lec 4-The Cardiac Cycle and ECG Review

Vocabulary terms and clinical definitions related to the cardiac cycle, cardiac pacemakers, ECG components, and Pressure-Volume loop analysis.

Sino-atrial (SA) node

The fastest pacemaker in the hierarchy of the mammalian heart.

AV pause

A slow conduction through the atrio-ventricular node that allows ventricular filling to occur before the electrical impulse is passed to the ventricle and prevents transmission of high rates from the atria.

P wave

The component of the ECG that represents atrial depolarisation.

Q wave

The component of the ECG that represents depolarisation of the septum towards the atria.

R wave

The component of the ECG that represents depolarisation of the ventricles towards the apex.

S wave

The component of the ECG that represents depolarisation of the ventricles towards the atria.

T wave

The component of the ECG that represents repolarisation of the ventricles towards the endocardium.

P-Q interval

The ECG interval representing atrial conduction and A-V nodal delay; pathology associated with this interval includes AV block.

S-T segment

The ECG segment where all of the ventricle is depolarised; abnormalities such as myocardial infarction can be identified here.

QRS duration

The ECG measurement representing ventricular conduction velocity; prolonged duration may indicate Bundle branch block.

Q-T interval

The ECG interval representing ventricular action potential duration; pathology associated with this is Long QT syndrome.

Atrial kick

The event where the left atrium contracts to provide the final flow of blood into the left ventricle during diastole.

Isovolumic contraction

The phase where the left ventricle contracts and pressure rises, but volume remains constant because the valves are closed.

Dicrotic notch

A pressure fluctuation seen when the left ventricular pressure falls below aortic pressure and the aortic valve shuts.

Isovolumic relaxation

The phase where the left ventricular pressure falls below the aortic pressure (closing the aortic valve) but remains above atrial pressure, occurring before the mitral valve opens.

Stroke Volume (SV)

Calculated as $EDV - ESV$, representing the volume of blood ejected per beat in $ml$. clusters

Ejection Fraction (EF)

A measure of systolic function calculated as $\frac{(EDV - ESV)}{EDV} \times 100$, expressed as a percentage.

Stroke Work

The area within the Pressure-Volume loop, measured in $mmHg \times cm^3$ or $cJ$.

Augustus Waller

The individual credited with the measurement of the first ECG in 1887 using a dog named Jimmie.

Willem Einthoven

The 1924 Nobel Prize winner in Physiology and Medicine who developed a better ECG recording device, Einthoven's Triangle, and the PQRST nomenclature.