI is greater than 5mm)
this isnât that important. Moving on.Â
Inferior STEMI. Could right ventricle be involved?Â
DO NOT GIVE NITRO DO NOT GIVE NITRO DO NOT GIVE NITRO.
is STE in lead III > lead II? likely RV involvement
INFERIOR MI? 15 LEAD NO NITRO
INFERIOR MI? 15 LEAD NO NITRO
INFERIOR MI? 15 LEAD NO NITRO
is it inverted? indicates recent ischemic changes.Â
is it significant? indicates old ischemic changes. will likely be present if followed rule number 1 of reading ECGs. (1 ECG is never enough= look at old ECGs).Â
I literally go through this list of 11 points in my head when Iâm reading an ECG, regardless of whether or not I have an atrial flutter jumping at my face or if I see a massive anterolateral STEMI. Obviously I needed background knowledge on ECGs and the physiology of the heart before constructing this list, but this basic checklist has been very, very useful to me so far. It might look lengthy, but it doesnât take a lot of time at all- a patient is not likely going to have all these issues with their heart.Â
 Anyway. I still donât love ECGs, but it feels pretty wonderful to be able to be able to evaluate it in a systematic manner, and get the theory behind interpreting the scribbles of an ECG reading. I donât get these moments as much as I would like to, but itâs that crosspoint where my classroom learning actually meets real-life applications that gives me happy brain-gasms for days. I love knowing things and more importantly, knowing why.
