WHAT CAUSES ARRHYTHMIA
INTRODUCTION
Arrhythmia, simplest put, is an ABNORMAL or IRREGULAR heartbeat. These occur when the electrical impulses controlling your heartbeat malfunction.
A normal heartbeat is conducted when electrical impulses start from the natural PACEMAKER of the heart, ie SA NODE located in the right atrium. The electrical impulses then traverse through the entire right and left atrium and both the atria contract. The impulses reach the ATRIOVENTRICULAR NODE where the signals are slowed down(so that ventricles contract later than atria allowing them filling of the blood from the atria). The signals pass through the bundle of his and then the Purkinje fibers and spread throughout the ventricles to make them contract leading to the completion of a normal heartbeat.
A normal heart rate is 60-100 beats/minute, though for athletes even less than 60 beats per minute is normal.
TYPES OF ARRHYTHMIA
#1 Supraventricular arrhythmia– arrhythmia which begins above the ventricles
Atrial fibrillation– Many impulses begin and spread through the atrium leading to an increased rate of atrial contraction. The rate is 350-550 beats/minute.
Atrial flutter- It is due to a single macro reentry tract, therefore it has a lower rate compared to atrial fibrillation. The rate is 250-350 beats/minute.
Premature atrial contractions- Rare. Early, extra heartbeats originating in the atria
Paroxysmal supraventricular contractions – A rapid rate rhythm caused by impulse starting from atria bypassing the av node and entering the bundle of his directly.
#2 Ventricular arrhythmia- arrhythmia beginning at the level of the ventricles
Premature ventricular contractions- Extra heartbeats originating in the ventricles. The most common type of arrhythmia and can be related to stress, caffeine, or nicotine.
Ventricular tachycardia- Rapid heart rate originating in the ventricle. Rate is more than 100 beats/minute
Ventricular fibrillation- An erratic, disorganized firing of the ventricles. The ventricles fail to pump blood to the body and it is a medical emergency.
CAUSES OF ARRHYTHMIA
Most common causes of arrhythmia include
Myocardial Infarction or heart attack
Fibrotic changes in heart tissue post a previous Myocardial Infarction
Diabetes mellitus(long-standing)
Hypertension
Hyperthyroidism
Coronary artery disease
Cardiomyopathy
Congestive Heart Failure
Electrical shock
Other causes include
Smoking
Alcohol
Caffeine
Drug abuse
Stress
Catecholamines like noradrenaline, adrenaline, dopamine
Certain conditions may increase your risk of developing arrhythmia
Coronary artery disease and previous heart surgery
Congenital heart disease
Thyroid Problem
Diabetes
Obstructive sleep apnea
Electrolyte imbalance of sodium, potassium, calcium, and magnesium trigger the arrhythmias.
Now to understand how arrhythmia is caused one needs to understand the electro-chemical changes occurring at the microcellular level(refer to images above). Normally a cell has a higher concentration of K+(potassium) ions inside and Na+(sodium) ions outside. Now in a normal heart cell potassium ions keep leaking from the cell to outside depolarising the membrane from the resting membrane potential of -90mV to -70mV which is the action potential and at that value, the impulses fire triggering the heartbeat. This is all done automatic and thus termed automaticity of the heart cells.
The role of Ca2+(calcium) ions, in this case, is to stabilize the membrane and prevent from the rapid unwanted firing of signals and the gradual achieving of the action potential.
In cases of Myocardial infarction, the blood supply to a part of the heart is stopped killing the cells. In that eventuality, the cells release a lot of potassium ions which depolarise the membrane causing rapid irregular signals leading to arrhythmia.
Therefore the combination of hyperkalemia(excess of potassium ions) and hypocalcemia(shortage of calcium ions) is detrimental to the individual and can trigger arrhythmia.
The symptoms seen in such cases include
Angina(chest pain)
Dizziness or fainting
Palpitation(able to feel one’s own heartbeat)
Breathlessness
Sweating
Treatment options for arrhythmia include-
Vagal maneuvers- Vagal massage is one of the simplest maneuvers a person can do to treat mild irregular heartbeats
Medications- It includes many medicines which can be given including Beta-blockers, calcium channel blockers, Digoxin, adenosine but different medications are allotted to different arrhythmia and should be taken only after expert consultation with a cardiologist
Cardioversion- In severe cases, electric shock is used to shock the heart back into a rhythm
Ablation therapy- For single or few points of erratic origin of electrical signal those particular regions can be ablated for relief from arrhythmias