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Angina Pectoris
- the principle symptom of ischemic heart disease
- it is a pain felt right int he middle of the chest, behind the sternum (not generally on the side)
- sensation of tightness, yet some people describe it as only midly painful discomfort
- can spread toward the neck or the jaw, the arm and the wrist, most often on the left side
- sometimes situated lower down, towards the pit of the stomach
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Categories of Angina Pectoris:
Stable
predictable in response to exertion, stress, etc; there is a fixed block that permits adequate flow under basal conditions but impedes higher levels of flow
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Categories of Angina Pectoris:
Unstable
- manifests as symptoms of angina at rest or worsening of exeritonal angina due to vasospasm, platelet aggregation, thrombus formation, and/or emboli transiently blocking downstream vessels
- has increased risk of myocardial infarction and/or death in comparison to stable angina pectoris
- need to use therapy in addition to that discussed below such as antiplatlet therapy (e.g. aspirin), oxygen, morphine for pain
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Categories of Angina Pectoris:
Vasopastic
- aka Printzmetal's angina
- angina caused by coronary artery spasm
- in contrast to stable angina, can produce pain at anytime including while asleep
- between attacks, there may be little to no evidence of coronary flow impairment
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The ischemic condition results from
- an imbalance between myocardial oxygen demand and myocardial oxygen supply
- this imbalance may be due to a decrease in myocardial oxygen supply, an increase in myocardial oxygen demand or both
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Factors that affect myocaridal oxygen demand
- contractility
- heart rate
- ventricular wall tension
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Ventricular Wall Tension
- Preload:
- the pressure that distends the ventricular wall during diastole
- some antianginal drugs increase venous capacitance which causes venous pooling, decreases venous return, decreases ventricular end-diastolic pressure, reduces cardiac work and thus decreases oxygen demand
- Afterload:
- the force distributed in the ventricular wall during ejection of blood (ventricular systolic wall tension) (it has to be greater than diastolic blood pressure to open the valves)
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Factors that affect myocardial oxygen supply:
Coronary Blood Flow
a function of aortic diastolic blood pressure and coronary vascular resistance
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Factors that affect myocardial oxygen supply:
Regional blood flow distribution
- subendocardial regions of the heart are more poorly perfushed than the subepicaridal regions
- decreasing preload decreases intraventricular pressure which allows for greater subendocaridal perfusion
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Organic nitrates
- –organic nitrates have been used for over 100 years, and are still primary drugs for the treatment of angina pectoris
- –cellular mechanism of action :
- organic nitrates are converted to nitric oxide (NO)
- -->stimulates guanylate cyclase to cause an increase in the formation of cyclic GMP
- -->dephosphorylates myosin light chains and causes vascular relaxation
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Organic nitrates
Pharmacological actions to reduce myocardial ischemia:
- –venous and arterial dilation, with dilation of veins predominating over that of arteries.
- •decreased preload and afterload results in decreased myocardial work and decreased oxygen demand.
- •the organic nitrates do not directly alter the inotropic (force of contraction) or chronotropic (rate) state of the heart.
- –effects on coronary blood flow
- •organic nitrates dilate large epicardial coronary arteries and collateral vessels to provide some increase in oxygen delivery to the ischemic myocardium
- •reduced preload decreases diastolic intraventricular pressure which favors subendocardial perfusion
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Mechanism of pain relief in angina for organic nitrate drugs
- –cause a marked reduction in myocardial work and concomitant reduction in oxygen demand
- –there may be some improvement in perfusion of the heart
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Nitrate pharmacokinetics
- –differences exist in the pharmacokinetics of the various organic nitrates
- –have low oral bioavailability due to extensive first-pass metabolism in the liver.
