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1. Transportation: The primary function of the circulatory system is to transport important physiological elements (cell, hormones, antibodies, oxygen, nutrients, etc) throughout the body.
2. Thermal Regulation: Assists in the regulation of body temperature through blood vessel constriction and dilation.
3. Waste Removal: With assistance from the lungs, kidneys, and liver, removes waste from the body.
4. Fluid Balance: Maintains a balance between fluid retention and loss.
* The heart is a muscular, cone-shaped, hollow organ approximately the size of a fist situated slightly to the left of midline in the mediastinum, posterior to the sternum.
- Apex: The inferior, pointed portion of the heart that rests on the diaphragm.
- Base: The broader superior aspect.
* Composed of three distinct layers:
- Epicardium: Outer layer.
- Myocardium: Thick, muscular middle layer.
- Endocardium: Inner layer comprising delicate endothelium tissue.
* Double membranous sac that envelopes the heart to protect and reduce friction.
- Parietal pericardium: Outermost pericardial layer.
- Visceral pericardium: Innermost pericardial layer.
* The heart contains four chambers:
- Atria: Two superior chambers that receive blood transported through veins.
-- Atria relax to receive blood and contract to force blood into the ventricles.
-- Atrial walls are not as thick as ventricles due to the short distance the blood is pumped.
-- Atrial Septum: Seperates the left and right atria.
- Ventricles: Two inferior pumping chambers that receive blood from the atria and pump to body parts.
-- Ventricular walls are much thicker than atria because of the force needed to pump the blood throughout the body.
-- Left ventricular myocardium is thicker than the right due to the greater distance the blood must be pumped.
-- Ventricular Septum: Continuous with the atrial septum, it seperates the left and right ventricles.
* Structures that ensure one-way bloodflow through the heart.
- Atrioventricular (AV) valves: Prevents the backflow of blood into the atria when the ventricles contract.
-- Tricuspid valve: Right AV valve composed of three flaps that permits flow of blood from right atrium to the right ventricle.
-- Bicuspid (mitral) valve: Left AV valve composed of two flaps that permits flow of blood from the left atrium to the left ventricle.
- Semilunar (SL) valves: Half-moon-shaped valves found in the major vessels arising from the ventricles.
-- Pulmonary valve: Valve at entrance of the pulmonary artery that prevents the backflow of blood into the right ventricle.
-- Aortic valve: Valve at entrance of the aorta that prevents backflow of blood into the left ventricle.
* Modified cardiac muscle that serves to initiate and maintain rhythmic heart contractions.
- Sinoatrial (SA) node: Specialized cells located in the right atrial wall near the superior vena cava.
-- Initiates each heartbeat and sets its pace (pacemaker).
-- The impulse travels across both atria causing them to contract.
-- Has an intrinsic rate of 60 to 80 impulses per minute.
- Atrioventricular (AV) node: Specialized cardiac muscle located in the lower right atrial septum.
-- The impulse travels from the SA to the AV node at a reduced velocity to permit both atria to contract.
-- Should the SA node malfunction, the AV node has an intrinsic rate of 40 to 60 impulses per minute.
- Specialized cells located in the ventricular septum.
-- The impulse travels from the AV node to the Bundle of His at an increased velocity.
-- Should the SA and AV node malfunction, the Bundle of His has an intrinsic rate of 20 to 40 impulses per minute.
- Bundle Branches: Two branches, extending from the Bundle of His, conduct impulses down the ventricular septum.
- Purkinje Fibers: Extend from the right and left bundle branches to the ventricular walls causing them to contract.
- Cardiac Plexus: Cluster of nerves located near the aortic arch comprising sympathetic and parasympathetic nerve fibers.
- Fibers from the cardiac plexus enter the heart by way of the coronary arteries.
- Fibers end in the sinoatrial node, atrioventricular node, and atrial wall.
* Complete heartbeat consisting of contraction (systole) and relaxation (diastole) of both atria and ventricles.
- Atrial Systole: Contraction of the atria.
-- Atrial contraction empties the blood into the ventricles.
-- The AV valves open, and the SL valves close.
- Ventricular Diastole: The ventricles are relaxed and filling with blood from the atria.
- Ventricular Systole: Contraction of the ventricles.
-- Ventricular contraction forces the blood through the SL valves to the major vessels, aorta, and pulmonary artery.
-- The AV valves are now closed.
