Abstract
To determine which factors may be of value in determining whether or not asynergic zones have residual contractile ability, the responsiveness of these zones to sublingual nitroglycerin (1/150 grs) was ALTHOUGH AORTOCORONARY bypass surgery is being increasingly utilized for patients with coronary heart disease and angina pectoris, its effect on left ventricular function has remained controversial.1-4 The ability of this procedure to improve left ventricular function depends in large part on the potential for improvement in zones of asynergy.5 There has been, therefore, mounting interest in developing a method which will allow an assessment of residual contractile ability of asynergic zones.6-9 Nitroglycerin has been found to unmask residual con- From tractile ability of asynergic zones as depicted ventriculographically, presumably by favorably altering the balance between oxygen demand and supply.`8 [10] [11] [12] This method hc_s been utilized in the present report to allow an evaluation of the factors which may be of value in determining the ability of asynergic zones to improve their contraction pattern.
Material and Methods Studies were performed in 36 patients undergoing cardiac catheterization for evaluation of coronary heart disease. Criteria for admission to the study were: 1) asynergy on ventriculography (defined as a localized abnormality of left ventricular contraction), 2) significant (. 75% decrease in diameter) obstruction of one or more of the three major coronary arteries (left anterior descending, right and circumflex arteries), 3) absence by catheterization of other etiologic heart disease. All patients were postabsorptive and premedicated with 50 mg nembutal, 50 mg demerol and 0.4 mg atropine.
Right heart catheterization was performed via an antecubital vein cutdown and left heart catheterization either percutaneously through a femoral artery or via a right brachial arteriotomy. Following recording of left ventricular
SUMMARY
To determine which factors may be of value in determining whether or not asynergic zones have residual contractile ability, the responsiveness of these zones to sublingual nitroglycerin (1/150 grs) was studied angiographically in 36 patients. The responsiveness of asynergy was correlated with the presence or absence of pathologic Q waves and coronary collaterals in the corresponding zones, as well as with anatomic location. Of the 25 asynergic segments which had corresponding pathologic Q waves, 11 (44.0%) responded to nitroglycerin while 14 (56%) remained unresponsive. In contrast, 30 (83.3%) of the 36 segments which did not have associated Q waves improved while only 6 (16.4%) did not (P < 0.005). Akinetic segments with Q waves were associated with a significant decrease in responsiveness (P < 0.02) compared to hypokinetic segments. Of the 26 segments with angiographically demonstrable collaterals, 22 (84.6%) improved and only 4 (15.4%) remained unchanged (P < 0.02). In contrast, of the 35 segments without collaterals, 19 (54.3%) were responsive and 16 (45.7%) did not respond. Seven (77.8%) of the 9 akinetic segments with collaterals exhibited improvement compared to only 5 (33%) of the 1o segments without collaterals (P < 0.05). In segments with pathologic Q waves, 70% of those associated with collaterals improved compared to only 27% without collaterals (P < 0.02). Relative to anatomic location, of 29 anterior wall segments, 24 (82.8%) responded compared to only 11 (45.8%) of 24 Figure 2 m Unresponsive Figure 1 The relationship of pathologic Q waves (> 0.04 sec) to improvement in asynergy of corresponding zones. Asynergic zones associated with Q waves respond less frequently than those without Q waves (P < 0.005). Responsive = improvement of asynergy during the effect of nitroglycerin. Unresponsive = no improvement in asynergy during nitroglycerin effect.
Pathologic Q Waves Figure 1 demonstrates the relationship of pathologic Q waves to improvement of asynergy. Of the 25 asynergic segments which had corresponding pathologic Q waves, 11 Relationship of coronary collaterals to improvement of asynergy in segments associated with corresponding pathologic Q waves. In the presence of Q waves, collaterals are associated with a significantly higher incidence of responsive asynergic zones (P < 0.02).
