Anatomy of the Heart

Anatomy of the Heart

• The heart is the main organ of the cardiovascular system
• It pumps blood throughout body while working with other systems to control heart rate and blood pressure
• Functions as a two-sided pump.

Location, Size, and Shape of the Heart

• Located in the mediastinum.
• Lies in front of the spinal column, behind the sternum, and between the lungs.
• Two-thirds of the heart lies to the left of the midline.
• The apex of the heart lies just above the diaphragm.
• The base of the heart is at the level of the third rib
• Roughly the size of owners closed fist

Layers of the Heart

• The pericardium is a closed, two-layered sac, includes parietal and visceral layers.
• The parietal pericardium is tough, nonelastic, and made of fibrous connective tissue.
• The visceral pericardium is a thin, serous inner layer of the pericardium.
• The epicardium is the smooth outer surface of the heart.
• The myocardium is the thick, middle layer of the heart composed of cardiac muscle cells, responsible for contractility.
• The endocardium is the innermost layer composed of connective tissue.

Valves of the Heart

• Four valves allow blood to flow in one direction.
• The two sets of valves are atrioventricular and semilunar.

Atrioventricular Valves

• Located between the atria and ventricles.
• Allow blood to flow from the atria into the ventricles.
• Prevent blood from flowing backward from the ventricles.
• The tricuspid valve has three cusps and is located between the right atrium and right ventricle.
• The mitral bicuspid valve has two cusps, located between the left atrium and left ventricle.

Semilunar Valves

• Prevent backflow of blood into the ventricles.
• Each semilunar valve contains three semilunar or moon-shaped cusps
• The pulmonic valve is located between the right ventricle and the pulmonary artery.
• The aortic valve is located between the left ventricle and the trunk of the aorta.

Heart Valve Function

• Chamber pressure governs the opening and closing of heart valves.
• Ventricular systole involves contraction of the ventricles, closing the atrioventricular valves and opening the semilunar valves.
• Ventricular diastole involves relaxation of the ventricles, opening the atrioventricular valves and closing the semilunar valves.

Coronary Arteries

• The two main coronary arteries are the left and right coronary arteries.
• The left coronary artery branches into the left anterior descending artery, the marginal branch, and the circumflex artery.
• The right coronary artery branches into the posterior descending artery.

Circulation

• Circulation is the movement of blood through a course (body) that leads back to the initial point (the heart).
• Blood exits the heart in arteries, exchanges waste for oxygen in capillaries, and returns to the heart in veins.

Cardiac Cycle

• The heart functions as a unit with both atria contracting.
• Ventricles fill with blood to their limits.
• Blood is ejected into both the pulmonary and systemic circulations when the ventricles contract.
• The cardiac cycle represents the actual time sequence between ventricular contraction and relaxation.

Ventricular Systole and Diastole

• Ventricular systole is the simultaneous contraction of the ventricles, closing the mitral and tricuspid valves.
• Ventricular diastole is the simultaneous relaxation of the ventricles, opening the mitral and tricuspid valves.
• Pulmonary and aortic valves open during systole and close during diastole.

Stroke Volume and Cardiac Output

• Stroke volume is the volume of blood pumped out of one ventricle of the heart in a single beat.
• Stroke volume is estimated to be 70 cubic centimeters per beat.
• Normal heart rate is 60 to 100 beats per minute (BPM)
• Tachycardia is an increased heart rate (over 100 bpm), while bradycardia is a decreased heart rate (under 60 bpm).

Calculating Cardiac Output

• Cardiac output measures the amount of blood pumped by the left ventricle in one minute.
• Cardiac Output = Stroke Volume x Heart Rate.
• For example, if heart rate is 80 BPM and stroke volume is 70 cc per beat, the resulting cardiac output would be 5,600 cc per minute or 5.6 L/min.
• Preload is the pressure in the ventricles at the end of diastole.
• Afterload is the resistance against which the heart must pump.
• Starling's Law states that the more the myocardial fibers are stretched, the more the subsequent contraction will be.
• Peripheral vascular resistance is the amount of opposition to blood flow offered by the arterioles.
• Vasoconstriction and vasodilation determine peripheral vascular resistance.
• Blood Pressure = Cardiac Output x Peripheral Vascular Resistance.