- Atrial Diastole: The atria are relaxed and filling with blood from the major veins, vena cavas and pulmonary veins, before the cycle is repeated with atrial systole.
- Artery: Vessels that carry blood away from the heart. Small arteries are arterioles. Arterioles provide resistance important in blood pressure.
- Veins: Vessels that carry blood toward the heart. Small veins are venules. Serve as collectors and reservoir vessels.
- Capillaries: Microscopic vessels that connect arterioles and venules. Permit the collection and delivery of important physiologic substances.
- Arteries & Veins: Composed of three layers.
-- Tunica Adventitia: Outermost layer comprising tough, fibrous connective tissue. Thickest layer in veins.
-- Tunica Media: Middle layer comprising smooth muscle tissue. Allows vessels to contract and dilate.
-- Tunica Intima: Innermost layer comprising endothelium. In veins forms semilunar valves to prevent backflow.
- Microscopic vessels composed of a single layer of endothelium to allow for the exchange of material between plasma and interstitial fluid.
1. Deoxygenated (CO2) blood returning to the heart from the body flows through the vena cavas.
- Blood returning from head, neck, and axilla flow through the superior vena cava.
- Blood returning from the torso and below flow through the inferior vena cava.
2. From the vena cavae, the blood enters the right atrium.
3. The right atrium contracts, forcing the blood through the tricuspid valve.
4. The blood enters the right ventricle.
5. The right ventricle contracts forcing the blood through the pulmonary valve.
6. The blood enters the pulmonary artery to be transported to the lungs for oxygenation (O2).
7. Once oxygenated in the lungs, the blood enters the pulmonary veins for transport back to the heart.
8. From the pulmonary veins, the blood enters the left atrium.
9. The left atrium contracts forcing the blood through the bicuspid (mitral) valve.
10. The blood enters the left ventricle.
11. The left ventricle contracts forcing the blood through the aortic valve.
12. The blood enters the aorta where it is transported to all body parts to deposit oxygenated blood and collect deoxygenated blood for return to the heart where the cycle is repeated.
1. Pulmonary: Arising from the right ventricle, it transports deoxygenated blood to the lungs for oxygenation.
2. Aorta: Largest artey arising from the heart where largest systemic arteries branch off from. The aorta is divided into the ascending, aortic arch, descending, and abdominal aorta.
3. Coronary: Right and left arteries branch off from the ascending aorta to supply the heart with blood.
4. Brachiocephalic: On of the three major branches of the aortic arch. It branches off to supply blood to both the neck and head, and the axilla and upper arm.
5. Subclavian: The left subclavian branches from the aortic arch; the right subclavian branches from the brachiocephalic to supply the arm and vertebrae.
6. Carotid: The left carotid branches from the aortic arch; the right from the brachiocephalic to supply the neck and head.
7. Facial: A branch of the carotid, it supplies the anterior face and cranium.
8. Occipital: A branch of the carotid, it supplies the neck, mastoid, lateral and posterior cranium.
9. Axillary: An extension of the subclavian, it supplies the axilla.
10. Brachial: An extension of the axillary, it supplies the upper arm.
11. Radial: A branch of the brachial on the thumb side, it supplies the forearm, wrist, and hand.
12. Ulnar: A branch of the brachial on the little finger side, it supplies the forearm, wrist, and hand.
13. Celiac: A branch of the abdominal aorta, it supplies the upper abdominal organs.
14. Splenic: Serves a similar function as the celiac.
15. Renal: A branch of the abdominal aorta, it supplies the kidneys, suprarenal glands, and ureters.
16. Mesenteric: a branch of the abdominal aorta, the inferior and superior mesenterics supply the intestine, colon, and rectum.
17. Iliac: A branching extension of the abdominal aorta, it supplies the abdominal, pelvic, and lower limb regions.
18. Femoral: An extension of the right and left iliac, it supplies the lower abdominal wall, genitalia, and upper leg.
19. Popliteal: An extension of the femoral, it supplies the knee and calf.
20. Tibial: An extension of the popliteal, the anterior tibial supplies the lower leg, ankle, and foot; the posterior tibial supplies the lower leg, foot, and heel.
21. Dorsalis Pedis:
21. Dorsalis Pedis: An extension of the anterior tibial, it supplies the foot.
1. Pulmonary: Vein that transports oxygenated blood from the lungs to the left atrium.
2. Coronary: Leading into the coronary sinus of the right atrium, it drains blood from the heart.
3. Vena Cava: Largest vein draining blood from the body into the right atrium. The superior vena cava drains the upper half of body; the inferior vena cava, the lower half.
