Determinants of collateral development in a canine model with repeated coronary occlusion

It is now accepted that repetitive 2-min coronary occlusion can develop collateral vessels to the area perfused by the occluded coronary artery. However, which factors influence collateral development has yet to be fully elucidated. The goal of the present study was to identify the determinants of the rate of coronary collateral development in dogs undergoing repeated coronary occlusion. The study was conducted in 19 conscious dogs instrumented for measurements of a subendocardial segment length in the area perfused by the left circumflex coronary artery (LCCA), LCCA flow, and left ventricular pressure. An externally inflatable pneumatic occluder was placed around the LCCA. After the recovery from surgery, 2-min LCCA occlusions were conducted eight times daily. Following 141 +/- 61 (SD) LCCA occlusions (20 +/- 7 days), an LCCA occlusion produced no reduction in segment shortening and negligible reactive hyperemia. The total number of LCCA occlusions needed for adequate collateral development (the rate of collateralization) correlated well with the severity of myocardial ischemia during the first occlusion, which was determined mainly by the extent of postsurgical initial collateral circulation. On the other hand, the response to the ischemic stimulus in the later stage of collateral development was independent of the extent of development of the initial postsurgical collaterals. It is concluded that the overall rate of collateral development is slower in dogs with initially poorer collaterals; however, the response of each dog to the ischemic stimulus in the later stage of collateral development was similar among dogs regardless of the extent of the initial collaterals.

Relationship between the preexistent coronary collateral circulation and successful intracoronary thrombolysis for acute myocardial infarction

The purpose of this study was to evaluate whether the existence of coronary collateral circulation influences recanalization rates of intracoronary thrombolysis. The study population consisted of 85 consecutive patients undergoing intracoronary thrombolysis within 6 hours after the onset of the first acute myocardial infarction, all of whom had a complete occlusion of the infarct-related coronary artery. Intracoronary thrombolysis with high-dose urokinase (960,000 IU) was attempted at a rate of 24,000 IU/min. Of 18 patients (group A) who had good angiographic collateral circulation to the area perfused by the infarct-related coronary artery, the obstructed artery was recanalized to a residual luminal diameter stenosis of less than or equal to 90% (successful recanalization) in only five (28%). In contrast, of 67 patients (group B) with poor or no collateral circulation, recanalization was successful in 40 (60%) (p less than 0.05). Antegrade flow of infarct-related arteries was observed following thrombolysis in 12 (67%) of 18 group A patients and in 56 (84%) of 67 group B patients (p = NS). It was concluded that (1) the presence of collaterals correlates with the presence of high-grade stenosis; (2) the presence of collaterals correlates with the presence of high-grade stenosis; (2) the presence of collaterals is inversely related to the efficacy of thrombolytic therapy; and (3) the difference in successful recanalization rates observed between the two groups probably reflects the impact of underlying stenosis severity on the effectiveness of lytic therapy.

Effects of diltiazem and verapamil on (+)-PN 200-110 binding kinetics in dog cardiac membranes

The effects of d-cis-diltiazem (diltiazem) and verapamil on 1,4-dihydropyridine binding to dog cardiac membranes were studied in competition, saturation and kinetic binding experiments with [3H](+)-PN200-110. Diltiazem increased [3H](+)-PN200-110 binding with an observed maximal effect at 50 microM, while verapamil decreased [3H](+)-PN200-110 binding in a dose-dependent manner. Scatchard analysis of saturation binding data revealed that diltiazem (50 microM) increased the maximal binding site density and verapamil (100 microM) increased the dissociation constant (KD) of [3H](+)-PN200-110 binding. The kinetic experiments demonstrated that diltiazem significantly reduced both the association and the dissociation rate of [3H](+)-PN200-110 binding, resulting in no significant change in the apparent KD. In contrast, verapamil accelerated dissociation and slowed down association of [3H](+)-PN200-110 binding. Diltiazem appears to alter both the number of [3H](+)-PN200-110 binding sites and the characteristics of [3H](+)-PN200-110 binding.

Heparin exercise treatment following percutaneous transluminal coronary angioplasty in a patient with effort angina

A 63-year-old female with chronic stable effort angina underwent percutaneous transluminal coronary angioplasty (PTCA) for a donating coronary artery of the collateral circulation to the jeopardized region. Because of the inefficacy of the procedure in increasing the collateral flow reserve, the patient was then put on an exercise regimen and also received heparin pretreatment. Her exercise tolerance improved remarkably with the development of improved collateral circulation.

