It is important that the provider be aware of the reason for the necessity of developing a familiarity with hypertrophy. For practical purposes, we will focus on left ventricular hypertrophy in this discussion, because it is absolutely essential that this pattern be recognized.
The reason for the necessity to know the criteria for LVH is at least two-fold:
- It is an extremely common finding, therefore the provider must recognize it readily.
- The pattern of LVH will often distort the ECG waveshape such that it may mimic changes of an acute MI, old MI or Ischemia.
Therefore, as we progress to look for ischemia or acute/old MI, we must take into account whether the patient has evidence of LVH or not.
First, let us define hypertrophy as defined by Dorland’s Medical Dictionary:
Hypertrophy: The morbid enlargement or overgrowth of an organ or part due to an increase in size of its constituent cells.
The provider should be aware that a common cause of LVH is long-standing hypertension and primary cardiac disease such as valvular disease. Either of these would place a chronic work load on the left ventricle, and the ventricle will hypertrophy to compensate for the extra work load.
The question simplifies to “What do we see on the electrocardiogram if the patient has LVH?”. There are many different lists of criteria in the literature for the diagnosis of LVH but they all have two things in common:
- They are indeed quite specific: if LVH is present on the ECG, the patient most likely has the condition.
- They are not very sensitive: many people who actually have LVH, do not have ECGs which reveal it.
The meaning of item #1 and #2 above is that if a group of patients are known to have LVH, significant numbers of their ECGs will NOT show LVH by our electrocardiographic criteria. On the other hand, if the ECG meets the criteria of LVH, then the patient most likely will indeed have LVH (This could ultimately be proven by echocardiogram,cardiac cath, MRI or autopsy).
Since the left ventricle myocardium is thickened in LVH it seems logical to suspect that:
- The voltage amplitude contribution from the left ventricle would be larger than normal.
- QRS might be slightly prolonged.
- There might be a slight left axis shift.
By far the most significant factor of the above three is that of number “1”, i.e. the VOLTAGE is enlarged. The diagnosis is centered on analysis of leads that “look” at the left ventricle, i.e. leads V1, V2, V3, V4, V5, V6 and of course limb Leads I and avL (lateral and high lateral leads).
As a compromise to the multitude of listings for the criteria of LVH, we will agree to the following list:
- S (Max Voltage of Lead V1, V2, V3) + R (Max Voltage of Lead V4, V5, V6) > 35 mm
2. R voltage of Lead avL > 12 mm
3. R-wave voltage of S-wave voltage > 20 mm in any Limb Lead (I, II, III, avR, avL, avF)
4. R-wave voltage or S-wave voltage > 25 mm in any precordial lead (V1, V2, V3, V4, V5, V6)
NOTE: It is important that the student be aware that the QRS voltage varies with age. More specifically, the voltage is greater in the younger individual and will be smaller for the older individual. As an approximate rule of thumb, age 35 can be used as a cutoff point, i.e. if the patient is 35 years or older, the above four criteria are valid.
If the patient is younger than 35, the criteria are less reliable and in fact it is wise to avoid making the diagnosis of LVH if the patient is younger than 35 years. If the diagnosis is suggested by the elctrocardiogram then it should be qualified with such statements as follows: “The ECG meets voltage criteria for LVH bu may be normal for stated age.”
The point is, that the criteria of LVH depends on the age of the patient and if the patient is very young, the criteria are no longer valid.
It is also important that the provider be aware that the QRS voltage will be less if the patient has lung disease (i.e. COPD, emphysema,pneumoconiosis, silicosis).
Those variables which cause a modification of the voltages will clearly effect the sensitivity and specificity of the criteria of LVH.