VENTRICULAR
HYPERTROPHY
Various terms have been used to describe the ECG picture of ventricular hypertrophy, including ventricular preponderance, strain, systolic or diastolic overload, and enlargement. Some of these describe a functional state of overwork of one ventricle versus the other, or refer to an anatomic condition with increased muscle of one ventricle compared to the other. Ventricular preponderance is an all-inclusive term that broadly includes most conditions, and enlargement covers both hypertrophy and dilatation.
The QRS forces
are directed to the right because of the thick right ventricle, which distorts
the horizontal loop to the right and forward, and is associated with tall R
waves relative to normal in leads V1 and V2 and deep S waves
in leads V4 and V5 (see Plate 2-21). The R/S amplitude ratio in lead V1 is abnormal, indicating a
tall R wave with respect to the depth of the S wave. Normally, this ratio
should be less than 1. Characteristically, the S-T segments and T waves are
opposite in direction to that portion of the QRS complex of greatest area (usually
the R wave), and also the T loop is opposite to the QRS loop. Thus the R wave
is up and the T wave down in leads V1 and V2, but in
leads V5 and V6 the S wave is always down and the T wave
up.
Right
ventricular hypertrophy may be caused by congenital or acquired heart disease,
and the hypertrophy may result from a pressure or volume overload. As a result,
the RV muscle thickens with respect to the LV, and a RV preponderance develops.
The net electric change of the whole heart writes the ECG and VCG, and
thus the QRS electric forces are directed in general from the left to the right
of the heart and of the body. Usually the direction of the electric forces will
be from the smaller muscle mass toward the larger mass, that is, from the
normal toward the hypertrophied ventricle.
The large
muscle mass of the left hypertrophied ventricle, compared to the right,
distorts the QRS loop toward the left scapula. This results in small R waves
and deep S waves in leads V1 and V2, with high R waves
and small or no S waves in leads V5, and V6 (see Plate 2-21). Again, the S-T segments
and T waves are opposite in direction to the major deflection of the QRS
complex, which means that in lead V1 the deep S wave is associated
with a positive S-T segment and T wave, whereas in lead V6
the tall R wave is associated with a negative S-T segment and T wave. In
the horizontal loop the early forces in the patient are from left to right and
to the front, later toward the left scapula, and finally returning to the zero
point. When the shifts of the S-T segments are characteristic of LV
enlargement, there is an open QRS-T loop in the VCG (i.e., beginning and end of
a QRS complex are at different levels), and usually a T wave follows that is
180 degrees discordant with the major portion of the QRS loop. The frontal loop is displaced toward the
left shoulder, with discordant QRS and T-wave relationships. An open loop may
be seen here as well.
The J point is
the junction between the end of the QRS complex and the beginning of the T wave
in the ECG. A point just in front of the J point, which is the end of the P-R
interval and the beginning of the QRS complex, is called the I point.
The open loop in the VCG is found when the I and J points in the ECG are at
different horizontal levels. Usually, in a normal person, the I and J points
are on the same level, often on the isoelectric line. With severe LV
hypertrophy, the J point shifts below the I point in lead V5, and in
severe RV hypertrophy, J is below I in lead V1. The I-J
relationships are also changed by digitalis, hypokalemia, MI, myocardial
ischemia, pericarditis, and bundle branch block.
RIGHT AND
LEFT VENTRICULAR HYPERTROPHY
When both RV
and LV hypertrophy exist, the muscle with the greater degr e of enlargement
will dominate the electrical picture.
