Cholesterol - A Silent Killer / HYPERLIPIDEMIA

Hyperlipidemia is a group of metabolic abnormalities resulting in combinations of elevated serum cholesterol. 

Cholesterol (TC) and triglycerides (TG) are two of the major lipids in the body. 

They are transported through the bloodstream by lipoproteins. 

Lipoproteins are made up of a phospholipid and specific proteins called apoproteins or apo lipoproteins. 

There are five main classes of lipoproteins: 

• Chylomicrons 
• Very low density lipoproteins (VLDL-C) 
• Intermediate density lipoproteins (IDL-C) 
• Low density lipoproteins (LDL-C) 
• High density lipoproteins (HDL-C).

Etiology

Etiologic factors include chronic diseases, such as diabetes, hypothyroidism, nephrotic syndrome, liver disease, obesity, dietary intake; conditions, such as pregnancy and alcoholism; medications, such as beta-adrenergic blockers and diuretics.

Consequences

Atherosclerotic plaque formation in blood vessels.

Causes narrowing, possible ischemia, and may lead to thromboembolus formation.

Result in cardiovascular, cerebrovascular, and peripheral vascular disease.

Clinical Manifestations

• Usually asymptomatic until significant target organ damage is done 
• May be metabolic signs, such as corneal arcus, xanthoma, xanthelasma, pancreatitis 
• Chest pain, MI 
• Carotid bruit, transient ischemic attacks, stroke 
• Intermittent claudication, arterial occlusion of lower extremities, loss of pulses

Diagnostic Evaluation and Management

1. Fasting (9 to 12 hour fast) lipoprotein profile every 5 years for people ages 20 and older.
2. Assess the presence of clinical atherosclerotic disease that confers high risk for CHD events. (These atherosclerotic diseases are known as CHD risk equivalents; diabetes is also considered a CHD risk equivalent.) 
3. Decreased intake of saturated fat /cholesterol (< 7% of calories or < 200 mg/day) 
4. Therapeutic dietary options for improving lipid levels (plant stanols/sterols, 2 g/day, soluble fiber 10 to 25 g/day, omega-3 oils three times per week) 
5. Smoking cessation 
6. Weight reduction 
7. Increased physical activity 30 minutes of moderate activity 5 days per week or 20 minutes of vigorous activity 3 times per week 
8. Consider adding drug therapy if LDL exceeds levels 
9. Consider drug simultaneously with TLC for CHD and CHD equivalents. 
10. Consider adding drug to TLC after 3 months for other risk categories. 
11. Identify metabolic syndrome and treat, if present, after 3 months of TLC
12. Treat elevated TGs (150 or higher). 
13. Aim for LDL goal, intensify weight management, and increase physical activity. 
14. If TGs are 200 mg/dL or greater after LDL goal is reached, set secondary goal for non-HDL-C (total cholesterol minus HDL) 30 mg/dL higher than LDL goal. 
15. If TGs are 200 to 499 mg/dL after LDL goal is reached, consider adding drug if needed to reach non-HDL goal (increase primary drug or add nicotinic acid or fibrate). 
16. If TGs are 500 mg/dL or greater, first lower TGs to prevent pancreatitis. 
17. Very low-fat diet (15% or fewer calories from fat) 
18. Weight management and physical activity 
19. Fibrate or nicotinic acid 
20. When TGs are less than 500 mg/dL, return to LDL-lowering therapy 
21. Treat low HDL (< 40 mg/dL) by aiming for LDL goal, intensifying weight management, increasing physical activity, achieving non-HDL goal and, possibly, adding nicotinic acid or fibrate.

Complications

Disability from MI, stroke, and lower extremity ischemia.

Nursing Interventions and Patient Education
Teach diet basics and obtain nutritional consult.

Teach patient to engage in exercise.

Engage patient in smoking-cessation program.

Tell patients that for every 1% increase in HDL-C there is a 2% to 3% increase in risk for CHD.

Explain goal of recommended cholesterol levels. Encourage patients to keep a log of lipid results.

