# help please...?



## Phridae (Feb 24, 2005)

I cant find a website or anything that explains how to read a 3-lead strip that I can undertand. I don't know anyting about heary rhythms. And I want to learn. I just keep getting confused. Can anyone help me with this? please?


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## rescuecpt (Feb 24, 2005)

Here are my basic cardiac notes - I have a pretty good powerpoint specifically on reading ECG's... but I don't think I can upload it here so PM me your email address and I'll send it on.

CARDIAC CYCLE:

Cardiac cycle – the sequence of events that occurs between the end of one heart contraction and the end of the next.

Diastole – the first phase of the cardiac cycle, the relaxation phase.  Blood enters the ventricles through the mitral and tricuspid valves.

Systole – the second phase of the cardiac cycle, where the heart contracts.  The atria contract first to empty their blood into the ventricles.  Atrial systole is relatively quick and occurs just before contraction, this atrial kick boosts cardiac output.  The pressure in the ventricles increases until it exceeds the pressure in the aorta and pulmonary artery, when blood flows into the arteries.


SYPATHETIC NERVOUS SYSTEM:
- fight or flight
- affects heart, lungs, liver, glands, skeletal muscles

Sympathomimetic adrenergic – drug has the same effect on body as if it came from the sympathetic nervous system.   
1.	increase heart rate
2.	increase contractility
3.	increase vasoconstriction
4.	increase bronchodilation
			Example: Epinephrine

Sympatholytic antiadrenergic – drug that blocks the actions of sympathetic nervous system.
1.	decrease heart rate
2.	decrease contractility
3.	increase vasodilation
4.	increase bronchoconstriction

Neurotransmitter: norepinephrine

Alpha receptors – located in the peripheral blood vessels, responsible for vasoconstriction.

Beta1 receptors – located in the heart, increase heart rate and contractility.

Beta2 receptors – located in lungs and peripheral blood vessels, cause bronchodilation and peripheral vasodilation.

Beta blockers – slow heart rate and lower blood pressure by blocking the beta1 receptors.  Ex: propranolol – drugs ending in “olol” are beta blockers.






PARASYMPATHETIC NERVOUS SYSTEM
- feed or breed
- increased smooth muscle activity (decreases BP)

Parasympathomimetic cholinergic – drug has the same effect as if made by the parasympathetic nervous system.
1.	decrease heart rate
2.	increase bronchoconstriction
3.	increased activity in gastric gland, pancreas, and lachrymal gland

Parasympatholytic anticholinergic – drug that blocks the actions of the parasympathetic nervous system.
1.	increase heart rate
2.	increase bronchodilation
Example: Atropine Sulfate
	- enhances sinus node automaticity
	- increases heart rate, but not strength
	- used to treat organophosphate (fertilizer) poisoning
	- may induce tachycardia
- increases load on heart
- harmful for patients with:
- coronary artery disease
- ongoing MC ischemia or infarction

Vagus nerve – the 10th cranial nerve.  Vagal nerve fibers primarily innervate the atria.  The neurotransmitter for the parasympathetic nervous system is acetylcholine which slows the heart rate and atrioventricular conduction.
	Stimulants:
Valsalva maneuver – forced expiration against a closed glottis.
Carotid sinus massage – pressure on the carotid sinus
Distension of the urinary bladder.

Chronotropy – pertaining to heart rate.  Positive increases heart rate, negative decreases.

Inotropy – pertaining to cardiac contractile force.  Positive strengthens contractions.

Dromotropy – pertains to the speed of impulse transmission.  Positive speeds impulse conduction.

Electrolytes – cardiac function depends heavily on electrolyte balances.
		Sodium (Na+)
		Calcium (Ca++)
		Potassium (K+)
		Chloride (Cl-)
		Magnesium (Mg++)

Atropine increases heart rate, blocks parasympathetic responses.


ELECTROPHYSIOLOGY
Types of cardiac muscle:  atrial, ventricular, specialized excitatory and conductive fibers

Intercalated discs – specialized bands of tissue inserted between myocardial cells that increase the rate in which the action potential is spread from cell to cell.

Synctium – group of cardiac muscle cells that physiologically function as a unit.

Cardiac depolarization – a reversal of charges at a cell membrane so that the inside of the cell becomes positive in relation to the outside; the opposite of the cell’s resting state in which the inside of the cell is negative in relation to the outside.  Contraction of the muscle follows depolarization.

Repolarization – return of a cell to its preexcitation resting state.  

CARDIAC CONDUCTIVE SYSTEM
Cardiac conductive system – stimulates the ventricles to depolarize in the proper direction, Initiates an impulse, spreads it through the atria, and transmits it quickly to the apex of the heart, thus stimulating the ventricles to depolarize from inferior to superior.

Cardiac cells are:
	Excitable – cells can respond to an electrical stimulus.
	Conductible – cells can propagate the electrical impulse from one cell to another
	Automaticity – pacemaker cell’s capability of self-depolarization
	Contractility – ability of muscle cells to contract, or shorten.

Internodal atrial pathways – connect the SA node to the AV node.  Conduct the depolarization of impulse to the atrial muscle mass and through the atria to the AV junction.

