Videodensitometric quantitation of aortic regurgitation by digital subtraction aortography using a computer-based method analyzing time-density curves

To assess the clinical role of computer analysis of time-density curves in the evaluation of aortic regurgitation (AR), digital subtraction aortography (DSA) and cineaortography were performed sequentially in 17 patients with varying degrees of AR (1+ to 4+) and in 4 control patients. DSA was performed at a rate of 30 frames/s on a 512 X 512 X 8 bit pixel matrix using the same total volume and injection rate, but with half the amount of contrast agent as standard cineaortography. A 30 X 30 pixel area of interest was identified in the aorta above the valve plane and in the left ventricle where the AR stream was seen. The density of both areas of interest and the ratio of left ventricular/aortic area of interest density was calculated in each frame and then plotted vs time. The ratio at the end of injection (LVd/Aod) had an excellent correlation with cineaortography (chi 2 = 19, p less than 0.001), ranging from 0 to 0.2 in patients with no AR, 0.2 to 0.5 in those with 1+ AR, 0.5 to 0.7 in those with 2+ AR, 0.7 to 0.9 in those with 3+ AR and more than 0.9 in those with 4+ AR. Thus, quantitative assessment of AR by computer analysis of time-density curves derived from DSA is a new and objective technique with significant clinical potential.

Effects of previous myocardial infarction on measurements of reactive hyperemia and the coronary vascular reserve

The measurement of coronary vascular reserve by the reactive hyperemic response to ischemia has been advocated as a practical method of assessing the physiologic significance of coronary stenoses. Because the concept of measuring coronary blood flow during maximal vasodilation assumes a normal arteriolar network and viable myocardium, the presence of previous myocardial infarction may cause a significant decrease in the coronary reserve unrelated to the severity of a coronary stenosis itself. To determine the potential importance of this effect, rest and hyperemic coronary blood flow were measured in 14 dogs in the regions subtended by the left anterior descending and left circumflex coronary arteries. One hour occlusion of the left anterior descending artery followed by reperfusion was performed in 10 dogs; the 4 remaining dogs in which no occlusion was performed served as control animals (group 3). One week later, rest and hyperemic blood flow measurements were repeated in all 14 dogs. Of the 10 dogs undergoing left anterior descending artery occlusion, 5 had a large infarct (group 1) and 5 had a small infarct (group 2). In group 1 in the 1 week study, both the coronary reserve in the left anterior descending artery zone and the ratio of the coronary reserve in this zone and the left circumflex artery zone decreased compared with values before occlusion (from 425 +/- 134 to 150 +/- 34% and from 1.56 +/- 0.40 to 0.68 +/- 0.31, respectively; both p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic significance of severe narrowing of the proximal portion of the left anterior descending coronary artery

To determine the prognostic importance of significant narrowings involving the proximal left anterior descending coronary artery (LAD), 866 medically treated patients with significant coronary artery disease (CAD) were followed after cardiac catheterization for a mean of 17 months (range 1 to 46). Coronary narrowings in all patients were evaluated based on site relative to large branches and on angiographic severity. Prognosis was best predicted by the presence of at least 70% diameter reductions in the LAD before the first 2 large branches (chi 2 = 16, p = 0.0001). At 3 years, there was a 94% cumulative survival rate in patients with less than 70% stenoses at this location, but an 82% survival rate in patients with 70% or more stenoses (p less than 0.0001). In addition, although the presence of proximal LAD narrowings was the best predictor of prognosis in patients with a low global ejection fraction, this was not so in patients with normal ejection fractions, as this subgroup had an excellent overall prognosis. Thus, the presence and severity of significant stenoses in the proximal LAD are stronger predictors of prognosis than stenoses elsewhere in the major coronary arteries. The presence of an angiographically significant narrowing in this anatomic location is highly correlated with an increased 1- to 3-year mortality rate.

