ECG and Heart
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What is the Septum?
Thick muscular wall that divides the heart into right and left halves.
Upper chambers of the heart. Pumps blood to ventricles.
Lower chambers of the heart. Pumps blood to the pulmonary artery and to the aorta.
What and where are the 4 valves in the heart?
- 1. Tricuspid valve - Between right atrium and right ventricle.
- 2. Mitral valve - Between left atrium and left ventricle.
- 3. Pulmonary valve - opening from the right ventricle into pulmonary artery.
- 4. Aortic valve - opening from left ventricle into the aorta.
What are the 4 layers of the heart?
- 1. Pericardium - The membrane sac surronding the exterior of the heart.
- 2. Epicardium - Ouside layer of tissue
- 3. Myocardium - middle layer of tissue, thick muscular wall essential for pumping.
- 4. Endocardium - inside layer of tissue delicate membrane that lines chambers.
What is the sinoatrial (SA) node?
Special tissue that acts as a pacemaker for the heart. Its where the impulse starts. The impulse is transmitted in a fraction of a second through the atria to the AV node.
What is the atrio-ventriclular (AV) node?
It conducts the impulse into the ventricular walls resulting in contraction of the ventricle. Impulse goes from the AV node to the bundle of his.
What is the bundle of his?
Its a bundle of contraction fibers which link the av node to the bundle branches.
What is the bundle branch?
Consists of two branches just below the bundle of his. Bundle branches descend through the interventricular spetim into the ventricles.
What is the Purkinjie fibers?
Its a network of ventricular muscle fibers which compromise the ventricular conduction systems.
What are the two phases of the pumping action in the heart?
Diastole - the relaxation phase. Oxygen poor blood returns from systemic circulation and accumulates in the right atrium which pours into the right ventriclue. Atrias contract at same time to press blood into relaxed ventricles.
Systole - valves between the atrium and ventricles close. Ventricles contract and force blood through pulmonary artery and the aorta. At end of contraction, the pulmonary and aortic valve snap shut preventing blood back into the ventricles.
What is the midsagittal plane?
A vertical plane through the midline of the body that divides the body or organs into equal right and left sides.
What is a Electrocardiogram (ECG)?
Graphic recording of the electrical stimulation of the heart at the body's surface. ECG waveform is a direct relationship to the mechanical action of the heart.
What is the mechanical action of the heart?
The right and left atriums contract at the same time and pump blood to the right and left ventricles. The ventricles contract at the same time. The right ventricle pumps blood to the pulmonary artery which leads to the lungs. The left ventricle pumps blood to the aorta which leads to the rest of the body. Both ventricles relax as they fill with blood to begin the cycle over again.
What is polarization, depolarization and repolarization?
- Polarization refers to the heart at rest. There is no impulse no stimulus contraction and no measurable activity.
- Depolarization is the discharge of electrical energy. The activity of the heart during the impulse that causes contraction. But is not the contraction itself.
- Reploarization is the electrical recovery of the heart as the cells recharge themselves.
What are the 3 main components of the ECG waveform?
- 1. P wave - atrium contracting (depolarization)
- 2. QRS complex - Ventricles contracting (depolarization) and pumping blood through the lungs and rest of body.
- 3. T wave - Ventricles relaxing (repolarization)
Explain the 3 main components and the order they happen.
First to appear is the P wave, it represents the impulse that causes the atria to contact and records the firing of the SA node. P wave is the atrial deploraization.
The QRS complex represents ventricular depolarization, journey of the electrical impulse from the AV node through the Purkinje network.
The T wave represents repolarization of the heart, as the cells recharge themselves in preparation for another impulse.
Define Heart Attack!
Condition in which the formation of a blood clot within a coronary artery may shut off the blood flow to a section of the heart muscle.
Define Heart Rate
Number of contractions per minute.
cycle of contractions of the heart muscle during which the chambers of the heart contract.
Inadequate supply of blood from the coronary arteries due to functional constriction or obsruction of the blood vessel.
What is normal sinus rhythem?
Its the complete cardiac cycle (P, QRS, and T wave) at a rate between 60 to 90 beats per minute.
What is Bradycardia?
An abnormal slowness of the heart rate and pulse. Generally below 60 beats per minute.
What is Tachycardia?
Abnormally rapid heart rate. Generally above 100 beats per minute.
Abnormal rhythem of the heart. Cardia cycle is abnormal.
Define Bipolar leads.
Also called standard limb leads, use a single positive and a single negative electrode between which electrical potentials are measured.
Define Unipolar leads.
Are the augmented leads and chest leads. Have a single positive recording electrode and use a combination of the other electrodes to serve as a composite negative electrode.
Where are the electrodes located for lead 1?
Positive electrode on the left arm and negative electrode on the right arm. LA (+) and RA (-)
Where are the electrodes located for lead 2?
Positive electrode is on the left leg and negative electrode is on the right arm. LL (+) and RA (-)
Where are the electrodes located for lead 3?
Positive electrode on left leg and negative electrode on left arm. LL(+) and LA(-)
The three bipolar limb leads form an equilaeral triangle called?
- Einthovens triangle.
Which leads view the electrical activity of the heart from the frontal plane? and which view the electrical activity of the heart from the plane perpendicular to the frontal plane?
The standard and augmented limb leads view the electrical activity from the frontal plane and the unipolar chest leads view the electrical activity from the plane perpendicular to the frontal plane.
Explain the path of the electrical impulse through the heart.
The SA node generates the electrical impulse that travels through the pathways in the atrium. The atrial muscle contracts to pump blood from the atria through the valves into the ventricles. The electrical impulse then travels to the AV node. The impulse is delayed by 100ms before it reaches the bundle of his and it divisions, the right and left bundle branches. These branches break into the purkinje system, which conducts the impulse to the inner wall of the ventricles, causing the ventricles to contract and pump blood from the right ventricle to the lungs and the left ventricle to the aorta.
Explain Diagnostic ECG
Contains more information then monitoring ECG. The bandwidth of diagnostic edg if wider (0.5Hz to 120Hz). There are more leads taken simultaneously.
Explain Monitoring ECG
If a patient was staying in the hospital they would monitor the heart rhythem. Use a bandwidth of 0.5Hz to 40Hz. Montioring provides information on early warning sign of major arrhythmias, immediate detection of fatal arrhythmias, feedback on effectiveness of treatment intervention.
What is a Holter ECG?
If a out patients ECG needs to be monitored over a extended period of time they will use a Holter ECG. It can record the patients heart rhythem continuously during normal daily activities. Patient wears a small ECG machine with a built in recorder.
Describe a few blocks from the following block diagram
- Amplifier : The magnitude of the ECG at the surface of the body is 1mV, this varies from patient to patient. So a amplifier is added to control the size of the ecg waveform.
- Right Leg Driven Circuit: Supresses the common mode signal so that it will not mask the ecg signal. Which comes from electrical equipment and wiring near by.
- Calibration pulse: Built in reference voltage of 1mV applied to unput of ecg. Reference signal is displayed on screen to inform user that machine is functioning properly.
What could cause abnormalities in ECG waveform?
- 1. Artifacts due to electrode problems
- 2. Artifacts due to physiological interference
- 3. Artifacts due to external interference
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