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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_2818_Библиотеки_им_академика_М_И_Перельмана
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Chapter 6
https://t.me/med1917
Rotation ofHeart
Learning Objectives
After studying this chapter, the reader will learn about:
• Vertical position of heart
• Horizontal position of heart
• Intermediate position of heart
• Clockwise rotation of heart
• Anticlockwise rotation of heart
Rotation of heart refers to rotation of the electrical forces. There is no anatomical
rotation. Theoretically, the heart rotates along two axes: the anteroposterior axis and
the longitudinal axis. Rotation around the anteroposterior axis reects the rotation
along the frontal plane, whereas rotation around the longitudinal axis reects rotation in the horizontal plane.
6.1 Rotation Around theAnteroposterior Axis
The rotation of electrical forces of heart across an anteroposterior axis, that runs
through the interventricular septum from anterior to the posterior surface of the
heart, leads to three different positions of heart:
• Vertical position
• Horizontal position
• Intermediate position
Ltd. 2024
T. K. Koley, Rapid Review of ECG,
https://doi.org/10.1007/978-981-99-9116-7_6
77© The Author(s), under exclusive license to Springer Nature Singapore Pte
78
https://t.me/med1917
6 Rotation ofHeart
6.1.1 Vertical Position
The depolarization wavefront of ventricles is directed mainly downward in vertical
position of the heart. Left ventricular complex (qR type of complex) is recorded in
lead aVF, as the positive pole of lead aVF is oriented exactly vertically downward.
Hence, PQRS complex of lead aVF resembles that of lead V6 (Figs.6.1 and 6.2).
The mean QRS axis is directed inferiorly (+75° or more). This is commonly seen in
tall and thin persons.
Fig. 6.1 Diagram of
vertical heart. RV, right
ventricle; LV, left ventricle
Fig. 6.2 ECG of vertical heart position. QRS complex of aVF resembles that of V6
V1
V2
V3
V4
V5
V6
6.1 Rotation Around theAnteroposterior Axis
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79
6.1.2 Horizontal Position
The depolarization wavefront of ventricles is directed mainly horizontally and to the
left in horizontal position of heart. Left ventricular complex (qR type of complex) is
recorded in leads I and aVL, as the positive poles of these leads are directed horizontally and to the left. The QRS complexes in leads I and aVL resemble that of
lead V6 (Figs.6.3 and 6.4). The mean QRS axis is between 0° and −30°. Horizontal
position of heart is seen in obese persons with broad chests.
Fig. 6.3 Diagram of
horizontal heart
I
10 mm = 1 mV. 25 mm/s.
Fig. 6.4 ECG showing horizontal position of heart. PQRS complex of lead aVL resembles that
of lead V6
II
III
aVR
aVL
aVF
80
V1
V2
V3
V4
V5
V6
10 mm = 1 mV
https://t.me/med1917
6 Rotation ofHeart
6.1.3 Intermediate Position
Intermediate position of heart is midway between the vertical and horizontal position. In this condition, QRS complexes of both lead aVL and lead aVF resemble that
of lead V6 (Fig.6.5). The mean QRS axis is approximately +30°.
I
Fig. 6.5 ECG showing intermediate position of heart. PQRS complex of both lead aVL and lead
aVF resembles that of lead V6
II
. 25 mm/s.
III
aVR
aVL
aVF
6.2 Rotation Around theLongitudinal Axis
https://t.me/med1917
81
Tips and Tricks
• If PQRS complex in lead aVF resembles that of lead V6, it is vertical heart.
• If PQRS complex in lead aVL resembles that of lead V6, it is horizontal heart.
• If PQRS complex in lead aVF and aVL both resemble that of lead V6, it is inter-
mediate heart.
6.2 Rotation Around theLongitudinal Axis
The longitudinal axis of heart runs through the interventricular septum from apex to
the base. Rotation is conventionally viewed from below the heart (through the diaphragm) looking upwards. Rotation around this axis results in clockwise and counterclockwise rotation (Fig.6.6).
Fig. 6.6 Diagram showing
rotation of heart. Rotation
along green coloured arrow
leads to counterclockwise
rotation, and rotation along
blue coloured arrow leads
to clockwise rotation. Look
at heart from foot end
(through the diaphragm)
82
V1 V2
V3
V4
V5 V6
10 mm = 1 mV
https://t.me/med1917
6 Rotation ofHeart
6.2.1 Clockwise Rotation
During clockwise rotation, the right ventricle is thought to come anteriorly and the
interventricular septum becomes parallel to the chest wall. As a result, most of the
chest leads will record a rS or RS complex, and the transition zone will shift to lead
V5 or V6 (Fig.6.7). However, no such anatomical change occurs. There is merely
the deviation of the electrical forces.