The Cardiac Conduction System

• The sinoatrial (SA) node is located in the upper posterior portion of the right atrial wall of the heart, acting as the primary pacemaker.
• The firing rate of the SA node is 60 to 100 beats per minute (BPM).
• Depolarization and myocardial contraction occur after the impulse leaves the SA node

Internodal Pathways

• Internodal pathways receive electrical impulses as they exit the SA node.
• Distribute the impulse throughout the atria.
• Transmit the impulse from the SA node to the AV node.

AV Node and Junction

• The atrioventricular (AV) node is located on the floor of the right atrium above the tricuspid valve.
• Electrical activity is delayed by 0.05 seconds to allow for more complete filling of the ventricles.
• It is the only pathway for atrial electrical impulses to reach the ventricles.
• The AV junction is where the AV node joins the bundle of His.
• If the SA node fails or slows significantly, AV junctional tissues initiate electrical activity as a secondary pacemaker.

Bundle of His and Bundle Branches

• The bundle of His is a conduction pathway that leads out of the AV node, located at the top of the interventricular septum.
• It is referred to as the common bundle, with the ability to self-initiate electrical activity at an intrinsic firing rate of 40 to 60 beats per minute.
• The bundle of His divides into two main bundle branches: the right and left bundle branches.
• Conduct electrical activity from the bundle of His to the Purkinje network

Purkinje Fibers

• Are a network of fibers that receive conductive signals from the AV nodes.
• Carry impulses directly to ventricular muscle cells.
• Simultaneously activate the left and right ventricles by directly stimulating the ventricular myocardium
• Firing rate of 20 to 40 beats per minute

Electrocardiogram (ECG/EKG)

• Used to determine or detect abnormal heart rhythms (arrhythmias), palpitations, blocked or narrowed arteries (coronary artery disease), or effectiveness of heart disease treatments.

Basis of the ECG

• Electrical activity is sensed by electrodes placed on the skin surface and recorded in the form of an electrocardiogram.
• A cardiac monitor depicts electrical impulses on a monitor screen or oscilloscope.
• Used to detect chest pain; dizziness, lightheadedness, or confusion; heart palpitations; rapid pulse; shortness of breath; weakness; fatigue; or a decline in exercise ability.

Electrocardiograph Components

• The electrocardiograph is the apparatus used to generate electrocardiograms.
• The ECG is the graphic tracing of electrical activity of the heart, NOT the mechanical activity.
• Electrical impulses from the heart are picked up by electrodes and conducted through lead wires into the machine.
• Electrodes are composed of a substance that is a good conductor of electricity.
• The electrical impulses given off by the heart are very small (around 0.002 volt).
• To produce a readable ECG, impulses are amplified by a device known as an amplifier, located within the electrocardiograph.
• Amplified voltages are changed into mechanical motion by a galvanometer and recorded on the electrocardiograph paper by a terminal print head.

ECG Graph Paper

• Electrical impulses present on the skin surface are very low voltage, so they are amplified by an ECG machine.
• The printed record of the electrical activity of the heart is called a rhythm strip, and the record is printed on graph paper at a set speed (25 mm/sec) to demonstrate the electrical conductivity of the heart.
• The recording is a plot of voltage on the vertical axis against time on the horizontal axis.
• Electrodes are connected to a galvanometer that records a potential difference.
• Electrocardiographic paper is divided into small squares, with each millimeter (mm) in width representing a time interval of 0.04 seconds.
• Darker lines divide the paper every fifth square, vertically and horizontally.
• Large squares measure 5 millimeters in height and width, representing a time interval of 0.20 seconds.
• Paper leaves the machine at a constant speed of 25 millimeters per second (mm/sec).
• Amplitude or voltage is measured on the vertical line on the graph paper (y-axis), and time is measured on the horizontal line (x-axis).
• Doubling the standard rate (25 mm/sec) can reveal subtle ECG findings hidden at slower rates.

