Class IV antidysrhythmics or calcium channel blockers have what action on the cardiovascular system?

According to the World Health Organization (WHO), noncommunicable diseases (NCDs) are the leading cause of death globally, accounting for 74% of all deaths. NCDs are chronic diseases that are not transmitted from person to person, such as cardiovascular diseases, cancers, chronic respiratory diseases and diabetes.The main risk factors for NCDs are modifiable behaviours, such as tobacco use, physical inactivity, unhealthy diet and the harmful use of alcohol.These behaviours can lead to metabolic risk factors, such as raised blood pressure, increased blood glucose, elevated blood lipids and obesity, which in turn increase the risk of developing NCDs. Therefore, lifestyle changes that reduce these risk factors can prevent or delay many NCDs and improve health outcomes.

Choice A is wrong because trauma is not a major contributing factor to many diseases.Trauma is an injury or damage to living tissue caused by an external force, such as accidents, violence or natural disasters.Trauma can result in acute or chronic conditions, such as infections, fractures, burns, bleeding or organ failure.

However, trauma is not a common cause of NCDs, which are the main burden of disease globally.

Choice C is wrong because congenital factors are not the greatest contributing factor to many diseases.Congenital factors are those that are present at birth, such as genetic disorders, birth defects or inherited diseases.Congenital factors can affect the development and function of various organs and systems in the body, leading to various health problems.

However, congenital factors are not the main cause of NCDs, which are largely influenced by environmental and behavioural factors.

Choice D is wrong because genetics is not the greatest contributing factor to many diseases.

Genetics is the study of how traits are inherited and expressed in living organisms.

Genetics can influence the susceptibility and resistance to various diseases, as well as the response to treatment and prevention strategies.

However, genetics is not the sole determinant of health and disease, as environmental and behavioural factors also play a significant role in modulating gene expression and function.

Class IV antidysrhythmics or calcium channel blockers decrease the flow of calcium ions into cardiac and vascular smooth muscle cells, thus decreasing heart rate and contractions.By reducing the calcium influx, they also decrease the slope of phase 0 and 4 and prolong phase 2 of the cardiac action potential.This results in vasodilation, reduced myocardial oxygen demand, and decreased conduction through the AV node.

Choice A is wrong because calcium channel blockers do not increase blood vessel spasm, but rather cause vasodilation.

Choice C is wrong because calcium channel blockers do not decrease refractory period, but rather prolong it by extending phase 2 of the cardiac action potential.

Choice D is wrong because calcium channel blockers do not increase heart rate, but rather decrease it by slowing down the pacemaker activity and AV nodal conduction.

Normal ranges for heart rate are 60 to 100 beats per minute, and for blood pressure are 120/80 mmHg or lower.