Electrophysiology of Heart

Electrophysiology of the Heart

Subject: Pharmacotherapeutics-I | Course: Doctor of Pharmacy (Pharm.D) | Topic: Electrophysiology of the Heart

1. Introduction

Cardiac electrophysiology is the study of the electrical activity of the heart, including how electrical impulses are generated and conducted to produce a normal heartbeat.

The heart generates its own impulses without stimulation from the brain. This property is called automaticity. Specialised cardiac cells produce the impulses, and the cardiac conduction system carries them to the myocardium, which then contracts and pumps blood.

Key points

•        The heart can initiate impulses independently of the nervous system.

•        The SA node is the natural pacemaker.

•        Electrical impulses control the rate and rhythm of the heartbeat.

•        The autonomic nervous system modifies heart rate and force of contraction but does not normally initiate each beat.

2. Automaticity

Definition: Automaticity is the intrinsic ability of specialised cardiac cells to generate electrical impulses spontaneously, without external stimulation.

•        It is an intrinsic property of pacemaker cells.

•        It allows the heart to beat independently of the nervous system.

•        The SA node normally fires at about 60–100 impulses per minute (the intrinsic rate is nearer 100/min; vagal tone slows the resting rate).

•        Latent pacemakers take over if the SA node fails: AV node about 40–60/min, Purkinje fibres about 20–40/min.

Clinical importance: Abnormal automaticity can cause cardiac arrhythmias.

3. Types of Cardiac Muscle Cells

The myocardium contains two major cell types.

A. Nodal (pacemaker) cells

•        Depolarise spontaneously.

•        Generate very little contractile force.

•        Have an unstable resting membrane potential.

•        Found mainly in the SA node and AV node.

Function: Generation and regulation of electrical impulses.

B. Contractile cells (working myocardium)

•        Form the bulk of the atrial and ventricular walls.

•        Contain contractile proteins (actin, myosin).

•        Have a stable resting membrane potential (about –90 mV).

•        Contract when stimulated by an impulse.

Function: Generating the mechanical force that pumps blood into the pulmonary artery and aorta.

4. Cardiac Conduction System

The conduction system is a network of specialised cells that generate and conduct impulses through the heart.

Pathway: SA node → atrial muscle (internodal pathways) → AV node → Bundle of His → right and left bundle branches → Purkinje fibres → ventricular muscle.

conduction pathway · 7 steps

The AV node holds the impulse for about 0.1 s so the ventricles can fill before they contract.

Component	Location and features	Function
SA node	Upper right atrium, near the opening of the superior vena cava; fires about 60–100/min	Natural pacemaker; initiates each heartbeat
Atrial conduction	Spread of the impulse through right and left atria	Atrial contraction; fills the ventricles
AV node	Lower right atrium, in the interatrial septum near the opening of the coronary sinus	Delays the impulse by about 0.1 s so the ventricles fill before they contract
Bundle of His	Passes from the AV node into the interventricular septum	Conducts impulses to the ventricles; divides into two branches
Right and left bundle branches	Run along the interventricular septum	Carry impulses to the right and left ventricles
Purkinje fibres	Subendocardial network in the ventricular walls	Rapid, coordinated ventricular depolarisation and contraction

5. Cellular Electrophysiology

Electrical activity arises from the movement of ions across the cell membrane.

•        Sodium (Na⁺): rapid depolarisation in contractile cells.

•        Potassium (K⁺): mainly repolarisation.

•        Calcium (Ca²⁺): depolarisation in nodal cells, and the trigger for contraction.

There are two types of cardiac action potential: the nodal (pacemaker) action potential and the contractile cell action potential.

6. Nodal Cell Action Potential (SA Node)

Nodal cells have no stable resting potential. The SA nodal action potential has three phases: 4, 0 and 3 (phases 1 and 2 are absent).

Phase 4 – Pacemaker potential (slow diastolic depolarisation)

•        Begins right after repolarisation, at the maximum diastolic potential (about –60 mV).

•        The funny current (I_f, through HCN channels) allows a slow inward flow of mainly Na⁺.

•        Outward K⁺ current decreases.

•        T-type Ca²⁺ channels open late in the phase and add to the depolarisation.

•        The membrane potential drifts upward until it reaches the threshold (about –40 mV).

Phase 0 – Depolarisation

•        At threshold, L-type Ca²⁺ channels open and Ca²⁺ enters the cell.

•        Result: a relatively slow upstroke.

Remember: In nodal cells phase 0 is caused by calcium; in ventricular contractile cells it is caused by sodium.

Phase 3 – Repolarisation

•        Ca²⁺ channels close.

•        K⁺ channels open and K⁺ leaves the cell.

•        The membrane potential returns to the maximum diastolic potential and the next pacemaker cycle begins.

7. Contractile Cell Action Potential (Ventricular Muscle)

Contractile cells have a stable resting potential of about –90 mV and a five-phase action potential (0, 1, 2, 3, 4).

