Physio B Lab Test 2

what is the cardiac axis?

the general direction of electrical impulses as they travel through the heart

what is normal cardiac axis?

from upper right to lower left

how do you determine an axis deviation?

observing the deflection patterns on Leads I, II, and III/avF

what is right axis deviation?

when the heart is anatomically or electrically deviated to the right

what do the leads look like in right axis deviation?

Lead I has a negative deflection pattern (the electrical vector moves toward the right arm electrode) while Leads II and III still deflect upwards

what conditions cause right axis deviation?

common in children and tall thin adults; thoracic or spinal deformity, enlarged heart

what is left axis deviation?

when the heart is anatomically or electrically deviated to the left resulting in an electrical vector toward the left side of the body

what do the leads look like in left axis deviation?

Lead I deflects upward, while Lead II and III/avF have a negative deflection pattern

what conditions cause left axis deviation?

normal in short and stocky individuals, emphysema, hyperkalaemia, tricuspid atresia

summarize the lead deflections for the different cardiac axes

1. Normal = positive for all leads

2. Right axis deviation = negative for Lead I, positive for Leads II & III

3. Left axis deviation = positive for Lead I, negative for Leads II & III

how to determine heart rate

note that 1 tiny box = 1mm = 0.04 seconds (1/25 of a second) and 1 big box = 5mm = 0.20 seconds

count number of boxes between the R waves

if you count using big boxes, the HR will be equal to 300/# of big boxes

if you count using tiny boxes, the HR will be equal to 1500/# of tiny boxes

what is the PR interval?

the time interval from the beginning of the P wave until the beginning of the QRS complex

what is the normal range of PR interval?

0.12 sec (3mm/3 tiny boxes) to 0.2 sec (5 mm/1 big box)

what does a prolonged PR interval indicate (>0.2 sec)?

heart block

what does an abnormally short PR interval (<0.12 sec) indicate?

less blood flow to ventricles and lower cardiac output

review what the intrinsic conduction system looks like

SA node —> AV node —> Bundle of His —> Bundle branches —> Purkinje fibers

Electrical signal goes through SA node; atria depolarize; signal travels through the septum into both ventricles, depolarizing them

what are some causes of heart block?

• age-related wear and tear to heart muscle

• diseases and conditions which can cause scarring or damage to the electrical system of the heart

• scar tissue from a previous heart surgery, especially in children

• side effect of medications (like a calcium channel or beta blocker)

what is an SA block (junctional rhythm)?

• when the AV node ends up becoming the pacemaker since the SA node no longer works (at the junction between the atria and ventricles)

• as a result, the electrical signal sent by the AV node escapes out the top and bottom at the same time

• the P wave and QRS occur at the same time, so the P wave ends up being obscured by the QRS wave

what is a first degree AV block?

• when there is a delay in the transmission of the impulse from the atria to the ventricles; this is reflected in the PR interval

• you can identify a first degree AV block by its prolonged PR interval (>0.20 sec) in all the leads

• the PR interval will be the same duration for each rhythm

what is a second degree AV block Mobitz I and Wenckebach?

• Type I demonstrates an increasing PR interval until the QRS is dropped

• you can usually see the P wave, but its impulse does not immediately initiate the ventricular response

what is a second degree AV block Mobitz II?

• Where there are multiple P waves prior to the QRS complex

• This is a fixed rate and will be consistent

  • You can either have a Mobitz II, 2:1 or 3:1

What is a third degree AV block (complete heart block)?

• This is where the atria and ventricles have no association

• The atria are stimulated by the SA node

• But the impulses are not conducted to the ventricles due to there being a block at the AV node

• Instead, another pacemaker becomes active below the block to generate the QRS complex (either bundle of His or in the ventricle)

• Hence, this produces no discernable pattern between the timing of the P waves and QRS waves

• Sometimes the P waves may be masked

what are bundle branch blocks?

when the bundle branch in either the left or right ventricle is blocked

how does the heart work around the bundle branch blocks?

it stimulates the ventricle through a tissue pathway leading to a delay in the ventricular contraction

what are some causes of bundle branch blocks?

• congenital heart disease

• cardiomyopathy

• myocardial infarction (heart attack)

• coronary artery disease

• heart failure

• hypertension

• myocarditis

• heart valve disease

RBBB specific:

• chronic obstructive pulmonary disease

• pulmonary embolism

• pulmonary hypertension

which leads will you use to look at bundle branch blocks?

chest leads (V1-V6)

what do you see on the leads if there is an RBBB?