- oral isosorbide dinitrate is completely absorbed, but only about 25% of the absorbed dose enters into the systemic circulation as intact drug
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Nitrate routes of administration
–the sublingual route of administration of organic nitrates is most useful for the treatment of acute attacks of angina pectoris
- –the oral (swallowed) and transdermal preparations have a slow onset and a long duration of action
- used to provide prophylaxis against anginal attacks
- must be given in sufficient dosage to saturate the liver’s capacity to degrade them
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Nitrate tolerance
–tolerance is apparent when repeated administration of a given dose of an organic nitrate produces a decreased effect or when increasingly larger doses must be taken to obtain the effects observed with the original dose
–the magnitude of tolerance is a function of the dose and frequency of administration of the nitrate, with frequent exposure to high oral or transdermal doses of organic nitrates leading to the development of tolerance
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Nitrate adverse effects
–generally, the acute adverse effects are direct extensions of the pharmacological effects of these drugs, and include:
- •vasodilatation – severe headache, facial flushing,
- •hypotension – dizziness, weakness
- •orthostatic hypotension
- •reflex tachycardia
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Nitrate use in angina pectoris
•sublingual and other rapid acting nitrates are used to treat acute attacks of angina
–will help for both stable and vasospastic forms of angina
- –if 2-3 sublingual pills taken at 5 min intervals fail to alleviate symptoms, head to ER for thrombolytic therapy (i.e., it’s a myocardial infarction)
- long acting oral and transdermal nitrates are used prophylactically to prevent angina
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Antianginal Drugs: b-Adrenergic receptor antagonists
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•These drugs bind to b-adrenergic receptors and reduce the response caused by the activation of these receptors by the sympathetic nervous system, thereby inhibiting many of the cardiovascular effects
- •b1-adrenergic receptors act:
- –on the heart muscle to increase contractility
- –on the cardiac conduction system to increase heart ratein the kidney to increase renin secretion
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Hemodynamic effects of b blockers in treating angina pectoris
- –the b blockers antagonize the actions of epinephrine and norepinephrine released by sympathetic stimulation during stress or exercise, reducing both heart rate and contractility
- –arterial blood pressure is also reduced by b blockers
- –the three major determinants of myocardial oxygen demand—heart rate, contractility and systolic wall tension—are reduced.
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Adverse effects of b blockers
- •respiratory - wheezing, bronchoconstriction in patients with airway disease, b2 > b1
- •cardiovascular – bradycardia, AV block in patients with conduction disturbances; abrupt withdrawal of b blockers can worsen angina
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Use and beneficial effects of b blockers in the treatment of angina pectoris
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• decrease frequency of anginal attacks
- • decrease nitroglycerin consumption
- • increase exercise tolerance
- •b blockers are used prophylactically to prevent exertional angina.
- –are NOT useful for vasospastic angina
- –most useful in patients whose attacks of angina are frequent and unpredictable
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Antianginal Drugs: Calcium Channel Blockers (CCB)aka CEB [calcium entry blockers])
Drug classes used to treat angina pectoris include:
- •phenylalkylamines: verapamil
- •benzothiazepines: diltiazem (effects lie between extremes of other 2 classes, we will not discuss further)
- •dihydropyridines: nifedipine, amlodipine, nicardipine, nimodipine, felodipine, isradipine
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Major therapeutic uses of calcium channel blockers include treatment of
- •angina pectoris
- •essential hypertension
- •cardiac arrhythmias
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Calcium effects on vascular smooth muscle
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•vascular smooth muscle contraction is dependent upon an increase in intracellular Ca2+
- •Ca2+ channel blockers bind to and inhibit L-type voltage-dependent Ca2+ channels in arterial smooth muscle.
- •CCB have little or no effect on the entry of calcium into the cell via other mechanisms
- •decreased intracellular Ca2+ in arterial smooth muscle results in coronary and peripheral vascular relaxation and a decrease in blood pressure (afterload)CCB have little or no effect on the veins and no effect on cardiac preload
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Class of Ca2+ channel blocker: verapamil (and diltiazem)
- –affects the SA node and AV conduction system, exerting effects that slow the heart rate
- –also causes a greater decrease in myocardial contractility (inotropy) than the dihydropyridines; can worsen heart function in a failing heart
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Class of Ca2+ channel blocker:
nifedipine and related dihydropyridines
- –do NOT have significant direct effects on the atrioventricular conduction system or the sinoatrial node that would slow heart rate
- –moreover, these drugs are better vasodilators than verapamil… this peripheral vasodilatation leads to a reflex increase in sympathetic tone, which increases heart rate à i.e., causes a reflex tachycardia
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•Initially approved for treatment of refractory angina
- •New class, definitely does exert beneficial antianginal effects –
- –~No effect on HR, BP or rate-pressure product… ?
- –Initially thought to work by modifying fatty acid metabolism
- –Now thought to work primarily by blocking a Na+ channel responsible for a late phase of influx (less Nai = greater driving force for Ca2+ extrusion via Na/Ca exchanger)
- –Prolongs QT interval, so fear was that it could trigger torsades de pointes
- •MERLIN-TIMI36 trial failed to demonstrate added benefit in non-ST elevated MI patients, its initial main target
- –Oops… fire 1/4 of employees
- –Oops again… noted that patients receiving ranolazine had significantly lower incidence of arrhythmias and no torsades
- •Recently approved as initial therapy for chronic angina
- •Testimonials suggest it is a miracle drug for some patients…
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