Multistage analysis of exercise radionuclide angiography in coronary artery disease

The hypothesis that serial assessment of left ventricular function during exercise radionuclide angiography provides improved diagnostic criteria for coronary artery disease (CAD) was examined. Fifty-eight consecutive patients without previous myocardial infarction were prospectively scheduled for cardiac catheterization and multistage radionuclide angiographic exercise studies. Forty-one patients had significant CAD. The traditional criterion--failure to achieve a 5% increment in ejection fraction (EF) during exercise compared with the value at rest--had 85% sensitivity but only 41% specificity for CAD. In 12 patients, EF increased early in exercise by at least 4% and then decreased a mean of 7.5%, often with worsening regional wall motion. This "up-down" EF pattern was applied as a diagnostic test in the overall study group. Analysis of changes in EF from the maximal value achieved to that at the end of exercise resulted in criteria with greater sensitivity (p less than 0.0001) for CAD than analysis of changes from rest, with similar specificity. Regional wall motion abnormalities occurring during the first exercise stage resulted in 94% specificity for CAD (p = 0.05 vs end-stage analysis), although sensitivity was low. Analyzing the maximal EF during exercise results in improved sensitivity, while analyzing the early onset of regional dysfunction results in high specificity for CAD.

Analysis of phases of contraction during graded acute myocardial ischemia

The quantitative effects of graded ischemia on the phases of contraction in ischemic and nonischemic myocardium were studied in 10 open-chest dogs. During progressive coronary stenosis, an index of the overall severity of ischemia, total myocardial blood flow deficit (TMFD), was measured using microspheres. Segment shortening (% delta L) during the isovolumic and ejection phases of systole in the ischemic and nonischemic zones was obtained with ultrasonic crystals. In the ischemic zone, total systolic and ejection phase % delta L decreased progressively as stenosis increased; isovolumic phase % delta L showed segment elongation (bulging) during mild ischemia, which was unchanged as ischemia became severe. Total % delta L in the nonischemic zone increased progressively with increasing stenosis, reaching 132 +/- 20% of the control value when TMFD was 24.8 +/- 6.5% of total expected left ventricular (LV) myocardial blood flow. The increase in total % delta L was entirely attributable to increased ejection % delta L and correlated with indices of preload (multivariate r = 0.65) and afterload (multivariate r = 0.62). Multiple linear regression analysis revealed that augmented contraction in the nonischemic zone was best described (multivariate r = 0.94) by a combination of four hemodynamic variables estimating LV preload and afterload, which correlated in turn with the overall severity of ischemia. Thus systolic bulging in the ischemic zone is primarily an isovolumic phase phenomenon that develops initially with mild ischemia. Little additional change occurs in the isovolumic phase as ischemic severity increases, although further reductions in shortening occur in the ejection phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Rate of left ventricular functional recovery by radionuclide angiography after exercise in coronary artery disease

To characterize determinants of the rate of recovery of left ventricular (LV) function after exercise-induced ischemia, sequential postexercise radionuclide angiography was performed prospectively in 38 consecutive patients with documented coronary artery disease (CAD). In each patient new or increased regional asynergy developed or absolute ejection fraction decreased at least 4% during exercise. Twenty patients showed immediate recovery of LV function after exercise (group 1) and 18 showed delayed recovery (group 2). Ejection fraction in the first postexercise period was significantly greater in group 1 (65 +/- 12%) than in group 2 (55 +/- 11%) (p less than 0.01). The mean number of coronary arteries with at least 70% diameter narrowing was greater in group 2 (2.7 +/- 0.5) than in group 1 (2.0 +/- 0.9) (p = 0.026); CAD score was also greater in group 2 than in group 1 (p = 0.005). The increase in LV end-diastolic volume from rest to end exercise was greater in group 2 than in group 1 (p = 0.005); neither the change in LV volume nor the change in heart rate or blood pressure after exercise separated the groups. The only independent predictor of the rate of functional recovery was the degree of exercise-induced regional myocardial asynergy (p less than 0.001). Thus, exercise radionuclide angiography in patients with CAD provides a model for evaluating postischemic myocardial function. Delayed functional recovery is associated with extensive exercise-induced regional asynergy as a result of severe CAD and is not primarily influenced by hemodynamic changes.

Prospective evaluation of the severity of coronary artery disease with exercise radionuclide angiography and electrocardiography

To evaluate the utility of exercise radionuclide angiography (RNA) and electrocardiography in assessing the severity of coronary artery disease (CAD), 185 patients undergoing coronary angiography were studied prospectively. To avoid work-up bias and to provide an appropriate control group, all patients were simultaneously scheduled for exercise RNA and electrocardiography and for coronary arteriography. All test results were interpreted blinded to other data. Of multiple exercise variables analyzed by stepwise linear discriminant analysis, the independent predictors of disease severity were exercise ejection fraction, ST segment change, and maximum heart rate. These three variables were used to create a set of four equations that determine probabilities of zero, one-, two-, or three-vessel disease (VD). The noninvasive estimate of number of VD in each patient was compared to the angiographic result. Patients without significant CAD were classified correctly 71% of the time, while those with three-VD were predicted correctly in 80%. Fully 90% of patients with predicted three-VD had two- or 3-VD. Conversely, 84% of patients predicted to have zero VD had zero or one-VD. Thus the combined use of exercise RNA and ECG data permits assessment of the presence and severity of CAD.

