EKGs Flashcards
How is the PR interval measured? What does the PR interval represent? How long does it normally last?
Measured from the beginning of the P wave to the beginning of the next deflection of the baseline.
It represents the time it takes an electrical impulse to be conducted through the atria and AV node.
Normally 0.12-0.20 seconds long (3-5 small squares)
How long does the QRS complex normally last?
0.12 seconds (3 small squares)
How is the ST segment measured?
From the end of the S wave to the beginning of the T wave.
What does an elevated T wave (greater than half the height of the QRS complex) indicate? An inverted T wave?
Elevated T wave - new ischemia of cardiac muscle
Inverted T wave - previous cardiac ischemia
How is the QT interval measured? How long should it be?
Measured from the beginning of the QRS complex to the end of the T wave.
A normal QT interval is < or = 1/2 the R to R interval of that complex
What is the definition of a regular rhythm?
If the R to R intervals or P to P intervals vary by less than 0.06 sec (1.5 small squares), then the rhythm is regular. A difference of greater than 0.06 sec means the rhythm is irregular
How can you calculate the rate?
calculation by a 6-sec rhythm strip - count the number of R waves in three long lines (30 large squares) and multiply by 10
Calculation by a 3-sec rhythm strip - count the number of R waves in two long lines (15 large squares) and multiply by 20
Calculation by division - (only used if the rhythm is regular) count the number of large squares (add 0.2 for each extra small square) between two R waves and divide 300 by this number
What is sinus bradycardia? sinus tachycardia? Sinus arrhythmia?
Sinus bradycardia - all electrical impulses originate from the SA node and follow the normal cardiac conduction pathway but the rate is slower than 60 bpm
Sinus tachycardia - all electrical impulses originate from the SA node and follow the normal cardiac conduction pathway but the rate is between 101-150 bpm
Sinus arrhythmia - the SA node initiates all electrical impulses but at irregular intervals, producing an irregular rhythm although a normal HR. When the patient inhales, the HR increases. When the patient exhales, the HR decreases.
What is a sinus block? What is a sinus arrest? How can you tell the difference between the two?
Sinus block - SA node initiates an electrical impulse that is blocked and is not conducted to the atria.
Sinus arrest - SA nodes does not initiate an electrical impulse
The pause of a sinus block is equal to exactly two cardiac cycles. In contrast, the pause of a sinus arrest is not equal to exactly two cardiac cycles because a different pacemaker cell in the heart takes over
When do atrial dysrhythmias arise? What are the types of atrial dysrhythmias?
Atrial dysrhythmias occur when the SA node fails to generate an electrical impulse, but other pacemaker cells within the atria initiate it instead.
Types:
Premature atrial contraction (PAC) (not a true atrial dysrhythmia because it is only one complex followed by normal rhythm again)
Paroxysmal atrial tachycardia
supraventricular tachycardia
Atrial flutter
Atrial Fibrillation
What is a premature atrial contraction? What types of pauses follow a PAC?
When the electrical impulse originates from any atrial site other than the SA node. The EKG looks the same as usual, except that the P wave is different or hidden in the T wave of the preceding complex.
The following pause can be:
noncompensatory - The distance between the R wave before the PAC to the R wave after the PAC is less than two times the R-R interval of the underlying rhythm
compensatory - The distance between the R wave before the PAC to the R wave after the PAC is exactly two times the R-R interval of the underlying rhythm
What is the difference between paroxysmal atrial tachycardia and supraventricular tachycardia? How are they similar?
They are both characterized by a sudden onset of a tachycardia > 151 bpm initiated by an irritable site in the atria. The only difference is that in a PAT, the beginning of the PAT is seen and the underlying rhythm is identified. If the onset of the PAT is not seen, it is called a SVT.
Why is tachycardia not tolerable for long periods of time?
When the rate is so rapid, 1) the ventricles do not have time to fill completely, causing a decrease ing cardiac output and 2) most of the blood flow through the coronary arteries occurs between heartbeats, causing the myocardium to not get enough oxygen
What is atrial flutter?
When a single site in the atria (other than SA node) initiates electrical impulses so rapidly that every impulse is not conducted to the ventricles. Characterized by flutter waves (F waves).
If two F waves with one QRS = 2:1 block
If three F waves with one QRS = 3:1 block
The number of F waves with one QRS is constant, the rhythm is regular. If it varies, the rhythm is irregular and is called atrial flutter with variable ventricular response.
What is atrial fibrillation?
When all the sites in the atria (other than the SA node) initiate electrical impulses. Most of the impulses are not conducted so the atria is not completely depolarized and there is no P wave - only a wavy line between each T wave and QRS. At irregular intervals, one electrical impulse is conducted, resulting in ventricular depolarization and an irregularly irregular rhythm.
What is first-degree heart block?
A delay in the conduction of an electrical impulse between the atria and AV node, although all impulses are eventually conducted to the ventricles.
Characterized by a prolonged PR interval (>0.2 sec)
What is second-degree heart block, type I (Mobitz type I)?
A delay in the conduction between the atria and the AV node that becomes longer with each impulse until the interruption completely blocks the conduction to the ventricles. The cycle of progressively delayed conduction is then repeated.
On EKG, PR interval becomes longer and longer until a QRS complex is dropped. Then the pattern repeats.
What is second-degree heart block, type II (Mobitz type II)?
Intermittent, non-conducted p waves due to a block below the AV node (i.e. in the His/purkinje system). Nonprogressive.
Two P waves before one QRS complex = 2:1 block
Three P waves before one QRS complex = 3:! block
What is third-degree heart block?
When the electrical impulse from the atria is completely blocked before it can reach the ventricles. Atria and ventricles function independently - no relationship between the P waves and the QRS complexes. QRS complexes are wide, abnormally shaped but consistent.
What is a bundle branch block?
When there is an interruption of the conduction system of either the right, left or both bundle branches, causing a delay in depolarization of the ventricle of the blocked bundle branch.
EKG is characterized by a single notched or widened QRS complex.
