Cardiomyocytes are the muscle cells of the heart. Their contractions are essential for the ability of the heart to pump blood. Connecting pores between these cells, called connexions, allow all the cardiomyocytes to fire almost simultaneously.
The SA (sinoatrial) node is responsible for setting the pace of the heart. When it fires, it sends a signal to the rest of the heart to fire and pump blood.
The heart is the organ that pumps blood throughout the body. The flow of blood occurs in the following direction:
body -> right atrium -> right ventricle -> lungs -> left atrium -> left ventricle -> body
A heart attack, or myocardial infarction, is when a blood clot gets lodged in a cardiac artery, cutting off blood supply to that region of the heart. This leads to cardiomyocyte death and can also be fatal to the patient. A sign of a heart attack on ECG is elevated ST segment, which is why it is also called a STEMI (ST Elevated Myocardial Infarction)
Atrial flutter is caused by the electrical signal circulating around the atrium, continuously causing the heart to fire during each cycle. This leads to a fast heart rate (tachycardia) and a distinctive "saw tooth" pattern on ECG.
Systolic heart failure
Systolic heart failure occurs when the heart because enlarged and weak ("big floppy heart"). This leads to the heart filling with more blood, but ejecting less blood. This is why it is also called HFrEF (Heart Failure with reduced Ejection Fraction) which is defined by an ejection fraction of < 40%. This leads to fluid buildup in the body which caused swelling/edema.
Diastolic Heart Failure
Diastolic heart failure occurs when the walls of the heart become enlarged. This leads to the heart filling with less blood, but still maintaining the ability to pump blood. This is why it is also called HFpEF (Heart Failure with preserved Ejection Fraction) which is defined by an ejection fraction of > 40%. Because the heart fills with less blood, and thus ejects less blood, this leads to fluid buildup in the body which caused swelling/edema.
Heart Attack -> Cardiomyocyte
During a heart attack, a blood clot gets lodged in one of the cardiac arteries. This cuts off blood supply to this section of the heart and can lead to death of cardiomyocytes. The clot can be dissolved with the administration of tPA (tissue plasminogen activator), which activates the body's clot-dissolving pathway.
Atrial Flutter -> SA Node
A fast heart rate (tachycardia) occurs in atrial flutter do to the electrical signaling spiraling through the atria and repeatedly activating the heart. This can be slowed down by blocking calcium channels with the cardiac-specific calcium channel blocker, diltiazem.
Systolic Heart Failure -> Heart
Systolic heart failure occurs when the heart because enlarged and weak ("big floppy heart"). Patients are usually fluid-overloaded and have edema, which can be treated with the loop diuretic furosemide. This drug blocks the NKCC2 channel in the kidney which prevents reabsorption of sodium and water.
Diastolic Heart Failure -> Heart
Diastolic heart failure is extremely difficult to treat as drugs won't remove the increased mass in the left ventricle/septum. Spironolactone is a mineralocorticoid receptor antagonist which acts as a weak diuretic, helping with the fluid symptoms of this form of heart failure (edema/swelling).