Analysis of systolic bulging. Mechanical characteristics of acutely ischemic myocardium in the conscious dog

To determine the mechanical factors affecting regional segmental motion after acute coronary occlusion, we studied seven conscious dogs, instrumented with sonomicrometers. Loading conditions were changed by the withdrawal of 500 ml of blood and the transfusion of 800 ml of blood. To express segmental motion, percent systolic shortening, percent systolic elongation, and early diastolic shortening were calculated. Blood withdrawal decreased left ventricular preload, increased percent systolic elongation (from 6.9 +/- 3.1% to 9.9 +/- 3.5%) and early diastolic shortening (12.9 +/- 5.3% to 16.6 +/- 5.3%), and decreased percent systolic shortening. Blood transfusion increased left ventricular preload, decreased percent systolic elongation (to 5.2 +/- 1.8%) and early diastolic shortening (8.8 +/- 2.9%), and increased percent systolic shortening. Manipulation of loading did not change regional myocardial blood flow. In acutely ischemic myocardium, the tension-length loop showed an exponential upstroke during isovolumic systole and a nearly superimposed exponential downstroke during the isovolumic relaxation phase after systole, compatible with essentially passive movement as seen with an elastic material. The changes in loading conditions affected the tension-length curve to a very minor extent. The uniformity of the curve and its exponential shape explain the load-dependency of systolic bulging and segmental motion. It is concluded that systolic bulging depends on the change in the preload tension due to the compliant portion of tension-length curve, and that shortening of ischemic myocardium during the isovolumic relaxation phase is a completely passive phenomenon.

Left ventricular ejection fraction after acute coronary occlusion in conscious dogs: relation to the extent and site of myocardial infarction

The change in left ventricular radionuclide ejection fraction after acute occlusion of the left anterior descending (LAD) or circumflex (LC) coronary artery was compared with the ultimate histologic extent of myocardial infarction in conscious dogs. The acute change in ejection fraction correlated with size of infarction in 14 dogs with occlusions of the LAD coronary artery (r = .89, y = 1.12x + 14.2) and in 27 dogs with occlusions of the LC coronary artery (r = .71, y = 0.73x + 7.9); the slope of the regression equation was greater (p less than .05) for those with LAD than for those with LC occlusions. Multivariate analysis revealed no independent contribution of left ventricular weight, the subendocardial extent of infarction, or change in heart rate to the acute change in ejection fraction. These data indicate that the decrease in ejection fraction after coronary occlusion is determined primarily by the size of the ischemic area, which also determines size of infarction. In dogs instrumented over a long term, infarcts in the LAD myocardial distribution result in greater decreases in ejection fraction than infarcts of comparable size in the LC distribution.

Relation between left ventricular global and regional function and extent of myocardial ischemia in the canine heart

To develop a quantitative relation between the overall severity of acute ischemia and left ventricular global and regional function, two minor axis internal diameters and myocardial wall thickness were determined using ultrasonic crystals in 10 open chest dogs with carotid-left anterior descending artery cannulation. The overall extent of ischemia produced by graded stenosis of the cannulation system was estimated by total myocardial blood flow deficit, calculated using radioactive microspheres and a balloon-reservoir perfusion technique permitting precise separation of ischemic from nonischemic tissue. Although cardiac output and left ventricular stroke work were maintained through chamber enlargement until total myocardial blood flow deficit was about 10%, ejection indexes of left ventricular function decreased progressively with increasing ischemia and correlated inversely with total myocardial blood flow deficit (r = -0.55 to -0.73). Ejection indexes of left ventricular global function correlated directly with regional function in the ischemic zone (r = 0.67 to 0.83), although global function decreased at a far slower rate than regional contraction during progressive coronary stenosis with an ischemic region comprising about 25% of total left ventricular weight. During myocardial ischemia, regional dysfunction resulted in progressive global contractile dysfunction; left ventricular hemodynamic status was maintained until ischemia was severe.