Encourage follow-up laboratory work repeat lipoprotein analysis and liver function test monitoring every 3 months for those on HMG-CoA reductase inhibitors.

Teach patient taking bile acid sequestrants not to take other medications for 1 hour before or 2 hours after, because it prevents absorption of many medications.

For more information on hyperlipidemia and TLC, refer to AHA: http://www.americanheart.org, or The National Heart, Lung, and Blood Institute diseases and conditions index: http://www.nhlbi.nih.gov/health/dci.

CARDIOVERSION (Synchronized)

Indications: 
Unstable tachycardia (altered LOC, dizziness, chest pain, hypotension).

Energy Levels: 100 J, 200 J, 300 J, 360 J.

Application: 
Use handheld paddles or remote adhesive pads.
Always use a conducting gel with paddles. 
For conscious patients explain the procedure and use a medication for sedation. 
Consider 2.5–5.0 mg of midazolam (Versed) or 5 mg diazepam (Valium).

Methods: 
Place defibrillator in synchronized (sync) mode.
Charge to appropriate level. 
Say, “I’m going to shock on three. 
One, I’m clear; two, you’re clear; three, everybody’s clear.” 
Perform visual sweep and press shock button. 
Reassess and treat according to appropriate algorithm.

Precautions: 
Reactivation of sync mode is required after each attempted cardioversion. Defibrillators default to unsynchronized mode. 
Place paddles and pads several inches away from an implanted pacemaker.

Sync mode delivers energy just after the R wave to avoid stimulation during the refractory, or vulnerable, period.

DEFIBRILLATION

Indications: VF or pulseless VT.

Energy Levels: 
Adult monophasic energy levels first shock 200 J, second shock 200–300 J, third shock 360 J; continue at 360 J for further shocks. 

Biphasic energy level shocks use lower energy levels, approximately 150 J.

Procedure: 
Use handheld paddles or remote adhesive pads.
Always use a conducting gel with paddles and apply firm pressure to chest to ensure good skin contact. 
Dry skin if wet, shave excessive hair.

Methods: 
Manual or automated.

Precautions: 
Place paddles and pads several inches away from an implanted pacemaker.
May be used on children aged 1–8 years. But always use pediatric paddles or pads and follow pediatric protocols.

MANUAL DEFIBRILLATION

A manual defibrillator is used to restore a normal heart rhythm.
For a patient experiencing sudden cardiac arrest, first use the ECG tracing to verify that the rhythm is either VF or pulseless VT, and then manually deliver an electric shock to the heart.

Procedure
1. Verify patient is in cardiac arrest, with no pulse or respiration. Have someone provide CPR, if possible, while the defibrillator is obtained and placed next to the patient.
2. Turn on defibrillator; verify all cables are connected.
3. Turn “lead select” to “paddles” or “defibrillator.”
4. Select initial energy level for an adult to 200 J.
5. Paddles: Use conducting gel and place on apex (lower left chest, midaxillary) and sternum (right of sternum, midclavicular). Pads: Place in same locations as you would put paddles.

6. Verify rhythm as VF or pulseless VT.
7. Say, “Charging defibrillator, stand clear!”
8. Charge defibrillator.
9. Say, “I’m going to shock on three. One, I’m clear; two, you’re clear; three, everybody’s clear.” Perform visual sweep to assure all rescue personnel are clear of patient, bed, and equipment.
10. Discharge defibrillator, reassess rhythm, and refer to appropriate treatment algorithm for resulting rhythm.


AUTOMATIC EXTERNAL DEFIBRILLATOR (AED)

An AED is a small, lightweight device used by both professionals and laypersons to assess heart rhythm by computer analysis. If necessary, it administers an electric shock to restore a normal rhythm in patients with sudden cardiac arrest. A shock is administered only if the rhythm detected is VF or VT.
Procedure
1. Verify patient is in cardiac arrest, with no pulse or respiration. Have someone provide CPR, if possible, while the AED is obtained and placed next to the patient.
2. Turn on AED. Follow voice prompts or visual messages.
3. Open adhesive pads and attach pads to cables.
4. Attach pads to right sternal border and apex or as pictured on each of the AED electrodes
5. Clear patient and stop CPR.
6. Press analyze button, if present.
7. If shock is advised, say, “I’m going to shock on three. One, I’m clear; two, you’re clear; three, everybody’s clear.” Perform visual sweep to ensure rescue personnel are not touching patient or equipment. Press shock button. Reanalyze after shock and continue as prompted by the AED.
8. If no shock is advised, check for a pulse. If no pulse, start CPR.


