Assessment of Right Ventricular Function

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--1. 111_ CHEST e~~~~I~I~NUMBER Assessment of Right Ventricular Function

I n this issue (see page 1169) Biernacki and colleagues

report the results of a study in which the endsystolic pressure-volume (ESPV) relationship was used to assess right ventricular (RV) contractility in a group of patients with chronic obstructive pulmonary disease and pulmonary hypertension. The ESPV relationship has been used to measure left ventricular contractility because it is relatively independent of both preload and afterload.t-' Critical to determining the RVESPV relationship is the accuracy of the RV volume measurement. Biernacki et al derived RV volume by dividing the RVEF (estimated by gated, equilibrium radionuclide ventriculography) into the stroke volume index that was simultaneously obtained by thermodilution. Although they claimed that the RVEFs esimated by this technique are reproducible in a given patient over time, have a low intra- and inter-observer variability, and correlate well with RVEFs determined by the first pass method, the data cited in support of these assertions are not convincing. The accuracy of equilibrium RVEFs is adversely affected by a substantial amount of background radio activity present in structures overlapping the RV (the LV, the RV outflow tract, and the right atrium). To minimize the error generated by this problem, Biernacki et al utilized the technique described by their group - in which " . . . the best projection that could be used to separate left and right ventricles and right ventricle from right atrium was a 20° left anterior oblique projection with a 20° caudal angulation. In this projection the proportion of the total counts in the right ventricular region due to the underlying right atrium was 30 percent." It seems prudent to be suspicious of any method in which up to 30 percent of the RV signal is noise from the right atrium (RA). The importance of this problem is not reduced by knowing that the RA contribution is constant within a given patient over time, or that the noise may be reproducibly included in the signal by the same or different observers. Right ventricular size correlates with the degree of pulmonary hypertension. Leitl et als have suggested that even a 40° LAO projection does not allow the RV to be separated from the LV when the RV is enlarged

6 I DECEMBER, 1988

and the LV is displaced posteriorly. While the RV signal should increase in the presence of increased RV afterload, RA size, as well as the volume of the outflow tract should also be reasonably well-correlated with the degree of RV afterload and, consequently, with the noise contributed to the RV signal. The signal -tonoise ratio could be variably affected. Xue et al 4 and Morrison et al6 both reported good correlations between the equilibrium and gated RVEFs in patients with RVEFs that were normal or were decreased secondary to a variety of disorders. Xue et al4 found a mean difference between the two techniques of 0.04 EF units (approximately 10 percent of the normal RVEF reported in this study) in patients with RVEFs ranging from approximately 25 to 63 percent. However, if the relationship between the RVEFs estimated by the two methods is examined in the subset of patients with abnormal RVEFs «40-45 percent), in whom one might suspect that RV afterload and, therefore, that RV overlap problems were increased, much greater differences are apparent. 4.(fig 3 ) Although Morrison et al" did not find a similar decrease in the comparability of the equilibrium and first-pass methods at lower RVEFs, the data of Xue et al suggest that the signal-to-noise ratio inherent in equilibrium RVEFs might decrease with increasing RV afterload. This problem would make interpretation of data utilizing the equilibrium method difficult at best. Another problem with the data presented by Biernacki et al is that they determined the ESPV relationship under only one ESPV condition. Virtually all of the studies utilizing the ESPV relationship to characterize LV contractility include data collected at several ESPV points. These allow a slope of ESPV relationships to be determined and a line of LV contractility to be characterized. Knowing the ESPV relationship at a single ESPV condition does not adequately characterize RV function, as this single point could be on any RV contractility line. Important contributions to patient care could be made by having the ability to investigate RV function noninvasively. However, tests of RV function are critically dependent on RV volume and the problem of obtaining accurate , noninvasive RV volume measurements is a difficult, unsolved one that continues to be investigated." Unless future studies more accurately document RV contractility and the accuracy of RVEFs CHEST I 94 I 6 I DECEMBER. 1988

1123

determined by the equilibrium blood pool technique in patients with pulmonary hypertension, data generated by this technique must be viewed with skepticism. Richard K. Albert, M.D., F.C.C.R

Seattle

Assistant Chief, Pulmonary and Critical Care, Veterans Administration Medical Center; Professor of Medicine, University of Washington.