Sinus rhythm mapping in healed experimental myocardial infarction: contrasting activation patterns for inducing ventricular tachycardia versus fibrillation

The inducibility of ventricular tachycardia (VT) and fibrillation (VF) is variable in healed myocardial infarction (MI) in the dog. To better understand the electrophysiologic basis for these arrhythmias, MI was produced in dogs by ligating the left anterior descending artery. One week later, epicardial mapping was performed with the dog in sinus rhythm using a hand-held bipolar electrode. Transmural mapping was performed with the dog in sinus rhythm with 4 pairs of bipolar electrodes mounted on a #14 needle. Ventricular arrhythmias were induced by the S1S2S3 technique or 3- to 5-beat burst pacing at twice diastolic threshold. Only VF could be induced in 11 dogs, while sustained VT was induced in 6 dogs. Significantly more marked and more extensive delay in activation was seen both in the epicardium and transmurally in dogs with VT than in dogs with VF. In addition, dogs with VT had morphologic evidence of a large transmural MI, whereas dogs with VF had only a subendocardial MI. It is concluded that inducible sustained VT in the dog is usually associated with a large transmural MI and an activation sequence in sinus rhythm characterized by an extensive area of marked delay in activation. This activation pattern in sinus rhythm presumably is necessary to provide the underlying electrophysiologic milieu for sustained reentry.

A sequential approach to the diagnosis of coronary artery disease using multivariate analysis

There has been considerable interest in recent years in enhancing the accuracy of noninvasive tests in diagnosing coronary artery disease. The recognition that no currently available test is a perfect predictor has led to the use of probability analysis as a means of assessing the presence or absence of coronary disease. In this article we present a multivariate approach to the diagnosis of coronary disease. One hundred forty-seven patients undergoing coronary angiography, thallium-201 imaging, and exercise ECG were studied. Patients were classified according to age, sex, and typical vs atypical chest pain. Sequential stepwise logistic regression analysis was performed to develop probability statements prior to testing, after exercise ECG, and after exercise ECG and thallium-201. The results indicate that this sequential approach can be used to develop strategies for the diagnosis of coronary disease in the same way as Bayes' theorem, while permitting integration of multiple characteristics into one model.

Influence of nitroglycerin on collateral blood flow during acute ischaemia in the dog

To investigate the effects of nitroglycerin on collateral blood flow 10 open chest dogs underwent coronary occlusion followed by nitroglycerin infusion (80 to 300 micrograms . min-1) to lower mean systemic blood pressure by 20 mmHg, followed by phenylephrine infusion (10 to 40 micrograms . min-1) to restore blood pressure to the pre-nitroglycerin level. Myocardial blood flow was measured with microspheres. The contribution of overlapping normal zone tissue in the ischaemic zone was evaluated with the balloon perfusion technique. Collateral flow was measured with microspheres in the most ischaemic tissue. In addition "load line" analysis was used to calculate collateral flow from retrograde flow. Nitroglycerin lowered blood flow to non-ischaemic tissue, and tended to lower blood flow to ischaemic tissue. Phenylephrine restored blood flow to the value after coronary occlusion. Load line analysis data was similar to data on myocardial blood flow from the microspheres. Collateral resistance changed little during the experiment. Th effects of nitroglycerin on collateral blood flow are, thus, minimal. While it is possible that under special circumstances there may be some decrease in collateral resistance, the bulk of data from this study and others do not support the idea that systemic infusion of nitroglycerin in the setting of an acute myocardial infarction will affect collateral flow.

Importance of total life consumption of cigarettes as a risk factor for coronary artery disease

Cigarette smoking is an established risk factor for the occurrence of cardiovascular events and mortality. Whether recent smoking history or total life consumption best represents the increased risk due to smoking has not been previously established. Thus, stepwise logistic regression analysis was used to determine the relative contributions of these factors to the risk of having significant coronary artery disease in 1,349 patients who underwent cardiac catheterization. Six risk factors were analyzed: total pack-years, current packs smoked per day, age, gender, family history and symptomatic status. The results of this analysis showed that total pack-years, but not current packs per day, is a significant independent risk factor for the development of coronary artery disease. This was true in every age group up to but not older than age 70 years. Although the overall risk was lower in younger patients and in patients with less typical symptoms of angina, the relative risk in cigarette smokers relative to pack-years was consistently greater. The risk of total life consumption of cigarettes is thus greater than has heretofore been realized, particularly in persons who would otherwise be categorized as low risk.

