ECG

anonymous asked:

Hi can you explain the difference between heart rate and rhythm? I'm studying atrial fibrillation and flutter and I can't understand the difference between the two...

Wow! That is a fantastic question!


To start, heart rate means how fast the heart is beating. How many “beats per minute.” The easiest way to measure the rate would be putting your fingers on a patient’s pulse. This can get tricky sometimes because the atrium(top) can beat, contract or pump at a different rate than the ventricles(bottom). The pulse you feel in the wrist corresponds to the ventricular contractions. Looking at an electrocardiogram, or ECG/EKG, you can measure the beats per minute by looking at the number of PQRST complexes. 

Now the rhythm corresponds to whether each P wave is followed by a QRS wave. Do the atrium and ventricles contract in succession? There are many variations to this and we call those arrhythmias. Each P wave being followed by a QRS wave is called Normal Sinus Rhythm. If there are no discernible P waves, meaning the atrium is not properly contracting, this is called Atrial Fibrillation because the atrium is fibrillating but not fully contracting.

During flutter the atria are contracting, but very very fast. So on the ECG you will see P waves. But not every P wave is followed by a QRS complex. Sometimes you see 2, 3 or 4 P waves prior to each QRS complex. It takes multiple atrial contractions for 1 ventricular contraction. It is called a “saw-toothed” pattern.

Hope this helps!!

Evaluating axis from ECG (Mnemonic)

Hi everyone! We are going to learn how to determine the axis from an electrocardiogram =D

First of all, do you know which two leads should be looked at to determine whether axis is in the normal quadrant or if it is Left Axis Deviation (LAD) or Right Axis Deviation (RAD)?

Look at lead I and lead II. Sounds simple! ^__^

An upright (positive) QRS in leads I and II is normal (–30 degrees to +105 degrees).
In left-axis deviation, there is an upright QRS in lead I and a downward (negative) QRS in lead II ( +105 degrees).

How do I remember this? @_@

Thumbs up method: Lead I = Left thumb, Lead II = Right thumb.

Wait, why lead I is left thumb and lead II is the right thumb?
Because left is a smaller word and it gets the smaller number, that is, one!
Right has more alphabets and it gets the bigger number, that is, two.

Left thumb up (I) + Right thumb up (II) = Normal.
Left thumb up (I) + Right thumb down (II) = LAD.
Left thumb down (I) + Right thumb up (II) = RAD.

Mnemonic method:
Left leaves, right returns.

That’s all!
Have a splendid week everyone

My heart skip skips a beat

HEARTBEATS!!

The pause is to allow the atria to fully empty into the ventricle.

Heartbeat on an ECG trace

P Interval (Ventricular Diastole)

  • Atria and ventricles are relaxed
  • blood is flowing into the atria from the veins. 
  • Atrial pressure increases above that of the ventricle, AV valves open allowing blood to flow into the ventricle

P Wave (Atrial Systole) P-Q

Signal transduction from SA to AV nodes. 

  • SA node fires 
  • Atria contract causing atrial systole 
  • which forces all blood into the ventricles
  • emptying the atria.

Q Interval (End of Ventricular Diastole)

Depolarisation of interventricular (IV) septum 

  • AV valves remain open - all remaining blood squeezed into the ventricles. 
  • impulse from the SA node reaches the AV node 
  • which spreads the signal throughout the walls of the ventricles via bundles of His and Purkinje fibres
  • R peak is the end of ventricular diastole and the start of systole.

R Interval (Ventricular Systole)

Ventricular contraction

  • All blood is now within the ventricles
  • so pressure is higher than in the atria - AV valves close
  • ventricles start to contract although pressure is not yet high enough to open the SL (semilunar) valves

ST Segment (Ventricular Systole)

Ventricular contraction

  • Pressure increases until it equals Aortic pressure,
  • SL valves open
  • blood is ejected into the Aorta (and pulmonary artery) as ventricles contract
  • At this time the atria are in diastole and filling with blood returning from the veins.
  • plateau in ventricular arterial pressure

T Wave (Ventricular Diastole)

T= moment of Ventricular repolarisation immediately before ventricular relaxation

  • Ventricles relax
  • ventricular pressure is once again less than the aortic pressure 
  • so SL valves close
ECG: quick and dirty

I’ve had countless sessions and lectures on ECGs. I don’t know how many websites I have bookmarked, or how many times my eyes glazed over reading Dubin. I’m 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. 

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. 

