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Flashcards in Physiology-Clinical Approach to ECG Deck (20)
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What 5 things must you systematically look for when analyzing and ECG?

Rate, rhythm, intervals, axis and morphology


How are the grid intervals assigned in an ECG?

Small box = 40 msec. Big box = 200 msec. 5 big boxes = 1 sec. 10 small boxes = 1 mV.


What is the heart rate in this patient?

Look at the QRS complex that falls on a heavy red line. Then recite, 300 for the next line, 150 for the next 100 for the next 75 for the next, 60 for the next and 50 for the last. This will give you the heart rate. An alternate way, is to count the number of QRS waves and multiply by 6 because each standard EKG reading is 10 seconds long.


What do you look for to determine that someone has normal sinus rhythm?

HR = 60-100. One and only on P-wave per QRS complex. Normal PR interval and upright P-waves in leads II, III and aVf (leads at bottom of heart).


What is this patient at particular risk for?

Clots, he does not have p-waves, the atria are beating like crazy and blood is not being moved through the heart.


What are the ranges of the P-wave, PR interval, QRS complex and QT interval you hope your patients fall into?

P wave = .06 - .1 second. PR = .12 - .2 seconds (3-5 boxes). QRS = .06 - .1 seconds (1.5-2.5 boxes). QT < .45 seconds. 


What does a slower PR interval tell you? What if it is faster?

Something is slowing conduction through the AV node. If it is faster, there is some abnormal connection that allows signal bypass of the AV node from the atria to the ventricles.


What does a wider QRS interval tell you?

One of the His bundle branches is broken and conduction to that ventricle is not occurring normally.


What does a slower QT interval tell you?

The heart is taking longer to repolarize.


What does a normal QRS interval reflect?

Signal passing through the AV node to the interventricular septum and then initially from left to right ventricles, making them contract rapidly and simultaneously.


What defines left axis deviation and right axis deviation? What condition is indicated by these conditions?

Normally, the signal will travel in the positive directions of lead 1 and lead 2…indicating normal axis. Left axis deviation (abnormally enlarged left ventricle) occurs when the signal is + in 1 and - in 2. Right axis deviation (abnormally enlarged right ventricle) occurs when the signal is - in 1 and + in 2.


What type of axis does this patient have?

The QRS wave is positive in lead 1 and negative in lead 2 so this patient has left axis deviation and may have an abnormally enlarged left ventricle.


What things go into your analysis of morphology of a patient's ECG?



Why is this considered a normal ECG?



What is the first thing you should think of when you see an abnormal T wave?

Potassium. Opening of potassium channels is what aids in repolarization and if repolarization defect is manifested in an abnormal T wave, that is a good thing to consider.


What would an ECG look like in a patient with a left bundle branch block (LBBB)?

The right ventricle depolarizes normally, but the left cannot rely on the bundle of His. It must rely on cell-to-cell conductance which is much slower. You will see a wide QRS as the right ventricle is activated and the signal propagates slowly to the left ventricle.


What would an ECG look like in a patient with a right bundle branch block (RBBB)?

You will still have the initial left to right deflection and a late negative deflection in V6 indicating slow depolarization of the right ventricle. You will have a wide QRS.


What differentiates left bundle branch block from right bundle branch block?

Left: you lose initial positive septal depolarization with a big negative deflection in V1 and you have a large positive QRS with a missing initial negative septal depolarization in V6. Right: you have normal initial negative deflection in V6 with left ventricle depolarization and late negative deflection due to late right ventricle depolarization. Additionally the QRS will be wider than three boxes. 


What condition would have a similar ECG reading as seen below? What causes this condition?

Wolfe- Parkinson- White. Notice the P-R interval is very short (less than 3 boxes, or 120 ms). Note the presence of a delta wave and a large QRS (3 boxes or 100 ms). This condition is a birth defect where you are born with a little bridge of muscle between the atria and the ventricles that bypasses the delay checkpoint AV node. This causes a wide QRS because His-Purkinje system is bypassed and you rely on cell-to-cell gap junction conductance for depolarization.


What is abnormal about the ECG seen below?


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