Phase	Name	Ion movement	Result
4	Resting	High K⁺ permeability (inward rectifier K⁺ current)	Stable potential of about –90 mV
0	Rapid depolarisation	Fast Na⁺ channels open; Na⁺ rushes in	Inside becomes positive
1	Initial repolarisation	Na⁺ channels inactivate; transient outward K⁺ current	Small, brief fall in potential
2	Plateau	Ca²⁺ influx (L-type) balances K⁺ efflux	Potential stays near constant
3	Rapid repolarisation	Ca²⁺ channels close; K⁺ efflux increases	Returns to about –90 mV

Importance of the plateau (phase 2)

•        Ca²⁺ enters and triggers contraction.

•        It prolongs the action potential.

•        It produces a long refractory period, which prevents sustained contraction (tetany).

Comparison: nodal vs contractile cells

Feature	Nodal cells	Contractile cells
Main function	Generate impulses	Produce contraction
Resting potential	Unstable	Stable (about –90 mV)
Phase 0	Ca²⁺ influx	Na⁺ influx
Phase 1	Absent	Present
Phase 2	Absent	Present
Phase 3	K⁺ efflux	K⁺ efflux
Phase 4	Pacemaker potential	Resting phase

action potentials · nodal vs contractile

Nodal cells reach threshold by slow drift and use Ca²⁺ for phase 0. Contractile cells start from a stable –90 mV, use Na⁺ for phase 0 and hold a Ca²⁺ plateau in phase 2.

8. Mechanism of Cardiac Muscle Contraction

Cardiac contraction occurs through excitation–contraction coupling: the process by which an electrical impulse produces mechanical contraction.

1.      Calcium entry: During phase 2, L-type Ca²⁺ channels open and Ca²⁺ enters from the extracellular fluid.

2.      Calcium-induced calcium release (CICR): Entering Ca²⁺ activates ryanodine receptors (RyR2) on the sarcoplasmic reticulum, which releases much more Ca²⁺ into the sarcoplasm.

3.      Binding to troponin C: Ca²⁺ binds troponin C, changing the shape of the troponin complex. Tropomyosin moves off the myosin-binding sites on actin.

4.      Cross-bridge formation: Myosin heads attach to actin.

5.      Power stroke: Myosin heads pull actin towards the centre of the sarcomere. The sarcomere shortens and the muscle contracts.

9. Intercalated Discs and Functional Syncytium

Cardiac muscle cells are joined end-to-end by intercalated discs, which give both mechanical and electrical connection.

Gap junctions

•        Channels formed by connexin proteins (mainly connexin 43).

•        Allow ions and small molecules to pass between neighbouring cells.

•        Let impulses spread rapidly, so cells contract in a coordinated way.

•        Function: electrical communication.

Desmosomes (and fascia adherens)

•        Provide strong mechanical attachment between cells.

•        Prevent cells from pulling apart during repeated contraction.

•        Function: mechanical attachment.

Functional syncytium: A group of individual cells that behave as a single unit because they are electrically connected through gap junctions. The heart has two syncytia:

•        Atrial syncytium: both atria contract together.

•        Ventricular syncytium: both ventricles contract together.

The fibrous skeleton of the heart electrically insulates the atria from the ventricles. Under normal conditions the AV node and His bundle are the only electrical connection between them.

10. Mechanism of Cardiac Muscle Relaxation

Relaxation (diastole) requires Ca²⁺ to be removed from the sarcoplasm.

1.      Ca²⁺ channels close: L-type channels close, so no more Ca²⁺ enters.

2.      Reuptake into the sarcoplasmic reticulum: SERCA (sarco/endoplasmic reticulum Ca²⁺-ATPase) pumps Ca²⁺ back into the SR using ATP. This is the main route of removal.

3.      Extrusion from the cell:

o        Na⁺/Ca²⁺ exchanger (NCX): brings in 3 Na⁺ and removes 1 Ca²⁺. It is driven by the Na⁺ gradient, not directly by ATP.

o        Plasma membrane Ca²⁺-ATPase (PMCA): uses ATP to pump Ca²⁺ out of the cell.

4.      Ca²⁺ detaches from troponin C: Tropomyosin covers the binding sites on actin again, and cross-bridges release.

Result: The muscle relaxes and the chambers refill with blood.

11. Role of ATP

•        Myosin detachment: ATP binds myosin and releases it from actin.

•        Myosin activation: ATP hydrolysis provides the energy for the power stroke.

•        Calcium reuptake: SERCA needs ATP.

•        Calcium extrusion: PMCA needs ATP.

•        Ionic balance: The Na⁺/K⁺-ATPase pumps 3 Na⁺ out and 2 K⁺ in per ATP, maintaining the gradients needed for electrical activity. It also keeps the Na⁺ gradient that drives NCX.