V1 or V2 will have a second R wave representing the separate stimulation of the right ventricle

what do you see on the leads if there is an LBBB?

V5 or V6 will have a second R wave representing the stimulation of the left ventricle; note that the R waves can slur into each other and create a wide QRS complex

what is the right AV valve?

tricuspid valve

what is the left AV valve?

bicuspid (mitral) valve

what is a parachute valve?

a valve that is concave when facing the ventricles

which valves are parachute valves?

AV valves

what is a hip-pocket valve?

a valve that is convex when facing the ventricles

which valves are hip-pocket valves?

semilunar valves

what is hypertrophy?

an increase in mass attributable to increase in cell size

hypertrophy refers to elevated mass in

ventricles

enlargement refers to elevated mass in

atria

what is the Frank-Starling Law of the Heart?

this states that the larger volume of blood in a chamber, the cardiac muscle fibers stretch, leading to an increased force of contraction and over time hypertrophy/enlargement

what does the horizontal axis on an ECG strip represent?

time of electrical activity (1mm = 0.04 sec)

what does the vertical axis on an ECG strip represent?

magnitude of electrical activity (1mm = 0.1 mV)

what is the normal size of a P wave?

less than 2.5 mm high (0.25 mV) and 2.5 mm wide (0.1 sec)

which leads do you use to diagnose atrial enlargement?

Lead II, III, and avF

what is the telltale sign of RAE?

a tall P wave (2.5 mm or more) in 2 out of the 3 inferior leads = RAE

what are the causes of RAE?

tricuspid stenosis or prolapse

what is the telltale sign of LAE?

a wide P wave (2.5 mm or more) in 2 out of the 3 inferior leads (II, III, avF) = LAE

what are the causes of LAE?

bicuspid stenosis/prolapse

what is another way to diagnose LAE?

examine Lead I for a wide P wave and V1 for a biphasic P wave

which leads do you use to diagnose ventricular hypertrophy?

V1 & V5 OR V2 & V6

what tells you that RVH is present? why?

opposite deflection pattern of what is normal; this is because the electrical vector will be directed to the right side, resulting in a positive deflection in the first two leads and a negative deflection in the last two leads

what is the cause of RVH?

pulmonary valve stenosis/prolapse

what tells you that LVH is present?

increased magnitude in the deflection pattern; specifically, if the sum of the S wave of V1/V2 and R wave of V5/V6 is greater than or equal to 35 mm (3.5 mV), LVH is present

what are the causes of LVH?

normal adaptation to exercise, aortic valve stenosis/prolapse

what is an ectopic focus/pacemaker?

an excitable group of cells that causes a premature heartbeat outside of the normal functioning SA node in the heart

is there a cause for ectopic rhythm?

no, there are currently no known causes

what are some factors that can cause or aggravate ectopic rhythm?

• alcohol

• caffeine

• smoking

• prescription medications

• illegal drugs

• high adrenaline

• chemical imbalance

• injury to heart muscle due to heart disease, infection, or high blood pressure

what is a premature ventricular contraction/complex (PVC)?

a PVC is when the stimulation of the ventricles occurs in one or more areas within the ventricles BEFORE the stimulation from the SA node arrives

what happens to an ECG when there is a PVC?

there are QRS complexes with prolonged duration and abnormal morphology

criteria to diagnose a PVC

1. No P Wave

2. Wide QRS complex (prolonged stimulation of ventricle from ectopic focus + normal conduction pathway)

3. T wave points in opposite direction of QRS wave

what are the types of PVCs?

• Unifocal PVC

• Multifocal PVC

• Continuous PVCs

  • bigeminy, trigeminy

what is a unifocal PVC?

the PVC originates in one focal point within the ventricle, meaning the PVC looks the same in any given lead

what is a multifocal PVC?

the PVC originates from more than one focal point in the ventricle, thus the PVC will look different in any given lead

what is a continuous PVC?

when the PVC has a pattern, such as occurring every second or third beat (bi/trigeminy)

what is ventricular tachycardia?

rapid and irregular heartbeat originating from ventricles; 3 or more PVCs in a row, looks like blades on a saw or teeth

what is R on T PVC?

when the R wave of the PVC occurs on the T wave of the preceding beat; more often than not this leads to V Fib due to cells not completely repolarizing

what is ventricular fibrillation?

when the heart’s ventricles quiver uselessly instead of pumping blood; shows up as a bunch of irregular lines

what is sudden cardiac arrest (SCA)?

the sudden loss of all heart activity due to an irregular heart rhythm; the breathing can stop and person becomes unconscious

following cardiac arrest, when do brain cells begin to die?

between 4-6 minutes

symptoms of SCA

collapse, no pulse, no breathing, loss of consciousness

• before a cardiac arrest, may see chest discomfort, shortness of breath, weakness, tachycardia, and palpitations

what are some causes of SCA?

coronary artery disease, heart attack, cardiomyopathy, heart valve disease, congenital heart defect, long QT syndrome, arrythmias like atrial flutter/fibrillation

what are the 3 phases of cardiac arrest?