REFERENCES 1 Grossman w Braunwald E, Mann l: McLaurin L~ Green LH. Contractile state of the left ventricle in man as evaluated from end-systolic pressure-volume relations. Circulation 1977; 56:84552 2 Mehmel HC, Stockins B, Ruffman K, van Olhausen K, Schuler G, Kubler W Linearity of the end-systolic pressure-volume relationship in man and its sensitivity for assessment of left ventricular function. Circulation 1981; 63:1216-22 3 Sagawa K. The end-systolic pressure-volume relation of the ventricle: definition, modification, and clinical use. Circulation 1981; 63:1223-27 4 Xue Q, MacNee w Flenley DC, Hannan WJ, Adie CJ, Muir AL. Can right ventricular performance be assessed by equilibrium radionuclide ventriculography? Thorax 1983; 38:486-93 5 Leitl G ~ Buchanan IN, Wagner HN. Monitoring cardiac function with nuclear techniques. Am J Cardio11980; 46:1125-32 6 Morrison DA, Turgeon J, Kotler J, Henry R. Gated first pass radionuclide ventriculography Methods, validation, and applications. Clin Nuc Med 1984; 9:506-12 7 Kass DA. Measuring right ventricular volumes. Am J Physiol: Heart Circ Physiol 1988; 254:H619-21

Disappointing Results of Coronary Artery Bypass Graft Surgery in Young Patients

Since the Korean War, coronary atherosclerosis has been recognized in young American males.' In the era before coronary artery bypass graft surgery Gertler et al2 recognized that in young patients, longterm prognosis worsened as the age at first myocardial infarction declined. In this issue of Chest (see page 1138), Kelly et al reviewed the surgical outcome and late follow-up in coronary artery bypass patients less than 40 years of age and compared them to the entire historic operative experience of a large teaching hospital. The cohort of patients (242) is the largest cohort of this type yet studied. Although these young patients had operative mortality rates similar to the older patients, their rates of recurrence of angina and reoperation were dramatically and disappointingly higher than those of the older age group. This difference occurred despite the fact that preoperative cardiac status appeared to be similar between groups. As noted in the discussion, these observations are comparable to those found by other authors.v' This study is important, however, 1124

because it confirms the findings of other authors which, although previously reported, may not have been widely recognized by the general medical community The large size of this cohort of patients makes evaluation of their risk factors significant. These young patients had a higher incidence of family history of heart disease, elevated cholesterol level, and smoking than did the older age group patients. The young patients, however, had a lower incidence of diabetes, hypertension and congestive heart failure. The incidence of previous myocardial infarction was the same in both groups. These differences in preoperative risk factors may be important and may also be related to the difference in long-term outcome. As in any other retrospective review one must be careful in drawing too many conclusions. Since the groups are neither case-matched nor prospectively randomized, bias related to year of operation, operative technique, or severity of disease may enter in. Such bias seems unlikely both because the article substantiates earlier findings and because it is comprehensive, involving all patients in each group from a single hospital. This article raises two important questions. First, would better risk factor modification alter the long-term outcome of these young patients? Second, are these young patients a different subgroup than patients who present with angina at a later age, or is the outcome related to some as yet unidentified technical problem related to age? In other words, could deferral of surgery in these patients through more aggressive medical therapy or angioplasty change the long-term results of their operation to more closely approximate that of the older age group? Since the time period when the majority of these patients were operated upon, the superior longevity of internal mammary artery grafts vs that of saphenous vein grafts has been recognized." Use of the internal mammary artery as the conduit of choice is encouraged when coronary artery bypass graft surgery is necessary in this subgroup of patients. The need for a study documenting long-term patency of the internal mammary artery in young patients seems obvious, as well as study of the alternative use of more aggressive medical management. David] Cohen, M.D., F.C.C.P. San Antonio Division of Cardiothoracic Surgery University of Texas Health Science Center at San Antonio.

REFERENCES 1 Enos WF, Beyer JC, Holmes RH. Pathogenesis of coronary artery disease in American soldiers killed in Korea. JAMA1955; 158:912 2 Gertler MM, White PD, Simon R, Gottsch LG. Long-term follow-upof young coronary patients. Am J Med Sci 1964;247:14554 3 Cohen DJ, Basamania C, Graeber GM, DeShong JL, Burge JR. Coronary artery bypass grafting in young patients under 36 years Editorials