12. Important Ions – Summary

Ion	Role
Sodium (Na⁺)	Rapid depolarisation in contractile cells (phase 0); contributes to the pacemaker current I_f
Potassium (K⁺)	Repolarisation; sets the resting potential
Calcium (Ca²⁺)	Nodal depolarisation (phase 0), plateau in contractile cells, and muscle contraction

13. Clinical and Pharmacological Importance

Abnormal impulse generation or conduction causes arrhythmias. Many cardiovascular drugs act by changing ion movement across cardiac cell membranes.

Drug	Class / target	Effect
Verapamil	Non-dihydropyridine Ca²⁺ channel blocker (blocks L-type channels)	Slows SA firing and AV nodal conduction
Diltiazem	Non-dihydropyridine Ca²⁺ channel blocker	Reduces Ca²⁺ entry; slows AV nodal conduction
Metoprolol	Selective β1-blocker	Decreases SA nodal firing rate and slows AV nodal conduction
Adenosine	Activates A1 receptors, increasing K⁺ efflux and hyperpolarising nodal cells	Transient AV nodal block; used to terminate certain supraventricular tachycardias
Amiodarone	Class III (mainly K⁺ channel blocker); also blocks Na⁺ and Ca²⁺ channels and has β-blocking action	Prolongs action potential duration and refractory period
Lidocaine	Class IB (Na⁺ channel blocker)	Acts mainly on ventricular tissue; used in ventricular arrhythmias

Clinical importance: Understanding cardiac electrophysiology explains how antiarrhythmic drugs work and how they are used.

14. Summary of Important Points

Topic	Key point
Cardiac electrophysiology	Study of the electrical activity of the heart
Automaticity	Spontaneous impulse generation
SA node	Natural pacemaker
AV node	Brief conduction delay (about 0.1 s)
Bundle of His	Conducts impulses towards the ventricles
Purkinje fibres	Rapid ventricular conduction
Nodal phase 0	Ca²⁺ influx
Contractile phase 0	Na⁺ influx
Phase 2	Plateau phase
Troponin C	Binds Ca²⁺
SERCA	Pumps Ca²⁺ into the sarcoplasmic reticulum
NCX	Exchanges 3 Na⁺ for 1 Ca²⁺
Gap junctions	Electrical communication
Desmosomes	Mechanical attachment
ATP	Energy for contraction and relaxation

CHF

 

CONGESTIVE HEART FAILURE (CHF)

ETIOLOGY, ETIOPATHOGENESIS AND PHARMACOTHERAPY

1. DEFINITION

Congestive heart failure (CHF) is a clinical syndrome in which the heart is unable to pump sufficient blood to meet the metabolic requirements of the body, or can do so only at the expense of increased cardiac filling pressures. It is characterized by inadequate tissue perfusion and/or congestion of the pulmonary and systemic circulations.

2. ETIOLOGY OF CONGESTIVE HEART FAILURE

The major causes of congestive heart failure are as follows:

Coronary artery disease: Narrowing of the coronary arteries reduces myocardial blood supply, leading to ischemia and impaired cardiac function.

Myocardial infarction: Death of myocardial tissue reduces ventricular contractility and may lead to heart failure.

Hypertension: Persistent elevation of blood pressure increases cardiac afterload, causing ventricular hypertrophy and eventual cardiac dysfunction.

Cardiomyopathy: Diseases of the cardiac muscle, such as dilated, hypertrophic, and restrictive cardiomyopathy, impair cardiac contraction or filling.

Valvular heart diseases: Aortic stenosis, aortic regurgitation, mitral stenosis, and mitral regurgitation increase cardiac workload.

Arrhythmias: Atrial fibrillation, persistent tachycardia, and severe bradycardia can impair cardiac output.

Congenital heart diseases: Structural abnormalities may cause pressure or volume overload.

Myocarditis: Inflammation of the myocardium can impair cardiac function.

Diabetes mellitus: Diabetes increases the risk of coronary artery disease and diabetic cardiomyopathy.

Chronic kidney disease: Sodium and water retention and hypertension increase cardiac workload.

Pulmonary hypertension: Increased pulmonary vascular resistance can lead to right-sided heart failure.

Severe anemia: Reduced oxygen-carrying capacity increases cardiac workload.

Thyroid disorders: Hyperthyroidism and hypothyroidism may contribute to cardiac dysfunction.

Cardiotoxic drugs and substances: Alcohol and certain anticancer drugs, such as doxorubicin, can damage the myocardium.

Precipitating Factors

The following factors may precipitate acute decompensation in patients with chronic heart failure:

Non-adherence to prescribed medication.

Excessive dietary sodium intake.

Acute myocardial infarction or myocardial ischemia.

Uncontrolled hypertension.

Infection, particularly pneumonia.

Arrhythmias.

Pulmonary embolism.

Worsening renal function.

Use of medicines that promote fluid retention, such as NSAIDs.

