Effect of drugs on heart rhythm

The activity of the heart is controlled by the autonomic nervous system through mediators. The mediator of the sympathetic nervous system is noradrenaline, the mediator of the parasympathetic is acetylcholine. The action of the heart is also influenced by adrenaline from the adrenal medulla. Acetylcholine depresses heart activity, while noradrenaline stimulates the heart. The effect of mediators is mediated by specific receptors located on the cell membrane. Cardiac activity depends on the presence of calcium in the extracellular space and in the endoplasmic reticulum.

Drugs affecting the rhythm (and other functions) of the heart pump include, but are not limited to, cardioinhibitors, cardiotonics, and '''antiarrhythmics. '''

Cardioinhibitors
Cardioinhibitors (drugs that reduce heart activity) act negatively chronotropically (by reducing heart rate) and inotropically (by reducing heart muscle contractility), which leads to a decrease in cardiac output and blood pressure. These changes reduce the activity of the heart and thus the consumption of oxygen by the myocardium. The mechanisms of action of these drugs also include a reduction in electrical conduction (negative dromotropic action).

The mechanical and metabolic effects of these drugs predispose them to treat hypertension, angina pectoris and heart - attack. Thanks to their effect on the electrical activity of the heart, they are also suitable for the treatment of cardiac arrhythmias. Some cardioinhibitors (especially certain β-blockers) are used in the treatment of heart failure.

Hypertension
It is caused by an increase in cardiac output or an increase in systemic vascular resistance. Cardioinhibitors reduce heart rate and stroke volume, which leads to a decrease in cardiac output and thus a decrease in blood pressure.

Angina pectoris a infarkt myokardu
Cardioinhibitors (by reducing heart rate, contractility and arterial pressure) reduce the work of the heart and its demands for oxygen. They can thus relieve the patient of anginal pains, which arise most often due to a lack of oxygen during greater exertion. The significance in the treatment of myocardial infarction lies not only in increasing the ratio of oxygen supply and demand, but also in the ability to inhibit post-infarction heart tissue remodeling.

Cardiac arrythmia
Cardioinhibitors alter pacemaker activity and conduction through the heart and are therefore useful in treating arrhythmias caused by both abnormal automation and conduction.

Heart failure
Although it may seem paradoxical that cardioinhibitors would be used in heart failure where the myocardium is functionally suppressed, clinical studies have shown that certain cardioinhibitors have been shown to improve heart function in certain types of heart failure. This effect may be derived from their blocking of the excessive sympathetic effects on the heart that damage the failing heart.

Třídy léků a obecné mechanismy jejich účinku
Klinicky využívané kardioinhibitory můžeme rozdělit do tří skupin: beta-blokátory, blokátory kalciových kanálů a centrálně působící sympatolytika.

Použitá literatura
Category:Patofyziology Category:Internal Medicine