Introduction to CVS – Heart Failure, Hypertension, Angina & Arrhythmias
This massive opening unit covers the pharmacology of the entire cardiovascular system. It begins with the hemodynamics (cardiac output, blood pressure regulation) and electrophysiology (action potential, pacemaker activity) of the heart — the scientific foundation for understanding all CVS drug classes. Then it systematically covers drugs for the four major cardiovascular diseases: Congestive Heart Failure (CHF), Hypertension, Angina Pectoris, and Cardiac Arrhythmias, plus Antihyperlipidemic agents.
Syllabus & Topics
- 1Hemodynamics of the Heart: Cardiac Output (CO) = Heart Rate × Stroke Volume. Blood pressure = CO × Total Peripheral Resistance (TPR). Preload (venous return, ventricular filling), Afterload (arterial resistance against which heart pumps). Frank-Starling law: ↑preload → ↑contractility (up to a limit).
- 2Electrophysiology: Cardiac action potential – Phase 0 (rapid Na⁺ influx – depolarization), Phase 1 (transient K⁺ efflux), Phase 2 (Ca²⁺ influx – plateau, sustains contraction), Phase 3 (K⁺ efflux – repolarization), Phase 4 (resting potential, spontaneous depolarization in pacemaker cells). SA node = primary pacemaker (automaticity).
- 3Congestive Heart Failure (CHF) – Pathophysiology: Heart fails to pump adequate blood → ↓CO → compensatory RAAS activation → Na⁺/water retention → edema + ↑preload. Sympathetic activation → ↑HR, ↑afterload. Vicious cycle of worsening failure.
- 4CHF – Cardiac Glycosides: Digoxin – inhibits Na⁺/K⁺-ATPase → ↑intracellular Ca²⁺ → positive inotropic effect (↑contractility). Also ↑vagal tone (↓HR). Narrow therapeutic index. Toxicity: arrhythmias, nausea, xanthopsia (yellow vision). Hypokalemia potentiates toxicity.
- 5CHF – Other Drugs: ACE inhibitors (Enalapril – ↓preload + ↓afterload, first-line), β-blockers (Carvedilol, Metoprolol – reverse remodeling, long-term mortality benefit), Diuretics (Furosemide – relieve congestion/edema), Vasodilators (Hydralazine + Isosorbide dinitrate), Phosphodiesterase inhibitors (Milrinone – IV for acute decompensation).
- 6Antihypertensive Drugs – Classification: (1) Diuretics (Thiazides – first-line). (2) ACE inhibitors (Enalapril, Ramipril). (3) ARBs (Losartan, Valsartan). (4) CCBs (Amlodipine). (5) β-blockers (Atenolol, Metoprolol). (6) Central sympatholytics (Clonidine, Methyldopa). (7) α-blockers (Prazosin). (8) Direct vasodilators (Hydralazine, Minoxidil, Sodium nitroprusside).
- 7Antihypertensives – RAAS Blockers: ACE inhibitors block Angiotensin I → II conversion → ↓vasoconstriction + ↓aldosterone. Dry cough (↑bradykinin). ARBs block AT1 receptors directly → no cough. Both are renoprotective in diabetic nephropathy. Contraindicated in pregnancy (teratogenic).
- 8Antihypertensives – Adrenergic Blockers: β-blockers (Atenolol – β1 selective → ↓HR, ↓contractility, ↓renin). α-blockers (Prazosin – first-dose postural hypotension). Central α2 agonists (Clonidine – ↓sympathetic outflow; Methyldopa – safe in pregnancy). Ganglionic blockers (obsolete, severe side effects).
- 9Anti-anginal Drugs – Organic Nitrates: Nitroglycerin (sublingual – acute attack), Isosorbide dinitrate/mononitrate (oral – prophylaxis). Release NO → ↑cGMP → venodilation (↓preload) + coronary dilation. Tolerance develops with continuous use → nitrate-free interval needed.
- 10Anti-anginal – Calcium Channel Blockers: Verapamil (↓HR, ↓contractility – unstable angina), Diltiazem (intermediate), Nifedipine/Amlodipine (peripheral vasodilators – ↓afterload, may cause reflex tachycardia). β-blockers (Atenolol, Propranolol – ↓HR, ↓O₂ demand, first-line for stable angina).