3. CLASSIFICATION OF CONGESTIVE HEART FAILURE

A. According to the Side of the Heart Involved

1. Left-Sided Heart Failure

Left-sided heart failure occurs when the left ventricle cannot pump blood effectively into the systemic circulation or cannot fill normally.

Clinical features:

Dyspnea.

Orthopnea.

Paroxysmal nocturnal dyspnea.

Pulmonary crackles.

Pulmonary edema.

Fatigue and reduced exercise tolerance.

2. Right-Sided Heart Failure

Right-sided heart failure occurs when the right ventricle cannot pump blood effectively into the pulmonary circulation, resulting in systemic venous congestion.

Clinical features:

Peripheral edema.

Raised jugular venous pressure.

Hepatomegaly.

Ascites.

Abdominal distension.

Weight gain due to fluid retention.

B. According to Left Ventricular Ejection Fraction

Heart Failure with Reduced Ejection Fraction (HFrEF): LVEF ≤40%.

Heart Failure with Mildly Reduced Ejection Fraction (HFmrEF): LVEF 41–49%.

Heart Failure with Preserved Ejection Fraction (HFpEF): LVEF ≥50%, with additional clinical and objective evidence supporting the diagnosis.

Heart Failure with Improved Ejection Fraction (HFimpEF): Previous LVEF ≤40%, followed by an improvement to >40%.

4. ETIOPATHOGENESIS OF CONGESTIVE HEART FAILURE

Etiopathogenesis describes the underlying causes and mechanisms responsible for the development and progression of congestive heart failure.

A. Initiation of Heart Failure

Heart failure begins when the myocardium is damaged or subjected to persistent pressure or volume overload. Common causes include myocardial infarction, hypertension, valvular heart disease, and cardiomyopathy.

These conditions produce the following changes:

Reduced myocardial contractility.

Impaired ventricular relaxation.

Increased ventricular stiffness.

Reduced stroke volume.

Increased ventricular filling pressures.

Reduced cardiac output in many patients.

The body activates compensatory mechanisms to maintain blood pressure and tissue perfusion. Although these mechanisms initially help maintain circulation, prolonged activation contributes to disease progression.

B. Sympathetic Nervous System Activation

Reduced cardiac output stimulates the sympathetic nervous system through baroreceptor-mediated mechanisms.

Mechanism:

Reduced cardiac output decreases effective arterial perfusion.

Sympathetic activity increases, resulting in the release of noradrenaline.

Stimulation of β1-adrenergic receptors increases heart rate and myocardial contractility.

Stimulation of α1-adrenergic receptors causes peripheral vasoconstriction.

Renal β1-receptor stimulation promotes renin release.

Initial benefits:

Maintenance of blood pressure.

Increased heart rate and contractility.

Preservation of perfusion to vital organs.

Long-term harmful effects:

Persistent tachycardia.

Increased myocardial oxygen demand.

Increased afterload.

Increased risk of arrhythmias.

Myocardial injury and adverse ventricular remodeling.

Pharmacological relevance: Evidence-based beta-blockers, such as carvedilol, metoprolol succinate, and bisoprolol, reduce harmful sympathetic stimulation and improve outcomes in appropriate patients with HFrEF.

C. Activation of the Renin-Angiotensin-Aldosterone System (RAAS)

Reduced renal perfusion, sympathetic stimulation, and reduced sodium delivery to the macula densa stimulate renin release.

Mechanism:

Reduced renal perfusion ↓ Renin release from juxtaglomerular cells ↓ Angiotensinogen is converted into angiotensin I ↓ Angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II ↓ Angiotensin II stimulates vasoconstriction and aldosterone secretion ↓ Increased sodium and water retention, increased afterload, and adverse cardiac remodeling.

Effects of RAAS activation:

Angiotensin II causes vasoconstriction, increasing systemic vascular resistance and cardiac afterload.

Aldosterone increases sodium reabsorption and potassium excretion in the kidneys.

Water retention increases circulating blood volume and ventricular preload.

Angiotensin II and aldosterone promote myocardial fibrosis and adverse ventricular remodeling.

Pharmacological relevance: ACE inhibitors, angiotensin receptor blockers (ARBs), angiotensin receptor-neprilysin inhibitors (ARNIs), and mineralocorticoid receptor antagonists (MRAs) act on different components of this pathway.

D. Antidiuretic Hormone (ADH) Secretion

Reduced effective arterial blood volume stimulates the release of antidiuretic hormone, also called vasopressin.

Mechanism and effects:

ADH acts on V2 receptors in the renal collecting ducts.

It increases aquaporin-2 insertion into the collecting duct membrane.

This increases free-water reabsorption.

Excessive water retention contributes to fluid overload and may cause dilutional hyponatremia.

E. Frank-Starling Mechanism

The Frank-Starling mechanism states that increased ventricular filling stretches myocardial fibers and initially increases the force of contraction and stroke volume.

