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Cardiovascular System key concepts

10 revision pages for Cardiovascular System, each with the key facts, a memory aid where one helps, and the exam traps.

  1. Atrioventricular node delay

    The atrioventricular (AV) node, located at the junction between the atria and the ventricles, introduces a brief delay to the electrical signal, so the atria can finish contracting first.

  2. Distributive shock and low total peripheral resistance

    Distributive shock is inadequate blood flow caused by widespread vasodilation (widening of the blood vessels), which lowers total peripheral resistance, the overall resistance to flow.

  3. Early afterdepolarisations and long QT syndrome

    An early afterdepolarisation is an extra upswing in a heart cell's voltage during prolonged repolarisation (return to resting voltage), as in long QT syndrome (ventricles slow to repolarise).

  4. First-degree AV block

    First-degree atrioventricular (AV) block is a delay rather than a true block: the AV node holds each electrical impulse back for longer than usual, yet every impulse still gets through.

  5. Frank-Starling law, venous return and stroke volume

    The Frank-Starling law says that, within the physiological (normal) range, a ventricle that fills more is stretched more and contracts harder, so it pumps out a larger stroke volume.

  6. Hypokalaemia: delayed repolarisation and arrhythmia risk

    Hypokalaemia (low blood potassium) delays repolarisation, with a risk of arrhythmia (an abnormal heart rhythm).

  7. Mean arterial pressure and organ perfusion

    Mean arterial pressure is the average pressure in the arteries over one whole cardiac cycle, and it is the pressure that drives blood to the organs.

  8. Re-entry loops and unidirectional block

    Re-entry is an impulse running round a circuit of two connected pathways instead of dying out, so it keeps re-triggering the heart and sustains a fast abnormal rhythm.

  9. Sinus rhythm on an ECG

    Sinus rhythm is the rhythm started by the sinoatrial node, the heart's natural pacemaker, seen as a P wave (atrial activation) before each QRS complex (ventricular activation).

  10. Third-degree (complete) AV block and escape rhythms

    In third-degree (complete) atrioventricular (AV) block, no impulses pass from the atria to the ventricles, so a slow backup pacemaker, called an escape rhythm, drives the ventricles.

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