4. Brachiocephalic: Left and right branches leading into the SVC, it drains the head, neck, and upper extremities.
5. Jugular: Branches leading into the brachiocephalic, it drains the head and neck.
6. Facial: Branches leading into the jugular, it drains the face and anterior cranium.
7. Occipital: Branches leading into the jugular, it drains the posterior cranium.
8. Axillary: Branches leading into brachiocephalic, it drains the axillary and upper arm region.
10. Cephalic: Superficial vein on the thumbside leading into the axillary, it drains the upper and lower arm.
11. Radial: Deep vein leading into the axillary that drains blood from the thumbside of the forearm and wrist.
12. Basilic: Superficial vein on the little-finger side leading into the axillary, it drains the upper and lower arm.
13. Ulnar: Deep vein leading into the axillary that drains blood from the little-finger side of forearm and wrist.
14. Splenic: Gastric, cholecystic: Leading into the portal hepatic vein, it drains the spleen, stomach, and gallbladder, respectively.
15. Mesenteric: Leading into the hepatic portal vein, it drains blood from the intestines, colon, and rectum.
16. Hepatic: Leading into the IVC, it drains the liver.
17. Renal: Leading into the IVC, it drains the kidneys, suprarenal glands, and gonads.
18. Iliac: a branching extension of the IVC, it drains the abdominal, pelvic, and lower limb regions.
19. Femoral: An extension of the right and left iliac, it drains the upper leg.
20. Popliteal: An extension of the femoral, it drains the knee and calf.
21. Saphenous: The longest vein; the GSV leads into the femoral and drains the medial leg. The SSV leads into the popliteal and drains the lateral lower leg.
22. Tibial: Leading into the popliteal, the anterior and posterior tibial drains the lower leg.
23. Dorsal Venous Arch: Leading into the tibial veins, it drains the foot.
- Specialized component of the circulatory system comprising lymph fluid, lymphatic vessels, lymph nodes, tonsils, thymus, and spleen.
- As part of the circulatory system, it functions to maintain fluid balance and provide immunity.
- Lymph Vessels serve to collect excess tissue fluid for transport into the veins before its return to the heart.
- The lymphatic system transports tissue fluid, proteins, fats, and other elements to the general circulation.
- Unlike the cardiovascular system, the lymphatic system is not a closed circuit.
2. Lymphatic Fluid: Clear, watery, isotonic fluid resembling blood plasma.
3. Lymphatic Vessels
* Two major electrical aspects of the heart:
1. Automaticity: The heart's ability to generate its own electrical stimulus.
2. Conductivity: The ability of cardiac cells to receive a stimulus from a neighboring cell and pass it to the next cell causing a wavelike motion to create a contraction.
1. Polarization: Cardiac cells are in a resting, negatively charged state.
2. Depolarization: Cells are discharging a positively charged electrical impulse to create a contraction.
3. Repolarization: Transformation of cells from a depolarized (active) to polarized (resting) state for recharging.
* Cardiac electrical activity generates, via automaticity, and spreads, via conduction, through the heart, creating an electrical wave that can be measured with an ECG.
* All beats appear as a similar pattern, equally spaced, comprising three major units: P wave, QRS complex, and T wave.
- ECG waves: Each beat comprises five major waves: P, Q, R, S, and T.
- P wave: Reflects the impulse emanating from the atria.
- QRS complex: The Q, R, and S wave, as a unit reflects the impulse passing through the the ventricles.
- T wave: Reflects repolarization of the ventricles.
- Isoelectric line (baseline or zero-volatge line): The point on the ECG wave where no (upward or downward) deflection is present indicating no electrical activity (voltage).
- Wave: Any upward or downward deflection from the isoelectric line.
- Segment: Lines between waves; distance between selected wave marks, but not including them; e.g., the ST segment is the distance between the S and T waves, but not including the S or T waves.
- Interval: Lines that contain waves; distance covering the beginning of one wave mark to the end of a second wave mark; e.g., the PR interval is the distance between the beginning of the P wave to the end of the R wave.
- Complex: Any arrangement of the QRS waves or PQRST waves in their entirety.
* The first upward deflection representing atrial depolarization (atrial contraction).
- Normal P wave: Three small blocks high and wide or less.
- Enlarged P wave: Found in mitral stenosis or chronic obstructive pulmonary disease, which would cause atrial hypertrophy.
