Basics of Heart Anatomy• The heart is the hardest working muscle in the human body.• Located at left side of the chest, the adult human heart is about the size of one fist.• The cardiovascular system, composed of the heart and blood vessels• Responsible for circulating blood throughout your body to supply the tissues with oxygen and nutrients
Intro to heart• The human heart has a mass of between 250 and 350 grams and is about the size of a fist. It is located anterior to the vertebral column and posterior to the sternum.• It is enclosed in a double-walled sac called the pericardium. The superficial part of this sac is called the fibrous pericardium. This sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood.• The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the pericardium. The middle layer is called the myocardium and is composed of muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves.• The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers. The pathway of blood through the human heart consists of a pulmonary circuit and a systemic circuit. Deoxygenated blood flows through the heart in one direction, entering through thesuperior vena cava into the right atrium and is pumped through the tricuspid valve into the right ventricle before being pumped out through the pulmonary valve to the pulmonary arteries into the lungs. It returns from the lungs through the pulmonary veins to the left atrium where it is pumped through the mitral valve into the left ventricle before leaving through the aortic valve to the aorta.
Consist of…• Four chambers (two atria and two ventricles) that receive blood from the body and pump out blood to it. – The atria receive blood coming back to the heart. – The ventricles pump the blood out of the heart.• Blood vessels, which compose a network of arteries and veins that carry blood throughout the body. – Arteries transport blood from the heart to the body tissues. – Veins carry blood back to the heart.• Four valves to prevent backward flow of blood. – Each valve is designed to allow the forward flow of blood and prevent backward flow.• An electrical system of the heart that stimulates contraction of the heart muscle.
The hearts electrical system• he hearts pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart.
• An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small mass of specialized tissue located in the right atrium (right upper chamber) of the heart.• The sinus node generates an electrical stimulus regularly (60-100 times per minute under normal conditions).• This electrical stimulus travels down through the conduction and causes the hearts lower chambers to contract and pump out blood.
• The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart).
• The electrical impulse travels from the sinus node to the atrioventricular node (also called AV node), where impulses are slowed down for a very short period, then continue down the conduction pathway via the bundle of His into the ventricles.• The bundle of His divides into right and left pathways to provide electrical stimulation to the right and left ventricles
• Normally at rest, as the electrical impulse moves through the heart, the heart contracts about 60 to 140 times a minute, depending on a persons age.• Each contraction of the ventricles represents one heartbeat.• The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract.
ELECTROCARDIOGRAPH• As the heart undergoes depolarization and repolarization, electrical currents spread throughout the body because the body acts as a volume conductor.• The electrical currents generated by the heart are commonly measured by an array of electrodes placed on the body surface and the resulting tracing is called an electrocardiogram (ECG, or EKG)• The Electrocardiograph is an instrument, which records the electrical activity of heart• ECG provides valuable information about wide range of cardiac disorders
• Electrodes are placed on each arm and leg, and six electrodes are placed at defined locations on the chest.• These electrode leads are connected to a device that measures potential differences between selected electrodes to produce the characteristic ECG tracings
ECG leads• ECG leads are – Bipolar leads (e.g., standard limb leads) that utilize a single positive and a single negative electrode between which electrical potentials are measured – Unipolar leads • Limb leads • Precordial leads • (augmented leads and chest leads) have a single positive recording electrode and utilize a combination of the other electrodes to serve as a composite negative electrode.
Bipolar limb leadsLead I: RA (-) to LA (+)Lead II: RA (-) to LF (+)Lead III: LA (-) to LF (+)
UNIPOLAR LIMB LEADS• LIMB LEADS: Two of the limb leads are tied together and recorded with respect to the third limb• aVR-Right arm is recorded with respect to a reference established by joining the Left arm and Left leg electrodes• aVL-Left arm is recorded with respect to common junction of RA and LL• aVF-Left leg is recorded with two arm electrodes tied together
Augmented unipolar limb leadsLead aVR: RA (+) to [LA & LF] (-)Lead aVL: LA (+) to [RA & LF] (-)Lead aVF: LF (+) to [RA & LA] (-)
Unipolar chest leadsV1 - Fourth intercostal space, right sternal border.V2 - Fourth intercostal space, left sternal border.V3 - Midway between V2 and V4.V4 - Fifth intercostal space, left midclavicular line.V5 - Level with V4, left anterior axillary line.V6 - Level with V4, left mid axillary line.
• Normally, when an ECG is recorded, all leads are recorded simultaneously, giving rise to what is called a 12-lead ECG• Each of the 12 leads represents a particular orientation in space, as indicated below (RA = right arm; LA = left arm, LF = left foot)
Electrodes, leads & wires• Between the patient and the ecg machine is a patient cable, and this is divided into a number of different coloured wires (10 wires for a 12 lead ecg).• A lead is a view of the electrical activity of the heart from a particular angle across the body, obtained by using different combinations of these wires.
The 12-Lead System• The most commonly used clinical ECG-system, the 12-lead ECg system, consists of the following 12 leads, which are: I , II , III aVR , aVL , aVF V1 ,V2 ,V3 ,V4 ,V5 ,V6
• To measure any electrical activity you need at least two electrodes (a positive and a negative) in order to form an electrical circuit• To obtain a 12 lead ecg you would have 4 wires attached to each of the limbs, and six wires placed around the chest, 10 wires in total but you get 12 "leads“
Precordial Leads• For measuring the potentials close to the heart, Wilson introduced the precordial leads (chest leads) in 1944. These leads, V1-V6 are located over the left chest as described in the figure.
BLOCK DIAGRAM BRIDGE LEAD POWER PRE AMP O/PSELECTOR AMPLIFIER CIRCUIT FREQUENCY SELECTIVE AUXILLARY FEED BACK CIRCUITS NETWORK CHART PEN MOTOR TRANSPORT MOTOR
DESCRIPTION• The potentials picked up by the patient electrodes are taken to the lead selector switch• Here the electrodes are selected TWO by TWO according to the lead program• The signal is then given to the preamplifier• A preamplifier (preamp), or control amplifier, is an electronic amplifier which prepares an electronic signal for further amplification or processing
• It is usually a 3 or 4 stage differential amplifier• The amplified O/P is then given to the power amplifier• The O/P of the power amplifier is fed to the pen motor which deflects the writing arm of the paper• Frequency selective network is an R-C network, which provides necessary damping of the pen
• The auxiliary circuits provide a 1 mV calibration signal and automatic blocking of the amplifier during change in the position of the lead switch• It also include a speed control circuit for the chart driver motor
Extras• Typical wave forms• Signal Characteristics• Einthovens Triangle• CMRR• valves present in heart?