Fully automatic AED analyzes the rhythm and delivers shock if indicated.
Semiautomatic AED analyzes the rhythm and tells operator that shock is indicated. If it is indicated, operator initiates shock.

Emergency Medications

ACE INHIBITORS (Angiotensin-converting Enzyme Inhibitors)

(Antihypertensive)

Captopril, enalapril, lisinopril, ramipril.

Indications: MI, hypertension (HTN), congestive heart failure (CHF), heart failure without hypotension, ST segment elevation, left ventricular dysfunction after MI.

Usually not started in emergency department, but within 24 hr after fibrinolytic therapy has been completed and blood pressure (BP) has stabilized.


ADENOSINE (Adenocard, Adenoscan) (Antiarrhythmic)

Indications: Narrow-complex tachycardias and PSVT.

Dose: 6 mg rapid intravenous push (IVP) over 1–3 sec followed by a 20-mL bolus of normal saline. Give 12 mg by IVP in 1–2 min if needed. A third dose of 12 mg IVP may be given in 1–2 min, max. 30 mg.


AMIODARONE (Cordarone, Pacerone) (Antiarrhythmic)
Indications: Wide- and narrow-complex tachycardia, polymorphic VT, shock-refractory VF or pulseless VT, SVT, PSVT.

Dose: Cardiac arrest 300 mg (diluted in 20–30 mL D5W) IVP; consider additional 150 mg IVP in 3–5 min. Wide- and narrowcomplex tachycardia (stable) 150 mg IVP over first 10 min (15 mg/min)—may repeat infusion of 150 mg IVP every 10 min as needed; slow infusion of 360 mg IV over next 6 hr (1mg/min); maintenance infusion of 540 mg over next 18 hr (0.5 mg/min).
Max. cumulative dose: 2.2 g IV in 24 hr.

NURSES RESPONSIBILITY

Draw up amiodarone through a large-gauge needle to reduce foaming. For slow or maintenance IV infusion, mix medication only in glass bottle containing D5W and administer through an in-line filter.

ASPIRIN (Acetylsalicylic Acid) (Antiplatelet)
Indications: Acute coronary syndrome, symptoms suggestive of cardiac ischemia.

Dose: 162–325 mg PO non-enteric coated for antiplatelet effect.

ATROPINE (Antiarrhythmic, Anticholinergic)
Indications: Symptomatic sinus bradycardia, asystole, PEA with rate 60 bpm, cholinergic drug toxicity and mushroom poisoning (antidote).

Dose: Cardiac arrest 1 mg IVP every 3–5 min (may give through endotracheal (ET) tube at 2.0–3.0 mg diluted in 10 mL normal saline, max. 0.03–0.04 mg/kg. Bradycardia 0.5–1.0 mg IVP every 3–5 min, max. 0.03–0.04 mg/kg.

BETA BLOCKERS (Antihypertensive)
Common Agents: Atenolol, esmolol, labetalol, metoprolol, propranolol.

Indications: MI, unstable angina, PSVT, A-fib, A-flutter, HTN.

CALCIUM CHLORIDE (Minerals/Electrolytes/Calcium Salt)
Indications: Hyperkalemia, hypocalcemia, hypermagnesemia; antidote to calcium channel blockers and beta blockers; given prophylactically with calcium channel blockers to prevent hypotension.

Dose: Hyperkalemia and antidote to calcium channel blocker 8–16 mg/kg (usually 5–10 mL) slow IVP, may be repeated as needed. Given prophylactically prior to IV calcium channel blockers 2–4 mg/kg (usually 2 mL) slow IVP.


