Exam1- Electrocardiogram

conduction system

• made up of electrical cells

• follows a specific pathway

• SA-AV-Bundle of HIS- Bundle of branches- Purkinje Fibers

EKG

• 6chest leads V1-V6

• 6 limb leads

  • Unipolar AVR, AVL, AVF

  • Bipolar I(LA), II(LL), III(LL) leads

SA NODE

• Receives blood from SA node artery which originates from the right coronary artery

• has intermodal pathways

AV NODE

• impulse delayed slightly

• Ventricle filling

• Supplied by the right coronary artery

AV NODE

• impulse delayed slightly

• Ventricle filling

• Supplied by the right coronary artery

Bundle of HIS

• Thin bundle of subendocardial threads (muscle fibers)

• Receives blood from branches of the anterior and posterior descending coronary arteries

RIGHT Bundle Branch

This signal tells the RV when to contract, pushing blood to the lungs to get oxygen

LEFT Bundle Branch

• signal makes LV contract, pumping oxygen rich blood out through aorta to the body

• then divides into smaller branches called fascicles that spread electrical signal deep into the LV muscle

• If the signal is blocked, LV get the signal late and the heartbeat can become uncoordinated

Purkinje Fibers

• quickly spread electrical impulses to all parts of ventricular muscle

• This makes R n L ventricles contract together-pushing

• Their fast conduction speed ensures the ventricles contract for full and efficiently

Purkinje Fibers

• quickly spread electrical impulses to all parts of ventricular muscle

• This makes R n L ventricles contract together-pushing

• Their fast conduction speed ensures the ventricles contract for full and efficiently

Intrinsic Rate

• SA NODE 60-100

• AV NODE 40-60

• Purkinje fibers 20-40 (ventricular)

Interpreting an EKG

Many cardiac disorders:

• check voltage calibration

• heart rhythm and rate

• Intervals (PR,ORS, QT)

• Mean ORS axis

• Abnormalities of P wave, QRS (hypertrophy, bundle branch block, infarction) ST segment n T wave

Voltage calibration

• standard setting used to measure and display the strength (amplitude) of electrical signals

• Normal 1mm vertical box on the EKG which represents 0.1mV (millivolts)

• Tall QRS complexes, most common cause of this finding is an enlargement of thickened heart muscle called Hypertrophy

The rectangular upward deflection at the beginning of each line is the Voltage Calibration signal

Normal sinus rate with a 70 BPM

Heart Rhythm

• P wave is followed by a QRS

• P wave is upright in leads I, II, III

• PR interval is 0.12 sec or greater (3small boxes)

• Normal sinus rhythm 60-100

• Bradycardia- less than 60 (slow)

• Tachycardia- more than 100 (fast)

Intervals (PR,QRS, QT)

Normal ranges:

• PR: 0.12- 0.20sec (3-5 boxes)

• QRS: less than 0.10sec (less than 2.5 boxes)

• QT: Males- less than 0.44s

  Females- less than 0.46s

Abnormalities of P wave

• aerial enlargement or loss of normal atrial activity

• P wave is usually visualized best in lead II

• When RA enlarges the initial P wave is larger than normal (taller than 2.5mm)

Abnormalities of QRS complex

• ventricular hypertrophy: R n L ventricles cause the affected chamber to generate greater than normal electrical amplitude

• Bundle branch blocks: may develop from ischemic or degenerative damage ex: fever

• Most common:

  • R n L Bundle Branch Block

  • Ventricular Tachycardia

  • Pacemaker

ST segment and T wave abnormalities

• common finding with wide range of causes, from benign conditions to life threatening ones like heart attack

• They can signal myocardial ischemia (lack of blood flow to the heart), electrolyte imbalances (like high or low potassium), left ventricular hypertrophy, certain drugs, or other structural or neurological problems

Examples of ST segment and T wave abnormalities

• Transient Myocardial Ischemia- temporary oxygen storage, no heart damage

• Acute ST (STEM)- complete blockage, serious damage, emergency (DANGER!)

• Acute non-ST (NSTEMI)- partial blockage, some damage, urgent treatment needed