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CHAPTER 42: INTRODUCTION TO THE CARDIOVASCULAR SYSTEM

Cardiovascular System - responsible for delivering oxygen and nutrients to all of the cells of the body and for removing waste products for excretion - consists: 1. heart 2. pump3. interconnected series of tubes THE HEART - hollow, muscular organ divided into 4 chambers: atriums ( “porch” or entryway) and ventricles ( lower part) - is the pump that keeps blood flowing through 60,000 miles of tubes, constituting the cardiovascular system *auricle- attached to each atrium; collects blood that is pumped into the ventricles by arterial contraction ** a partition called a septum separates the right half of the heart from the left. The right receives deoxygenated blood from everywhere in the body through the veins ( vessels that carry blood toward the heart) and directs that blood into the lungs… *** arteries- where aorta delivers blood into the systemic circulation - vessels that carry blood away from the heart

mitral or bicuspid valve- valve on the left side of the heart; composed of two leaflets or cusps * systole - the contraction of ventricles

* absolute refractory period * The heart’s series of one- way valves keeps the blood flowing on the correct direction, as follows: 1. Deoxygenated blood: right atrium, though tricuspid valve to right ventricle, through pulmonary valve to the lungs 2. Oxygenated blood: through the pulmonary veins to ventricle, through aortic valve to the aorta CONDUCTION SYSTEM OF THE HEART - consist of: 1. SA node- located in top of the right atrium, acts as the pacemaker of the heart 2. AV nodes- slows the impulse, allowing for the delay needed for ventricular filling, and sends it from the atria into the ventricles by way of the bundle of His 3. Bundle of His- w/c enters the septum and divides into three bundle branches 4. Bundle branches- w/c conduct impulses through the ventricles 5. Purkinje fibers- w/c delivers the impulse the ventricular cells ***Sinoatrial (SA) node

CARDIAC CYCLE - … each period of the ventricles followed by a period of systole= cardiac cycle… * myocardium - fibers of cardiac muscle - form two intertwining networks called atrial and ventricular syncytia * Starling’s law of the heart -occurs when muscle fibers of the heart are stretched by the increase volume of blood that has returned spring back to normal size; is similar to stretching a rubber band… * Diastole - the period of cardiac muscle relaxation where the heart from the systemic and pulmonic veins, w/c flow into the right and left… * tricuspid- valve on the right side of the heart; composed of 3 leaflets or cusps

CONDUCTIVITY - where the specialized cells of the heart can conduct an impulse rapidly through the system so that the muscle cells of the heart are stimulated at approximately the same time…

AUTOMATICITY - where the cells can generate action potentials or electrical impulses without being excited to do so by external stimuli 5 phases: 1. Phase 0- points of stimulation; where: sodium gates open along the cell membrane, and sodium rushes into the cell, resulting in a positive state—an electrical potential called depolarization 2. Phase 1- when Na ions concentrations are equal inside and outside of the cell 3. Phase 2 (plateau stage)- cell membrane becomes less permeable to Na Ca slowly enters the cell K slowly leaves the cell 4. Phase 3- rapid repolarization  K rapidly moves out of the cell 5. Phase 4- cell comes to rest as the sodium- potassium pump returns the membrane spontaneous repolarization begins again

***** SA node is the dominant influences most of the time, keeping the resting heart rate at 70 to 80 beats per minute * Sarcomere- the basic unit of the cardiac muscle - made up of two contractile proteins: actin (thin filament) and myosin (thick filament) kept apart by the protein troponin * Degree of shortening- determined by the amount of Ca present—the more Ca is present, the more bridges will be formed… ARRYTHMIA OR DYSRYHTHMIA - a disruption in cardiac rate or rhythm - interfere with the work of the heart and can disrupt cardiac output, which affects every cell in the body - occurs when there is a shift in the pacemaker of the heart from the SA node to some other sit, called ectopic focus FIBRILLATION - very serious arrhythmias arise when the combination of ectopic foci and altered conduction set off an irregular, uncoordinated twitching of the atrial or ventricular muscle ELECTROCARDIOGRAPHY -is a process of recording the patterns of electrical impulses as they move through the heart - an important diagnostic tool in the care of the cardiac patients ELECTROCARDIOGRAPHY MACHINE - detects the patterns of electrical impulse generation and conduction though the heart and translates that information to a recorded pattern ELECTROCARDIOGRAM -a measure of electrical activity; provides no information about the mechanical activity of the heart The normal ECG pattern is made up of main waves: 1. P wave- formed as impulses originating in the SA node or pacemaker pass through the atrial tissue 2. P wave- precedes the contraction of the atria 3. Ta wave- appear around the QRS complex