DIGOXIN IMMUNE FAB (Fragment Antigen Binding) (Digibind)

(Antidote to Digoxin, Digitoxin)

Indications: Symptomatic digoxin toxicity or acute ingestion of unknown amount of digoxin.

Dose: Dependent on serum digoxin levels. One 40-mg vial binds to approximately 0.6 mg of digoxin. Dose typically administered over 30 min.

DIGOXIN (Lanoxin) (Inotropic, Antiarrhythmic)

Indications:To slow ventricular response in A-fib or A-flutter, as a positive inotrope in CHF, pulmonary edema. May be used as an alternative drug for PSVT.

Dose: Loading dose of 10–15 g/kg, administered over 5 min.

Maintenance dose determined by body size and renal function.

NURSES RESPOSIBILITIES
Avoid electrical cardioversion of stable patients. 
If the patient’s condition is unstable, use lower current settings such as 10–20 J. 
Use cautiously in elderly patients. 
Correct electrolyte abnormalities, monitor digoxin levels, monitor for clinical signs of toxicity.

DILTIAZEM (Cardizem) (Calcium Channel Blocker)

Indications: A-fib, A-flutter, PSVT refractory to adenosine with narrow QRS complex and adequate BP.

Dose: 15–20 mg (0.25 mg/kg) IVP over 2 min. May repeat in 15 min at 20–25 mg (0.35 mg/kg) IVP over 2 min. Start maintenance drip at 5–15 mg/hr and titrate to HR.

DOPAMINE (INTROPIN) (Vasopressor, Inotropic)

Indications: Symptomatic bradycardia and hypotension, cardiogenic shock.

Dose: Continuous infusions (titrate to patient response): Low dose 1–5 g/kg/min; moderate dose 5–10 g/kg/min (cardiac doses); high dose 10–20 g/kg/min (vasopressor doses). Mix 400 mg/250 mL in normal saline, lactated Ringer’s solution, or D5W (1600 g/mL).

NURSES RESPOSIBILITIES
Hypovolemia, MI. Adjust dosage in elderly patients and in those with occlusive vascular disease. Ensureadequate hydration prior to infusion. 
Taper slowly. 
Do not mix with sodium bicarbonate. 
Use care with peripheral administration; infiltration can cause tissue necrosis. 
Central line is preferred.

EPINEPHRINE (Adrenalin) (Adrenergic Agonist)

Indications: Cardiac arrest: PEA, asystole, pulseless VT, VF; severe hypotension; symptomatic bradycardia; anaphylaxis; severe allergic reactions.

Dose: Cardiac arrest 1 mg IVP (10 mL of 1:10,000 solution) every 3–5 min; follow each dose with 20 mL IV flush; higher doses (up to 0.2 mg/kg) may be used if 1-mg dose fails. Give 2.0–2.5 mg diluted in 10 mL normal saline if administering by ET tube. For continuous infusion add 30 mg (30 mL of 1:1000 solution) to 250 mL normal saline or D5W, run at 100 mL/hr, and titrate to response. Profound bradycardia or hypotension 2–10 g/min IV (add 1 mg of 1:1000 solution to 500 mL normal saline or D5W and infuse at 1–5 mL/min).

Anaphylaxis/asthma 0.1–0.5 mg SC or IM of 1:1000 solution every 5–15 min, may be followed by 1–4 g/min continuous infusion.

EPINEPHRINE

Side Effects: Angina, HTN, tachycardia, VT, VF, nervousness, restlessness, tremors, weakness, headache, nausea.

NURSES RESPOSIBILITIES
Use caution in HTN and increasing heart rate (may cause increased myocardial oxygen demand). Higher doses can contribute to postarrest cardiac impairment, but they may be required to treat poison- or drug-induced shock.

FIBRINOLYTIC AGENTS (Thrombolytic, Fibrinolytic)

Common Agents: Alteplase (Activase, t-PA), anistreplase (Eminase), reteplase (Retavase), streptokinase (Streptase), tenecteplase (TNKase).

Indications: Within 12 hr from onset of symptoms of acute MI. Alteplase is the only fibrinolytic agent approved for acute ischemic stroke and must be started 3 hr from onset of symptoms.