* Extends from the beginning of the P wave to the onset of the QRS. It represents conduction of the impulse through the atria from the SA to the AV node.
- Normal: Three to five small blocks wide (0.12 to 0.20 second).
- Lengthened PR Interval: Seen when the impulse is forced to travel at a slower rate, which can occur in arteriosclerosis, inflammation, insufficient oxygen supply, or scarring from rheumatic heart disease. It can also occur as an effect of depressant drugs or digitalis.
- Consists of 3 deflections:
-- Q wave: The downstroke before the R wave.
-- R wave: The first upward deflection.
-- S wave: The downstroke following the R wave.
- Not every QRS complex shows a discrete Q, R, S wave, but the configuration is still referred to as the QRS complex to denote a ventricular impulse. It represents transmission of the impulse from the AV node to the Purkinje fibers.
- Normal: Duration is 2.5 small squares or less (0.10 second).
- Enlarged Q wave: Over a small square wide or greater in depth than one-third the height of the QRS complex may indicate a myocardial infarction.
- Tall R wave: Usually indicates enlarged ventricles.
- The ST segment begins at the end of the S wave (the point where the line turns right) and ends at the beginning of the T wave. It represents the transition from ventricular depolarizationto repolarization.
- ST elevation: Seen in an acute myocardial infarctionor muscle injury.
- ST depression: Seen when the heart muscle is not getting a sufficient supply of oxygen, or as an effect of digitalis; usually transient.
- Represents electrical recovery (repolarization) to allow cells to recharge in preparation for ventricular depolarization (contraction).
- Normal: No more than 10 small blocks (10mm) high in the precordial (chest) leads and five small blocks (5mm) high in the remaining leads.
- Flat/Inverted T wave: Seen in response to ischemia, position change, food intake, or certain drugs.
- Elevated T wave: Seen when the serum potassium is elevated.
- Represents the time from beginning of the Q wave (downward deflection following the P wave) through the QRS and the T wave. It includes the time until the T wave is completed (goes back to the baseline). It demonstrates the impulse from the beginning of ventricular contraction to complete recovery.
- Normal: Should be less than one-half of the R-R interval (from the peak of one R wave to the peak of the next R wave).
- Prolonged QT interval: Drugs such as quinidine, procainamide hydrochloride (Pronestyl) and disopyramide phosphate (Norpace) can prolong the QT interval predisposing one to ventricular tachycardia.
- A prolonged QT time presents an extended opportunity for stray impulses to excite the heart tissue and trigger dangerous ventricular rhythms.
- Small upward deflection following the T wave. It is seldom present, but may occur when the serum potassium level is low.
- Following the U wave the stylus returns to the baseline representing no electrical activity (polarized state) or rest period between beats.
- Electrical flow in the heart is measured by externally applied electrodes relative to a direct line, called an axis, between two poles.
- A lead comprises one negative pole, one positive pole, and one ground.
- Leads create an electrical picture of the heart taken at different angles.
- Sensors (electrodes): Uses 10 sensors -- 4 limb sensors and 6 chest to create 12 leads.
* 6 of the 12 leads are called limb leads.
- Bipolar (standard) limb leads: Measures cardiac electrical activity between 2 extremities; between a negative and positive electrode (pole).
-- Lead 1: Measures electrical activity from the right arm to the left arm (RA to LA).
-- Lead 2: From right arm to left leg (RA to LL).
-- Lead 3: From left arm to left leg (LA to LL). The right-leg position is not displayed as part of the flow of current through the heart, as it is used for grounding system
* Unipolar (augmented) limb leads: Measures electrical activity between the heart and 1 extremity. Each lead measures activity from the posterior heart to the positive pole (the positive electrode) on the anterior chest.
- aVR: Augmented vector right-side.
- aVL: Augmented vector left-side.
- aVF: Augmented vector foot (left).
* Limb lead electrodes are applied to the patient's extremities.
- 6 unipolar chest leads that require a combination of electrodes from the extremities to represent one pole (at the posterior heart).
- The positive electrode is then attached to the anterior chest in 6 specified locations.
- The precordial leads provide points of reference across the chest wall. They differentiate right-sided and left-heart events.
- Lead V1: Electrode is placed at the 4th intercostal space just to the right of the sternum.
- Lead V2: 4th intercostal space just to the left of the sternum.
- Lead V4: The left midclavicular line in the 5th intercostal space.
- Lead V3: The line midway between leads V2 & V4.
