PLZ HELP...ST elevation/depression? - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 11-20-2010
USMLE Forums Scout
 
Steps History: ---
Posts: 95
Threads: 30
Thanked 33 Times in 27 Posts
Reputation: 43
EKG PLZ HELP...ST elevation/depression?

Hi, I had a question about ECG. For which diseases (or better way of saying it is "when would"...) would you see a ST ELEVATION? And when would you see ST DEPRESSION?

Basically I am confused as to what does ST elevation and depression represent? And what causes these to happen? And what is the effect of these 2?

Please help!!!! Thanks
Reply With Quote Quick reply to this message



  #2  
Old 11-20-2010
USMLE Forums Scout
 
Steps History: 1 + CK
Posts: 88
Threads: 12
Thanked 177 Times in 49 Posts
Reputation: 187
Default

The ST segment represents a period of ventricular depolarization,it begins at J-point (junction btw QRS complex and ST segment) just before repolarization(T-wave) begins. It lasts 0.08secs and is normally Isoelectric (flat)
The ventricles are still contracting. The pattern of the ST segment reflect changes in the contractile properties of the ventricular myocardium. This can be affected by ischemia, infarction, inflammation or even hypertrophy.

ST Segment Elevation;
In Precordial leads, > 2mm above isoelectric line.
In Limb leads, > 1mm above isoelectric line.
causes: 1). Myocardial ischemia( ST elevation in affected leads)
2). Acute pericarditis(Widespread ST elevation)
3). Ventricular aneurysm

ST Segment Depression:
In precordial leads, > 1.5mm below isoelectric line
In Limb leads,> 1mm below isoelectric line
Causes: 1). Myocardial Ischemia
2). Non- ischemic causes: side effect of Digoxin, Hypokalemia, RVH or LVH, WPW, RBBB or LBBB, Hypothermia, Tachycardia, Mitral valve proplapse.

I hope this helps.
Reply With Quote Quick reply to this message
The above post was thanked by:
dr z (11-21-2010), Krazy (01-13-2014), noone_123i (11-21-2010)
  #3  
Old 11-21-2010
axax's Avatar
USMLE Forums Addict
 
Steps History: 1+CK+CS
Posts: 115
Threads: 3
Thanked 266 Times in 41 Posts
Reputation: 276
Default

Quote:
Originally Posted by noone_123i View Post
Hi, I had a question about ECG. For which diseases (or better way of saying it is "when would"...) would you see a ST ELEVATION? And when would you see ST DEPRESSION?

Basically I am confused as to what does ST elevation and depression represent? And what causes these to happen? And what is the effect of these 2?

Please help!!!! Thanks
It's a simple concept of how the ions behave during myocardia injury. The EKG lead is recoding this change in ion inside and outside the myocardial cells. Remember not in a single cell but rather as an aggregate of whole. The EKG leads tells you where are the ion moving during a particular moment in time or during a particular cardiac cycle. All chest leads are positive leads so if a depolarizing current is moving toward it there is a positive deflection and the tracing moves up and if it is moving away from the positive lead then there is negative deflection e.g. Q is a negative wave and R is a positive wave. I hope you have a basic concept on EKG.

Now let's understand what is the deal with ST elevation and ST depression and then the Q wave.

Now all these ECG changes tell us that there is myocardial ischemia but the question is what type of ??? subendocardial ischemia, transmural ischemia or the infarction which is replaced by scar tissue.

In subendocardial infarction there is ST depression but why? Why not ST elevation?

Myocardium is divided into three layers the top most is the epicardium, then myocardium and then the endocardium. In subendocardial infarction endocardium is injured. Just picture there is a chest electrode facing this injured area.
In normal ST segment is a straight line on the EKG paper that represent completion of cardiac depolarization, as all the myocardial cells are now loaded with positive ions inside the cell and there is no net movement of ions in or out . This is why there is no positive or negative deflection on EKG. Now in subendocardial infarction, during this ST phase there is an influx of Cations from the surrounding area and area above it to the injured cells. So the chest electrode see there positive ions moving away from it (remember the chest electrode is directly above it)and makes a negative deflection. This negative deflection that occurs in ST phase is called ST depression.

In transmural (ALL 3 layers) infarction there is ST elevation why?

So again during the ST phase of depolarization normally all the cardiac cells are electrically silent as there is no net movement of ions but in transmural infarction during this ST phase there is an influx of Cations from the surrounding area to the injured cells. Because the infarction is all the way to the top layer and just above it is the chest electrode, the electrode sees cation rushing towards it, so it records the positive deflection during the ST phase which is ST elevation

Now why there is persistent Q wave in old myocardial infarction.

The old infarcted myocardial tissue is replaced by collagen fibers and this fiber does not conduct electrical current so it is electrically silent. Now think of the old infarcted myocardial tissues as a hole in the myocardium (going through all three layers), and there is a chest electrode directly above it. Now during depolarization, the scarred myocardial tissue is electrically silent (think of it as a hole) so the chest electrode sees directly opposite myocardial tissue electrical activity. During depolarization It sees the electrical current moving away from it hence you have the Q wave a negative wave. This is why in old infarct you have persistent Q wave.


I hope this clears your basic concept on cardiac electrical physiology

Good luck for USMLE

Cheers......
Reply With Quote Quick reply to this message
The above post was thanked by:
anamta (12-20-2015), ashishkabir (11-21-2010), dr z (11-21-2010), gauravkem (12-28-2014), Krazy (01-13-2014), noone_123i (11-21-2010), pkul85 (01-29-2014)
  #4  
Old 11-21-2010
ashishkabir's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 625
Threads: 19
Thanked 371 Times in 220 Posts
Reputation: 391
Default

Also, to add to this discussion - you see ST depression in Stable or Unstable angina and ST elevation in Prinzmetals Angina
Reply With Quote Quick reply to this message



Reply

Tags
Cardiovascular-, Pathology-

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Anaclitic Depression timing! dranant USMLE Step 1 Forum 4 12-28-2010 12:17 PM
depression counseling accurate USMLE Step 2 CS Forum 2 12-02-2009 11:16 AM
Isolated AST Elevation Sabio USMLE Step 2 CK Bits & Pieces 0 11-22-2009 09:51 PM
Avoiding Depression rasheed General Topics Forum 0 08-17-2009 10:23 PM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)