Critical points of the ECG are as follows : 1. P-R interval: reflects the delay of conduction at the AV node 2. Q-T interval: reflects the critical timing of repolarization of the ventricles 3. S-T segment: reflects the important information about the repolarization of the ventricles

- also referred as arterial system - where the vessels can either constrict or dilate, increasing or decreasing resistance, based on the needs of the body

TYPES OF ARRHYTHMIAS 1. Sinus arrhythmias - has a slower- than- to normal heart rate (usually less than 60 beats/ min) w/ Normal- appearing ECG pattern 2. Supraventricular Arrhythmias - arrhythmias that originate above the ventricles but not in the SA node - feature an abnormally shaped P wave - includes the following: a. Premature atrial contractions (PAC’s)- reflect an ectopic focus in the atria that is generating an impulse out of the normal rhythm b. Paroxysmal atrial tachycardia (PAT)- runs of rapid heart originating in the atria c. Atrial flutter- characterized b sawtooth- shaped P waves reflecting a single ectopic focus that is generating a regular, fast atrial depolarization d. Atrial fibrillation- w/ irregular P waves representing many ectopic foci firing in an uncoordinated manner through the atria 3. Ventricular Arrhythmias - impulses that originate below the AV node originate from ectopic foci that do not use the normal conduction pathways

* capillary fluid shift - shifting of fluid in the capillaries - carefully regulated between hydrostatic (fluid pressure) forces in the arterial end of the capillary and oncotic pressure ( the pulling pressure of the large, vascular proteins)

ATRIOVENTRICULAR BLOCK - also called heart block - reflects a slowing or lack of conduction at the AV node -occur because of structural damage, hypoxia, or injury to the heart muscle - First degree of heart block= P-R interval beyond the normal 0.16 to 0.20 seconds

* end- artery circulation - a pattern of circulation

CARDIOVASCULAR SYSTEM CIRCULATION - follows two courses: 1. Heart lung or pulmonary circulation: the right side of the heart sends blood to the lungs, where carbon dioxide and some waste products are removed from the blood and oxygen is picked up by the red blood cells 2. Systemic circulation: the left side of the heart sends oxygenated blood out to all of the cells in the body * resistance system

* capillary system - where blood from tiny arterioles flows - connects the arterial and venous system

*Capacitance system - also referred as venous system - where the veins has the capacity to hold large quantities of fluid * sinuses of Valsalva - where the myocardium receives its blood through 2 main coronary arteries that branch off the base of the aorta *coronary arteries - these arteries encircle the heart in pattern resembling a crown *pulse pressure - the pressure that fills the coronary arteries - it is systolic minus diastolic blood pressure readings

The main forces hat determine the heart’s use of oxygen or oxygen consumption are as follows: 1. Heart rate: the more the heart has to pump, the more oxygen it will require to do that 2. Preload ( amount of blood that is brought back to the heart to be pumped around): the more blood that is returned to the heart, the harder it will have to work to pump the blood around. The volume of blood that is determinant of preload 3. Afterload ( resistance against which the heart has to beat): The higher the resistance in the system, the harder the heart will have to contract to force open the valves and pump the blood along. The blood pressure is measure of afterload SYTEMIC ARTERIAL PRESSURE * Hypotension

- occur if the blood pressure falls, either from the loss of blood flowing from high- pressure to low pressure areas - if severe, it can progress to shock and even death as cells are cut off from their oxygen supply * Hypertension - excessive high blood pressure - can damage the fragile lining of blood vessel - cause disruption of blood flow to the tissues - caused by neurostimulation of the blood vessels that cause them to constrict and to raise pressure * Vasomotor Tone - work to dilate the vessels if more blood flow is needed in an area *Cardiovascular center - the coordination of these impulses through the medulla RENIN – ANGIOTENSIN SYSTEM -determinant of Blood pressure - activated when the blood flow to the kidneys is decreased -…cells in the kidney release an enzyme called rennin - Angiotensin I travels to lungs  Angiotensin- converting enzyme (ACE)  reacts  Angiotensin II = Vasoconstriction (read: p. 635) CONGESTIVE HEART FAILURE - if the heart fails to do its job of effectively pumping through the system, blood backs up and system becomes congested - results: hydrostatic pressure on the venous end of the capillaries

CHAPTER 43: DRUGS AFFECTING BLOOD PRESSURE -

altering the body’s regulatory mechanisms alter the normal reflexes that control BP does not cure the disease but is aimed at maintaining the BP within normal limits to prevent the damage that hypertension can cause

Stepped-Care Approach to Treating Hypertension by the Seventh Joint National Committee on Prevention, Detection, Evaluation, and Treatment of Hypertension, from the National Institute of Health Step o o o o o

1: Lifestyle Modifications weight reduction reduction of sodium intake moderation of alcohol intake smoking cessation increased physical activity

Step 2: Inadequate Response o continue lifestyle modifications o initial drug selection

1. 2.

