Hexaxial reference system

The hexaxial reference system is a diagram that is used to determine the heart's electrical axis in the frontal plane.

Cabrera circle (captions in German)

Diagram showing how the polarity of the QRS complex in leads I, II, and III can be used to estimate the heart's electrical axis in the frontal plane.

The hexaxial reference system, also known as the Cabrera system, is a convention to present the extremity leads of the 12 lead electrocardiogram, that provides an illustrative logical sequence that helps interpretation of the ECG, especially to determine the heart's electrical axis in the frontal plane. The most practical way of using this is by arranging extremity leads according to the Cabrera system, reversing polarity of lead aVR and presenting ECG complexes in the order (aVL, I, -aVR, II, aVF, III). Then determine the direction the maximal ECG vector is "pointing", i.e. in which lead there are most positive amplitude - this direction is the electrical axis - see diagram. Example: If lead I has the highest amplitude (higher than aVL or -aVR), the axis is approximately 0°. Conversely, if lead III has the most negative amplitude it means the vector is pointing away from this lead, i.e. towards -60°.

An alternative use is to locate the most isoelectric (or equiphasic) lead (I, II, III, aVR, aVL, or aVF) on a diagnostic quality ECG with proper lead placement. Then find the corresponding spoke on the hexaxial reference system. The perpendicular spoke will point to the heart's electrical axis. To determine which numerical value should be used, observe the polarity of the perpendicular lead on the ECG.

For example, if the most isoelectric (or equiphasic) lead is aVL, the perpendicular lead on the hexaxial reference system is lead II. If lead II is positively deflected on the ECG, the heart's electrical axis in the frontal plane will be approximately +60°.

Normal axis: -30° to +90°
Left axis deviation: -30° to -90°
Right axis deviation: +90° to +180°
Extreme axis deviation: -90° to -180°

Volumes	Stroke volume = End-diastolic volume – End-systolic volume Cardiac output = Heart rate × Stroke volume Afterload Preload Frank–Starling law of the heart Cardiac function curve Venous return curve Aortic valve area calculation Ejection fraction Cardiac index

Dimensions	Fractional shortening = (End-diastolic dimension – End-systolic dimension) / End-diastolic dimension

Interaction diagrams	Cardiac cycle Wiggers diagram Pressure volume diagram

Tropism	Chronotropic (Heart rate) Dromotropic (Conduction velocity) Inotropic (Contractility) Bathmotropic (Excitability) Lusitropic (Relaxation)

Conduction system/ Cardiac electrophysiology	Cardiac action potential Atrial action potential Ventricular action potential Effective refractory period Pacemaker potential EKG P wave PR interval QRS complex QT interval ST segment T wave U wave Hexaxial reference system

Chamber pressure	Central venous pressure/right atrial pressure → Right ventricular pressure → Pulmonary artery pressure → Pulmonary wedge pressure/left atrial pressure → Left ventricular pressure → Aortic pressure

Other	Ventricular remodeling

Vascular system/
Hemodynamics

Blood flow	Compliance Vascular resistance Total peripheral resistance Pulse Perfusion

Blood pressure	Pulse pressure Systolic Diastolic Mean arterial pressure Jugular venous pressure Portal venous pressure

Regulation of BP	Baroreflex Kinin–kallikrein system Renin–angiotensin system Vasoconstrictors/Vasodilators Autoregulation Myogenic mechanism Tubuloglomerular feedback Cerebral autoregulation Paraganglia Aortic body Carotid body Glomus cell

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Hexaxial reference system

Hexaxial reference system

See also

Categories

Cardiovascular physiology

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Human heart

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Stroke volume

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Suggestions

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Right axis deviation

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Circulatory system

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Left axis deviation

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Electrophysiology

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