Cardiovascular Concepts - Physiology & Pathophysiology
Part 1: Physiology Overview
What Is the Cardiac Cycle?
The cardiac cycle is the complete sequence of mechanical and electrical events that the heart undergoes during one heartbeat. This process ensures the continuous circulation of blood throughout the body, delivering oxygen and nutrients to tissues and removing waste products.
Main Phases of the Cardiac Cycle
Diastole:
Relaxation phase of the heart chambers.
Ventricles are relaxed and fill passively with blood from the atria.
Includes both passive filling and active filling during atrial systole.
Systole:
Contraction phase of the heart.
Ventricles contract, increasing pressure, and force blood out through the aortic and pulmonary valves.
Key Concepts
Atrial Systole: Active contraction of the atria that "tops off" ventricular filling.
Isovolumetric Contraction: Ventricles contract with no volume change; all valves are temporarily closed.
Ventricular Ejection: When ventricular pressure exceeds arterial pressure, the aortic and pulmonary valves open, ejecting blood.
Isovolumetric Relaxation: Ventricles relax with all valves closed, resulting in no volume change.
Rapid and Reduced Filling Phases: Initial rapid passive filling followed by a slower reduced filling period until the next atrial contraction.
Important Pressures and Volumes
End-Diastolic Volume (EDV): Maximum volume of blood in ventricles at the end of diastole; key determinant of preload.
End-Systolic Volume (ESV): Blood volume remaining after ventricular contraction.
Stroke Volume (SV): The amount of blood pumped per heartbeat (SV = EDV - ESV).
Ejection Fraction (EF): Percentage of blood ejected from the ventricle with each contraction (EF = SV/EDV); crucial for assessing cardiac function.
Cardiac Output (CO): Total volume of blood ejected per minute (CO = SV × Heart Rate).
Part 2: Key Pathophysiology Concepts
Disorders Affecting the Cardiac Cycle
Heart Failure:
May be systolic (reduced EF) or diastolic (preserved EF but impaired filling).
Characterized by decreased cardiac output, leading to symptoms like fatigue, dyspnea, and edema.
Valve Diseases:
Stenosis: Narrowed valves obstruct blood flow (e.g., aortic stenosis causes left ventricular hypertrophy).
Regurgitation (Insufficiency): Leaky valves cause backward blood flow (e.g., mitral regurgitation causes left atrial and ventricular volume overload).
Arrhythmias:
Irregular heart rhythms that disrupt the timing and coordination of cardiac cycles (e.g., atrial fibrillation).
Pericardial Effusion/Cardiac Tamponade:
Fluid accumulation in the pericardial sac impedes ventricular filling, reducing stroke volume and cardiac output.
Part 3: Clinical Correlations
High-Yield Clinical Insights
S1 Heart Sound: Closure of the mitral and tricuspid valves at the start of systole.
S2 Heart Sound: Closure of the aortic and pulmonary valves, marking the end of systole.
Jugular Venous Pressure (JVP): An indirect marker of right atrial pressure; elevated JVP suggests right-sided heart failure or pericardial tamponade.
Pulse Pressure: Difference between systolic and diastolic blood pressures; widened in conditions like aortic regurgitation and narrowed in severe heart failure.
Murmurs: Sounds caused by turbulent blood flow; their timing, location, and quality provide vital diagnostic clues.
Gallops (S3 and S4 Sounds): Extra heart sounds indicating abnormal ventricular filling, often seen in heart failure.
Preload and Afterload:
Preload: Degree of ventricular stretch at the end of diastole (influenced by venous return).
Afterload: Resistance the ventricles must overcome to eject blood (influenced by arterial pressure).
Part 4: Summary Mind Map (to be Created Visually)
Key Points for Mind Map
Cardiac Cycle
Diastole
Ventricular Filling (Passive and Active)
Atrial Systole
Systole
Isovolumetric Contraction
Ventricular Ejection
Important Volumes and Pressures
End-Diastolic Volume (EDV)
End-Systolic Volume (ESV)
Stroke Volume (SV)
Ejection Fraction (EF)
Cardiac Output (CO)
Pathologies
Heart Failure (Systolic and Diastolic)
Valve Disorders (Stenosis and Regurgitation)
Arrhythmias
Pericardial Effusion/Cardiac Tamponade
Clinical Markers
Heart Sounds (S1, S2, Murmurs, Gallops)
Jugular Venous Pressure (JVP)
Pulse Pressure
Preload and Afterload