Leads

• Electrodes are adhesive pads containing conductive gel which attach to patient's skin, enabling electrical impulses to be recorded from the heart.
• Leads are how electrodes are connected to the cardiac monitor which include positive, negative, and ground.
• Bipolar leads have one positive and one negative.
• Limb leads include leads I, II, and III, with lead II being the most common as it visualizes the P-wave.
• Lead I runs from the right arm (-) to the left arm (+).
• Lead II runs from the right arm (-) to the left leg (+).
• Lead III runs from the left arm (-) to the left leg (+).

Einthoven's Triangle

• Imaginary inverted triangle formed around the heart through proper placement of bipolar leads
• Top is formed by Lead I, the right side by Lead II, and the left side by Lead III.
• Einthoven stated that Lead I + Lead III = Lead II, which is called Einthoven's law.
• Each lead represents a different view of the heart.

ECG Planes

• The 12-lead ECG views the heart in two distinct planes: the frontal plane and horizontal plane.
• The frontal plane is what the limb leads look at, while the horizontal plane is what the vector (V) leads look at

Positioning and Placement of Electrodes

• Two-arm leads should be placed between the shoulder and wrist.
• Two-leg leads should be placed between the hips and ankles.
• Augmented limb leads include aVR, aVL, and aVF, utilizing the four limb leads.
• The heart is the focal point, and current flows from the heart outward to the extremities.
• The ECG machine must boost amplification due to positions of these leads.
• Chest leads, called precordial or vector (V) leads, look at the horizontal or transverse plane.

Quality of the ECG and Standardization

• The electrocardiograph must be standardized to ensure an accurate and reliable recording for QRS complex amplitude.
• An application of one 1 millivolt (mV) of electricity causes the stylus to move ten 10 millimeters high or ten (10) small squares.
• The standardization mark is automatically recorded by three-channel electrographs on the tracing.
• Most ECG machines automatically place a standardization mark at the beginning of the tracing.
• Ensure this is at the beginning of each patient's tracing.
• The paper consists of a black or blue base with a white plastic coating.
• A heated stylus moves over the heat-sensitive paper and melts away the plastic coating, resulting in the recording of the ECG.

ECG Wave Forms and Intervals

• Wave or waveform refers to movement away from the baseline or isoelectric line, positive deflection is above the isoelectric line and negative deflection is below.
• Electrical impulses that leave the SA node produce waveforms on the graph paper.
• One complete cardiac cycle is represented by the P, Q, R, S (QRS complex), and T waves.
• First wave is produced by an electrical impulse from the SA node with a smooth, rounded upward deflection.
• Representing depolarization of the left and right atria occurring in 0.10 seconds.
• Also the time for an impulse to travel from the SA node through internodal pathways in the atria toward the ventricles.
• Time interval from the start of the P wave to the start of the QRS complex is 0.12 to 0.20 seconds.
• Includes Q, R, and S waves which represents conduction of the impulse from the bundle of His through the ventricular muscle, causing ventricular depolarization.
• Time interval for QRS is less than 0.12 seconds measured from the start to end.
• Isoelectric Point
• Time interval during which the ventricles are depolarized and repolarization begins.
• Follows the ST segment, representing ventricular repolarization, is slightly rounded, and has a positive deflection.

T Wave and QT Interval

• Represents the resting phase of the cardiac cycle. From the beginning of the QRS complex to the end of the T wave, which represents all ventricular activity (depolarization and repolarization), the QT interval is normally 0.28-0.44 sec.
• A U wave is usually absent but if present, its height should be < 1/3 of the T wave.
• When a tall U wave presents, it indicates electrolytes imbalance mainly low K+ in blood (Hypokalemia).
• Leads I, II, III, QRS is a positive deflection while aVR QRS is a negative deflection.
• aVL QRS is biphasic and aVF QRS is a positive deflection.
• V1 QRS is a negative deflection.
• QRS progresses through until V6.
• V6 QRS is a positive deflection.