- 11Antiarrhythmic Drugs – Vaughan-Williams: Class IA (Quinidine, Procainamide – moderate Na⁺ block), Class IB (Lidocaine, Phenytoin – mild Na⁺ block, post-MI), Class IC (Flecainide – marked Na⁺ block, life-threatening only), Class II (β-blockers – Propranolol), Class III (Amiodarone, Sotalol – K⁺ channel block, prolong repolarization), Class IV (Verapamil, Diltiazem – Ca²⁺ channel block, supraventricular).
- 12Antiarrhythmics – Key Drugs: Amiodarone – most effective, blocks Na⁺/K⁺/Ca²⁺ channels + β-receptors. Extremely long t½ (~40 days). ADRs: pulmonary fibrosis, thyroid dysfunction (iodine content), corneal microdeposits, skin photosensitivity. Adenosine – ultra-short acting IV drug of choice for paroxysmal SVT (terminates re-entry circuits).
- 13Antihyperlipidemic – Statins: HMG-CoA reductase inhibitors (Atorvastatin, Rosuvastatin) – most effective LDL-lowering drugs. ↓LDL 30-50%, ↑HDL, ↓triglycerides moderately. ADRs: myopathy, rhabdomyolysis (especially with fibrates), hepatotoxicity.
- 14Antihyperlipidemic – Other Classes: Fibrates (Gemfibrozil, Fenofibrate – PPARα activation → ↓triglycerides, ↑HDL). Bile acid sequestrants (Cholestyramine – bind bile acids → ↓LDL). Niacin (↓VLDL secretion → ↓LDL + ↓TG + ↑HDL. Flushing is major ADR → aspirin pretreatment). Ezetimibe (blocks intestinal cholesterol absorption at NPC1L1 transporter).
Learning Objectives
Frequently Asked Questions (FAQs)
Q1. Why Are ACE Inhibitors Considered First-Line for CHF?
ACE inhibitors such as Enalapril and Ramipril are considered first-line therapy in Congestive Heart Failure because they interrupt the overactivated renin–angiotensin–aldosterone system (RAAS). By inhibiting angiotensin-converting enzyme, they reduce formation of angiotensin II, leading to decreased vasoconstriction (reduced afterload) and reduced aldosterone secretion (less sodium and water retention, lowering preload). They also increase bradykinin levels, promoting vasodilation, and help prevent adverse cardiac remodeling, thereby reducing mortality in heart failure.
Q2. What Is Nitrate Tolerance and How Is It Prevented?
Nitroglycerin and other nitrates can produce tolerance when used continuously, resulting in reduced responsiveness within 24–48 hours. This occurs due to depletion of sulfhydryl groups required for nitric oxide generation and increased oxidative stress in vascular tissues. Tolerance is prevented by maintaining a daily nitrate-free interval of approximately 8–12 hours, often scheduled overnight.
Q3. Why Is Amiodarone Both the Most Effective and Most Toxic Antiarrhythmic?
Amiodarone blocks multiple cardiac ion channels (sodium, potassium, and calcium channels) and also exhibits beta-adrenergic blocking effects. This broad mechanism allows it to treat many types of arrhythmias effectively. However, its long half-life (about 40 days), high iodine content, and strong lipophilicity cause accumulation in tissues, leading to adverse effects such as pulmonary fibrosis, thyroid dysfunction, liver toxicity, corneal deposits, and photosensitivity.
Q4. What Is the Most Dangerous Side Effect of Statins?
A rare but serious adverse effect of statins such as Atorvastatin is rhabdomyolysis, a condition involving severe breakdown of skeletal muscle. This releases myoglobin into the bloodstream, which may cause acute kidney failure. The risk increases when statins are combined with interacting drugs such as Gemfibrozil, Erythromycin, or Cyclosporine.
Q5. Why Is Methyldopa the Preferred Antihypertensive in Pregnancy?
Methyldopa is widely used for treating hypertension during pregnancy because of its long-established safety profile. Unlike ACE inhibitors and Angiotensin receptor blockers, which are contraindicated due to teratogenic risks, methyldopa lowers maternal blood pressure without significantly affecting uteroplacental blood flow, making it safer for both mother and fetus.