FUROSEMIDE (Lasix) (Diuretic, Loop Diuretics)

Indications: CHF with acute pulmonary edema, hypertensive crisis, postarrest cerebral edema, hepatic or renal disease.

Dose: 0.5–1.0 mg/kg slow IVP over 1–2 min, may repeat at 2 mg/kg slow IVP over 1–2 min.

NURSES RESPOSIBILITIES
Use cautiously in severe liver disease accompanied by cirrhosis or ascites, electrolyte depletion, diabetes mellitus, pregnancy, lactation, risk for ototoxicity with increased dose or rapid injection. 
Monitor electrolytes closely.

IBUTILIDE (Corvert) (Antiarrhythmic)

Indications: SVT, including A-fib and A-flutter; most effective for conversion of A-fib or A-flutter of short duration.

Dose: Patients ≥60 kg 1 mg IVP over 10 min, may repeat same dose in 10 min. Patients 60 kg 0.01 mg/kg IVP over 10 min, may repeat same dose in 10 min.

NURSES RESPOSIBILITIES
Precautions: Monitor ECG for 4–6 hr after administration, with defibrillator nearby. 
Correct electrolyte abnormalities prior to use. 
If A-fib 48 hr, anticoagulation is required before cardioversion with ibutilide.

ISOPROTERENOL (Isuprel) (Sympathomimetic, Beta-Adrenergic Agonist)

Indications: Symptomatic bradycardia, refractory torsade de pointes unresponsive to magnesium, bradycardia in heart transplant patients, beta blocker poisoning.

Dose: IV infusion: mix 1 mg/250 mL in normal saline, lactated Ringer’s solution, or D5W, run at 2–10 g/min, and titrate to patient response. In torsade de pointes titrate to increase heart rate until VT is suppressed.

LIDOCAINE (Xylocaine) (Antiarrhythmic, Anesthetic)

Indications: VF or pulseless VT, stable VT, wide-complex tachycardia of uncertain origin, wide-complex PSVT.

Dose: Cardiac arrest from VF or VT 1.0–1.5 mg/kg IVP (or 2–4 mg/kg via ET tube), may repeat 0.5–0.75 mg/kg IVP every 5–10 min, max. 3 mg/kg. Stable VT, wide-complex tachycardia of uncertain origin use 0.5–0.75 mg/kg and up to 1.0–1.5 mg/kg, may repeat 0.5–0.75 mg/kg every 5–10 min; max. total dose 3.0 mg/kg. If conversion is successful, start an IV infusion of 1–4 mg/min (30–50 g/kg/min) in normal saline or D5W.

NURSES RESPOSIBILITIES
 Reduce maintenance dose (not loading dose) in presence of impaired liver function or left ventricular dysfunction or in the elderly.
Stop infusion if signs of toxicity (prolonged PR interval, QRS widening, or CNS changes) develop.

MAGNESIUM SULFATE (Electrolyte, Antiarrhythmic)

Indications:Torsade de pointes, VF refractory to lidocaine, digoxin-induced VT/VF.

Dose: Cardiac arrest (in hypomagnesemia or torsade de pointes) 1–2 g (2–4 mL of a 50% solution) diluted in 10 mL of D5W IVP. Digoxin-induced VT or VF 1–2 g IVP. Torsade de pointes (non-cardiac arrest) load with 1–2 g mixed in 50–100 mL of D5W infused over 5–60 min IV, then infuse 0.5–1.0 g/hr IV (titrate to control torsade). Acute MI load with 1–2 g mixed in 50–100 mL of D5W over 5–60 min IV, then infuse 0.5–1.0 g/hr IV for up to 24 hr.

MORPHINE (Opioid Agonist Analgesic)

Indications: Chest pain unrelieved by nitroglycerin, CHF and dyspnea associated with pulmonary edema.

Dose: 2–4 mg IVP (over 1–5 min) every 5–30 min.

NURSES RESPOSIBILITIES

Administer slowly and titrate to effect. Reverse with naloxone (0.4–2.0 mg IVP). Use caution in cerebral edema and pulmonary edema with compromised respiration.

