ECG Flashcards
Things you can detect on an ECG
cardiac rhythm, detection of myocardial ischemia and infarction, conduction system abnormalities, preexcitation, long QT syndromes, atrial abnormalities, ventricular hypertrophy, pericarditis
ECG is used in the evaluation of syncope. T/F
True
contraindications to performing an ECG?
No absolute contraindications to performing an ECG exist, other than patient refusal. Some patients may have allergies or, more commonly, sensitivities to the adhesive used to affix the leads; in these cases, hypoallergenic alternatives are available from various manufacturers.
Prep/positioning for ECG?
patient lying quietly in the supine position
skin is clean and trimmed of excess hair in the areas in which the leads are to be placed.
Which lead is placed at the fourth intercostal space at the right sternal border?
V1
Placement for lead V2?
Lead V2 is placed at the left sternal border directly across from lead V1, also in the fourth intercostal space.
Which lead is placed in the fifth intercostal space at the mid clavicular line
Lead V4
due to obfuscation of bony landmarks in women with large breasts, it is recommended that the electrodes be placed overlying, rather than beneath, the breast. T/F
False
it is recommended that the electrodes be placed beneath, rather than overlying, the breast.
Steps in reviewing an ECG
Rate: Normal versus tachycardia versus bradycardia
Rhythm: Abnormal versus normal sinus
Intervals: PR, QRS, QT
Axis: Normal versus left deviation versus right deviation
Chamber abnormality: Atrial enlargement, ventricular hypertrophy
QRST duration: Q waves, poor R-wave progression, ST-segment depressions/elevations, or T-wave changes
How much time does each ECG box represent
On the horizontal axis, each large box represents 0.2 seconds at a typical paper speed of 25 mm per second, which is then divided into five smaller boxes that each represent 0.04 seconds
Placement of lead V5?
lead V5 is placed in the same horizontal plane as that of lead V4 in the anterior axillary line or midway between leads V4 and V6 when the anterior axillary line is not readily discernible.
Placement of lead V6?
Lead V6 is placed in the horizontal plane of V4 at the mid-axillary line
What can be determined by the interval between 2 successive QRS complexes
Heart rate, when cardiac rhythm is regular
How to calculate heart rate on ECG?
300 / (no. of large boxes between 2 successive QRS complexes) bpm
The ECG displays a period of 8 seconds. T/F
F
the ECG displays a period of 10 seconds
How to obtain average heart rate when heart rate is irregular
If the heart rate is irregular, count the number of QRS complexes on the ECG and multiply by 6 to obtain the average heart rate in bpm (the ECG displays a period of 10 seconds; thus, 6 × 10 seconds = 60 seconds [1 minute]).
P wave represents?
atrial depolarization
The normal P wave morphology is upright in what leads?
I, II, and aVF, but it is inverted in lead aVR.
Abnormal p wave?
The P wave is typically biphasic in lead V1 (positive-negative), but when the negative terminal component of the P wave exceeds 0.04 seconds in duration (equivalent to one small box), it is abnormal.
What do you suspect with increased p wave duration
Left atrial enlargement
What does right atrial enlargement look like on ECG?
Right atrial enlargement is associated with a peaked P wave taller than 2.5 mm in the inferior leads and more than 1.5 mm tall in leads V1 and V2.
What represents the time from the depolarization of the sinus node to the onset of ventricular depolarization
PR interval
Normal duration of PR interval?
between 0.12 to 0.20 seconds.
The measurement starts from the beginning of the P wave to the first part of the QRS complex
Ventricular depolarization ECG?
QRS complex
Normal duration for QRS complex
0.06 to 0.10 seconds
ST segment?
interval between ventricular depolarization and ventricular repolarization.
QT interval
The QT interval measures the depolarization and repolarization of the ventricles. QT prolongation is associated with development of ventricular arrhythmias and sudden death.
The QT interval is dependent on the heart rate. A faster heart rate leads to a shorter QT interval, whereas a slower heart rate leads to a longer QT interval.
Positive deflection in ECG?
A positive deflection is when the direction of the overall electrical activity is toward that lead.
Where does normal cardiac axis lie?
The normal cardiac axis is expected to lie between -30º and 90º, which means the overall direction of electrical activity is toward leads I, II, and III.
if the QRS complex is upright in both leads I and II, is the axis deviated?
if the QRS complex is upright in both leads I and II, then the axis must fall somewhere between -30º and 90º and the axis is normal.
Lead AVR should always be negative. T/F
True
If not, possible limb lead reversal
Axis deviation if the complexes are negative in lead I and positive in lead aVF
Right axis deviation
Causes of right axis deviation
normal variation
right ventricular hypertrophy, left posterior fascicular block, ventricular ectopic beats, preexcitation, and dextrocardia
Axis deviation if the complexes are positive in lead I but negative in lead II
Left axis deviation
The causes of left axis deviation include
normal variation, left ventricular hypertrophy, left anterior fascicular block, congenital heart disease with primum atrial septal defect or endocardial cushion defect, ventricular ectopic beats, and preexcitation syndromes.
Inferior leads
II, III and AVF
Drugs that slow AV node conduction
Beta blockers and calcium channel blockers. They also slow the rate of SA node firing and therefore reduce heart rate
What can prolong QRS intervals?
Bundle branch blocks or drugs that slow ventricular depolarization
What can prolong QT interval?
drugs that block ventricular repolarization
How does slowing heart rate affect diastole
Increase
What is R-R interval
Distance b/w QRS complexes
Used to determine heart rate
Slower heart rate on EKG?
Decrease in SA node firing rate
Increase in R-R interval, QT interval, and time of diastole
Reasons for increased R-R intervals at slower heart rates
Ventricular depolarization takes longer, therefore QT interval prolongs
Also, at slower HR, it takes longer for the heart to generate a new P wave, time in diastole increases
How does a fall in sinus rate affect diastole?
Increase it
Conduction through where occurs after atrial depolarization (Start of P wave) and before ventricular depolarization (start of QRS complex)
Conduction through the AV node, HIS bundle, bundle branches and purkinje fibers
Prolonged conduction through any of these structures can increase the PR interval
AV node, HIS bundle, bundle branches and purkinje fibers
Which interval is affected by bradycardia and tachycardia
Q-T interval
Prolonged Q-T interval
anything over 500 ms
T wave extends beyond halfway point between 2 QRS complexes
Examples of Q-T prolonging medications
many antiarrhythmic drugs and macrolide antibiotics
Classic findings of hypokalemia
Muscle weakness, U waves on ECG
Loop diuretics increase potassium excretion (eg furosemide given in congestive heart failure)
Hyperkalemia?
Muscle weakness,
No U waves
Peaked T waves
Hypercalcemia?
short QT interval
Volume depletion
Confusion
Hypocalcemia
Prolonged QT interval
Muscle spasms
Tetany
Conduction velocity, fastest vs slowest
Purkinje>Atria>Ventricles>AV node