• electrical phase

• circulatory phase

• metabolic phase

what happens during the electrical phase?

takes place 0-4 minutes after cardiac arrest; heart still has oxygen and glucose, resuscitation conditions are favorable and heart responds to defibrillation

what happens during the circulatory phase?

takes place 4-10 minutes after cardiac arrest; the oxygen stores are exhausted and myocardial cells switch to anaerobic metabolism; need CPR to restore oxygen and glucose supply to increase successful defibrillation

what happens during the metabolic phase?

takes place 10+ minutes after cardiac arrest; heart is acidic and ischemic and starts to die; chances of resuscitation are unfavorable

what is the AHA adult chain of survival for out-of-hospital cardiac arrest management?

• activation of emergency response

• high quality CPR

• defibrillation

• advanced resuscitation

• post-cardiac arrest care

• recovery

what is resuscitation?

emergency care provided to restore vital body functions; focus on managing airway, ventilation, oxygenation, and restoring circulation

which heart rhythms is defibrillation advised for?

V tach and V fib

which heart rhythms is defibrillation not advised for?

asystole (absence of electrical activity) or pulseless electrical activity

what is a crash cart?

a self-contained mobile unit that contains lifesaving supplies and equipment to be used during a cardiac or respiratory emergency

what is in drawer 1 of a crashcart?

medications like alcohol swabs, epinephrine, dopamine, lidocaine

what is in drawer 2 of a crashcart?

intubation materials like laryngoscope, tongue depressors, lubricating jelly, flashlight

what is in drawer 3 of a crashcart?

airway suction materials like suction catheter, magill catheter forceps, and tape

what is in drawer 4 of a crashcart?

IV starting equipment like a start kit, vacutainers, angiocatheters, tourniquet tubing

what is in drawer 5 of a crashcart?

IV solutions such as sodium chloride or dextrose

what is in drawer 6 of a crashcart?

prepackaged kits like sterile gloves, suction supplies, ecg electrodes

What delivers blood to the heart wall (myocardium)?

The coronary arteries

Which way does blood flow in terms of the layers of the heart?

From epicardium to endocardium

how does a myocardial contraction work to prevent tetanus?

there are various stages of the contraction; there is a prominent plateau phase where an influx of calcium is electrically balanced through efflux of potassium, resulting in slow repolarization

muscle cells around the endocardium are the first to ____ and the last to ____

depolarize; repolarize

muscle cells around the epicardium are the last to _____ and the first to _____

depolarize; repolarize

what is ischemic heart disease?

aka Coronary Artery Disease; where the blood vessels are narrowed or blocked, resulting in ischemia and hypoxia to the heart muscles; this can cause myocardial infarction (heart attack)

what are some causes of heart disease?

1. Smoking (increases LDL and decreases HDL, increases blood pressure and increases platelet function)

2. Hypertension (increases risk of injury of the walls of the vessel)

3. High Blood LDL (increased bad fat in the blood can cause blockages)

4. Diabetes (increased solutes can cause injury to the vessels)

what is the endothelial injury hypothesis?

1. the endothelial lining of the blood vessels is injured, resulting in platelet aggregation

2. platelets secrete PDGF

3. This stimulates smooth muscle growth, narrowing the lumen

4. can lead to blockages

how do you diagnose ischemic heart disease?

ischemic heart disease manifests as changes in the ST segment on the ECG; normally, ST segment is at the same horizontal level as the baseline

what does ischemia cause in terms of an ECG?

ST segment depression

what is non-transmural ischemia?

where a myocardial infarction does not involve the whole thickness of the myocardium

what is happening in ST segment depression?

there is an increase in baseline of the ECG due to signal not permeating the whole myocardium; note that the AP is still sent

what are the three types of ST segment depression?

1. Downsloping

2. Upsloping

3. Horizontal

what does a horizontal or downsloping ST indicate?

myocardial ischemia

what does an upsloping ST depression indicate?

nothing; does not tell us if there is myocardial ischemia

what does a ST segment elevation indicate?

diagnosis of a myocardial infarction/heart attack