- Lead V5: The anterior left axillary line at the same level as lead V4.
- Lead V6: The left midaxillary line at the same level as lead V4.
- Each of the 12 leads has a unique individual axis. Any lead may be used to monitor cardiac activity for the occurence of arrhythmias.
- The most important leads in relation to the anatomy of the heart are:
-- V1, aVR: right side of heart.
-- V2, V3, V4: transition between right and left sides of heart.
-- V5, V6, I, aVL: left side of heart.
-- II, III, aVF: inferior heart.
- The area of pathology shown on the ECG can be localized by analyzing tracings from different leads.
* The ECG presents a visible record of the heart's electrical activity by means of a heated stylus that traces the activity on a continuously moving strip of special heat-sensitive paper.
- Composed of 1mm squares where every 5th line is darkened creating large blocks of 5 small blocks high and 5 wide.
- Cardiac voltage is measured on the vertical scale & time on the horizontal.
- Horizontally, each large block represents 0.2 seconds; whereas, vertically, it represents 0.5 millivolts of electricity.
- The paper moves through the ECG machine at the rate of 1 inch per second (standard setting).
- Main Power Switch: Turns the instrument on and off.
- Record Switch: Controls amplifier and paper drive.
-- Amp off: Places instruments in standby mode. In some models it is the STOP button.
-- Amp on: Activates the amplifier so the stylus can react to heart beat. In some models, it is the RUN button.
-- Run 25: Engages the paper drive to move the paper 25mm (1 inch) per second. Standard speed.
-- Run 50: Doubles paper drive speed, moves paper 50mm (2 in) per second. Used to show detail of wave configuration on patients with tachycardia.
- Sensitivity Control: Regulates output of amplifier.
-- One-half: Produce a 5mm deflection. Used when the machine is picking up high electrical voltage; adjusts for abnormally large peaks & valleys of waves.
-- 1:10mm deflection (standard setting).
-- 2:20mm deflection. Used when the machine is picking up low electrical voltage; adjusts for abnormally small peaks and valleys of waves.
- Standard (STD) button: Manual check of instrument calibration.
- Standardization adjustment knob: Adjusts the deflection to the proper height when the STD button is pushed.
- Stylus control knob: Moves stylus so recording will be in the center to the strip.
- Lead selector: Changes the leads to be recorded (older models).
- Stylus heat control: Raises or lowers the heat in the tip of the stylus.
- Marker button: Allows for manual identification of the different leads being recorded (older models). Marking codes uses dashes and dots:
- Supine positon and remain still
- Place the sensors as marked on the fleshy parts of the limbs, not the ankles or wrists.
- Connect the lead cables to the proper sensors so that the connector is pointing toward the patient's feet.
- Ensure that the lead cables follow the contour of the body, avoiding large loops and crossed cables.
- Turn on main power switch. Warm-up may be required.
- Standardize the instrument: Digital units do not reqire standardization.
-- Set the lead selector switch to STD (standard) and the sensitivity control switch to 1.
-- Press the STD button. The stylus should be deflected 1cm (10mm or two large squares).
-- If not, turn the standarization adjustment knob and repeat until it is calibrated.
- Automatic models will record and mark the entire ECG at the touch of a button.
-Turn off machine.
* Defects on the EKG not caused by the electrical activity of the heart.
- Somatic Tremor: Often produced by muscle movement of the patient, such as in Parkinson's disease.
- AC (Alternating Current) Interference: Standard source for electrical power present in electrical equipment and wires. Inproper grounding of nearby electrical equipment, concealed electrical wiring, lead cables being crossed, or dirty electrodes.
- Wandering Baseline: Electrodes applied too loosely or tightly, too little gel, tension on lead wires, skin creams or lotions where electrodes are applied, excessive hair, or dirty electrodes.
- Rhythm: Regularity may be determined using calipers or any device that can be marked to show a fixed interval for comparison.
- Cardiac Rate: Each large block on the ECG paper represents 0.20 second, 300 large blocks represent 1 minute. If rhythm is regular, count the large blocks between two R waves and divide 300 by this figure.
-- Count the complexes in a 6-inch strip (30 large blocks) and multiply by 10 (useful for irregular rhythms).
- The provider can locate the damage by noting which leads show indicative changes.
- About 15% of infarcts show no changes on the initial tracing. ECG changes evolve later in hours or days as tissue damage changes electrical impulse conduction pathways.