Step o o o

diuretic or β-blocker ACE inhibitor, calcium channel blocker, α-blocker, α- and βblocker

3: Inadequate Response increase drug dose, or substitute another drug, or add a second drug from another class

Step 4: Inadequate Response o add a second or third agent or diuretic if not already prescribed Diuretics ↑ the excretion of sodium and water from the kidney first agents tried in mild hypertension ↑ urination and disturb electrolyte and acid-base balances Sympathetic Nervous System Blockers

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block the effects of the SNS useful in blocking many of the compensatory effects of the SNS

β-blockers

α- and βblockers

α-adrenergic blockers

α1-blockers

α2-agonists

block vasoconstriction; ↓ HR; ↓ muscle cardiac contraction; ↑ blood flow to kidneys; used in monotherapy in Step 2 blocking of all receptors in SNS; patients complain of fatigue, loss of libido, inability to sleep, GI and GU disturbances inhibit postsynaptic α1adrenergic receptors, ↓ sympathetic tone in the vasculature and causing vasodilation; diagnose and manage episodes of pheochromocytoma block postsynaptic α1-receptor sites, ↓ vasculature and causing vasodilation; do not block presynaptic α2-receptor sites stimulate α2-receptors in the CNS and inhibit the CV centers, ↓BP; many adverse CNS, GI effects, cardiac dysrhythmias

Angiotensin-Converting Enzyme (ACE) Inhibitors -

block the conversion of angiotensin I to angiotension II in the lungs as monotherapy or combined with diuretics

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well absorbed, widely distributed metabolized in liver, excreted in urine and feces

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cross the placenta and associated with serious fetal abnormalities

Contraindications allergy impaired renal function pregnancy and lactation Caution CHF salt/volume depletion Adverse Effects effects of vasodilation and alterations in blood flow o reflex tachycardia, chest pain, angina, CHF, cardiac arrhythmias o GI irritation, ulcers, constipation, liver injury o renal insufficiency, renal failure, proteinuria o rash, alopecia, dermatitis, photosensitivity unrelenting cough associated with fetal pancytopenia and MI Drug-Drug Interactions - allopurinol = risk of hypersensitivity reactions ↑ Food-Food Interactions food = absorption of oral ACE inhibitors ↓

Prototype: captopril (Capoten) for hypertension, congestive heart failure (CHF), diabetic neuropathy, left ventricular dysfunction after MI associated with fatal pancytopenia, cough, GI distress

Nursing Considerations encourage patient to implement lifestyle changes administer on empty stomach, 1 or 2 hours before meals monitor fluid volume

Therapeutic Actions and Indications ↓ BP and aldosterone release indicated for treatment of hypertension, alone or with other drugs

Angiotensin II Receptor Blockers (ARBs) selectively bind the angiotensin II receptors in blood vessels to prevent vasoconstriction prevents the release of aldosterone in the adrenal cortex

Pharmacokinetics

Prototype: losartan (Cozaar) used alone or as part of combination therapy treatment of diabetic neuropathy with an elevated serum creatinine an d proteinuria Therapeutic Actions and Indications selectively bind with angiotensin II receptor sites in vascular smooth muscle and in the adrenal gland to block vasoconstriction and aldosterone release treatment of hypertension and for CHF in patients who are intolerant to ACE inhibitors Pharmacokinetics well absorbed, metabolized in liver excreted in urine and feces crosses the placenta, associated with serious fetal abnormalities and death Contraindications allergy pregnancy and lactation Cautions hepatic or renal dysfunction hypovolemia Adverse Effects headache, dizziness, syncope, weakness hypotension, GI complaints symptoms of upper respiratory tract infections and cough - rash, dry skin, alopecia Drug-Drug Interactions phenobarbital = risk of ↓ serum levels and loss of effectiveness ↑ Nursing Considerations encourage patient to implement lifestyle changes administer without regard to meals; give with food - suggest use of barrier contraceptives monitor fluid volume

