Cardiac Cycle

Echocardiography, Stroke volume, Stroke work, etc.

Echocardiography: Fractional Shortening of the Left Ventricle M-mode of Parasternal Long Axis FS = Fractional shortening = (LVIDd - LVIDs)/LVIDd LVIDd = LV internal dimension in diastole LVIDs = LV internal dimension in systole TTE: non invasive. Look at fractional shortening. Different than ejection fraction Aortic outflow determined using doppler echo: apical-long view--left ventricular outflow tract Method of determining stroke volume using echocardiography: •Determine the velocity time interval (VTI), which is distance blood travels during a heart beat = column of blood ejected. •Determine the cross-sectional area of the aortic outflow tract (CSA = r2) •Calculate SV = CSA (cm2) x VTI (cm) •SV = (3.14 x 1.02 cm2) x 17.0 cm = 53.4 ml Down peak: blood leaving thru aorta. Integrate area underneath to get velocity time interval. Ejection fraction (EF) is the fraction of end-diastolic ventricular volume that is ejected into the aorta during a single beat. EF = (EDV-ESV)/EDV = SV/EDV--More accurate? Will do this calculation on the exam! No echocardiography Commonly used clinical parameter to determine cardiac performance Normal LV ejection fraction is 55 to 70 percent.--Animals have higher value Stroke work (SW) is the external work performed by the ventricle on a per beat basis. SW = SV x Mean Aortic Pressure (MAP) Cardiac work (CW) is the product of stroke work and heart rate. CW = SV x MAP x HR

Rules of interpreting events of cardiac cycle

Electrical (i.e. ECG) activity precedes associated mechanical (i.e. pressure, volume, flow) action. When upstream pressure is higher than downstream pressure, flow across valves is proportional to the difference between upstream and downstream pressures. When downstream pressure is greater than upstream pressure, flow is zero (no reflux allowed by normal valves). Electrical & Mechanical Events of Ventricles 3 stages of ventricular systole: Isovolumic contraction (Phase 2) Rapid ejection (Phase 3) Slow ejection (Phase 4) 4 stages of ventricular diastole Isovolumetric relaxation (Phase 5) Rapid ventricular filling (Phase 6) Slow ventricular filling (Phase 7) Filling due to atrial contraction (Phase 1) Ventricular pressure must be greater to move blood to aorta V pressure must be lower than A during filling. P: atrial depolarize. QRS: ventricular contraction. T: ventricular relaxation. Atrial relaxation buried in QRS S1=mitral/tricuspid S2=aortic/pulmonary (A before P) S3=rushing blood--quiet S4=atrial sound Last part of diastole is atrial contraction. A wave then x descent (atria relax).

Phases of Cardiac Cycle

Lecture Outline Phases of the Cardiac Cycle Cardiac Definitions Wiggers diagram Atrial and Ventricular Waves Heart Sounds Echocardiography Cardiac cycle (i.e. single heart beat) can be divided into 2 main phases: Diastole-the cardiac muscle is relaxing. Systole-the cardiac muscle is contracting Cardiac Output is the flow out of the heart per minute • Product of heart rate (HR, contractions per minute) and stroke volume (SV, volume ejected by the ventricle per contraction). CO = HR x SV End-diastolic volume (EDV) is the volume of the cardiac chamber at the end of diastole. End-systolic volume (ESV) is the volume of the cardiac chamber at the end of systole. Ventricular stroke volume (SV) is calculated as the difference between end-diastolic ventricular volume and end-systolic ventricular volume. EDV - ESV = SV

Atrial Pressure Waves

Positive Waves • a wave (atrial contraction) • c wave (ventricular contraction) • v wave (venous return filling the large veins) If ventricle/atria are off sync and atria contract when AV valve is closed--large a wave--called canon a wave Negative Waves • x descent (follows "a-wave" and is caused by right atrial relaxation) • x' descent (follows "c-wave" and is caused by widening of atrial base due to ventricular contraction • y descent (follows "v-wave" and is due to blood flowing into the ventricle

Phase 4: Slow ejection of ventricle

• Approximately 150-200 msec after the QRS, ventricular repolarization occurs (T-wave). • This causes ventricular active tension to decrease and the rate of ejection (ventricular emptying) to fall. • Ventricular pressure falls slightly below outflow tract pressure; however, outward flow still occurs due to kinetic (or inertial) energy of the blood. • Atrial pressures gradually rise due to venous return.

Phase 7: Slow filling of ventricle

• As the ventricles continue to fill with blood and expand, they become less compliant and the intraventricular pressures rise. This reduces the pressure gradient across the AV valves so that the rate of filling falls. • Aortic pressure (and pulmonary arterial pressure) continues to fall during this period.

