STEP 6;ST SEGMENT ABNORMALITIES

STEP 6 :ST SEGMENT
The ST segment represents the early part of ventricular repolarization.
The ST segment is the line that from the end of the QRS complex to beginning of the T wave. 

Normal ST segment is flat/ isoelectric, 
 
GIVES IMPORTANT INFORMATION ON THE CORONARY BLOOD SUPPLY TO THE HEART VIA THE CORONARY ARTERIES.

1.ST SEGMENT ELEVATION-suggests myocardial infarction due to blocked coronary arteries causing a dead/necrosis to a specific segment of the heart.

2.ST SEGMENT  DEPRESSION- Suggests myocardial ischemia due to a partially blocked coronary artery causing a poor perfusion of oxygen to the heart muscle/myocardium.

PLEASE DON'T MISS TO DIAGNOSE THESE ST SEGMENT ABNORMALITIES.
YOU MIGHT LOOSE YOUR PATIENT.

ALERT THE CONSULTANT CARDIOLOGIST/PHYSICIAN FOR ACTION.
URGENT CORONARY ANGIOGRAPHY WOULD BE REQUIRED.

ECG INTERPREATATION HALLMARK OF TRAINING: HEART AXIS

5.IMPORTANT STEP :ECG HEART AXIS
Indicates the direction of the average electrical depolarization with an arrow (vector). This is the heart axis.
A change of the heart axis or an extreme deviation can be an indication of pathology.
To determine the heart axis you look at the LIMB leads only (not chest leads V1-V6).
  On leads I, II, and AVF you can make a good estimate of the heart axis.

 An important concept in determining the heart axis is the fact
-electricity flow towards a lead yields a positive deflection in the electric recording of that lead.

YOU remember the the EINTHOVENS TRIANGLE -

• Positive  QRS deflection in lead I: the electrical activity is directed to the left (of the patient)
• Positive QRS deflection in lead AVF: the electrical activity is directed down.                                                                                             Clinical application
  
• • A left heart axis is present when the QRS in lead I is positive and negative in II and AVF. (between -30 and -90 degrees)
  • A right heart axis is present when lead I is negative and AVF /II positive. (between +90 and +180)
  • An extreme heart axis is present when both I and AVF/II are negative. (axis between +180 and -90 degrees) 
    

    Left axis deviation

    
    

    

    Left heart axis
    
    

    

    Left anterior hemiblock
    
    Causes of left axis deviation include:
    
  • Normal variation (physiologic, often with age)
  • Mechanical shifts, such as expiration, high diaphragm (pregnancy, ascites, abdominal tumor)
  • Left ventricular hypertrophy
  • Left bundle branch block
  • left anterior fascicular block
  • Congenital heart disease (e.g. atrial septal defect)
  • Emphysema
  • Hyperkalemia
  • Ventricular ectopic rhythms
  • Preexcitation syndromes
  • Inferior myocardial infarction
  • Pacemaker rhythm 
  
  

  Right axis deviation

  
  

  

  Right heart axis deviation
  
  Causes of right axis deviation include:
  
• Normal variation (vertical heart with an axis of 90º)
• Mechanical shifts, such as inspiration and emphysema
• Right ventricular hypertrophy
• Right bundle branch block
• Left posterior fascicular block
• Dextrocardia- heart in the right position
• Ventricular ectopic rhythms
• Preexcitation syndromes
• Lateral wall myocardial infarction
• Right ventricular load, for example Pulmonary Embolism or Cor Pulmonale (as in COPD)

• 
  

ECG INTERPRETATION HALLMARK OF THE TRAINING PART 2

3.T wave 

The T wave indicates the repolarisation of the ventricles. 

Follows the QRS complex. Take note of T waves which have a 1.downward (negative) deflection ischemic changes indicates  or 2. tall, pointed peaksT waves- indicates hyperkalemia

 
Sometimes we see a U wave.
4.The U-wave is a small upright, rounded bump. When observed, it follows the T-wave.indicates Late repolarisation of the ventricles.

 

 
    STEP 4.INTERVALS

I -PR INTERVAL

The PR Interval indicates AV conduction time.   

The interval is  from where the P wave begins till  the beginning of the QRS complex.  

