Cardiovascular: Cycle Phases, Action Potential, ECG

Ventricular Diastole

Semilunar valves close

Rapid ventricular filling

Atrial Systole

Atrial kick

End-Diastolic Volume

Isovolumetric Contraction

Ventricles begin to contract

AV valves close

Ventricular Ejection

Semilunar valves open

Blood is ejected from ventricles (End-Systolic Volume)

Isovolumetric Relaxation

Ventricles relax, all valves are closed

Pacemaker Action Potential: Phase 4 (Spontaneous Depolarization)

Funny current (mixed Na/K+)

Influx of Ca2+ through T-type channels

Pacemaker Action Potential: Phase 0 (Depolarization)

Large Ca2+ influx from L-type channels 

Pacemaker Action Potential: Phase 3 (Depolarization)

Inactivation of Ca2+ channels

Efflux of K+

Non-Pacemaker Action Potential: Phase 4 (Resting Membrane Potential)

Resting membrane potential

Non-Pacemaker Action Potential: Phase 0 (Depolarization)

Influx of Na+ through voltage-gated channels

Non-Pacemaker Action Potential: Phase 1 (Repolarization)

K+ efflux

Na+ channel inactivation

Non-Pacemaker Action Potential: Phase 2 (Plateau Phase)

Ca2+ influx through L-type channels

K+ efflux 

Non-Pacemaker Action Potential: Phase 3 (Final Depolarization)

Inactivation of L-type Ca2+ channels

K+ efflux

P wave

Atrial depolarization

PR interval

Beginning of atrial depolarization (P wave) to end of ventricular depolarization (QRS complex)

QRS complex

Ventricular depolarization

ST segment

Plateau phase

T wave

Ventricular repolarization

QT interval

Beginning of ventricular depolarization (Q wave) to end of ventricular repolarization (T wave) 

U wave

Seen after T

Hypokalemia or Bradycardia