Heart Sounds

• First heart sound or "lub" Atrioventricular valves and surrounding fluid vibrations as valves close at beginning of ventricular systole (M1 normally before T1; reverse order with RBBB when RV contracts sooner)--right bundle branch block • Second heart sound or "dub" Results from closure of aortic and pulmonary semilunar valves at beginning of ventricular diastole (A2 is normally before P2) • Third heart sound (occasional) Caused by turbulent blood flow into ventricles and detected near end of first one-third of diastole (SLOCH-ING-in or LUB-DUB-da) • Fourth heart sound (occasional) Occurs during atrial contraction and immediately before S1. Occurs in less compliant ventricles, e.g. diastolic dysfunction. (a-STIFF-WALL or a-LUB-DUB). Movement of mitral valve leaflets during the cardiac cycle: echo with M-mode of parasternal long axis. E=passive filling of LV. A=atrial contraction. C=closing of mitral valve

Phase 5: Isovolumic relaxation of ventricle

• In Phase 5, the ventricles continue to relax and intraventricular pressures fall below aortic and pulmonary pressures. • The pressure reversal causes the aortic and pulmonic valves to abruptly close (aortic precedes pulmonic) causing the Second Heart Sound (S2). • Valve closure is associated with a small backflow of blood into the ventricles and a characteristic notch (incisura or dicrotic notch) in the aortic and pulmonary artery pressure tracings. The decline in aortic and pulmonary artery pressures is not as abrupt as in the ventricles because of potential energy stored in outflow vessel walls. • Ventricular pressures decrease; however, volumes remain constant because all valves are closed. • The volume of blood that remains in a ventricle is called the end-systolic volume (ESV) and is ~50 ml in the left ventricle. • Atrial pressures continue to rise due to venous return.--V wave--climax at end of phase 5

Phase 6: Rapid filling of ventricle

• In Phase 6, the ventricular pressures fall below atrial pressures, after which the AV valves open and ventricular filling begins. • The ventricles continue to relax despite the inflow, which causes intraventricular pressure to continue to fall by a few additional mmHg. • The opening of the AV valves causes a rapid fall in atrial pressures and a fall in the jugular pulse. The peak of the jugular pulse just before the valve opens is the v-wave. This is followed by the y-descent of the jugular pulse. • If the AV valves are healthy, no prominent sounds will be heard during filling. When a Third Heart Sound (S3) is audible, it may represent tensing of chordae tendineae and AV ring during ventricular relaxation and filling. This heart sound is normal in children; but is often pathological in adults and caused by ventricular dilation.

Phase 2: Isovolumetric contraction of ventricle

• Phase 2 is initiated by the QRS complex of the ECG which represents ventricular depolarization followed by contraction. • Early in this phase, the rate of ventricular pressure development (dP/dt) becomes maximal. • The abrupt rise in pressure causes the A-V valves to close, resulting in the First Heart Sound (S1). This sound is normally split (~0.04 sec) because mitral valve closure precedes tricuspid closure. • Isovolumic contraction, ventricular pressure rises rapidly without a change in ventricular volume (no ejection occurs). However, individual fibers contract isotonically (shortening contraction), while others contract isometrically (no change in length). The ventricular chamber geometry becomes more spheroid in shape (circumference increases and atrial base-to-apex length decreases). • Atrial pressures increases due to continued venous return and bulging of AV valves back into the atrial chambers. The "c-wave" (jugular pulse) is due to increased right atrial pressure that results from bulging of tricuspid valve leaflets back into right atrium. Just after the peak of the c-wave is the x'- descent.

Phase 1: Atrial contraction

• Phase I is initiated by the p-wave of the ECG, followed by atrial contraction. • Atrial pressure rises (a-wave, jugular pulse) causing a rapid flow of blood into the ventricles. • Just following the peak of the a-wave is the x-descent. • Atrial contraction accounts for ~10% of left ventricular filling. • After contraction, the atrial pressure begins to fall causing a pressure gradient reversal across the AV valves. This causes the valves to float upward (pre-position) before closure. At this time, the ventricular volume is maximal, which is termed the end-diastolic volume (EDV). • The left ventricular EDV (LVEDV), which is typically about 120 ml, comprises the ventricular preload and is associated with end-diastolic pressures of 8-12 mmHg and 3-6 mmHg in the left and right ventricles, respectively. • A heart sound is sometimes noted during atrial contraction (Fourth Heart Sound, S4). This sound is caused by vibration of the ventricular wall during atrial contraction. It is more noted when the ventricle compliance is reduced ("stiff" ventricle) as occurs in ventricular hypertrophy.

Phase 3: Rapid ejection of ventricle

• When the intraventricular pressures exceed the pressures within the aorta and pulmonary artery, the aortic and pulmonic valves open and blood is ejected out of the ventricles. How fast pressure rises indicates health of the heart • During this phase, ventricular pressure normally exceeds outflow tract pressure by only a few mmHg. • Although blood flow across the valves is very high, the relatively large valve opening (low resistance) requires only few mmHg of a pressure gradient to propel flow across the valve. • Maximal outflow velocity is reached early in the ejection phase, and maximal (systolic) aortic and pulmonary artery pressures are achieved. • No heart sounds are ordinarily noted during ejection. The opening of healthy valves is silent. The presence of sounds during ejection (i.e., ejection murmurs) indicate valve disease or intracardiac shunts. • Atrial pressure initially decreases as the atrial base is pulled downward, expanding the atrial chamber. Blood continues to flow into the atria from their respective venous inflow tracts.