Cardiac contractility

Cardiac Contractility

Cardiac contractility refers to the intrinsic ability of the heart muscle (myocardium) to contract. It is a crucial aspect of cardiac function, influencing the heart's ability to pump blood effectively throughout the body. Cardiac contractility is determined by the interaction of actin and myosin filaments within the cardiac muscle cells, and it is modulated by various physiological and pathological factors.

Physiology of Cardiac Contractility

Cardiac contractility is primarily governed by the Frank-Starling mechanism, which describes the relationship between the volume of blood filling the heart (end-diastolic volume) and the force of contraction. The greater the volume of blood entering the heart, the more forcefully the heart contracts, up to a physiological limit.

Molecular Mechanisms

The contractile process in cardiac muscle cells is initiated by the influx of calcium ions (Ca²⁺) during the action potential. Calcium binds to troponin, causing a conformational change that allows actin and myosin filaments to interact, leading to muscle contraction. The strength of contraction is influenced by the amount of calcium available and the sensitivity of the contractile proteins to calcium.

Regulation

Cardiac contractility is modulated by several factors:

• Sympathetic Nervous System: Activation of the sympathetic nervous system increases cardiac contractility through the release of norepinephrine, which binds to beta-adrenergic receptors on cardiac cells, enhancing calcium influx.
• Parasympathetic Nervous System: The parasympathetic nervous system has a negative inotropic effect, reducing contractility by decreasing calcium availability.
• Hormones: Hormones such as epinephrine and thyroid hormones can increase cardiac contractility.
• Drugs: Certain medications, such as beta-blockers and calcium channel blockers, can decrease contractility, while others like digitalis can increase it.

Pathophysiology

Alterations in cardiac contractility can lead to various cardiac conditions:

• Heart Failure: Reduced contractility is a hallmark of heart failure, where the heart is unable to pump sufficient blood to meet the body's needs.
• Hypertrophic Cardiomyopathy: This condition is characterized by increased contractility due to thickened heart muscle, which can lead to obstruction of blood flow.
• Myocardial Infarction: Damage to the heart muscle from a heart attack can impair contractility.

Measurement of Cardiac Contractility

Cardiac contractility can be assessed using several methods:

• Echocardiography: This imaging technique can evaluate the heart's pumping ability and measure ejection fraction, an indicator of contractility.
• Cardiac Catheterization: Direct measurement of pressures and volumes in the heart can provide information on contractility.
• Magnetic Resonance Imaging (MRI): Cardiac MRI can assess myocardial function and contractility.

Also see

• Cardiac output
• Ejection fraction
• Heart failure
• Myocardial infarction
• Sympathetic nervous system

Cardiovascular disease A-Z

Most common cardiac diseases

• Cardiac arrhythmia‎
• Cardiogenetic disorders‎
• Cardiomegaly‎
• Cardiomyopathy‎
• Cardiopulmonary resuscitation‎
• Chronic rheumatic heart diseases‎
• Congenital heart defects‎
• Heart neoplasia‎
• Ischemic heart diseases‎
• Pericardial disorders
• Syndromes affecting the heart‎
• Valvular heart disease‎

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

• Accelerated idioventricular rhythm
• Acute decompensated heart failure
• Arteriosclerotic heart disease
• Athletic heart syndrome
• Atrial flutter
• Atrioventricular fistula
• Cardiovascular disease in Australia
• Autoimmune heart disease

B

• Brown atrophy of the heart

C

• Ebb Cade
• Cardiac allograft vasculopathy
• Cardiac amyloidosis
• Cardiac asthma
• Cardiac tamponade
• Cardiogenic shock
• Cardiogeriatrics
• Cardiorenal syndrome
• Cardiotoxicity
• Carditis
• Coronary artery aneurysm
• Coronary artery anomaly
• Coronary artery disease
• Spontaneous coronary artery dissection
• Coronary artery ectasia
• Coronary occlusion
• Coronary steal
• Coronary thrombosis
• Coronary vasospasm
• Cœur en sabot
• Coxsackievirus-induced cardiomyopathy

D

• Duke Treadmill Score
• Duroziez's disease

E

• Eisenmenger's syndrome
• Embryocardia
• Endocardial fibroelastosis
• Eosinophilic myocarditis

H

• Heart attack
• Heart failure
• Heart failure with preserved ejection fraction
• Heart to Heart (1949 film)
• High-output heart failure
• Hyperdynamic precordium

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

I

• Idiopathic giant-cell myocarditis
• Interventricular dyssynchrony
• Intraventricular dyssynchrony
• Isolated atrial amyloidosis

K

• Keshan disease

L

• Loeffler endocarditis

M

• Mydicar
• Myocardial bridge
• Myocardial disarray
• Myocardial rupture
• Myocardial scarring
• Myocardial stunning
• Myocarditis

N

• Nonbacterial thrombotic endocarditis

O

• OLR1
• Ostial disease

P

• Papillary fibroelastoma
• Pathophysiology of heart failure
• Postpericardiotomy syndrome
• Pulmonary vein stenosis

R

• Right axis deviation
• Roemheld syndrome

S

• Saturated fat and cardiovascular disease
• SCAR-Fc
• Shone's syndrome
• Strain pattern
• Subacute bacterial endocarditis
• Sudden cardiac death of athletes

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

T

• Traumatic cardiac arrest

V

• Ventricular aneurysm
• Vibroacoustic disease
• Viral cardiomyopathy

W

• Waon therapy