1.05 S4 Heart Sound.

Cardiovacular system reveiw for the USMLE Step 1 exam.

• The S4 heart sound, also called an S4 gallop or atrial gallop, is an extra sound that is heard in late diastole, just before S1
• It is caused by a stiff ventricle
• S4 is mostly pathogenic and almost never normal, unlike S3
• It is associated with diseases that cause the ventricles to stiffen like hypertrophic cardiomyopathy and diastolic heart failure
• In the case of an athlete with physiological hypertrophy of the ventricles, growth of the ventricles can be a normal response to cardiovascular conditioning and lead to them developing an S4 heart sound
• S4 can be heard best when at the apex of the heart when the patient is placed in the left lateral decubitus position

1.06 Systolic Heart Murmurs

Cardiovacular system reveiw for the USMLE Step 1 exam.

• Heart murmurs occur when blood flow is turbulent in the heart, producing a whooshing or swishing sound
• 4 different sounding systolic murmurs discussed: Ventricular septal defect, patent ductus arteriosus, aortic stenosis, and mitral/tricuspid regurgitation
• Patent ductus arteriosus is a machine-like murmur that is constant (heard during systole and diastole)
  • Patent ductus arteriosus: "People who constantly PDA deserve to be thrown in a machine"
• Ventricular septal defect produces a harsh holosystolic murmur (only heard during systole)
  • Ventricular septal defect: "Holy cow, its harsh being born with a VSD"
• Aortic stenosis produces a crescendo-decrescendo systolic ejection murmur (heard during systole)
  • Aortic stenosis: "ASS CD (insert your least favorite band here, I'll say Nickelback)"
• Mitral and tricuspid regurgitation produces a holosystolic high pitched "blowing" murmur (heard during systole)
  • Mitral and tricuspid regurgitation: "It sucks to climb Mt regurgitation. Climbing Mt regurgitation blows."
• The location and cause of the murmur can indicate whether it is mitral or tricuspid regurgitation

1.04 S3 Heart Sound

Cardiovacular system reveiw for the USMLE Step 1 exam.

• The S3 heart sound, also called an S3 gallop or ventricular gallop, is an extra sound that occurs in early diastole during the ventricular filling phase
• It can be normal for some people and a sign of disease in others
• It is caused by a dilated or floppy ventricle and is associated with dilated or floppy ventricles.
• S3 can also be caused by increases in volume load on the ventricles
• It is commonly found in children and young adults, athletes, and people who are pregnant
• It is heard best when at the apex of the heart when the patient is placed in the left lateral decubitus position

1.03 Hemodynamics.

Cardiovacular system reveiw for the USMLE Step 1 exam.

• Hemodynamics studies blood flow through the body
• Volumetric flow rate (Q) describes the volume of material moving through space per unit time, in terms of psychiatry it is the amount of blood moving through a vessel per unit time
• Volumetric flow rate is proportional to radius to the 4th power, so when radius increases, volumetric flow rate increases
• Resistance is a measure of a blood vessel's opposition to blood flow
• Resistance is inversely proportional to radius to the 4th power, so when vessel radius is increased, resistance decreases
• For vessels in series, you can simply add the resistances of each up to get the total resistance
• For vessels in parallel, the total resistance is equal to the sum of the inverses of the resistances each vessel

1.01. Cardiac Output Equations

Cardiovascular system reveiew for the USMLE Step 1 exam.

• Equations that describe cardiac output and cardiac performance
• Cardiac output (CO) is the amount of blood volume pumped by the heart per min, typically given in L/min
• CO is equal to stroke volume (SV) times heart rate (HR)
• SV is influenced by preload, afterload, and contractility
• Pulse pressure is the difference between systolic and diastolic blood pressure (PP = SBP-DBP)
• High pulse pressure can be caused by stiffening of the major arteries
• Mean arterial pressure (MAP) is the average arterial pressure during one cardiac cycle
• MAP is equal to CO * TPR and MAP is equal to ⅔ DBP + ⅓ SBP
• Diastolic blood pressure contributes more to MAP than systolic pressure

1.01. S1, S2, and the Cardiac Cycle.

Cardiovascular system reveiew for the USMLE Step 1 exam.

• Two main heart sounds are s1 and s2, also known as "lub" and "dub"
• S1 corresponds to closure of the mitral and tricuspid valves
• S2 corresponds to closure of the aortic and pulmonic valves
• The pause between s2 and s1 is longer than the pause between s1 and s2 in a normal cardiac cycle
• Elevated heart rate can make it harder to distinguish the two sounds
• The noise produced by the valves slamming shut, like a door being slammed shut
• The Atria contracts before the ventricles, and the mitral and tricuspid valves separate the atria from the ventricles, so they shut first which produces S1
• The ventricles contract and push blood through the aortic and pulmonic valves, and These shut after this event producing S2.