NITROGLYCERIN (Nitrostat, Nitrolingual Pumpspray) (Antianginal, Nitrate)

Indications: Angina, CHF associated with acute MI, hypertensive crisis.

Dose: Sublingual route, 0.3–0.4 mg (1 tablet), repeat every 5 min, max. 3 doses/15 min. Aerosol, spray for 0.5–1.0 sec at 5- min intervals (provides 0.4 mg/dose), max. 3 sprays/15 min. IVP at 12.5–25.0 g (if no sublingual or spray used). IV infusion: mix 25 mg/250 mL (100 g/mL) in D5W, run at 5–20 g/min, and titrate to desired response.

NURSES RESPOSIBILITIES
Do not mix with other medications; titrate IV to maintain systolic BP 90 mm Hg. Mix only in glass IV bottles and infuse only through tubing provided by manufacturer; standard polyvinyl chloride tubing can bind up to 80% of the medication, making it necessary to infuse higher doses.

OXYGEN (Gas)

Indications: Cardiopulmonary emergencies with shortness of breath and chest pain, cardiac or respiratory arrest.

Dose: Nasal cannula 1–6 L/min (24%–44% oxygen), Venturi mask 4–8 L/min (24%–40% oxygen), simple mask 5–8 L/min (40%–60% oxygen), partial rebreathing mask 6–15 L/min (35%–60% oxygen), nonrebreathing mask 6–15 L/min (60%–90% oxygen), bag-valve-mask 15 L/min (up to 100% oxygen).

PROCAINAMIDE (Pronestyl) (Antiarrhythmic)

Indications: Recurrent VT or VF, PSVT refractory to adenosine and vagal stimulation, rapid A-fib with Wolff-Parkinson-White syndrome, stable wide-complex tachycardia of uncertain origin, maintenance after conversion.

Dose: 20 mg/min IV infusion or up to 50 mg/min under urgent conditions, max. 17 mg/kg loading dose. Maintenance IV infusion: mix 1 g/250 mL (4 mg/mL) in normal saline or D5W, run at 1–4 mg/min.

NURSES RESPOSIBILITIES
Monitor BP every 2–3 min while administering procainamide. 
If QRS width increases by 50% or more, or if BP decreases to 90 systolic, stop drug. 
Reduce total dose to 12 mg/kg and maintenance infusion to 1–2 mg/min if cardiac or renal dysfunction is present. 
Use cautiously in myasthenia gravis and in hepatic or renal disease and with drugs that prolong QT interval (e.g., amiodarone, sotalol).

SODIUM BICARBONATE (Alkalizing Agent, Buffer)

Indications: Prolonged resuscitation with effective ventilation; hyperkalemia; diabetic ketoacidosis; cocaine toxicity; tricyclic antidepressant, diphenhydramine, or acetylsalicylic acid overdose; metabolic acidosis; shock associated with severe diarrhea.

Dose: 1 mEq/kg IVP, may repeat 0.5 mEq/kg every 10 min.

NURSES RESPOSIBILITIES
CHF, renal disease, cirrhosis, toxemia, concurrent corticosteroid therapy. 
Not recommended for routine use in cardiac arrest patients because adequate ventilation and CPR are the major “buffer agents” in cardiac arrest. Incompatible with many drugs; flush line before and after administration.

VASOPRESSIN (Pitressin Synthetic) (Vasopressor, Hormone)

Indications: Vasodilatory (septic) shock, an alternative to epinephrine in shock-refractory VF and pulseless VT.

Dose: Cardiac arrest 40 units IVP single dose.

VERAPAMIL (Calan, Isoptin) (Calcium Channel Blocker, Antiarrhythmic, Antihypertensive)

Indications: PSVT (with narrow QRS and adequate BP) refractory to adenosine, rapid ventricular rates in A-fib, A-flutter, or MAT.

Dose: 2.5–5.0 mg slow IVP over 2 min; may give second dose, if needed, of 5–10 mg IVP in 15–30 min, max. dose 20 mg. An alternative second dose is 5 mg IVP every 15 min, max. dose 30 mg.