In heart failure:

Ventricular filling pressures increase.

The failing myocardium becomes less responsive to additional stretching.

Further increases in filling pressure produce limited improvement in cardiac output.

Excessive filling pressures cause pulmonary or systemic congestion.

F. Ventricular Remodeling

Chronic pressure overload, volume overload, myocardial injury, and neurohormonal activation cause structural changes in the heart.

These changes include:

Ventricular dilation.

Myocardial hypertrophy.

Interstitial fibrosis.

Altered calcium handling.

Reduced contractile efficiency.

Progressive ventricular dysfunction.

Functional mitral regurgitation in some patients.

Ventricular remodeling increases myocardial stress and contributes to the progression of heart failure.

Pharmacological relevance: ARNIs, ACE inhibitors, ARBs, evidence-based beta-blockers, and MRAs help reduce adverse remodeling in appropriate patients with HFrEF.

G. Natriuretic Peptide System

Stretching of the atria and ventricles stimulates the release of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP).

Their physiological effects include:

Increased sodium excretion.

Increased water excretion.

Vasodilation.

Inhibition of renin and aldosterone secretion.

These mechanisms help counteract excessive fluid retention and vasoconstriction. However, their effects are insufficient to overcome persistent neurohormonal activation in established heart failure.

BNP and NT-proBNP are also used as biomarkers in the diagnosis and assessment of heart failure.

H. Development of Pulmonary Congestion

Left ventricular dysfunction increases left ventricular filling pressure and left atrial pressure. This pressure is transmitted to the pulmonary veins and capillaries.

Consequences:

Increased pulmonary capillary hydrostatic pressure.

Fluid accumulation in the pulmonary interstitium.

Alveolar fluid accumulation in severe cases.

Impaired gas exchange.

Dyspnea, orthopnea, and pulmonary edema.

I. Development of Systemic Venous Congestion

Right ventricular dysfunction increases systemic venous pressure.

Consequences:

Increased hydrostatic pressure in peripheral capillaries.

Fluid accumulation in dependent tissues.

Peripheral pitting edema.

Hepatic congestion and hepatomegaly.

Ascites.

Renal venous congestion, which may worsen renal function.

J. Final Pathophysiological Outcome

The combined effects of reduced cardiac performance, neurohormonal activation, fluid retention, vasoconstriction, and ventricular remodeling result in progressive heart failure.

The major outcomes are:

Reduced tissue perfusion.

Increased ventricular filling pressures.

Pulmonary congestion.

Systemic venous congestion.

Exercise intolerance.

Progressive cardiac dysfunction.

5. CLINICAL FEATURES OF CHF

Symptoms

Dyspnea on exertion.

Orthopnea.

Paroxysmal nocturnal dyspnea.

Fatigue and weakness.

Reduced exercise tolerance.

Ankle swelling.

Rapid weight gain due to fluid retention.

Abdominal distension.

Nocturia in some patients.

Signs

Tachycardia or abnormal heart rhythm.

Raised jugular venous pressure.

Pulmonary crackles.

Peripheral pitting edema.

Third heart sound (S3) in some patients.

Hepatomegaly.

Ascites.

Cool extremities and hypotension in severe low-output states.

6. INVESTIGATIONS

Electrocardiogram (ECG): Detects arrhythmias, ischemia, and evidence of previous myocardial infarction.

Echocardiography: Evaluates ejection fraction, ventricular function, valves, and cardiac structure.

BNP or NT-proBNP: Supports the diagnosis and assessment of heart failure.

Chest X-ray: May demonstrate cardiomegaly, pulmonary congestion, or pulmonary edema.

Complete blood count: Detects anemia and possible infection.

Serum creatinine and estimated glomerular filtration rate: Assess renal function.

Serum electrolytes: Detect sodium and potassium abnormalities.

Liver function tests: Assess hepatic congestion or other liver disease.

Thyroid function tests: Identify thyroid disorders that may contribute to heart failure.

Troponin: Evaluates myocardial injury when clinically indicated.

Urinalysis and urine albumin assessment: Evaluate associated renal disease when appropriate.

7. PHARMACOTHERAPY OF CONGESTIVE HEART FAILURE

The objectives of pharmacotherapy are:

To relieve pulmonary and systemic congestion.

To improve symptoms and exercise tolerance.

To reduce hospitalization.

To reduce mortality.

To prevent adverse ventricular remodeling.

To treat underlying causes and precipitating factors.

Treatment depends on ejection fraction, clinical stability, blood pressure, renal function, serum potassium, and the degree of congestion.

A. Pharmacotherapy of HFrEF

The four foundational medication classes for eligible patients with HFrEF are:

Angiotensin receptor-neprilysin inhibitor (ARNI), or an ACE inhibitor/ARB when appropriate.

Evidence-based beta-blocker.

