Bio 436 ECG Lab

Dipole

a separation of electrically charged regions so momentarily one region can be polarized and another depolarized

P-Wave

atrial depolarization

QRS Complex

ventricular depolarization (atria repolarizing simultaneously)

T-wave

ventricular repolarization

Arrhythmia

Abnormal heart rhythm at rest

Myopathese

Damage to the heart wall

Bradycardia

less than 60 beats per min at rest

Tachycardia

more than 100 beats per min at rest

PVC

pre-ventricular contraction

1st Degree AV Block

when conduction through AV node greater than 0.1 sec (causes long P-R interval (greater than 0.2 seconds)

2nd Degree AV Block

when only 1 out of 2-4 atrial AP's can pass to ventricles (Causes P waves with no QRS)

3rd Degree AV Block

no atrial activity passes to ventricles (ventricles driven slowly by bindle of His or Purkinjes)

Ischemic Heart Disease

detectable changes in S-T segment of ECG

Myocardial Infarction

a heart attack (diagnosed by high levels of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH)

What occurs at first heart sound?

AV valves close

What occurs at second heart sound?

Lunar valves close

What is an ECG?

-An electrical activity record of the heart, using surface electrodes

-consists of both depolarization and repolarization events

- Follows depolarization of atria first then ventricle cells ECG is not action potential

Can we see pacemaker cells on ECG?

we cannot see pacemaker cells on an ECG because they makeup at most 1% of cells of the heart

Complete conduction pathway of the heart

SA Node --> interatrial pathway or the AV Node --> AV Node to Bundle of HIS --> Purkinje Fibers

How long is AV node pause?

0.10 sec

Time of P-R interval

0.12-0.20 seconds

Time of the QRS complex

under 0.10 seconds to generate the force required to eject blood out

Time of Q-T interval

under 0.38 seconds

Atrial events on ECG

P wave - Some of QRS complex

Ventricular events on ECG

Some of QRS complex - T wave

How do leads see the dipole?

Leads "see" the dipole of the heart by triangulating. Dipole is in the middle of three leads so by triangulating you can understand exactly where the dipole is. Based on where you put the leads and where the dipole is the profile of the dipole will look different. Looking at Leads I, II, and III, only give a frontal perspective a three dimensional aspect requires more than just three leads, cardiologist looks at 12. This is the way a cardiologist can determine the direction of the dipole in the heart.

Lead 1

right arm to left arm

Lead 2

right arm to left leg

Lead 3

left arm to left leg

What can an ECG tell you?

Heart rate,

arrhythmia's,

damage to heart walls "myopathies,"

damage to the conduction system

Flutter

contraction rates can be 200-300/min (300 is usually the fastest any human heart can beat), still shows normal pattern for heart beat, still pumping a small amount of blood with each beat, flutter can quickly become fibrillation

Fibrillation

myocardial cell depolarizations become asynchronous- the heart begins to quiver and no blood is pumped to the body, ventricular fibrillation is more severe because it is life threatening

How long does each block on chart paper represent?

0.2 seconds

What does 4 squares between every QRS complex represent?

75 BPM

What does electrical defibrillation do?

resynchronizes heart by depolarizing all cells at the same time

Properties of a PVC

No P wave,

large spread out QRS complex (depolarization is spreading slowing compared to when pacemaker cells are used),

compensatory pause (allows time for heart to reset for a normal beat)

Can be caused by heart wall being stretched or compressed, medication

How can an ECG tell you about myopathies?

-heart attack causes a portion of the heart wall to stop working and die off, the area fills with scar tissue

- the pattern will appear incorrect, can see location of myopathies on ECG when a cardiologist looks at all 12 leads

When will a physician recommend a pacemaker?

between 2nd and 3rd degree block. A 3rd degree block requires the use of a pacemaker

When will AV node depolarize?

50 mV

When will Purkinje Fibers depolarize?

30 mV

True/False The autonomic system only acts on the SA node

True