AV junction – the “gatekeeper”, slows the impulse and allows the ventricles time to fill.

AV node – conducts the impulse from the atria to the ventricles through AV fibers.

Bundle of His – groups of AV fibers in the ventricles.  Divides into the right and left bundle branches.

Right bundle branch – delivers the impulse to the apex of the right ventricle to the Purkinje system.

Purkinje system – spreads the impulse across the myocardium.

Left bundle branch – divides into anterior and posterior fascicles that ultimately terminate in the Purkinje system.

Intrinsic rates of self-excitation:
	SA node: 60 – 100 bpm
	AV  node: 40 – 60 bpm
Purkinje system: 15 – 40 bpm


ANATOMY

Heart is located in the center of the chest in the mediastinum.

Top of the heart is the base.

Bottom of the heart is the apex.

Heart has three layers:
	Endocardium – innermost
	Myocardium – middle layer, can create and conduct electrical impulses
	Pericardium – protective sac around heart




ELECTROCARDIOGRAM

Positive impulses – upward deflections

Negative impulses – downward deflections

Absence of impulses – isoelectric line (flat)

Artifacts – deflections on the ECG produced by factors other than the heart’s electrical activity, such as muscle tremors, shivering, patient movement, loose electrodes, 60 hertz interference, machine malfunction.


ECG PAPER
	Moves across the stylus at 25mm/sec
		Light lines are 1mm apart
		Heavy lines 5mm apart
			1 small box = .04 sec
			1 large box = .20 sec


P Wave – atrial depolarization

QRS Complex – ventricular depolarization

T Wave – repolarization of ventricles

U Wave – follows T wave, usually positive.  May be associated with electrolyte abnormalities

P-R Interval – distance from the beginning of the P-wave to the beginning of the QRS complex.  Normal = .12 - .20.  Prolonged PRI = delay in AV node.

QRS Interval – distance from the first deflection of the QRS complex to the last.  Represents time necessary for ventricular depolarization.  Normal = .08 - .12.

S-T Segment – distance from the S wave to the beginning of the T wave.  Usually isoelectric.


MYOCARDIAL INFARCTION

Ischemia – lack of oxygen, causes S-T segment depression or an inverted T wave.

Injury – elevates the S-T segment

Necrosis – cell death, infarction.  As tissue dies, a significant Q wave appears, at least .04 sec or more than 1/3 height of the QRS complex.

DYSRHYTHMIAS
Dysrhythmia – any deviation from the normal electrical rhythm of the heart.

Enhanced automaticity – results when ectopic foci (heart cells other than pacemaker cells) automatically depolarize, producing ectopic (abnormal) beats.

Originating in SA Node
	Sinus bradycardia
•	Rate < 60
•	Rhythm regular
•	Pacemaker site = SA Node
•	P waves upright and normal
•	P-R interval normal
•	QRS complex normal

	Sinus tachycardia
•	Rate > 100
•	Rhythm regular
•	Pacemaker site = SA Node
•	P waves upright and normal
•	P-R interval normal
•	QRS complex normal

	Sinus dysrhythmia
•	Rate 60 < 100
•	Rhythm irregular
•	Pacemaker site = SA Node
•	P waves upright and normal
•	P-R interval normal
•	QRS complex normal

	Sinus arrest
•	Rate normal to slow
•	Rhythm irregular
•	Pacemaker site = SA Node
•	P waves upright and normal
•	P-R interval normal
•	QRS complex normal

Originating in Atria
	Wandering Atrial Pacemaker
•	Rate normal
•	Rhythm slightly irregular
•	Pacemaker site = SA Node, atrial tissue, AV junction
•	P waves change from beat to beat or disappear
•	P-R interval varies
•	QRS complex normal

Originating in AV Junction
	Junctional Escape
•	Rate 40< 60
•	Rhythm irregular in single complex, regular in JE rhythm
•	Pacemaker site = AV junction
•	P waves inverted, before or after QRS complex
•	P-R interval before QRS, less than .12sec
•	QRS complex normal

	Accelerated Junctional Rhythm
•	Rate 60 < 100
•	Rhythm regular
•	Pacemaker site = AV junction
•	P waves inverted, before or after QRS complex
•	P-R interval before QRS, less than .12sec
•	QRS complex normal


CARDIAC OUTPUT

Cardiac Output = Heart Rate x Stroke Volume

Stroke volume – the amount of blood ejected by the heart in one cardiac contraction.

Cardiogenic shock – shock caused by insufficient cardiac output, the inability of the heart to pump enough blood to perfuse all parts of the body.


ANGINA PECTORIS

Angina – chest pain that results when the blood supply’s oxygen demands exceed the heart.  Caused by plaque buildup/rupture, arterial spasm

	Stable – when activity stops, pain goes away
	Unstable – pain continues (pre-infarction angina)


Morphine
Oxygen
Nitroglycerin
Aspirin


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## ffemt8978 (Feb 24, 2005)

Wow, that was fast.

Thanks, RescueCpt.


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## Wingnut (Feb 24, 2005)

Wow, that's awesome cpt!  

I'm going to copy that for a study tool if ya don't mind!


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## medic03 (Feb 24, 2005)

look at lead II


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