Quantitative thallium-201 imaging: limitations in detecting pathophysiologically significant obstructive coronary artery disease

Washout of thallium-201 after stress testing has been proposed as a method of detecting abnormal zonal myocardial perfusion without relating it to a reference "normal" area. Therefore, 18 patients with single-vessel coronary artery disease, undergoing percutaneous transluminal coronary angioplasty, underwent maximum stress testing and thallium imaging. A myocardial perfusion defect was seen in the immediate postexercise images in all 19 zones (one patient studied twice) supplied by the vessel with the obstructive lesion. Delayed images showed improvement in 15 of the 19 segments. Of the four zones which did not improve, three had evidence of a prior nontransmural myocardial infarction. Quantitative analysis of washout curves showed that counts decreased in 17 of 19 zones after background subtraction and in all 19 zones if background was not subtracted. In the corresponding normal zones directionally similar decreases in counts were seen. Thus washout characteristics were similar for both diseased and normal zones. These data indicate that washout curves are limited in their ability to detect the presence of a physiologically significant lesion.

Pseudocoarctation of the aortic arch in a patient with Turner's syndrome

Pseudocoarctation of the aortic arch is a rare congenital anomaly which resembles true coarctation by the presence of a narrowing in the descending thoracic aorta immediately distal to the origin of the left subclavian artery. However, it is differentiated from that entity by the absence of a significant hemodynamic obstruction and by the presence of aneurysmal dilatation proximal and distal to the area of narrowing. As a result, the commonly observed clinical findings of coarctation such as a prominent collateral circulation and decreased blood pressure in the lower extremities are not observed. "Kinking" or "buckling" are common adjectives used to describe the roentgenographic appearance of the aortic arch in this condition. The association of various congenital cardiac abnormalities with pseudocoarctation has been reported, and are similar to those commonly seen with true coarctation. We now present the first reported case of pseudocoarctation associated with a probable bicuspid aortic valve in a patient with Turner's syndrome.

Contrasting incidence, inducibility, and transmural sites of origin of ventricular arrhythmias during acute coronary occlusion and reperfusion

The incidence, inducibility, and sites of origin of ventricular arrhythmias were studied in 16 open-chest dogs. The dogs were placed on cardiopulmonary bypass. Electrograms from ischemic endocardium and epicardium and normal epicardium were recorded with bipolar composite electrodes. Burst pacing was used to induce arrhythmias. Dogs were studied in the control state, 15 minutes after left anterior descending coronary artery occlusion, and during reperfusion performed after 20 minutes of occlusion. Ventricular fibrillation was seen more commonly (in 8 of 14 dogs) during reperfusion than during occlusion (in 4 of 13 dogs). Continuous fragmented electrical activity was first recorded on the ischemic zone epicardium in six of eight episodes during occlusion arrhythmias and on the endocardium in 25 of 33 episodes during reperfusion. These data may relate to the effects of varying degrees of ischemia and reperfusion on conduction characteristics of the respective layers.

Evaluation of "ischemia at a distance": effects of coronary occlusion on a remote area of left ventricle

The effect of coronary occlusion on blood flow and function in a remote zone of the left ventricle was studied in 21 open-chest dogs. Group A consisted of 6 dogs not undergoing left circumflex (LC) coronary artery cannulation. The other 15 dogs underwent cannulation of the LC artery followed by partial occlusion to 40 mm Hg diastolic perfusion pressure. Of these dogs, 7 with constant perfusion pressure (group B) were separately evaluated from 8 with declining perfusion pressure (group C). Sequentially more proximal left anterior descending (LAD) occlusions were performed in each group. Blood flow in the LC zone remained unchanged in group A after sequential LAD occlusions, whereas in groups B and C distal and proximal LAD occlusions caused progressive reduction in LC flow. Although in group A segment shortening improved in the LC zone after distal LAD occlusion, in groups B and C progressive impairment in segmental shortening was observed in the LC zone after distal and proximal LAD occlusions. Thus, in the setting of critical coronary stenosis in a zone, total occlusion in another coronary artery can initiate a series of events leading to decreased blood flow in the territory of the stenotic coronary artery, resulting in ischemia and impaired segmental function.

