Vectorcardiography

A method of recording the direction and magnitude of the electrical forces of the heart.

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A normal vectorcardiogram showing the electrical activity of the heart.

Vectorcardiography (VCG) is a method of recording the magnitude and direction of the electrical forces generated by the heart using a continuous series of vectors that form curving lines around a central point.

Vectorcardiography was developed by Ernest Frank in the mid-1950s. Since the human body is a three-dimensional structure, the primary objective is to construct three orthogonal leads encompassing all the electrical information. These three leads are represented by the right-left axis (X), head-to-feet axis (Y), and front-back (anteroposterior) axis (Z).

Frank’s Lead System

To calculate Frank’s leads X, Y, and Z using the standard electrocardiogram (ECG) leads system, the following expressions are used:

• X = -(-0.172 V1 - 0.074 V2 + 0.122 V3 + 0.231 V4 + 0.239 V5 + 0.194 V6 + 0.156 DI - 0.010 DII)
• Y = (0.057 V1 - 0.019 V2 - 0.106 V3 - 0.022 V4 + 0.041 V5 + 0.048 V6 - 0.227 DI + 0.887 DII)
• Z = -(-0.229 V1 - 0.310 V2 - 0.246 V3 - 0.063 V4 + 0.055 V5 + 0.108 V6 + 0.022 DI + 0.102 DII)

Various methods have been proposed to evaluate a vectorcardiogram. Grygoriy Risman introduced an advanced approach known as Spatial Vectorcardiometry (SVCM), which refines the analysis of vectorcardiograms.

Spatial QRS-T Angle

The spatial QRS-T angle (SA) is derived from a vectorcardiogram, a three-dimensional representation of the 12-lead ECG created through computerized matrix operations. The SA represents the deviation between two vectors:

• The spatial QRS-axis, which reflects the electrical forces generated by ventricular depolarization.
• The spatial T-axis, representing the electrical forces generated by ventricular repolarization.

In healthy individuals, the SA is relatively sharp due to the near-opposite orientation of depolarization and repolarization. The normal SA varies by gender and age, averaging 66° in young females and 80° in young males, with similar values in older populations. The SA is categorized as:

• Normal: Below 105°
• Borderline abnormal: 105–135°
• Abnormal: Greater than 135°

A broad SA often reflects pathological changes in the heart and is associated with discordant ECG patterns, structural myocardial alterations, and impaired ion channel functioning. This can be observed in conditions such as hypertension, left ventricular hypertrophy (LVH), and myocardial infarction.

Clinical Significance

The SA is a significant marker of cardiac morbidity and mortality, often outperforming conventional ECG markers like ST depression, T wave inversion, and QT prolongation. Studies indicate that in hypertensive patients, the SA is significantly larger in those with elevated blood pressure. Additionally, it enhances the accuracy of diagnosing LVH, increasing diagnostic precision from 57% to 79% when included in ECG assessments.

Despite its predictive value, the SA is not routinely measured in clinical ECG evaluations. However, computerized vectorcardiography software is widely available and offers an unbiased, efficient method for assessing cardiac repolarization abnormalities. As further research supports its clinical utility, the SA may become a standard parameter in predicting cardiac risk.

Vectorcardiography in Myocardial Infarction

A simplified evaluation of vectorcardiograms can identify patients with a diaphragmatic infarction that may not be apparent on a standard ECG.

See Also

• Electrocardiography

External links

• Vectorcardiography: A Review - National Center for Biotechnology Information