Subepicardial Segmental Function during Coronary Stenosis and the Role of Myocardial Fiber Orientation

In six open-chest, anesthetized dogs, segmental shortening was measured with one pair of ultrasonic dimension gauges placed in the subendocardium (used as a marker for regional ischemia) and two pairs in the epicardium. One of the epicardial crystal pairs was aligned parallel with the surface fibers and the other was oriented circumferentially, parallel with the short axis. During control conditions, with uniform transmural perfusion measured by microspheres (endo/epi ratio 1.17 ± 0.10), epicardial systolic shortening measured by parallel and circumferential segment pairs was comparable but significantly different (9.2 ± 2.4% and 7.3 ± 1.0%, respectively). Partial circumflex coronary artery narrowing produced subendocardial ischemia (blood flow reduced from 0.99 ± 0.24 to 0.29 ± 0.07 ml/min per g, P < 0.01 from control), characterized by elimination of subendocardial shortening (−1.3 ± 1.7%, P < 0.01) Outer myocardial perfusion remained unchanged [0.86 ± 0.17 to 1.00 ± 0.37 ml/min per g, not significant (NS)] and parallel epicardial shortening was not significantly reduced (8.4 ± 3.7%, NS); however, circumferential epicardial shortening was eliminated (−0.8 ± 2.2%, P < 0.01). With complete coronary occlusion, severe transmural ischemia was produced (including the subepicardial layer), and systolic lengthening was observed in the subendocardial as well as both epicardial segments. We conclude that circumferential and parallel epicardial shortening are comparable under conditions of uniform transmural perfusion (normal conditions and complete coronary occlusion), but that considerable nonuniformity of transmural contraction occurs during partial coronary narrowing associated with nonuniform transmural blood flow. Thus, unidimensional measurements of epicardial motion without regard to fiber orientation can lead to variable results under the latter conditions. Despite sustained epicardial blood flow, circumferential epicardial function correlated well with impaired subendocardial shortening during ischemia, indicating that a portion of the myocardium in the outer third of the wall is constrained from shortening during partial ischemia.

[1]  T. Arts,et al.  Measurement of deformation of canine epicardium in vivo during cardiac cycle. , 1980, The American journal of physiology.

[2]  P. Hugenholtz,et al.  Quantification of function in normal and infarcted regions of the left ventricle. , 1972, Cardiovascular research.

[3]  G. Diamond,et al.  Noninvasive analysis of regional myocardial wall motion: cardiokymography. , 1977, The American journal of physiology.

[4]  G. Diamond,et al.  Photokymography: a noninvasive method of detecting ischemic segmental myocardial wall motion abnormalities. , 1979, The American journal of cardiology.

[5]  A. Liedtke,et al.  Development and use of a new high-frequency, low mechanical impedance strain gauge. , 1979, The American journal of physiology.

[6]  J. Downey.  Myocardial contractile force as a function of coronary blood flow. , 1976, The American journal of physiology.

[7]  H. Schelbert,et al.  Observations on Factors Affecting Local Forces in the Left Ventricular Wall during Acute Myocardial Ischemia , 1971, Circulation research.

[8]  N. Reid,et al.  A Simple Nonparametric Test for Trend: An Example Based on a Biological Model for Cancer of the Pancreas , 1978 .

[9]  I G McDonald,et al.  The shape and movements of the human left ventricle during systole. A study by cineangiography and by cineradiography of epicardial markers. , 1970, The American journal of cardiology.

[10]  D. Waters,et al.  Early changes in regional and global left ventricular function induced by graded reductions in regional coronary perfusion. , 1977, The American journal of cardiology.

[11]  R. W. Brower,et al.  Direct method for determining regional myocardial shortening after bypass surgery from radiopaque markers in man. , 1978, The American journal of cardiology.

[12]  S. E. Logan,et al.  Effect of graded reductions in regional coronary perfusion on regional and total cardiac function. , 1975, The American journal of cardiology.

[13]  N B Ingels,et al.  Stereo photogrammetric studies on the dynamic geometry of the canine left ventricular epicardium. , 1971, Journal of biomechanics.

[14]  E. D. Rest,et al.  Statistical Theory and Methodology in Science and Engineering , 1963 .

[15]  J W Covell,et al.  Regional Differences in Myocardial Performance in the Left Ventricle of the Dog , 1975, Circulation research.

[16]  R. Helfant,et al.  The Relationship between Myocardial Blood Flow and Contraction by Myocardial Layer in the Canine Left Ventricle during Ischemia , 1981, Circulation research.

[17]  M. Pagani,et al.  Effects of propranolol on regional myocardial function, electrograms, and blood flow in conscious dogs with myocardial ischemia. , 1977, The Journal of clinical investigation.

[18]  J. Ross,et al.  Significance of Regional Wall Thickening Abnormalities Relative to Transmural Myocardial Perfusion in Anesthetized Dogs , 1980, Circulation.

[19]  S. Vatner,et al.  Effects of isoproterenol on regional myocardial function, electrogram, and blood flow in conscious dogs with myocardial ischemia. , 1976, The Journal of clinical investigation.

[20]  J. Ross,et al.  Fiber Orientation in the Canine Left Ventricle during Diastole and Systole , 1969, Circulation research.

[21]  L. N. Balaam,et al.  Statistical Theory and Methodology in Science and Engineering , 1966 .

[22]  F. Kiil,et al.  Local dimensional changes of the myocardium measured by ultrasonic technique. , 1969, Scandinavian journal of clinical and laboratory investigation.

[23]  D Franklin,et al.  Regional Myocardial Function during Acute Coronary Artery Occlusion and Its Modification by Pharmacologic Agents in the Dog , 1974, Circulation research.

[24]  S. Vatner.  Correlation between Acute Reductions in Myocardial Blood Flow and Function in Conscious Dogs , 1980, Circulation research.

[25]  J I Hoffman,et al.  Blood flow measurements with radionuclide-labeled particles. , 1977, Progress in cardiovascular diseases.

[26]  J. Downey,et al.  Nitroglycerin and heterogeneity of myocardial blood flow. Reduced subendocardial blood flow and ventricular contractile force. , 1973, The Journal of clinical investigation.