Epicardial, endocardial and transmural mapping in assessing electrophysiological effects of 14-C lidocaine and 14-C propafenone on activation times in experimental chronic myocardial infarction. Correlations with myocardial drugs concentrations

The electrophysiological effects of lidocaine (L) and propafenone (P) in chronic myocardial infarction in relation to tissue drug concentrations (TDC) are unknown. Thus of 16 dogs with one week old myocardial infarction, 8 received propafenone 2 mg/kg and 8 lidocaine 5 mg/kg followed by 0.2 mg/kg/min of either drug for 60 min. Epicardial (EPI) mapping (greater than 30 points) was performed with a bipolar electrode. Endocardial (ENDO) and transmural (TRANS) mapping (greater than 20 points) were performed with 4 pairs of needle mounted bipolar electrodes. The % change in activation times (% delta AT) in EPI, ENDO and TRANS was evaluated in normal (N) and infarcted (I) zones at control and 60 min after drugs. Ventricular arrhythmias (VA) were studied with programmed extra stimulation. Results (P less than 0.01 to L, P less than 0.01 to N zone, # P less than 0.05 to ENDO): (Table: see text) At 60' ventricular tachycardia and ventricular fibrillation were both still inducible in 50% in the lidocaine group (37% in control), while only in 16% in the propafenone group (62% in control). Despite lower drug concentrations in the infarct, the effects on AT are comparable to normal zones for both drugs. In conclusion lidocaine reduces and propafenone increases AT, affecting in opposite directions the inducibility of reentrant ventricular arrhythmias.

Critical analysis of the application of Bayes' theorem to sequential testing in the noninvasive diagnosis of coronary artery disease

The utility of Bayes' theorem in the noninvasive diagnosis of coronary artery disease (CAD) was analyzed in 147 patients who underwent electrocardiographic stress testing, thallium-201 perfusion imaging and coronary angiography. Eighty-nine patients had typical anginal chest discomfort and 58 had atypical chest pain. Sensitivity and specificity of the tests and prevalence of CAD at each level of testing were tabulated and compared with the results generated from Bayes' theorem. The sensitivity of electrocardiographic stress was higher in patients with multivessel CAD than in patients with 1-vessel CAD. Sensitivity, but not specificity, of each test was dependent, in part, on the result of the other test. However, the probabilities calculated from Bayes' theorem when used for sequential testing are remarkably close to the tabulated data. Thus, Bayes' theorem is useful clinically despite some evidence of test dependence. Sequential test analysis by Bayes' theorem is most useful in establishing or ruling out a diagnosis when the pretest prevalence is approximately 50% and when the 2 tests are concordant.

Variable effects of intracoronary nitroglycerin on myocardial blood flow and segmental shortening according to dose and degree of coronary occlusion

The effects of intracoronary nitroglycerin were determined in 21 open-chest dogs. Six dogs with severe stenosis (25 mm Hg diastolic perfusion pressure) and nine dogs with moderate stenosis (40 mm Hg) received a 12 micrograms bolus followed by 44 micrograms/min intracoronary nitroglycerin. In addition, six dogs with moderate stenosis (40 mm Hg) received 5 micrograms followed by 5 micrograms/min nitroglycerin. Myocardial blood flow was measured with radioactive microspheres and segment shortening with ultrasonic crystals. At 40 mm Hg, high-dose but not low-dose nitroglycerin raised epicardial blood flow, while at 25 mm Hg nitroglycerin had no effect. Subendocardial blood flow was not affected in any group. Partial occlusion resulted in a decrease in segment shortening in the 25 mm Hg group but not at 40 mm Hg. High-dose nitroglycerin had no effect on shortening at either level of occlusion. Thus, in the presence of coronary vascular reserve, high-dose nitroglycerin may overcome coronary autoregulation. A dose equivalent to one that simulates the amount of nitroglycerin delivered to the coronary circulation by a systemic infusion did not affect myocardial blood flow. In addition, even a large dose of nitroglycerin did not affect segment shortening.

