Sick sinus syndrome pathophysiology

Sick sinus syndrome revolves around an improperly propagated signal from the sinoatrial(SA) node. Some of the causes for this propagation abnormality include degenerative fibrosis of the SA node, abnormalities in ion-channel conduction, and and a remodeling of the node itself. As a disease of the elderly, it is most commonly thought to be secondary to the age-related idiopathic fibrosis of the nodal tissue. Studies on familial and congenital presentations of sick sinus syndrome have also revealed genetic contributions to dysfunctional ion channels. Recent research has revealed a higher incidence of SSS in carriers of a rare variant of the MYH6 gene, which encodes the alpha heavy chain subunit of cardiac myosin, further delineating a possible genetic basis to the disease.

In some patients, heart failure and atrial fibrillation can also be causes of remodeling of the SA node leading to increased sinus node recovery time, abnormal propagation of the action potential from the node and changes in nodal sensitivity. Hemochromatosis, sarcoidosis, amyloidosis and other infiltrative disease process may contribute to intrinsic dysfunction of the sinoatrial node, as can chronic ischemia secondary to atherosclerotic changes of arteries supplying the SA node.

References

Cardiovascular	Amyloidosis, atherosclerosis, atrial septal defect, cardiac surgery in children, cardiomyopathies, carotid sinus hypersensitivity, congenital heart disease, coronary artery disease, Ebstein anomaly, electrolyte imbalance, hemochromatosis, hyperkalemia, hypertension, hypocalcemia, hypoxia, ischemic heart disease, Lyme disease, myocardial infarction, myocarditis, neurocardiogenic syncope, pericarditis, rheumatic fever, sinus node fibrosis, tachycardia-bradycardia syndrome
Chemical/Poisoning	Grayanotoxin, rhododendron sp
Dental	No underlying causes
Dermatologic	Lyme disease, systemic lupus erythematosus
Drug Side Effect	Amiodarone, antiarrhythmics, beta blockers, calcium channel blockers, cimetidine, clonidine, digitalis, disopyramide, guanethidine, lanatoside C, lidocaine, lithium, methyldopa, phenytoin, procainamide, propranolol, quinidine, reserpine, verapamil
Ear Nose Throat	No underlying causes
Endocrine	Amyloidosis, hemochromatosis, hypocalcemia, hypothyroidism
Environmental	No underlying causes
Gastroenterologic	Hemochromatosis, sarcoidosis, scleroderma
Genetic	Friedreich ataxia, HCN4 mutation, hemochromatosis, muscular dystrophy, myotonic dystrophy
Hematologic	Hemochromatosis
Iatrogenic	No underlying causes
Infectious Disease	Chagas disease, diphtheria, Lyme disease, pericarditis, rheumatic fever, sepsis
Musculoskeletal/Orthopedic	Friedreich ataxia, hemochromatosis, muscular dystrophy, myotonic dystrophy, systemic lupus erythematosus
Neurologic	Friedreich ataxia, hypothermia, muscular dystrophy, myotonic dystrophy, sleep apnea
Nutritional/Metabolic	Amyloidosis, electrolyte imbalance, hyperkalemia
Obstetric/Gynecologic	No underlying causes
Oncologic	Neoplasm
Ophthalmologic	Hypertension
Overdose/Toxicity	No underlying causes
Psychiatric	No underlying causes
Pulmonary	Hypoxia, sarcoidosis, scleroderma
Renal/Electrolyte	Electrolyte imbalance, hyperkalemia, hypertension, hypocalcemia, systemic lupus erythematosus
Rheumatology/Immunology/Allergy	Amyloidosis, rheumatic fever, sarcoidosis, scleroderma, systemic lupus erythematosus
Sexual	No underlying causes
Trauma	Cardiac surgery in children
Urologic	No underlying causes
Miscellaneous	Hypothermia, idiopathic

Causes in Alphabetical Order

Amiodarone Amyloidosis Antiarrhythmics Atherosclerosis Atrial septal defect Beta blockers Calcium channel blockers Cardiac surgery in children Cardiomyopathies Carotid sinus hypersensitivity Chagas disease Cimetidine Clonidine Congenital heart disease Coronary artery disease Digitalis Diphtheria Disopyramide Ebstein anomaly Electrolyte imbalance Friedreich ataxia Grayanotoxin Guanethidine HCN4 mutation Hemochromatosis Hyperkalemia Hypertension Hypocalcemia Hypothermia Hypothyroidism

Hypoxia Idiopathic Ischemic heart disease Lanatoside C Lidocaine Lithium Lyme disease Methyldopa Muscular dystrophy Myocardial infarction Myocarditis Myotonic dystrophy Neoplasm Neurocardiogenic syncope Pericarditis Phenytoin Procainamide Propranolol Quinidine Reserpine Rheumatic fever Rhododendron sp Sarcoidosis Scleroderma Sepsis Sinus node fibrosis Sleep apnea Systemic lupus erythematosus Tachycardia-bradycardia syndrome Verapamil