Importance of myocardial ischemia for coronary collateral development in conscious dogs

The purpose of this study was to evaluate the effects of myocardial ischemia on the development of collateral circulation. Thirteen conscious dogs were instrumented for serial measurements of subendocardial segment length in the area perfused by the left circumflex coronary artery, left circumflex coronary artery flow and left ventricular pressure. In 6 dogs (group A), 1 min left circumflex coronary artery occlusions were carried out at 30 min intervals. When the 442nd 1 min left circumflex coronary artery occlusion produced a reduction in segment shortening and a significant reactive hyperemia, the occlusion time was increased to 2 min. In the remaining 7 dogs (group B), 2 min left circumflex coronary artery occlusions were conducted hourly. In group A, following 451 +/- 201 (SD) min of total occlusion time with the mixture of 1 and 2 min left circumflex coronary artery occlusions (43 +/- 18 days) a left circumflex coronary artery occlusion produced no reduction in segment shortening and negligible reactive hyperemia. By contrast, in group B, 218 +/- 99 min of total occlusion time (18 +/- 8 days) was required to develop adequate collateral circulation. The relative contribution of the first and second 1 min of left circumflex coronary artery occlusion to the collateral development was mathematically evaluated. This analysis indicated that the second 1 min of left circumflex coronary artery occlusion is 4.43-fold more effective than the first 1 min of occlusion in terms of the collateral induction. We concluded that severe myocardial ischemia plays an important role in the development of collateral circulation.

[Induction of coronary arterial spasm by intracoronary administration of acetylcholine in patients with vasospastic angina]

To examine whether intracoronary injections of acetylcholine induce coronary artery spasm in patients with vasospastic angina, incremental doses (20, 30 and 50 micrograms) were injected directly into the coronary arteries in 12 patients with variant angina (Group A: rest angina with electrocardiographic ST-segment elevation during attacks), 19 with vasospastic angina (Group B: rest angina and/or effort angina with variable threshold in the treadmill exercise stress test), 11 with organic coronary artery stenosis but without angina (Group C), and 14 without coronary artery disease (Group D). A temporary cardiac pacemaker was positioned in the right ventricle. Coronary artery spasm was defined as severe vasoconstriction (greater than or equal to 90% of reduction in the luminal diameter) with chest pain and/or ischemic changes in the electrocardiogram. Intracoronary injection of acetylcholine induced spasm of at least one coronary artery in all 12 patients (100%) of Group A, in 18 (95%) of Group B, in two (18%) of Group C, and in two (14%) of Group D. Thus, the sensitivity of this method for inducing coronary spasm was 100% in group A, 95% in Group B, and 97% in Group A plus Group B. The specificity for inducing spasm was 86% in Group D, and 84% in Group C and Group D. When acetylcholine was injected separately into the left and right coronary arteries, spasm of both the coronary arteries was observed in two (40%) of Group A, in five (33%) of Group B, and none (0%) of Group C and Group D. Acetylcholine (20 micrograms) induced coronary spasm in 10 (83%) of Group A and only in nine (47%) of Group B.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in isovolumic segment shortening following acute coronary occlusion: disproportionate effects of anterior versus posterior ischemia

We evaluated the changes in left ventricular pressure and isovolumic segment shortening in both the ischemic and nonischemic areas following acute coronary occlusion in 12 conscious dogs instrumented for the measurement of subendocardial segment lengths perfused by the left circumflex coronary artery and left anterior descending coronary artery, and left ventricular pressure. An externally inflatable pneumatic occluder was placed around the left circumflex coronary artery. In 6 dogs, another occluder was installed around the proximal left anterior descending coronary artery. Under the resting conditions, the isovolumic segment shortening in the areas supplied by the left anterior descending coronary artery and the left circumflex coronary artery were 2.1 +/- 0.5% (SE) and -0.1 +/- 0.5% (P less than 0.01; versus values in the area of the left anterior descending coronary artery), respectively. During a 1-min occlusion of the left circumflex coronary artery, the isovolumic shortening in the anterior segment increased to 3.8 +/- 0.5% (P less than 0.001; versus values in the basal state), while the posterior segment produced isovolumic elongation (-2.2 +/- 0.5%, P less than 0.001; versus values in the basal state). By contrast, during a 1-min occlusion of the left anterior descending coronary artery, the extent of isovolumic bulge in the anterior segment and the augmentation in the isovolumic shortening in the posterior segment was less prominent compared with the occlusion of the left circumflex coronary artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of pre-infarction angina for occurrence of post-infarction angina

We evaluated the factors determining the occurrence of post-infarction angina in 41 patients who had intra-coronary thrombolysis within 6 h of the onset of acute myocardial infarction. Pre-infarction angina was considered to be present if it occurred more than one week before acute myocardial infarction. Post-infarction angina was defined as typical chest pain occurring within 10 days following the infarction. Collateral flow to the infarct zone was determined to be present if any portion of the infarct-related epicardial artery or side branches was visualized. In cases of successful thrombolysis, the prevalence of post-infarction angina was not significantly influenced by pre-infarction angina and the extent of collateral circulation. However, in patients without recanalization, pre-infarction angina and collateral blood flow supply to the area at risk caused a high prevalence of angina after infarction. It is concluded that pre-infarction angina indicative of myocardial ischemia is associated with post-infarction angina especially in patients with conventional therapy, because the jeopardized myocardium is salvaged substantially by collateral circulation with a limited flow reserve.