12 Lead ECG Flashcards
What are the three types of cardiac cells?
-pacemaker: have automaticity
-conducting
-myocardial
What are the specialized nodes and cells in the heart? An where are the nodes located?
-SA node (upper part of RA)
-AV node (triangle of Koch)
-bundle of his (AV fibers)
-purkinje fibers
What are the intrinsic rates of SA, AV, and purkinje fibers?
SA: 80-100
AV: 40-60
P: 20-40
What is the amplitude and duration of a normal P wave?
0.5-2.5mm amplitude and 0.11 sec (3mm)
What does the PR interval represent? And what is a normal interval?
Time for electrical activity to move b/w the atria to the ventricles. Normally 0.12-0.2 sec (3-5mm).
What does the ST segment represent?
Isoelectric line representing the time b/w ventricle depol and repol.
What does ST segment depression imply?
Myocardial ischemia
What does ST segment elevation imply?
Myocardial infarct
What does the QT interval represent? And how long is it normally?
Represents the time for ventricles to depol and then repol. Normally <0.4 sec (10 small boxes or 2 large boxes). It is usually less than half of one R-R interval.
What is the ECG paper speed?
25mm/sec
What is the difference b/w an ECG electrode and an ECG lead?
Electrode: conductive pad attached to skin to record electrical activity
Lead: graphical representation of the heart’s electrical activity using several electrodes
What does the QRS axis reflect? Where does the QRS axis normally lie?
Reflects the general direction of electrical flow during depol. Usually lies left and downward (-30 and +90 degrees)
How does ventricular mass effect axis deviation?
More mass means more intense electrical activity (more to depol).
What factors cause right axis deviation?
-normal in the young and thin
-myocardial infarction
-anything that causes RV hypertrophy or stress (ex. severe COPD, PE)
What ECG changes might be seen with right axis deviation?
-P waves larger due to RA enlargement in leads II, III and aVF
What factors cause left axis deviation?
-may be normal in the older and obese (increased afterload)
-myocardial infarction
-dextrocardia
-high diaphragm (pregnancy, acites)
Where is the J point?
Right after the QRS wave
What is myocardial ischemia indicated by?
-depressed ST segment greater than 1mm below baseline at the J point in 2 or more contiguous leads
-hyperacute inversion of T waves
Where are the V1-V6 electrodes placed?
V1: fourth intercostal space on right sternum
V2: fourth intercostal space on left sternum
V3: midway b/w V2 and V4
V4: fifth intercostal space at midclavicular line
V5: anterior axillary line on same horizontal level as V4
V6: mid axillary line on same level of 4 and 5
What changes are seen on ECG if there is myocardial injury?
-ST segment elevated greater than 1mm above the baseline at 0.4sec past the J point
-ST segment returns to baseline with restored perfusion–> injury may be reversible
What changes are seen on ECG when there is myocardial infarction (necrosis)?
-ST elevation
-pathological Q waves appear if old MI present (abnormal if they are greater than 0.4 sec wide and greater than 25% the height of R wave, appear hours to days following acute MI, generally remain for the duration of the pts life)
What is the primary criteria for a BBB?
Wide QRS (greater than 0.12 sec) for a complete block.
What chest leads are used to look at most commonly for BBB?
Right: V1 and V2
Left: V5 and V6 (V1 can also tell info on LBBB)
What medical conditions can affect the R heart and are screening for with RBBB?
-PE
-chronic lung dx
-septal disorders