Artifacts

• Produced by something other than than the electrical activity of the patient's heart.
• Indicates a technical problem with either the patient set-up, or with the ECG instrument itself.
• Erratic spikes of varying sizes that can interrupt wave forms or the baseline.
• Patient is the source usually found only in affected leads.

Troubleshooting Artifacts

• Ensure that the patient is relaxed and comfortable and that body parts are well supported on the bed
• Ask patients to place hands under their buttocks to reduce involuntary shaking and check limp sensor position to ensure that there are no tremors
• Move limp sensor to torso if tremors cannot be controlled
• Has dry electrodes, dangling lead wires, loose electrodes or broken lead wires, use new electrodes and change the wires.

AC Artifacts

• Looks as a series of uniform small spikes, making the baseline like a thick line, alternative name is 60 Hz interference.
• Electrical currents in nearby equipment or a bad wiring can leak small amounts of the electrical energy that the ECG picks up.
• Has a poorly grounded ECG machine or it is not equipped to filter out the electrical interference, loose or broken ground connector or power cord.

Electrical Equipment

• Right leg electrode may be improperly connected or not connected at all.
• Patients' bed may not grounded; patient touching metal frame.
• Electrodes and/or cable tips may be corroded or dirty.
• Use three-pronged grounded outlet, do not cross lead wires, unplug other electrical appliances in the room, move table away from wall, and turn off fluorescent lights.
• The filters on the ECG are used to remove high frequency muscle artifact and external interference.
• However, it will cause slight adjustments to the ST segments and most ECGs are done with the filter "on".

Holter Monitor

• Used to rule out intermittent arrhythmias or ischemia that could be missed on a routine EKG.
• It records the electrical activity of the heart for 24 -72 hours and detects cardiac abnormalities that occur while the patient is engaged in daily activities.
• Explain each step of the procedure to the patient and allow them to ask questions.

Application of the Holter Monitor

• Apply the monitor has been prepared and after the patient (clothing and position has been prepped).
• Prepare skin by abrading a thin layer of skin where electrodes will go.
• Place and tape the five electrodes to trunk of body (instead of arms and legs).
• The EKG signals are recoded on a magnetic tape or digital flash media; Give patient care; instructions/guidelines for Holter monitor and diary.
• Patient returns after prescribed hours/days (typically 1-3) to the facility and the data is entered into a Computer.
• Computer scans for abnormalities.

Quality of a Holter Monitor Recording

• Correct patient information.
• Baseline of tracing smooth Standardization mark present.
• Einthoven's Law is met (II= I + III), aVR lead is a negative or downward deflection.
• R wave progression in chest leads and Lead II is a positive deflection.

Adapted Use of Holter Monitors

• Performed inside medical facility; Uses 3 or 5 electrodes on chest.
• Transmits to a central location where multiple patients may be monitored.
• Patient diary not required.
• Twelve-lead is the standard form and 5-lead monitoring take electrodes that are electrodes that are used for the limbs in 12-lead monitoring and place them on the chest wall.
• 5-lead monitoring is the same as 3-lead monitoring, with two additional electrodes to enable the monitoring of extra leads and help improve ST elevation readings.
• monitors leads I, II, III aVR, aVL, aVF, and V.
• Uses 5 electrodes (RA, RL, LA, LL and Chest).
• Monitor displays the bipolar leads (I, II and III) and a single unipolar lead (depending on position of the brown chest lead (positions V1–6).

Electrode Systems

• In this system you are recording Right arm (RA – white) - below the right, Left arm (LA – black) – below the left clavicle and Left leg (LL - red) - on the lower part of the ribcage, on the left-hand side.
• These systems are simple, cheap and easy to use.
• The available leads with this setup are I, II and III

Transtelephonic Monitoring

• Monitoring is primarily used to evaluate pacemaker function or monitor patients for 30 days or more.
• Information stored in the monitor; methods of transmission Telephone land line, Cell phone tower and Wi-Fi.
• It has two types
  • Post-symptom event monitor
  • Loop memory monitor