Mineralocorticoid receptor antagonist (MRA).

Sodium-glucose cotransporter-2 (SGLT2) inhibitor.

These therapies should generally be introduced early and titrated according to tolerance and clinical status.

1. Angiotensin Receptor-Neprilysin Inhibitor (ARNI)

Drug: Sacubitril/valsartan.

Mechanism of action:

Sacubitril inhibits neprilysin, increasing the activity of natriuretic peptides.

Valsartan blocks angiotensin II AT1 receptors.

The combination promotes vasodilation and natriuresis while reducing RAAS-mediated vasoconstriction and adverse remodeling.

Common adult dosage:

Initial dose: 24/26 mg or 49/51 mg orally twice daily, depending on previous treatment and clinical status.

Target dose: 97/103 mg orally twice daily, if tolerated.

Adverse effects:

Hypotension.

Hyperkalemia.

Worsening renal function.

Angioedema.

Monitoring:

Blood pressure.

Serum potassium.

Renal function.

Precautions:

Sacubitril/valsartan must not be administered with an ACE inhibitor.

A minimum 36-hour washout period is required after discontinuing an ACE inhibitor before starting sacubitril/valsartan.

Avoid in pregnancy and in patients with a relevant history of angioedema.

2. Angiotensin-Converting Enzyme (ACE) Inhibitors

Examples: Enalapril, lisinopril, and ramipril.

Mechanism of action: ACE inhibitors reduce the conversion of angiotensin I to angiotensin II, resulting in reduced vasoconstriction and aldosterone secretion.

Common adult enalapril dosage:

Initial dose: 2.5 mg twice daily, when appropriate.

Target dose: 10 mg twice daily, if tolerated.

Adverse effects:

Dry cough.

Hypotension.

Hyperkalemia.

Worsening renal function.

Angioedema.

Monitoring:

Blood pressure.

Renal function.

Serum potassium.

ACE inhibitors are alternatives when ARNI therapy is not feasible or tolerated. They must not be combined with an ARNI.

3. Angiotensin Receptor Blockers (ARBs)

Examples: Valsartan and candesartan.

Mechanism of action: ARBs block angiotensin II AT1 receptors, reducing vasoconstriction, aldosterone-mediated sodium retention, and adverse cardiac remodeling.

Common adult dosages:

Valsartan: Initial dose 40 mg twice daily; target dose 160 mg twice daily.

Candesartan: Initial dose 4–8 mg once daily; target dose 32 mg once daily.

Adverse effects:

Hypotension.

Hyperkalemia.

Worsening renal function.

Monitoring:

Blood pressure.

Renal function.

Serum potassium.

ARBs may be used when ACE inhibitors are not tolerated and ARNI therapy is not feasible. They should not be routinely combined with an ACE inhibitor or ARNI.

4. Beta-Blockers

Examples: Carvedilol, metoprolol succinate, and bisoprolol.

Mechanism of action: Beta-blockers reduce excessive sympathetic stimulation, heart rate, myocardial oxygen demand, arrhythmia risk, and adverse ventricular remodeling.

Common adult dosages:

Carvedilol: Initial dose 3.125 mg twice daily; target dose 25 mg twice daily for many patients.

Metoprolol succinate extended-release: Initial dose 12.5–25 mg once daily; target dose 200 mg once daily.

Bisoprolol: Initial dose 1.25 mg once daily; target dose 10 mg once daily.

Adverse effects:

Bradycardia.

Hypotension.

Fatigue.

Temporary worsening of congestion during initiation or dose titration.

Precautions:

Initiate treatment when the patient is clinically stable and reasonably euvolemic.

Do not initiate or increase the dose during cardiogenic shock or significant acute decompensation.

Use caution in severe bradycardia and advanced heart block without a pacemaker.

5. Mineralocorticoid Receptor Antagonists (MRAs)

Examples: Spironolactone and eplerenone.

Mechanism of action: MRAs block aldosterone receptors, reducing sodium retention, potassium loss, myocardial fibrosis, and adverse cardiac remodeling.

Common adult dosages:

Spironolactone: Initial dose 12.5–25 mg once daily; usual target dose 25–50 mg daily.

Eplerenone: Initial dose 25 mg once daily; target dose 50 mg once daily.

Adverse effects:

Hyperkalemia.

Worsening renal function.

Gynecomastia and sexual adverse effects with spironolactone.

Monitoring:

Serum potassium.

Renal function.

Blood pressure.

MRAs are generally considered in eligible HFrEF patients with eGFR above 30 mL/min/1.73 m² and serum potassium below 5.0 mmol/L at initiation. Potassium and renal function must be monitored regularly.

6. Sodium-Glucose Cotransporter-2 (SGLT2) Inhibitors

Examples: Dapagliflozin and empagliflozin.

Mechanism of action: SGLT2 inhibitors reduce glucose and sodium reabsorption in the proximal renal tubule. Their heart failure benefits extend beyond glucose lowering, although the full mechanisms are not completely understood.