Count the small boxes  to determine PR Intervals. 

Normal PR  interval is 0.12 to 0.20 seconds (3 to 5 small boxes) 

This interval shortens with increased heart rate.
 

Evaluate if PR Intervals are constant or varying across the EKG strip. 

If they vary, determine if the variations are a steady lengthening until the point where an expected QRS does not appear.

PR Interval questions to address:

• Does the PR-Interval fall within the norm of 0.12-0.20 seconds/120-200 ms?


• Is the PR-Interval constant across the ECG tracing?

II-QT INTERVAL

The QT interval represents the time of ventricular activity including both depolarization and repolarisation. Measured from the beginning of the QRS complex to the end of the T wave. 

Normal, the QT interval is 0.36 to 0.44 seconds (9-11 boxes). The QT interval will vary with patient gender, age and heart rate. 

Criteria-Another guideline is that normal QT Intervals is less than half of the R-R Interval for heart rates below 100 bpm.

Abnormalities associated.-LONG QT SYNDROME.

ECG INTERPRETATION -HALLMARK OF THE TRAINING PART 1

7 STEP METHOD OF  ECG INTERPRETATION

The following steps are required for interpretation of an ECG.
1.Rhythm
2.Rate
3.Waveforms- P ,QRS complex, T wave.
4.Intervals,-PR, and R-R
5. Heart axis
6. ST Segment
7.Abnormalities- e.g Hypertrophy, AV blocks,pericardial effusion


1.The  Rhythm.
There are 3 main types of rhythms.
 1.sinus rhythm- .there is evidence of P waves on the ECG strip indicating the source as sinoatrial node.
Lead 2 (THE GOLDEN LEAD) is ideal in determining presence of P waves.
Absence P waves would suggest-
            ATRIAL FIBRILLATION,
            ATRIAL FLUTTER.
  2.AV junctional rhythm- evident when sinoatrial node fails and hence the AV  node takes over the pacing mechanism of the heart.
 Common with patients with AV block. 2nd  and 3rd Degree AV blocks
 QRS COMPLEXES ARE BROAD  AND WIDE>120ms

 3.Idio-ventricular rhythm-The origin being the purkinje system of fibres.
  This is an emergency with patients being in ICU.
  Very low voltage and wide QRS complexes


2.The Rate.
Expressed in Bpm ( beats per minute)
The easiest and fastest way to calculate the rate is to use two R waves on the ECG strip.
Using a factor of 1500 divide it by the number of small boxes in between the two R waves.
Ideal in ICU EMERGENCY CASES.

Other ways exist such as -
Counting  NUMBER OF R WAVES OF 6 SECOND STRIP OF AN ECG STRIP AND MULTIPLYING THE  NUMBER BY A FACTOR OF 10.

The 300 METHOD is inaccurate and I don't advice you to use it.It involves dividing the factor of 300 by the number of large boxes in between 2 R waves.


3.THE WAVEFORMS
1.The P WAVE.-Indicates atrial contraction/DEPOLARISATION.
A normal P wave is upright /POSITIVE in Lead 2.

The P wave represents atrial depolarization. In normal ECGs the P-wave preceeds the QRS complex. It looks like a small bump upwards from the baseline. The amplitude is normally 0.05 to 0.25mV (0.5 to 2.5 small boxes). Normal duration is 0.06-0.11 seconds (1.5 to 2.75 small boxes). The shape of a P-wave is usually smooth and rounded.


ASK YOURSELF P-wave questions:

• Are they present?


• Do they occur regularly?


• Is there one P-wave for each QRS complex?


• Are the P-Waves smooth, rounded, and upright?


• Do all P-Waves have similar shapes?

2.QRS COMPLEX
The QRS complex indicates  ventricular depolarization. Depolarization triggers contraction of the ventricles.
Because of the larger tissue mass, the QRS complex is larger than the P wave. .

In this step, measure the QRS interval from the end of the PR interval to the end of the S wave.  Normal QRS  interval is 0.08 to 0.12 seconds/60-120 ms  (2 to 3 boxes).

ASK YOURSELF QRS questions:

• Does the QRS interval fall within the range of 0.08-0.12 seconds?


• Are the QRS complexes similar in appearance across the ECG tracing?
•