Exam 2 USE

what is an electrocardiogram (ECG/EKG)

records the electrical activity of the heart.

ECG does not

directly measure contraction, instead it measures the electrical impulses that cause the heart to contract

electrical conduction pathway

SA node→ Inernodal pathways→ AV node→ bundle of his→ right and left bundle branchecs→ purkinje fibers→ ventricular muscle

explain the electrical conduction pathway of the heart

electrical activity begins in the SA node, the natural pacemaker of the heart. The impulse spreads across both atria, causing depolarization. The signal then reaches the AV node, where it is briefly delayed to allow the ventricles time to fill. Next, the impulse travels through the bundle of His, into the right and left bundle of branches, and finally through the Purkinje fibers, causing ventricular depolarization and concentration

SA node location and function

upper right atrium near the superior vena cava. natural pacemaker

SA node normally fires between

60-100 b/min

AV node location and purpose

lower right atrium. Delays the electrical impulse

why does the AV node delay the electrical impulse?

To allow the atria to finish contracting before the ventricles begin

SA vs AV

SA= Starts the heartbeat

AV= Allows ventricles to fill

Bundle of His

carries electricity from the AV node into the inter ventricular septum.

Bundle Branches

carry electricity down each side of the septum

purkinje fibers

spread electricity rapidly throughout both ventricles resulting in rapid, coordinated ventricular contraction

P wave

atrial depolarization, causing atrial contraction

QRS complex

ventricular depolarization, causes ventricular contraction

what else happens in the QRS complex

atrial repolarization but is hidden because the QRS complex is larger

T wave

ventricular repolarization. the ventricles relax and prepare for the next beat

why isnt atrial repolarization seen on the ECG.

atrial repolarization occurs at the same time as ventricular depolarization. Because the ventricles generate a much larger electrical signal, the small atrial repolarization wave is hidden within the QRS complex.

depolarization

the cardiac cells becomes electrically activated leading to contraction

repolarization

the cardiac cells return to its resting electrical state leading to relaxation

depolarization= contract

repolarization= relax

PR interval

measured from the beginning of P wave to the beginning of the QRS represents.

PR interval represents

time required for electrical conduction from the atria to the ventricles. (includes AV delay)

QRS duration represents

time needed for ventricular depolarization. normally very short

QT interval represents

total time for ventricular depolarization and repolarization

why is the AV node delay important

the AV node delays electrical conduction so the atria can completely empty blood into the ventricles before ventricular contraction begins. Without this delay, ventricular filling would be reduced, decreasing stroke volume

electrical events always comes before mechanical events (exampls)

electrical signal→ muscle contraction. p wave→ atrial contraction. QRS→ ventricular contraction. T wave→ ventricular relaxation

HR from ECG

300 / number of large boxes between R wave

HR example from ecg

1 box = 300bpm. 2 boxes = 150 bpm. 3 boxes = 100bpm. 4 boxes 75 bpm. 5 boxes = 60 bpm

why is the QRS complex larger than the p wave

the ventricles contain much more muscle mass than the atria. becuase more cardiac muscle is depolarizing, the electrical signal is much larger, producing the larger QRS complex

common ECG sequence

SA node fires→ p wave→ atria contract→ AV delay→ QRS→ ventricles contract→ T wave→ ventricles relax

what does an ECG measure

the electrical activity of the heart

Does an ECG measure contraction?

No, it measures the electrical signal that causes contraction

what is the natural pacemaker

SA node

what does the p wave represent..

atrial depolarization..

What does the QRS complex represent..

ventricular depolarization..

what does the T wave represent..

ventricular repolarization..

what electrical event is hidden in the QRS complex..

Atrial repolarization..

why is the AV node important

It delays conduction to allow ventricular filling

what structure carries impulses rapidly through the ventricles

purkinje fibers

what does the PR interval represent

conduction time from the atria to ventricles

what does the QT interval represent

total ventricular depolarization and repolarization time

why is the QRS larger than the P wave

the ventricles have more muscle mass

what occurs immediately after ventricular depolarization

ventricular contraction

what is the electrical axis

overall direction that the electrical impulse travels through the ventricles during depolarization

Mean QRS axis

Overall average direction of ventricular depolarization.

vector has

direction and magnitude

why does the left ventricle dominate

thicker walls, more muscle, more electrical activity

the hexaxial reference system

divides the heart into angles

Lead I angle

0

Lead II angle

+60

Lead III angle

+90

The qudrant method steps

look at only 2 leads (Lead I and Lead aVF)

is lead I positive or negative

is lead aVF positive or negative

The qudrant method example

Lead I (positive) + Lead aVF (positive)= normal axis

Lead I (positive) + Lead aVF (negative)= left axis deviation

Lead I (negative) + Lead aVF (positive)= right axis deviation

Lead I (negative) + Lead aVF (negative)= Extreme NW axis

look

3 lead method (little more accurate)

uses Lead I, lead II, aVF Rule

Rule

Lead I Positive->  Check Lead II. If Lead II is Positive= Normal Axis

Lead I Positive-> Lead II Negative= Left Axis Deviation

Lead I Negative-> Look at aVF, Positive= Right Axis

Negative=Extreme Axis

Isoelectric lead method

Find the lead whose QRS is most equally positive and negative (the smallest net deflection).

That lead is called the isoelectric lead.