- Elevation of the ST segment followed by T wave inversion, which in turn is followed by a large Q wave. As the infarct heals, the Q wave may remain as the only sign of an old infarction.
- The P wave, the PR interval, and the QRS complex are on normal configuration. The difference lies in the regularity and rate of the impulses.
- All complexes are normal, but the heart rhythm is irregular. The rate increases with inspiration, and decreases with expiration. This irregularityis common in children and may occur in adults relative to certain respiratory patterns. It does not decrease cardiac output and does not lead to more serious arrhythmias.
- Heart rate is more than 100. Caused by excessive sympathetic nerve stimulation, physical activity, anxiety, and fever, or a compensatory response to decreased cardiac output.
- Heart rate below 60. Seen in well-trained athletes, in patients on digitalis, propranolol (Inderal), and morphine. A significant slowing may cause a decrease in cardiac output that can lead to cerebral or coronary insufficiency.
- A beat is not transmitted out of the SA node. No P, QRS, or T wave is present at the cycle interval for one or more beats.
- The SA node fails to send out an impulse for a period of time.
- Portions of atrial tissue may become excitable and initiate impulses. These ectopic foci will control the heartbeat as they occur at a rate faster than impulses from the SA node.
- A beat initiated by an ectopic atrial focus appearing early in the cycle, before the next expected sinus beat. the P wave may be superimposed on the preceding T wave. Frequent PACs may be warnings of more serious atrial arrhythmias and may be treated with quinidine.
- An abrupt episode of tachycardia with the heart rate usually between 140 and 250 beats per minute, averaging about 170.
-- The patient frequently complains of a sudden pounding or fluttering in the chest associated with weakness or breathlessness.
-- The fast rate stresses the heart and increases its need for oxygen.
-- Tachycardia may also diminish cardiac output because of the shortened ventricular filling time.
-- Treatment: Stimulation of the vagus nerve, which slows the heart rate. Measures that stimulate the vagus nerve include vomitting, stimulating the anal sphinchter, and applying pressure to the eyeball.
- The impulses are coming so rapidly, the AV node cannot accept and conduct each one, and therefore some degree of blockage occurs at the node. A fast cardiac rate is relatively ineffectual and may lead to congestive heart failure. The quickest way to slow a very fast flutter is by electrocardioversion. By using low voltage, depolarization of all heart tissue is accomplished with the elecatrical energy of the defibrillator paddles. Cardioversion permits the sinus node to gain control.
- A very fast atrial rate rising from many ectopic foci. The total atrial configuration may resemble a wavy baseline or almost straight line. This occurs in enlarged atrial chambers often impaired by arteriosclerotic heart disease, scar tissue from surgery, or infections such sa rheumatic fever.
- Av node functions to receive the impulse, delay it for an instant, an then conduct it to the ventricular pathway.
- When an impulse arises in the junctional area, it will activate the atria through retrograde (backwards) conduction, causing the P wave to be inverted (downward in leads where the P would normally be upright).
- AV block: The AV node is diseased & has difficulty conducting the P waves into the ventricles. The most common causes are arteriosclerosis & myocardial infarction. Scarring, inflammation, or edema prevents or slows transmission of the electrical impulse by the AV node.
- Ventricular arrhythmias may diminish the ability of the heart to function as a pump. Without adequate blood flow, all body organs deteriorate.
- Premature ventricular contraction (PVCs): Occur in most myocardial infarction patients. They are also seen in normal persons, and may be caused by smoking, coffee, or alcohol.
-- Originate in the ventricles below the AV node, showing a bizarre QRS configuration.
-- Characteristics of PVCS:
--- Usually occur early in the cycle.
--- Are not usually preceded by a P wave.
--- Have a wide & distorted QRS.
--- Have a large looping ST segment opposite in direction to that of the QRS.
--- The interval between the R waves before and after the PVC is twice the normal R-R interval.
- Series of multiple (three or more), consecutive PVCs occurring at a rate usually between 150 and 200 beats per minute. Ventricular tachycardia is very dangerous because it leads to reduced cardiac output and, many times, to ventricular fibrillation.
- Numerous ectopic foci in the ventricles are firing erratically. Thus, there is no effective contraction of the cardiac musculature, and the patient has no pulse. Death is imminent without prompt treatment.
- Unit that generates a pulse to stimulate the myocardium to produce a ventricular contraction when the sinus pacemaker activity malfunctions or the heart does not maintain a sufficiently rapid rate.
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