Responsive E Unresponsive Figure 6 Relationship of anatomic location to improvement of asynergy. The apical zone is less responsive than the remaining segments (P < 0.005). LAD = left anterior descending artery segment; apex = apical zone; anterior = anterior wall; RCA = right coronary artery segment; LCF = left circumflex artery segment. 11 (45.8%) of the 24 apical segments responded while 13 (54.2%) did not. The difference in responsiveness between anterior wall segments, right coronary segments and circumflex segments was not statistically significant ( fig. 6 ).
Hemodynamic Changes
The left ventricular hemodynamic and volume changes were similar for those segments which did and did not respond to nitroglycerin (table 2) .
Discussion
An asynergic zone consisting essentially of chronically ischemic but viable myocardium should logically have residual contractile ability, while an extensively infarcted area should remain noncontractile. The presence of pathologic Q waves on the surface electrocardiogram is generally recognized to be indicative of transmural infarction16 and correlates well with the presence of scar tissue in corresponding zones of the left benjamin02@example.net.`8 Recent studies from our laboratory indicate that pathologic Q waves are associated with severe degrees of asynergy (i.e., akinesis and dyskinesis) in 72% of cases.`" These types of asynergy have been taken as the ventriculographic equivalent of a ventricular aneurysm"3 and are less likely to respond to an intervention which unmasks residual contractile ability than hypokinetic segments.6 8 10 The present study shows that the majority of asynergic zones which exhibited corresponding Q waves did not respond to nitroglycerin, whereas only one-sixth of those asynergic segments not associated with Q waves were unresponsive ( fig. 1) . Of the akinetic segments, 71.4% of those associated with Q waves were unresponsive while only 20% without Q waves did not change ( fig. 2) . Thus, the presence of pathologic Q waves adversely affects the chances of improvement of asynergy when severe asynergy exists, presumably by denoting extensiveness of zonal scar formation.
The clinical importance of the coronary collateral circulation is controversial. '5 20"24 Previous studies have shown that presence of these collateral channels does not protect from the development of asynergy or hemodynamic abnormalities."5 22 The present study, however, indicates that collaterals may serve an important protective function in preserving myocardial viability in these asynergic segments ( fig. 3) . Thus, these zones retain the ability to improve their contraction pattern in response to an intervention which improves the balance between oxygen supply and demand. The response of the akinetic zones was particularly striking. While more than three-fourths of the akinetic segments with collaterals showed improvement, only one-third without collaterals responded ( fig. 4 ). It should be pointed out, however, that these data could be explained conversely. It is possible that the presence of viable, ischemic myocardium in potentially reversible asynergic zones stimulates the development of collaterals and that this explains the association of the two. In this regard, several studies have suggested that ischemia is a major stimulus for the development of collaterals."1 22, 25, 26 It was interesting to find that 70% of asynergic segments exhibiting both Q waves and collaterals improved compared to only 26.7% without collaterals ( fig. 5 ). Therefore, in this situation a significant amount of myocardium in or more likely surrounding these areas may be viable despite the preseiice of pathologic Q waves in the corresponding zone. In this regard, recent experimental studies in our laboratory utilizing tension and length gauges have shown that only the border zones of an infarct exhibit improvement in contractile characteristics following nitroglycerin administration while there is no change in the central infarct zone. 27 The finding that the apex was less responsive than the remaining zones of left ventricle ( fig. 6) The assessment of asynergy by single plane cineangiography has inherent limitations. The right anterior oblique projection employed in this study provides no information regarding the wall motion of the true posterior wall and the septum. Although biplane angiography would be ideal in the absence of such a facility, this would require four ventriculograms to accurately delineate the true posterior and the septal motion and would not be practical for routine clinical usage in most laboratories. The right anterior oblique ventriculogram before and after administration of nitroglycerin would adequately reflect changes in wall motion of the anterior and inferior wall. Its limitations should thus be kept in mind when assessing asynergy by single plane ventriculography.

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