Cardiac Physiology II Frank A. Acevedo, PA-C

Excitation

Conduction

Lead Placement When an action potential starts on the right and proceeds toward the left side of the heart, a positive inflection will be seen in lead one. 0 degrees

Lead Placement The negative electrode is connected to the RIGHT ARM. The positive electrode is connected to the LEFT LEG. 60 degrees

Lead Placement Lead III is the last of the three standard limb leads. 120 degrees

Lead Placement Unlike leads I, II, III, the augmented leads utilize a central negative terminal. This virtual "electrode" is calculated by the EKG computer to measure vectors originating roughly at the center of the heart degrees

Lead Placement The negative electrode is the central termininal. The positive electrode is connected to the LEFT ARM. -30 degrees

Lead Placement The negative electrode is the central termininal. The positive electrode is connected to the LEFT LEG. +90 degrees

Lead Placement Einthoven's triangle

Lead Placement Super-imposing the augmented leads over Einthoven's triangle demonstrates the vector relationship.

Lead Placement These leads provide essental information used in localizing ischemic or infarcted tissue during a cardiac event.

Refractoriness Absolute refractory period Relative refractory period

Relative Refractory Period An impulse during the relative refractory period may cause a premature contraction. In this situation, the chambers are not filled completely. According to the Frank-Starling Law, this decreased preload will cause cardiac output to decrease.

Toilet Analogy

Normal EKG

Methodology of EKG Interpretation Always begin you analysis by asking the following questions: Is the rate fast or slow? Are the atrial and ventricular rates the same? Are the P-P interval and R-R interval regular or irregular? If the rhythm is irregular, is it consistent or irregular Irregularity? Is there a P-wave before each QRS? Is there a QRS before every P- wave? Are the P-waves and QRS complexes identical and normal in configuration? Are the P-R and QRS intervals within normal limits?

Sinus Rhythm Sinus Rhythms originate at the SA node travel through the entire conduction system without inhibition a conducted P-wave P-R interval between 0.12 and 0.20 seconds The QRS width should be 0.04 to 0.12 seconds and all QRS's are preceded by a P- wave

Sinus Rhythm

Measuring Time on EKG’s The Y axis represents VOLTAGE, the X axis represents TIME. Each large box equals 200 msec. 5 large boxes equals 1 second.

Measuring Time on EKG’s 1 large box = 300 bpm. 2 large boxes = 150 bpm. 3 large boxes = 100 bpm. 4 large boxes = 75 bpm. 5 large boxes = 60 bpm.

Intervals

Electrical Correlation

Bradycardia

Sinus Bradycardia

Tachycardia

Sinus Tachycardia

Premature Atrial Contractiions