Common adult dosage:

Dapagliflozin: 10 mg orally once daily.

Empagliflozin: 10 mg orally once daily.

Benefits:

Reduces heart failure hospitalization.

Improves heart failure outcomes.

Provides benefits in patients with and without diabetes.

Adverse effects:

Genital fungal infections.

Volume depletion.

Rare euglycemic diabetic ketoacidosis.

An initial decline in eGFR may occur.

Precautions: Assess renal function and volume status. Follow product-specific instructions regarding withholding treatment before major surgery or prolonged fasting.

B. Diuretics

Diuretics are used to relieve fluid overload and improve symptoms of congestion.

1. Loop Diuretics

Examples: Furosemide, torsemide, and bumetanide.

Mechanism of action: Loop diuretics inhibit the sodium-potassium-chloride cotransporter in the thick ascending limb of the loop of Henle, increasing sodium and water excretion.

Common adult oral furosemide dosage:

Initial dose: 20–40 mg, adjusted according to congestion, previous treatment, renal function, and response.

Indications:

Pulmonary congestion.

Peripheral edema.

Fluid overload.

Adverse effects:

Hypokalemia.

Hyponatremia.

Hypomagnesemia.

Dehydration.

Hypotension.

Worsening renal function.

Ototoxicity at high exposure.

Monitoring:

Body weight.

Urine output.

Blood pressure.

Renal function.

Serum electrolytes.

2. Thiazide and Thiazide-Like Diuretics

Examples: Hydrochlorothiazide and metolazone.

These medicines may be added to a loop diuretic in selected patients with inadequate diuretic response.

Adverse effects:

Hypokalemia.

Hyponatremia.

Dehydration.

Worsening renal function.

Close monitoring is necessary because combined diuretic treatment may cause severe electrolyte abnormalities.

C. Other Drugs Used in Selected Patients with HFrEF

1. Ivabradine

Mechanism of action: Ivabradine inhibits the funny current (If) in the sinoatrial node, reducing heart rate without directly reducing myocardial contractility.

Indication: Selected stable, symptomatic HFrEF patients in sinus rhythm with an elevated resting heart rate despite maximally tolerated beta-blocker therapy, or when beta-blockers cannot be used appropriately.

Common adult dosage:

Initial dose: 5 mg twice daily, adjusted according to heart rate and tolerance.

Adverse effects:

Bradycardia.

Atrial fibrillation.

Luminous visual phenomena.

2. Hydralazine and Isosorbide Dinitrate

Mechanism of action:

Hydralazine reduces arterial resistance and afterload.

Isosorbide dinitrate causes venodilation, reducing preload.

Indications: Selected patients with persistent symptoms despite standard therapy or those unable to tolerate appropriate RAAS-modifying medicines. The combination is particularly beneficial in selected self-identified Black patients with persistent symptomatic HFrEF.

Adverse effects:

Headache.

Hypotension.

Dizziness.

Hydralazine-associated lupus-like syndrome.

3. Digoxin

Mechanism of action:

Inhibits the sodium-potassium ATPase enzyme.

Increases intracellular calcium availability and myocardial contractility.

Increases vagal tone and slows atrioventricular nodal conduction.

Indications: Selected patients with persistent symptoms despite appropriate HFrEF therapy, or selected patients with atrial fibrillation requiring ventricular rate control.

Adverse effects:

Nausea and vomiting.

Confusion.

Visual disturbances.

Bradyarrhythmias.

Potentially fatal arrhythmias.

Monitoring:

Renal function.

Serum potassium and magnesium.

Heart rate.

Serum digoxin concentration when indicated.

Digoxin may reduce hospitalization in selected patients but has no proven mortality benefit in chronic HFrEF.

4. Vericiguat

Mechanism of action: Vericiguat stimulates soluble guanylate cyclase, enhancing cyclic GMP signaling.

Indication: Selected high-risk patients with HFrEF who have recently experienced worsening heart failure despite standard treatment.

5. Intravenous Iron

Intravenous iron may be considered in selected patients with HFrEF or HFmrEF and documented iron deficiency. It can improve symptoms and quality of life and may reduce heart failure hospitalizations in appropriate patients.

8. PHARMACOTHERAPY OF HFpEF AND HFmrEF

A. SGLT2 Inhibitors

Dapagliflozin and empagliflozin are important treatment options for eligible patients with HFpEF and HFmrEF. They reduce the risk of heart failure hospitalization and cardiovascular complications.

B. Diuretics

Loop diuretics are used to relieve pulmonary and systemic congestion. The dose should be adjusted to achieve euvolemia while avoiding excessive dehydration and renal dysfunction.

C. Management of Associated Conditions

Control hypertension.

Manage diabetes mellitus and obesity.

Treat atrial fibrillation and other arrhythmias.