NURSES RESPOSIBILITIES 
Concurrent oral beta blockers, CHF, impaired hepatic or renal function; may decrease myocardial contractility. 
In geriatric patients administer dose slowly over 3 min.

Home care after CABG

• Omit play outside for several weeks.
• Avoid activities in which the child could fall and be injured, such as bike riding, for 2 to 4 weeks.
• Avoid crowds for 2 weeks after discharge.
• Follow a no-added-salt diet if prescribed.
• Do not add any new foods to the infant’s diet (if an allergy exists to the new food, the manifestations may be interpreted as a postoperative complication).
• Do not place creams, lotions, or powders on the incision until completely healed.
• The child may return to school usually the third week after discharge, starting with half-days.
• The child should not participate in physical education for 2 months.
• Instruct the parents to discipline the child normally.
• Instruct the parents about the importance of the 2-week follow-up.
• Avoid immunizations, invasive procedures, and dental visits for 2 months; following this time period, the immunization schedule and dental visits need to be resumed.
• Advise the parents regarding the importance of a dental visit every 6 months after age 3 years and to inform the dentist of the cardiac problem so that antibiotics can be prescribed if necessary.
• Instruct the parents to call the physician if coughing, tachypnea, cyanosis, vomiting, diarrhea, anorexia, pain, or fever occur, or any swelling, redness, or drainage occurs at the site of the incision.

BASIC PRINCIPLES OF CARDIAC ELECTROPHYSIOLOGY

Depolarisation
Depolarisation is the stimulation of the cardiac cell. A change in the cell membrane permeability results in electrolyte concentration changes within the cell. This causes the generation of an electrical current, which spreads to neighbouring cells causing these in turn todepolarise. Depolarisation is represented on the ECG as P waves and QRS complexes.


Repolarisation
Repolarisation is the process by which the cardiac cell returns to its original resting state. Ventricular repolarsiation is represented on the ECG as T waves (atrial repolarisation is not visible on the ECG as it is masked by the QRS complex).


Automaticity
Automaticity is the ability of specialised cardiac cells (automatic or pacemaker cells) to initiate electrical impulses without any external stimulation. The sinus node normally has the fastest firing rate and therefore assumes the role of pacemaker for the heart. If another focus in the heart has a faster firing rate, it will then take over as pacemaker.


Cardiac action potential
Cardiac action potentialis the term used to describe the entire sequence of changes in the cell membrane potential, from the beginning of depolarisation to the end of repolarisation, i.e. from the beginning of the P wave to the end of the T wave.Resting cardiac cells have high potassium and low sodium concentrations (140mmol/l and 10mmol/l, respectively). This contrasts sharply with extracellular concentrations (4mmol/l and 140mmol/l, respectively) 

The cell is polarised and has a membrane potential of -90mV.

Cardiac action potential results from a series of changes in cell permeability to sodium, calcium and potassium ions. Following electrical activation of the cell, a sudden increase in sodium permeability causes a rapid influx of sodium ions into the cell. This is followed by a sustained influx of calcium ions. The membrane potential is now +20mV. This is referred to as phase 0 of the action potential. The polarity of the membrane is now slightly positive.

Phases of the cardiac action potential
Phase              Action
0                     Upstroke or spike due to rapid depolarisation
1                     Early rapid depolarisation
2                     The plateau
3                     Rapid repolarisation
4                     Resting membrane potential and diastolic depolarisation

Coronary Arteries

There are left coronary artery and right coronary artery.

Left coronary artery branches -3 branches

The artery from the point of origin to the first major branch is called the left main coronary artery. 

Two branches arise from the left main coronary artery: the left anterior descending artery, which courses down the anterior wall of the heart, and the circumflex artery, which circles around to the lateral left wall of the heart.

The right coronary artery, which leads to the inferior wall of the heart. The posterior wall of the heart receives its blood supply by an additional branch from the right coronary artery called the posterior descending artery.

Superficial to the coronary arteries are the coronary veins. Venous blood from these veins returns to the heart primarily through the coronary