I II III
. 25 mm/s.
Fig. 6.7 ECG of clockwise rotation of heart. Transition zone is shifted to lead V5in which the
height of R wave and the depth of S wave are more or less equal
aVR aVL aVF
V1
V2
V3
V4
V5
V6
10 mm = 1 mV
6.2 Rotation Around the Longitudinal Axis
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6.2.2 Counterclockwise Rotation
Counterclockwise rotation brings the left ventricle more anteriorly. As a result, the
changes will be opposite to that described in clockwise rotation. The transition zone
is shifted to lead V1 or V2 (Fig.6.8).
I
Fig. 6.8 ECG showing counterclockwise rotation of heart. Transition zone is shifted to lead V1in
which the height of R wave and the depth of S wave are more or less equal
II
. 25 mm/s.
III
aVR
aVL
aVF
84
https://t.me/med1917
6 Rotation ofHeart
Tips and Tricks
• RS complex in lead V5 or V6 indicates clockwise rotation of heart.
• RS complex in lead V1 or V2 indicates counterclockwise rotation of heart.
Self-Assessment Questions
1. The vertical position of the heart can affect the amplitude and duration of the
QRS complex on an ECG.True or false?
2. The horizontal position of the heart does not affect the timing of the P wave on
an ECG.True or false?
3. In counterclockwise rotation, the transition zone shifts to lead V1. True or false?
4. A vertical heart position can cause a rightward shift of the QRS axis on an
ECG.True or false?
5. A horizontal heart position can cause a leftward shift of the QRS axis on an
ECG.True or false?
Answers
1. True 2. True 3. True 4. False 5. True
Chapter 7
https://t.me/med1917
Electrical Axis
Learning Objective
After studying this chapter, the reader will learn about:
• Axial reference system
• Basic concept of mean QRS axis
• Calculation of QRS axis
It is often very difcult, for a beginner, to understand the concept of electrical axis.
However, it becomes easy, if the basic aspects of the leads and generation of waves
and complexes are understood well. Electrical axis means the direction of the net
electrical force of the heart. Mean QRS axis represents the overall direction in
which the wave of ventricular depolarization travels.
Ventricular activation starts at the upper part of the interventricular septum. From
left to right, a small initial electric wavefront (vector) is generated. Next the free
walls of the ventricles are activated, generating a series of vectors that vary in magnitude and direction. These vectors add up if they are in the same direction and
cancel each other if they are in opposite direction. They may increase or decrease in
size and change direction if they are at an angle to each other (Fig.7.1). The vectors,
exactly opposite to each other and of equal magnitude, neutralize each other totally.
The larger vectors dominate and, because of maximum muscle mass, the largest
electric force is produced close to the apex of the left ventricle and adjacent wall of
the left ventricle. It is directed mainly to the left and downwards. The mean vector
is the dominant vector, out of all these multiple vectors and the direction of the
mean vector is called the mean QRS axis (Fig.7.2).
Ltd. 2024
T. K. Koley, Rapid Review of ECG,
https://doi.org/10.1007/978-981-99-9116-7_7
85© The Author(s), under exclusive license to Springer Nature Singapore Pte
86
https://t.me/med1917
Fig. 7.1 Genesis of mean QRS axis. Multiple wavefronts (vectors) generated during ventricular
depolarization add up and the resultant mean vector is equal to the mean QRS axis
7 Electrical Axis
Fig. 7.2 Mean QRS axis. The rst vector generated is the septal vector at the top of the interventricular septum. After this, numerous vectors are generated in both the ventricles (green in left
ventricle and blue in right ventricle). The vectors generated in left ventricle are dominant vectors
which neutralize the vectors generated in right ventricle. The direction of the mean vector is the
mean QRS axis
7.1 Axial Reference System
7.1.1 Triaxial Reference System
The three standard limb lead axes are aligned in a way, that they form an equilateral
triangle with the heart at its centre. This is known as Einthoven’s triangle. By
redrawing the lead axes (the three axes are passing through a common point), a triaxial reference system can be constituted with each axis separated from the other by
60° (Fig.7.3). However, the polarity and the orientation of the lead axes are not
changed.
Similarly, another triaxial reference system is constituted by the three lead axes
of the augmented unipolar leads (Fig.7.4).
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