| What are the disorders in PR interval? | Short PR (WPW syndrome - accessory pathway conducting impulse without AV delay called delta-wave) |
| What is an EKG? | Representation of the electrical events in the cardiac events
Each event has a distinct wave form
Gives an insight into pathophysiology |
| What can be identified by EKGs? | Arrythmias, Myocardial ischemia and infarction, pericarditis, chamber hypertrophy, electrolyte disturbances (hyper/hypokalemia), drug toxicity (digoxin prolongs QT interval) |
| What are the pacemakers of the heart? | SA node (dominant pacemaker, rate 60-100 bpm)
AV node (back up, 40-60 bpm)
Ventricular cells (back up, 20-45 bpm) |
| What is the standard calibration of EKG? | 25mm/s, 0.1 mV/mm
If an electrical impulse is going towards the electrode appears positive, if away appears negative. |
| What do each EKG wave refer to? | P wave: atrial depolarization
QRS: Ventricular depolarization (and atrial repolarization)
T wave: Ventricular repolarization |
| How is the ECG paper? | . |
| What are the EKG leads? | They measure difference in potential between two points, either unipolar or bipolar.
12 leads, 6 limb leads (3 std and 3 augmented) and 6 precordial leads |
| What are the std limb leads and where are they installed? | Right arm, left leg and left arm
Lead I (bipolar, RA to LA 0 degrees)
Lead II (bipolar RA to LL +60 degrees)
Lead III (Bipolar LA to LL +120 degrees) |
| What are the augmented limb leads and where are they installed? | aVR (unipolar, -150 degrees at right arm)
aVL (unipolar, -30 degrees at left arm)
aVF (unipolar, +90 degrees at left leg) |
| Where are precordial leads installed? | V1 right lower sternum, V2 left lower sternum (septal pulse)
V3 between V2 and V4, V4 midclavicular (anterior pulse)
V5 between V4 and V6, V6 midaxillary (Lateral pulse) |
| What are right and posterior leads? | right placement like left for dextrocardia
Posterior leads (3 cords under the scapulae. |
| How are the anatomic grouping of EKG leads? | . |
| What are the 10 rules of EKG? | 1-PR interval between 3-5 little squares (120-200 ms)
2-QRS less than 3 little square (110 ms)
3-QRS positive in leads I and II
4- QRS and T waves have same direction in limb leads
5-aVR all negative
6-R and S grow from V1 to V4 And S disappears in V6
7-ST segment starts isoelectric except V1 and V2
8-P wave upright in I, II and V2-V6
9-No Q or small Q I,II, v2-v6 (1 little square)
10-T wave upright in I, II, V2-V6 |
| How is the P wave? | Always positive in I and II and negative in aVR
<3 squares duration and 2.5 amplitude
Biphasic in V1, best seen in lead II
Biphasic (first phase is for right atrial contraction and second is for left atrial contraction) |
| What are the disorders in P wave? | P Pulmonale (right atrial enlargement, pointed p wave and tall >2.5 squares)
P Mitrale (left atrial enlargement, bifid p wave) |
| What is PR interval? | It is from the beginning of P till the beginning of QRS
Represents atrial depolarization + delay in AV junction which allows time for atria to contract fully before ventricular contraction. |
| What are the disorders in PR interval? | Short PR (WPW syndrome - accessory pathway conducting impulse without AV delay called delta-wave)
Long PR (First degree heart block (AV block)) |
| What are QRS complexes characteristics? | Q wave nonpatho in I,III, aVL, V5 and V6.
R wave in V6 smaller than V5
S wave depth not more than 30mm
Patho Q wave if >25% of R wave ampitude |
| What are the pathologies in QRS wave? | Right Ventricular Hypertrophy (V1 less positive R and V6 less negative)
Left Ventricular Hypertrophy (V1 more negative and V6 more positive, Sokolow and Lyon criteria: R >11-13mm)
Tall R (Right BBB, posterior MI, Type A WPW syndrome, RVH) |
| What is the ST segment? | Between end to QRS and Beginning of T, isoelectric, considered elevated or depressed by 1 mm
Elevated in case of Acute MI (AMI_ |
| What is the T wave? | Asymmetrical, less that 2/3 of R amplitude follows QRS axis direction |
| What is an abnormal T wave? | abnormal T waves are symmetrical, tall, peaked, biphasic or inverted. |
| How is the QT interval? | It is the duration of depolarization and repolarization.
As heart rate increase, QT decrease, should be between 0.35 and 0.45 s and shouldn't exceed more than half of RR interval |
| What are the U waves? | • U wave related to afterdepolarizations which
follow repolarization
• U waves are small, round, symmetrical and
positive in lead II, with amplitude < 2 mm
• U wave direction is the same as T wave
• More prominent at slow heart rates |
| How to calculate HR using 300s rule? | count big boxes between RR, divide 300 by the number of boxes |
| How to calculate HR using 10s rule? | Count all the waves in the display under and multiply by 6 (for waves that are irregular) |
| What is the QRS axis? | It represents the overall direction of the hearts electrical activity.
abnormalities hint at ventricular enlargements and conduction blocks.
Normal axis is between -30 deg and +90 deg |
| What are the abnormal QRS axis? | -30 , -90 this is Left axis deviation
+90 , +180 this is right axis deviation
+180 , -90 this is indeterminate axis |
| What is the quadrant approach to get the QRS axis? | See Leads I (0 degree) and aVF (+90 degree).
If both positive -->normal
If Lead I negative and aVF positive --> RAD
If both negative -->indeterminate
If Lead I positive and aVF negative --> check Lead II if Positive normal if negative LAD |
| What is the equiphasic approach to get the QRS axis? | Check the most equiphasic QRS among the limb leads, QRS is the lead 90 degrees away from the most equiphasic, it can be positive or negative |
