Harrison's Ch 228: ECG Flashcards
The smallest (1 mm) horizontal divisions on the ECG correspond to what time period?
0.04 seconds
The heavier lined horizontal divisions on the ECG correspond to what time period?
0.20 seconds
What does “deflection” refer to in an ECG?
The amplitude of a wave
With standard calibration, how many mm= 1mV on an ECG?
10 mm = 1 mV
What are the 4 major ECG intervals?
#RR #PR #QRS #QT
How can the heart rate be calculated from the RR interval?
Divide # of large time units (0.2) between consecutive R waves into 300 or the # of small units (0.04) into 1500
What does the PR interval measure? What is a normal PR interval?
#The time between atrial & ventricular depolarization. #Normally 0.12-0.2 seconds
What does the QRS interval measure? What is a normal QRS interval?
#Reflects duration of ventricular depolarization #Normally ≤ 0.10 sec
What’s the QT interval, anyway?
It measure the time of both ventricular depolarization & repolarization. It varies inversely with heart rate.
How do you get a “corrected” QT interval, or a QTc?
What is a normal QTc interval?
#The QT interval divided by the square root of the RR interval, or QT/√RR # ≤ 0.44 seconds
The QRS is divided into specific deflections, or waves. What are they?
#If the intial deflection is negative, it's Q-wave #First positive deflection is R-wave #Negative deflection after R is S-wave
What do you call an entirely negative QRS complex?
A QS wave
Where do the 6 frontal plane leads go?
#V1: 4th intercostal just to the right of sternum #V2: 4th intercostal just to left of sternum #V3: Midway btwn V2 & V4 #V4: 5th intercostal space, midclavicular line #V5: Anterior axillary line, same level as V4 #V6: Midaxillary line, same level as V4 & V5
A normal P-wave will be positive & negative in what leads?
#Positive: Lead II #Negative: aVR
Activation of the atria by an ectopic pacemaker in the lower atrium or from the AV junction may produce what kind of P-waves?
#Negative in lead II #Positive in aVR
Right atrial overload (acute or chronic) may lead to what ECG finding?
- Increased P-wave amplitude
* Tall, peaked P-waves in limb or precordial leads
Left atrial overload or enlargement may produce what ECG finding?
#Biphasic P-wave in V1 with a broad negative component, or #Broad, often-notched P-waves in 1 or more limb leads #Often called "left atrial abnormality" because this pattern may occur in left atrial conduction delays even without atrial enlargement
Right ventricular hypertrophy due to pressure load (e.g. pulmonic valve stenosis or pulmonary artery hypertension) may lead to what ECG change?
- Relatively tall R-wave in lead V1 (R ≥ S)
* Usually with R axis deviation
Left ventricular hypertrophy may cause what ECG changes?
- ST-segment depression
* T-wave inversion in leads with prominent R wave
Acutecor pulmonaledue to pulmonary embolism may result in no ECG changes, or the following ones:
Sinus tachycardia most common
Other tachyarrythmias may occur # Slow R-wave progression # ST abnormalities in V1-V4 simulating acute anterior infarction
Chroniccor pulmonaledue to obstructive lung disease may cause the following ECG changes:
- Small R-waves in R-to-mid precordial leads
* Low voltage complexes r/t hyperinflation of lungs
The presence of left atrial abnormality increases likelihood of underlying left ventricular hypertrophy in which cases?
Cases with borderline voltage criteria
The sensitivity of conventional voltage criteria for LVH is decreased in what 2 groups of people?
#Obese patients #Smokers
In bundle branch blocks, the QRS vector (axis) is oriented in what direction?
The direction of the region where depolarization is delayed.
In plain English: TOWARD the block.So if the patient has a RBBB, the axis may be shifted to the right.
