LEllERS TO THE EDITOR

HEMODYNAMICS IN MYOCARDIAL INFARCTION

In their recent article Russell and co-workers1 used both pulmonary arterial end-diastolic pressure and left ventricu- lar end-diastolic pressure as indicators of “left ventricular filling pressure.” They feel that pulmonary arterial end- diastolic pressure “reliably reflected” left ventricular end- diastolic pressure1 in acute myocardial infarction, a thesis that needs to be examined critically.2

Falicov et al.” and Bouchard et a1.4 have shown that pul- monary arterial end-diastolic pressure does not provide a reliable estimate of left ventricular end-diastolic pressure in the presence of chronic left ventricular disease. We have shown previously that pulmonary arterial end-diastolic pressure does not accurately reflect left ventricular end- diastolic pressure after acute myocardial infarction.5 Since Russell et al. did not present tabulated data for each indi- vidual patient, it is difficult to know the precise range of differences between pulmonary arterial end-diastolic pres- sure and left ventricular end-diastolic pressure in their pa- tients with acute myocardial infarction. Figure 6 of their article showed a comparison of pulmonary arterial end-dia- stolic pressure and left ventricular end-diastolic pressure and demonstrated that there was a considerable scatter of points. In their patients, the probable difference between pulmonary arterial end-diastolic pressure and left ventricu- lar end-diastolic pressure averaged 2.1 mm Hg with 1 stan- dard deviation of 4.5 mm Hg and a P value of <O.OOl. In spite of this significant difference between the two pres- sures, if changes in left ventricular end-diastolic pressure were consistently and accurately reflected in pulmonary ar- terial end-diastolic pressure, then monitoring of the latter could be useful as an indicator of ventricular performance. Unfor&nately, in many patients this does not occur. For example, Figure 6 from Russell’s data’ shows that in one patient left ventricular end-diastolic pressure and pulmo- nary arterial end-diastolic pressure were the same at 20 mm Hg, but at another time, when left ventricular end-dia- stolic pressure had increased to 30 mm Hg, pulmonary ar- terial end-diastolic pressure was unchanged at 20 mm Hg. In another patient both pressures were 18 mm Hg and when left ventricular end-diastolic pressure increased to 29 mm Hg, pulmonary arterial end-diastolic pressure fell to 16 mm Hg. Further, it has also been shown previously that various maneuvers may result in changes in the indirect es- timates of left ventricular end-diastolic pressure (such as pulmonary arterial end-diastolic pressure) that are differ- ent not only in magnitude but also in direction from the changes seen in left ventricular end-diastolic pressure.2,4

The use to which the various measured pressures are to be put is clearly important. As we have pointed out pre- viously 2v5 if left ventricular filling pressures are monitored in pati&ts with acute myocardial infarction, the following data are important: (1) left ventricular end-diastolic pres- sure to assess the performance characteristics of the left ventricle, and (2) mean left atria1 pressure or mean pulmo- nary arterial wedge pressure or left ventricular diastolic pressure, pre a wave, to assess the pulmonary venous pres- sure and, thus, the risk to the patient that pulmonary edema will develop. Pulmonary arterial end-diastolic pres- sure gives a good indication of pulmonary venous pressure, but after myocardial infarction pulmonary arterial end-dia- stolic pressure may not be the same as mean pulmonary ar- terial wedge pressure because of some increase of pulmo- nary vascular resistance in many patients.5 The difference

between the two pressures may create a problem because it is easier to monitor pulmonary arterial end-diastolic pres- sure than mean pulmonary arterial wedge pressure over a period of several days. A Swan-Ganz catheter can be placed in the pulmonary artery and pulmonary arterial end-dia- stolic pressure and mean pulmonary arterial wedge pres- sure determined. If there is a discrepancy between the two pressures, the magnitude of the difference can be taken into account during monitoring of pulmonary arterial end- diastolic pressure.

In conclusion, in normal subjects the indirect estimates of left ventricular end-diastolic pressure (for example, pul- monary arterial end-diastolic pressure and mean pulmo- nary arterial pressure) are usually the same as left ventric- ular end-diastolic pressure, and “left ventricular filling pressure” may be used as a convenient term to refer to all of these indexes. However, in patients with left ventricular dysfunction the indirect estimates of left ventricular end- diastolic pressure are often not the same as left ventricular end-diastolic pressure and, further, may not accurately re- flect changes in this pressure. Therefore, it would seem in- appropriate to use the general term “left ventricular filling pressure” in patients with left ventricular dysfunction. It would be preferable to refer to the specific index measured instead of using “filling pressure” to cover all indexes.2 Such a practice would be more accurate and would allow maximal utilization of data from studies performed by var- ious investigators.

Acknowledgment

I thank Gary L. Gankemeier, PhD. Department of Statistics, Oregon State University. Cowallis. Oregon for statistically analyzing data from Figure 6 of the paper by Russell et aI.

S. H. Rahimtoola, MD, FACC Department of Medicine University of Oregon Medical School Portland Oregon

References

Russell RO Jr, Hunt 0. Ftsckley CE: Left ventricular hemodynamics in anterior and inferior myocardiil infarction. Am J Cardiol 32:6-16, 1973 Rahbntoola SH; Left ventricular end-diastolic and filling pressures in assessment of ventricular function. Chest 63~656-660. 1973 Fallcov RA, Resnekov L: Relationship of the pulmonary artery enddiistolic pressure to the left ventricular endtiastolic and mean filling pressures in patients with and withoui left ventricular dysfunction. Circulation 42:65-73, 1970 Souchard RJ, Gsulf JH, Ross J Jr: Evaluation of pulmonary arterial enddiastolic pressure as an estimate of left ventricular end-diastolic press& in patients with nor- mal and abnormal left ventricular Derformance. Circulation 44:1072-1079. 1971 Rahfmtoola SH, Loeb HS, Ehsanl A. et al: Relationship of pulmonary a&y to left ventricular diastolic pressures in acute myocardial infarction. Circulation 46:263- 290. 1972

REPLY

We appreciate the interest expressed by Dr. Rahimtoola in our recent article’ and the opportunity to clarify and amplify our position concerning the interpretation and clinical usefulness of pulmonary arterial end-diastolic pres- sure in acute myocardial infarction. We agree that each in- vestigator and clinician should specify the variable mea- sured in discussion of his results.2 However, once clearly specified, it seems defensible and reasonable to employ some term such as left ventricular filling pressure3 in refer- ence to diastolic pressure events in the left ventricle to re- mind the clinician constantly that the Frank-Starling prin- ciple can be employed to manage acutely ill patients, in- cluding those with acute myocardial infarction.

May 1974 The American Journal of CARDIOLOGY Volume 33 691