2. RATE. Look at the number on top of the printed ECG. It’s stupid not to use that number. Yes, you should know the rule, 300-150-100-75-60-50. People say you shouldn’t trust the machine because… well, it’s a machine, and it can make mistakes. This is true. I don’t like to look at their “diagnosis” 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 it’s tachy, brady, etc. If the machine is telling you it’s 200 and if it looks tachy, then it’s probably the right number. 
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. It’s 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 it’s between 0 and +90, then it’s normal axis. If the number isn’t provided, or if your preceptor doesn’t believe in the convenience of machines/technology, look at the QRS complex of lead I and lead II. 
  • 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 hypertrophy…PE)
5. did someone say HYPERTROPHY?
  • look at V1
  • is the R wave tall? (greater than 7mm?) right ventricular hypertrophy.
  • is the S wave tall? (greater than 11mm?) left ventricular hypertrophy.
  6. P-waves
  • look at lead II
  • is it wide? left atrial enlargement.
  • is it tall? right atrial enlargement.
7. PR interval
  • 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 there’s some sort of block at the AV node. 
  • 1st deg block. PR interval is long. everything else is normal. cool. 
  • 2nd deg block
  • type I: PR interval progressively gets long. eventually a dropped QRS.
  • type II: PR interval is constant, but randomly dropped QRS. 
3rd deg block “complete block”
  • 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. 
8. QRS complex
  • narrow or wide? 
  • narrow: good. signal coming from somewhere above ventricles. 
  • wide: think BBB (bundle branch block)
  • LOOK AT V1 ONLY.
  • if the last deflection of QRS is DOWN, then it’s a left BBB
  • if the last deflection of QRS is UP, then it’s a right BBB. super easy. no more of this bunny ears crap. 
9. ST segment
  • always look from J point, and compare with the isoelectric line of T-P segment (NOT PR interval). 
  • elevated/depressed… STEMI… duh. indicates ACUTE ischemic changes. 
  • 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.  
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. 
  • massive discordance is abnormal. (STEMI is greater than 5mm)
  • this isn’t that important. Moving on. 
Inferior STEMI. Could right ventricle be involved? 
  • DO NOT GIVE NITRO DO NOT GIVE NITRO DO NOT GIVE NITRO.
  • order a 15 lead
  • 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
10. T waves
  • is it inverted? indicates recent ischemic changes. 
11. Q waves
  • 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). 
I literally go through this list of 11 points in my head when I’m 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 doesn’t take a lot of time at all- a patient is not likely going to have all these issues with their heart.    Anyway. I still don’t 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 don’t get these moments as much as I would like to, but it’s 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.

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This diagram shows how the mechanics of the heart co-ordinate with the heart sounds and the ECG (EKG).

By keeping this diagram in mind, it can make identifying murmurs much easier, by taking the pulse whilst auscultating.  

The pulse represents the maximum arterial pressure, which as you can see in the diagram occurs in between heart sounds 1 and 2. Once you have identified which heart sound is which, you can more easily identify systole, and diastole, and describe with greater accuracy the nature of a murmur if present. 

External image

Murmur Murmur

Here’s some causes of murmur patterns:

Ejection Systolic Murmurs

AorticStenosis - Ejection systolic murmur, radiates to carotids (In Aortic Sclerosis, there is no carotid radiation)

Pulmonary Stenosis  - Ejection systolic murmur which radiates to back/left scapula (may obscure second heart sound)

Atrial Septal Defect - sounds like pulmonary stenosis

Hypertrophic Cardiomyopathy - Harsh Ejection systolic murmur, palpable

Pansystolic Murmurs

Mitral Regurgitation - Best heard at apex, radiates to axilla

Tricuspid Regurgitation - Best heard at left lower sternal edge (tricuspid region) 

Ventricular Septal Defect - Best heard at left sternal edge

Early Diastolic Murmurs

Aortic Regurgitation - best heart at left sternal edge, in expiration, with patient leaning forward

(Rarely) Pulmonary Regurgitation

Mid-Diastolic Murmurs

Usually Mitral Stenosis - Best heard with Bell of stethescope at apex, with patient rolled to left

Rarely Tricuspid stenosis - sounds simliar to Mitral Stenosis

Continuous Murmur - referred to as a ‘machinery murmur’, although I don’t think anyone knows what machine it sounds like.

Patent Ductus Arteriosus - rare in adults. Best heard over upper left sternal border, radiates to back/left scapula

2

Today I taught myself about reading EKG’s and where they actually line up with things going on in the heart with regards to MIs. Basically you have 3 coronary arteries that get occluded in most MIs: Left Anterior Descending (LAD), Left CircumfleX (LCX), and Right Coronary Artery (RCA). LAD feeds the anterior heart and the septum. LCX feeds the lateral and some posterior heart. RCA feeds the right ventricle and some posterior heart, as wells as the SA node in 60% of people.

Now EKGs are confusing and complicated, but it gets easier if you remember where they measure relative to the anatomy. This little diagram helps me get started:

I’ve overlaid the heart over this in the diagram up top. Now remember, those arrows are vectors which is reflected in an EKG read by the upstrokes and downstrokes of the read. (I’m oversimplifying things, but physics makes my brain hurt, and this has worked for me so far.) Practically, what it means is that if the arrow is pointing towards the damage you get ST elevations. For example, in an inferior infarct, you get ST elevations in II, III and aVF, which point towards the inferior part of the heart.

You also have leads V1-V6 which are arranged like so:

(Image from wikipedia)

Notice their vectors point anteriorly. So an anterior infarct shows up at ST elevations in some or all of V1-V6. Meanwhile a posterior infarct will show up as ST depression in V1-V3 which point away from the posterior part of the heart.

To take it one step further you can figure out which artery is blocked. But that’s just a matter of knowing the blood supply, which is basically just what’s nearby. When I’m trying to figure it out on a test, sometimes I draw out this 5 second diagram (aka artistic masterpiece):