Calcium Channel Blockers prevent the movement of calcium into the cardiac and smooth muscle cells when the cells are stimulated leading to loss of smooth muscle tone, vasodilation, ↓ peripheral resistance ↓ BP - very effective for treatment of angina Prototype: diltiazem (Cardizem, Tiamate) sustained-release preparation treatment of hypertension Therapeutic Actions and Indications inhibit the movement of calcium ions across the membranes of myocardial and arterial muscle cells Pharmacokinetics well absorbed, metabolized in liver, excreted in urine cross the placenta, enters breast milk Contraindicaitons allergy heart block or sick sinus syndrome renal or hepatic dysfunction pregnancy or lactation Adverse Effects CNS effects

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GI effects CV effects skin flushing, rash

Drug-Drun Interactions cyclosporine = ↑ serum levels and toxicity of cyclosporine Vasodilators produce relaxation of the vascular smooth muscle, ↓ peripheral resistance and reducing BP do not block reflex tachycardia reserved for use in severe hypertension and hypertensive emergencies Prototype: nitroprusside (Nitropress) used intravenously

-

-

treatment of hypertensive crisis and maintain controlled hypertension during surgery toxic levels cause cyanide toxicity

Therapeutic Actions and Indications act directly on vascular smooth muscle to cause muscle relaxation, leading to vasodialtion and drop in BP Pharmacokinetics rapidly absorbed and widely distributed metabolized in the liver and excreted in urine cross the placenta and enter breast milk Contraindications allergy pregnancy and lactation cerebral insufficiency Cautions peripheral vascular disease, CAD, CHF, tachycardia Adverse Effects related to changes in BP cyanide toxicity may occur with nitroprusside o dyspnea o imperceptible o headache pulse o vomiting o absent reflexes o dilated pupils o dizziness o ataxia o pink color o distant heart o loss of consciousne sounds o shallow breathing ss Nursing Considerations monitor BP and fluid volume Other Hypertensive Agents only drug: mecamylamine (Inversine) ganglionic blocker that occupies cholinergic receptor sites of autonomic neurons, blocking the effects of acetylcholine at both sympathetic and parasympathetic ganglia can cause o severe hypotension, CHF

o o

o

CNS symptoms of dizziness, syncope, weakness, vision changes parasympathetic blocking symptoms of dry mouth, glossitis, nausea, vomiting, constipation, urinary retention impotence

hypertension, bradycardia dizziness, vision changes, vertigo, headache problems with urination

calcium flow into the myocardial cells and causing increased contraction, positive inotropic effect

Drug-Drug Interactions risk of ↑ effects and toxicity of cardiac glycosides, beta-blockers, alphaadrenergic agents, corticosteroids if taken with midodrine

4. CARDIOTONIC DRUGS - drugs that affect the intracellular calcium levels in the heart muscle, leading to increased contractility - increase in contraction strength leads to increased cardiac output, which causes increased renal blood flow decreases rennin release -increases urine output -decreased blood flow - relieve CHF - has two types:

o o o

ANTIHYPOTENSIVE AGENTS -

severe hypotension leads to shock sympathomimetic drug: first choice drug for treating shock

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Sympathetic Adrenergic Agonists effects of a sympathetic stress response: o ↑ BP o ↑ blood volume o ↑ strength of cardiac muscle contraction only drug: midodrine (ProAmatine) treat orthostatic hypotension Therapeutic Actions and Indications activates alpha-receptors in arteries and veins to ↑ in vascular tone and BP indicated for the symptomatic treatment of orthostatic hypotension Pharmacokinetics rapidly absorbed in GI tract metabolized in liver and excreted in urine Contraindications

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supine hypertension, CAD, pheochromocytoma acute renal disease urinary retention

Cautions pregnancy and lactation visual problems renal or hepatic impairment Adverse Effects related to stimulation of alpha-receptors o piloerection, chills, rash

Nursing Considerations monitor BP do not administer to bedridden patients monitor HR regularly - monitor patients with visual problems encourage patients to void before taking drug

CHAPTER 44: CARDIOTONIC AGENTS Congestive heart failure (CHF) -condition where the heart fails to effectively pump blood around the body - called “dropsy’ or compensation

A. CARDIC GYCOSIDES - used for hundred of years - derived form foxglove or digitalis plant Drugs: 1. Digoxin (Lanoxin, Lanoxicaps) -treatment of acute congestive heart failure, atrial arrhythmias

TREATMENTS OF CHF: 1. VASODILATORS - used to treat CHF because they can decrease the workload of the overworked cardiac muscle 2. DIURETICS - use to decrease blood volume, which decreases venous return and blood pressure - end result: decrease in afterload ...