Limited Echocardiography for Hypertensive Left Ventricular Hypertrophy

Technology

Echocardiography has been used as a standard procedure for the calculation of LV muscle mass for more than 25 years.¹¹ Primary measurements of LV dimensions are made according to American Society of Echocardiography standards using the leading edge method of interface recognition and by identifying end diastole and end systole at the QRS onset and nadir of posterior systolic motion of the interventricular septum.^{12 13 14} Adequate M-mode images for calculation of LV mass can be obtained in approximately 90% of patients in an experienced echo laboratory.^{15 16 17} Assessment of the degree of LVH should include measurements of the posterior wall and septal thickness and calculation of LV mass index. However, even in patients with good-quality studies, there is significant intrareader and interreader variability of LV mass.¹⁵ For instance, in the Treatment of Mild Hypertension Study, the variance between the two readers was 23.8% (49.2g), and the intrareader variance was approximately 8.5%. Temporal variability of LV mass measurements in hypertensive patients and normotensive subjects was also highly variable.^{18 19 20}

LVH can also be assessed by methods that are simpler or more complex than conventional echocardiography. Less complex and less expensive are ECG methods; but classic ECG criteria, although accurate when positive, are highly insensitive, identifying only 20% of patients with true LVH.^{21 22 23} At the other extreme of the technology spectrum, the most precise index of LV geometry can be obtained by the three-dimensional imaging technologies. Thus, ECG-gated magnetic resonance imaging, computed tomography, and three-dimensional echocardiography also provide LV mass and volume with great precision^{24 25 26} but at a higher cost and with varied availability. Patients with marked obesity and severe chronic obstructive lung disease may provide poor images, and subcostal imaging may yield a more useful study instead of the standard approach. Transesophageal echocardiography, which provides excellent cardiac images, can be used in selected circumstances for assessment of LVH, but this procedure is not recommended routinely.

Recommendations for the Use of Limited Echocardiography

The use of the limited echocardiogram for assessment of LVH risk is appropriate in untreated hypertensive patients with stage 1 blood pressure levels (systolic pressure 140 to 159 mm Hg and/or diastolic pressure 90 to 99 mm Hg) and no other evidence of LVH or other cardiovascular risk factors, and a standardized, high-quality procedure is feasible. It should not be obtained routinely in all patients with hypertension, nor should it be used for therapy selection because all classes of antihypertensive agents will diminish LV mass, providing that blood pressure is controlled. Identification of increased LV mass in an individual having hypertension of lesser stages of severity (eg, “high normal,” stage 1 primarily and stage 2 rarely) is extremely valuable in helping the clinician decide whether to initiate antihypertensive drug therapy. However, in patients with stages 2 through 4 blood pressure levels (systolic pressure ≥160 mm Hg and/or diastolic pressure ≥100 mm Hg) or those with LVH and/or other cardiovascular risk factors associated with stage 1 or 2 hypertension, identification of echocardiographic evidence of increased LV mass is unnecessary because in these patients, vigorous control of pressure with antihypertensive therapy is already necessary.

Follow-up limited echocardiograms in patients whose LV mass is already known is not indicated if blood pressure has not been controlled successfully. In such patients, further and more aggressive management with optimal control of pressure is clearly required. Office, ambulatory, and self blood pressure measurements (at work and home) would indicate whether blood pressure has been successfully reduced and controlled. Finally, one should not consider reduction of LV mass as a substitute for prevention of cardiovascular disease events when assessing the success of an antihypertensive agent.

Indications and situations when limited echocardiography is and is not indicated are presented in Tables 2 and 3⇓⇓, respectively.

Cost Considerations

When a more targeted approach to the management of hypertensive patients at higher risk is being considered, the availability of limited echocardiography would allow carefully selected hypertensive patients to undergo useful risk stratification, possibly without increasing the aggregate amount of financial and technical resources used. Although some younger patients with hypertension may be undergoing a more comprehensive echocardiographic procedure for other specific clinical indications, it may be more appropriate and cost-effective to obtain limited echocardiograms for these younger patients when the primary clinical issue is assessment of LVH.