Evaluate and treat coronary artery disease.

Assess and manage chronic kidney disease.

Evaluate iron deficiency and anemia.

Identify and treat valvular disease and other specific underlying causes.

D. Other Pharmacological Options

MRAs, ARBs, and ARNIs may be considered in selected patients depending on the ejection fraction, clinical status, blood pressure, renal function, potassium level, and applicable treatment guidelines.

9. PHARMACOTHERAPY OF ACUTE DECOMPENSATED HEART FAILURE

Acute decompensated heart failure requires urgent assessment and treatment. Severe breathlessness, hypoxemia, chest pain, confusion, or signs of shock require emergency medical care.

A. Initial Assessment

Assess airway, breathing, and circulation.

Measure oxygen saturation and blood pressure.

Assess peripheral perfusion and congestion.

Perform ECG and appropriate laboratory investigations.

Identify and treat precipitating causes.

B. Treatment

Intravenous loop diuretics: Used in patients with significant fluid overload.

Supplemental oxygen: Administered when hypoxemia is present.

Noninvasive ventilation: Considered in selected patients with severe respiratory distress.

Intravenous nitrates: May be considered in acute pulmonary edema when blood pressure is adequate.

Inotropes: Dobutamine or milrinone may be used in selected patients with cardiogenic shock or severe low-output states under specialist supervision.

Treatment of precipitating factors: Includes management of acute coronary syndrome, arrhythmias, infections, and uncontrolled hypertension.

During treatment, monitor urine output, blood pressure, renal function, and serum electrolytes.

Chronic heart failure medicines should generally be continued when clinically appropriate. Temporary adjustment may be necessary in shock, severe hypotension, acute kidney injury, or significant hyperkalemia.

10. NON-PHARMACOLOGICAL MANAGEMENT

Patient education and medication adherence.

Regular monitoring of body weight and symptoms.

Avoidance of excessive dietary sodium.

Individualized fluid restriction when clinically indicated.

Regular physical activity and cardiac rehabilitation when stable.

Smoking cessation.

Avoidance of excessive alcohol consumption.

Review of medicines that may worsen heart failure, particularly NSAIDs.

Management of associated conditions such as hypertension, diabetes, and chronic kidney disease.

Assessment for implantable cardioverter-defibrillator (ICD) or cardiac resynchronization therapy (CRT) when indicated.

11. IMPORTANT DRUG PRECAUTIONS

ACE inhibitors, ARBs, ARNIs, and MRAs may increase serum potassium and require renal function monitoring.

Sacubitril/valsartan must not be combined with an ACE inhibitor. A minimum 36-hour washout is required after stopping an ACE inhibitor.

NSAIDs may worsen fluid retention and renal function.

Potassium supplements and potassium-containing salt substitutes may cause hyperkalemia in patients receiving RAAS-modifying drugs.

Beta-blockers should not be initiated during cardiogenic shock or significant acute decompensation.

Verapamil and diltiazem are generally avoided in HFrEF because of their negative inotropic effects.

Digoxin toxicity is more likely in renal impairment and in patients with hypokalemia or hypomagnesemia.

SGLT2 inhibitors require assessment of volume status and ketoacidosis risk.

12. CLINICAL CASE EXAMPLE

Case: A 62-year-old man presents with progressive breathlessness, orthopnea, bilateral ankle edema, and fatigue. His blood pressure is 146/90 mmHg, pulse rate is 104 beats/minute, and examination reveals bilateral basal crackles and raised jugular venous pressure. Echocardiography shows a left ventricular ejection fraction of 30%.

Assessment: The findings suggest heart failure with reduced ejection fraction (HFrEF) with clinical congestion. Further investigations are required to identify the underlying cause and any precipitating factors.

Management plan:

Assess clinical severity and determine the need for hospitalization.

Relieve congestion using an appropriate loop diuretic.

Evaluate renal function, serum electrolytes, ECG, and blood pressure.

Initiate the four foundational HFrEF medication classes when clinically stable and appropriate.

Titrate medicines according to tolerance and evidence-based target doses.

Investigate and treat underlying coronary artery disease, hypertension, arrhythmias, or other causes.

Provide education regarding medication adherence, symptom monitoring, and follow-up.

13. CONCLUSION

Congestive heart failure is a clinical syndrome caused by structural or functional abnormalities of the heart. Its pathogenesis involves impaired cardiac performance, sympathetic nervous system activation, RAAS activation, fluid retention, and adverse ventricular remodeling.

The pharmacological management of HFrEF is based on four foundational medication classes: ARNI or an appropriate alternative, evidence-based beta-blocker, MRA, and SGLT2 inhibitor. Diuretics are used to relieve congestion, while additional medicines are selected according to the patient's symptoms and clinical characteristics. Acute decompensated heart failure requires prompt treatment based on congestion, blood pressure, oxygenation, perfusion, and the underlying precipitating cause.