PULSE- CASE 2:

ELECTRICITY OF THE HEARTRob Freed, 2nd year MS

Penn State College of Medicine

rfreed@hmc.psu.edu

Layout of the Lecture

Sit back, relax and learn!

Ask questions!

Most of all… Have fun!

When one of these appears, I will pose a question for thought

4 steps to a heartbeat:

-Left and right atria contract

-Bicuspid and Tricuspid valves close

-Left and right ventricles contract

-Aortic and Pulmonary valves close

How does the timing work so perfectly?

The AV node tends to be slow in transmitting the signal downwards to the ventricles. Why might that be a GOOD thing?

Demo Time!

Volunteer for the SA node?

The “elder, wiser one” of the heart!

Demo Time!

3 volunteers to act as the muscle contraction

Demo Time!

The brick wall-

Seperates atrium from ventricles

Demo Time!

Atria ventricles

So, how does the heart rate change?

Recall that the WHOLE process started with the Sinus(SA) node!

Therefore, to change the heart rate, you must affect the SA node!

Your body does this automatically during exercise/sleep using the “autonomic nervous system”

During exercise:Build up CO2, not enough O2

in blood… nervous system speeds up the SA node

Faster!!!

Quick things to consider…

When the heart speeds up, the contraction portion DOES NOT go faster…

Instead, the time in rest DECREASES!ie:

H.R. of 75 beats/s

H.R. of 55 beats/s

H.R. of 120 beats/s

So, how does the heart rate change?

Recall that the WHOLE process started with the Sinus(SA) node!

Therefore, to change the heart rate, you must affect the SA node!

Your body does this automatically during exercise/sleep using the “autonomic nervous system”

During exercise:Build up CO2, not enough O2… nervous system speeds up the SA node

Faster!!!

So, how does the heart rate change?

Recall that the WHOLE process started with the Sinus(SA) node!

Therefore, to change the heart rate, you must affect the SA node!

Your body does this automatically during exercise/sleep using the “autonomic nervous system”

During sleep:Body is resting, no need for fast heart rate… nervous system puts the “brakes” on the heart

Slow Down!!!

Arrhythmia, sounds tough… not too hard!

Normally electrical wiring of the heart forces the heart beat to originate from the SA node

In an arrhythmia, another part of the heart acts as the “SA node”, this is termed an “ectopic beat”

Arrhythmia in Atria

Atria ventricles

Videos for Arrhythmias

http://www.nhlbi.nih.gov/health/dci/Diseases/arr/arr_types.html

http://www.youtube.com/watch?v=VKxQgjj2yVU&feature=related

What can happen with Arrhythmias?

The ONLY function of the heart is to provide blood to all parts of the body- brain, arms, feet, essential organs…

In arrhythmias, atrial or ventricular contraction is diminished and can result in a lack of flow to these critical organs!

Slight decrease in blood flow to the brain HUGE decrease in blood flow to the brain Decrease in flow to the hands/feet Decrease in flow to the eyes Odd electrical conduction through the heart Decrease in blood flow through the coronary arteries?

If you’re a doctor- “syncope”… for everyone else- “passing out”

As mentioned before, with a large enough decrease in blood flow to the brain, one will pass out! Or have a “syncope” episode!

Assuming nothing serious, the body will recover quickly and you will pick yourself up and keep going!

Going off an a tangent…

Let’s hypothesize why humans(or goats) would quickly recover from a bout of syncope(fainting)?

Hint: Think about gravity

Decrease in flow through the coronary arteries?

Remember the aortic valve:

•Separates the Left Ventricle from the Aorta

•Is a “semilunar valve” with 3 valve leaflets (see below)

My best attempt to draw coronary blood flow….

During diastole, while Left Ventricle fills with blood from the atria, coronary arteries receive blood

During systole, while Left Ventricle FORCEFULLY CONTRACTS, the aortic valve leaflets block the openings to the coronary arteries… thus they are BLOCKED from bloodflow!

Arryhthmia cont.

Diastole(Relaxation)

Systole(contraction)

•Considering that MOST arrhythmias cause rapid, fast heart beat… this LIMITS the time the heart spends in diastole

•This will cause a net _______ in blood flow through the coronary arteries

•This can cause arrhythmia symptoms such as chest pain, poor heart pumping ability and even DEATH

Arrhythmia: Atrial vs. Ventricular Atrial arrhythmia Leads to leftover blood in atria

(can cause clotting-discuss)

Slightly less blood delivered to ventricles

With less delivered to ventriclesless blood pumped to brain, etc.

(what symptoms might occur?)

Ventricular arrhythmia Leads to lots of leftover blood

in ventricles

Large decrease in blood pumped to the brain

OVERALL: Patients present with mild symptoms of “chest flutter”

Very few patients will die from atrial arrhythmias

OVERALL: Patients will pass out from first episode of V. arrhythmia and will NEED medical treatment ASAP. CPR, AED needed immediately.

All patients will die unless medical treatment is immediate!

So your heart stops, what happens now?

Within seconds, blood flow to the brain ceasessyncope

However, there is no fast recovery since their heart isn’t BEATING!

If untreated, within 5-10 minutes, irreversible brain damage has occurred

Death is inevitable after 15-20 minutes

“Man survives after heart stops beating for 58 minutes”- Oct. 2006

Cardiopulmonary resuscitation (CPR)

A method used to continue the pumping action of the heart in someone who no longer has a heart beat

CPR is unlikely to restart the heart, but rather its purpose is to maintain a flow of oxygenated blood to the brain and the heart, thereby delaying tissue death

Cardiopulmonary resuscitation (CPR)

We will not discuss the specifics of CPR because only those who are trained should perform CPR!

BUT, Anyone and Everyone can become certified in CPR through local ambulance affiliations and local chapters of the American Heart Association

americanheart.org

Learn CPR at home in 22 minutes!

Note: Although this is an official learning tool through the AHA, this does not give you official CPR certification necessary for EMS, lifeguarding, etc.

CPR followed quickly by AED

Defibrillator: Supplies an electric current through the chest in an attempt to restart the heart’s normal rhythm

Abundancy of AEDs throughout communities

Most communities now have AEDs near athletic fields, nursing homes, schools

Although the AED is VERY easy to use (It speaks to you the directions), it is very good to have experience and confidence in using it correctly!

“Studies have shown the importance of immediate CPR followed by defibrillation within 3–5 minutes of sudden VF cardiac arrest improve survival. In cities such as Seattle where CPR training is widespread and defibrillation by EMS personnel follows quickly, the survival rate is about 30 percent. In cities such as New York City, without those advantages, the survival rate is only 1-2 percent.”