One recent report indicated that in asymptomatic patients with hypertension and a normal clinical cardiac examination, a limited echocardiographic study rarely misses significant LVH.¹⁷ Moreover, any further clinically relevant information would be provided by a more comprehensive echocardiographic study in less than 10% of patients.¹⁷ When the expense of long-term antihypertensive drug therapy, especially for newer drugs, is being considered, it may be more cost conserving to use limited echocardiography as part of a screening strategy for initiating antihypertensive drug treatment.^{27 28}

The more comprehensive and costly M-mode, 2-D, and Doppler echocardiographic evaluations may be warranted in the following patients: (1) hypertensive patients with chest pain, unexplained dyspnea, or other cardiac symptoms to assess LV systolic or diastolic function; (2) patients with systolic or diastolic murmurs to help define their cause or significance; and (3) patients with comorbid cardiac problems. More comprehensive echocardiographic examination may also be of value in distinguishing physiological from pathological hypertrophy in athletes.

Economic Information About Limited Echocardiography

The Medicare claims data analyzed initially by the American Medical Association for 1992 through 1994 were reviewed and the following noted: (1) The volume of 2-D, M-mode echocardiograms (CPT code 93307) increased over that period from 3 191 922 to 3 596 686; (2) the volume of limited echocardiograms (CPT code 93308) declined for the same period from 53 131 to 43 110 (Figure⇓); (3) in 1994, essential hypertension was one of the top eight diagnostic codes listed on claims that included 2-D, M-mode echocardiography (CPT code 93307), and 7% of the claims for that procedure had an associated diagnosis of essential hypertension (ICD-6 code 401); and (4) on a line-item basis for echocardiography performed in 1994, essential hypertension was listed as one of the top eight diagnostic codes, representing 4% of the diagnoses identified as justifying this procedure (these data are consistent with limited echocardiographic Medicare data from 1986 to 1993).

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Figure 1.

Annual volumes of limited echocardiographic procedures from Medicare data.

The foregoing data, although interesting, must be cautiously interpreted before any conclusions are drawn regarding the actual current use of limited and/or 2-D, M-mode echocardiography for the evaluation of hypertensive LVH. Since justification for this procedure may have been considered disallowable, an alternative diagnosis may have been selected. Other potentially useful data sets (eg, the Uniform Hospital Discharge Data Set, or UHDDS) have not been evaluated to delineate further the precise utilization of these procedures in the overall hypertensive population and to support or refute the Medicare claims data findings. The only known and available data are presented in this report.

Medicare has two data files that have been of particular value. The American College of Cardiology has analyzed the 1986-1993 Medicare procedure files, which include 100% of actual claims (submitted by physicians through the Part B Medicare Annual Data (BMAD) files) (Table 4⇓). In addition, the Medicare beneficiary file has proved useful. The latter file consists of a 5% longitudinal sampling of all beneficiaries capturing code ICD-9 diagnostic aligned with each procedure code; this is required by the Health Care Financing Administration as a means of justifying the procedure. The CPT codes used to identify echocardiographic services have been in a state of flux for years and have undergone coding changes. Before 1990, two coding systems existed, one for radiology (70000 series) and the other for cardiology (93300 series). At the same time, evolution of the technology led to consolidation of the codes (2-D, M-mode, etc). These issues have obviously complicated the data.

Possible explanations for the reduction in the frequency of utilization of limited echocardiograms during the later period include: (1) A general awareness developed that a more limited procedure was not broadly appreciated by the physicians interested in the study; (2) greater third-party reimbursement was available by ordering 2-D, M-mode, and Doppler echocardiograms; and (3) with the broadened interest of physicians in hypertensive heart disease, those who were concerned about that problem may have ordered the more costly procedure without considering a less-expensive alternative. This possibility seems likely, especially when one considers that the concept of limited echocardiography had not been recommended broadly in peer-reviewed cardiovascular journal articles.

In conclusion, echocardiography is a safe, sensitive, and accurate tool for assessment of cardiac function in patients with hypertension. Despite some limitations, the determination of LV mass by echocardiography is a powerful predictor of cardiovascular risk. Limited echocardiography has been used less frequently in recent years. A limited echocardiogram for the detection of increased LV mass in carefully selected hypertensive patients would be appropriate in a targeted approach to the detection of patients at increased risk as part of a program to reduce their morbidity and mortality by the use of antihypertensive medications in addition to lifestyle changes. The overall effect could be a reduction in the cost of the lifetime management of hypertension in those selected patients.