The Mean QRS Axis will be approximately 90° (perpendicular) to that lead.

Then use another lead (often Lead I) to determine which of the two possible directions is correct.

why is an isoelectric lead

the ecg lead in which the positive and negative portions of the QRS complex are nearly equal, resulting in a net amplitude close to zero. The mean QRS axis lies approx. 9- degrees from this lead

left axis deviation (LAD)

QRS axis Between -30 degrees and -90 degrees

common causes of LAD

left ventricular hypertrophy, left bundle branch block, left anterior fascicular, inferior myocardial infraction

Right Axis deviation (RAD)

QRS complex between + 90 degrees and +18- degrees

common causes of RAD

right ventricular hypertrophy, pulmonary hypertension, chronic lung disease

why does axis shift?

the electrical axis shifts toward the side of the heart producing the greatest electrical force.

why does left ventricular hypertrophy cause Left axis deviation

left ventricular hypertrophy increases the amount of muscle in the left ventricle. more muscle produces a larger electrical signal during ventricular depolarization. Because the left ventricle dominates the electrical activity, the mean QRS Axis shifts toward the left

what is the mean QRS axis

the average direction of ventricular depolarization

which chamber mainly determines the normal QRS axis

left ventricle

why does the left ventricle dominate the electrical axis

it has the greatest muscle mass

what two leads are used in the quadrant method

Lead I and aVF

Lead I positive, aVF positive

normal axis

Lead I positive, aVF negative

left axis deviation

Lead I negative, aVF positive

right axis deviation

Lead I negative, aVF negative

Extreme NW axis

what is an isoelectric lead?

the lead with nearly equal positive and negative QRS deflections

The mean QRS Axis is approx. how many degrees from the isoelectric lead

90

what causes left axis deviation

increases left sided electrical forces, such as left ventricular hypertrophy or left anterior fascicular block

what does Lead I measure

electrical activity along the 0 degree axis

what does lead II represent

+60 degrees

what angle does lead aVF represent

+90 degrees

why do vectors add together

because electrical activity occurring in similar directions combine into one larger resultant factor

cardiovascular disease progression

poor lifestyle/genetics→ high bp & cholesterol→ atherosclerosis develops→ coronary artery disease→ reduced blood flow→ angina→ complete blockage→ myocardial infraction→ heart failure

hypertension

chronically elevates arterial blood pressure. forces the heart to work harder to pump blood

why is hypertention called the “silent killer”

many people have no symptoms until significant damage has already occured

Risk factors of CVD non-modifiable

age, family history, genetics

Risk factors of CVD modifiable

obesity, smoking, high sodium diet, physical inactivity, diabetes, high cholesterol, stress

why is hypertension dangerous

high pressure damages the inner lining of arterioles→ inflammation develops→ plaque forms more easily→ atherosclerosis accelerates

why is hypertension dangerous detailed

hypertension causes chronic damage to the walls of blood vessels. This damage promotes inflammation and plaque formation, increasing the risk of coronary artery disease, heart attack, stroke, kidney disease, and heart failure. Becuase many people have no symptoms, hypertention is often called the silent killer

atherosclerosis

the buildup of fatty plaques inside arteries

plaques contain

cholesterol, lipids, calcium, inflammatory cells, fibrous tissue

what happens in atherosclerosis?

healthy artery→ damage to endothelium → LDL cholesterol enters vessel wall→ inflammation→ macrophages consume LDL→ foam cells develop→ Fatty streak→ plaque→ narrow artery→ reduced blood flow

explain how atherosclerosis develops

atherosclerosis begins with damage to the endothelial lining of an artery. LDL cholesterol enters the damaged area and becomes oxidized. White blood cells (macrophages) engulf the cholesterol and become foam cells, creating fatty streaks. Over time, smooth muscle cells and fibrous tissue accumulate, forming plaques that narrow the artery and reduce blood flow.

Coronary artery disease (CAD)

occurs when coronary arteries become narrowed by atherosclerosis. as a result, the heart muscle receives less oxygen

symptoms of COD

chest pain, shortness of breath, fatigue

Angina

chest pain caused by temporary myocardial ischemia (heart muscle is alive just not receiving enough oxygen

stable angina

occurs during exercise. Improves with rest. predictable

unstable angina

occurs unexpectedly. Can occur at rest. Medical emergency. often due to plaque rupture.

difference between stable and unstable angina

stable angina occurs when increased oxygen demand during exercise exceeds blood supply because of a narrowed coronary artery. Symptoms improve with rest. Unstable angina occurs when plaque rupture and clot formation suddenly reduce blood flow. symptoms may occur at rest and indicate a high risk for myocardial infraction

myocardial infraction (heart attack)

complete blockage of a coronary artery → no oxygen reaches part of the myocardial→ cardiac muscle dies

common cause of MI

plaque ruptuure→ blood clot→ complete obstruction

symptoms of MI

chest pain, left arm, jaw, shoulder, back pain, shortness of breath, sweating nausea

Explain what happens during a myocardial infarction.

A myocardial infarction usually occurs when an atherosclerotic plaque ruptures inside a coronary artery. A blood clot rapidly forms and blocks blood flow. Without oxygen, cardiac muscle cells begin to die. The longer blood flow is interrupted, the more permanent damage occurs.

ischemia

reduced blood flow, muscle is still alive, potentially reversible