Influence of nifedipine on collateral blood flow during acute ischemia in the dog

Vasodilators have been found effective in increasing blood flow in the lateral border surrounding a central zone of infarction, but any change in blood flow to this border zone may be to the normal tissue in this zone, rather than to the ischemic tissue. In this study of the effects of nifedipine on collateral blood flow, 31 open chest dogs underwent coronary occlusion followed by nifedipine infusion, either 3 or 1 microgram/kg per min. A balloon perfusion microsphere labeling device was used to separate the influence of normally perfused tissue overlapping with ischemic tissue in the lateral border zone. Nifedipine increased blood flow in the border zone, but this increase could be accounted for by the effect of nifedipine on admixed normal tissue. In the central ischemic zone, nifedipine administration resulted in a decrease in collateral blood flow. Thus, to fully understand the effect of a vasodilator on ischemic zone blood flow, it is necessary to account for flow in overlapping normal tissue.

Contrasting effects of nifedipine and verapamil on myocardium and vascular smooth muscle at two levels of coronary occlusion in the dog

The calcium flux inhibitors nifedipine and verapamil have recently been used in the setting of both classical Heberden's and variant angina. It has also been suggested that these agents may preserve function and viability of threatened myocardium. The effects of these agents on the relationship between myocardial blood flow and contraction in the setting of partial coronary occlusion is unknown. Thus 39 open-chest dogs underwent partial coronary occlusion to diastolic perfusion pressures of 25 or 40 mm Hg. The dogs then received intracoronary infusions of 10 micrograms nifedipine or 100 micrograms verapamil. Myocardial blood flow was measured with tracer microspheres and myocardial shortening was assessed with ultrasonic crystals. At 25 mm Hg nifedipine improved myocardial shortening while blood flow did not change. In contrast, verapamil caused shortening to be abolished but also did not change blood flow. At 40 mm Hg nifedipine, while not affecting shortening, caused a "redistribution" of blood flow from endocardium to epicardium; in contrast, verapamil again caused shortening to be abolished, but only increased epicardial blood flow leaving endocardial flow intact. Thus verapamil and nifedipine have differing effects. Nifedipine is a potent vasodilator at doses having no negative inotropic effects. In addition, nifedipine can cause a transmural "redistribution" of blood flow from endocardium to epicardium. In contrast, verapamil is also a potent vasodilator, but has profound negative inotropic effects.

Contrasting ischemic contraction patterns by zone and layer in canine myocardium

The effect of graded coronary occlusion on myocardial shortening in different zones of the left ventricle is not clear. Therefore, in 15 dogs ultrasonic crystals were used to evaluate the effect of graded coronary occlusion on subendocardial and subepicardial contraction in both the left anterior descending coronary artery (LAD) and left circumflex coronary artery (Circ) distributions. Subepicardial shortening was evaluated along both the long and short axes. In the LAD zones, segment shortening decreased in parallel in the subendocardium and subepicardium. In the circumflex zone subendocardial and subepicardial long axis shortening fell off in parallel, while subepicardial short axis shortening fell off more rapidly. Thus there is a close relationship between endocardial and epicardial segment shortening following graded coronary occlusion. In the circumflex zone, however, fiber orientation may affect the measurement of segment motion.

Comparative effects of nitroglycerin and nifedipine on myocardial blood flow and contraction during flow-limiting coronary stenosis in the dog

Both nifedipine and nitroglycerin are used to treat angina pectoris. The comparative effects of these agents on myocardial blood flow and contraction in the setting of flow-limiting coronary stenosis are poorly understood. Thus 24 open chest dogs underwent carotid to left anterior descending coronary arterial perfusion with coronary flow probe and perfusion pressure monitoring. Segment length was measured with ultrasonic crystals in the subendocardial ischemic and nonischemic zones. Myocardial blood flow was measured with radioactive microspheres. Partial coronary occlusion was performed to attain a diastolic perfusion pressure of 40 mm Hg. Twelve dogs received intravenous nifedipine, 3 micrograms/kg per min, and 12 received intravenous nitroglycerin to reduce aortic pressure by 20 mm Hg. Partial occlusion resulted in a slight but significant decrease in segment shortening in the ischemic zone. Neither nitroglycerin nor nifedipine affected shortening in the ischemic zone. After occlusion, blood flow decreased in the subendocardial ischemic zone but was unchanged in the subepicardium. Nifedipine increased subendocardial blood flow in the nonischemic zone and decreased it in the ischemic zone but caused no change in subepicardial flow in the ischemic zone. In contrast, nitroglycerin decreased subendocardial and subepicardial blood flow in both the ischemic and nonischemic zones. In the setting of coronary stenosis, different classes of vasodilators may have varying effects on myocardial blood flow, suggesting different sites and mechanisms of action. In addition, segment function may not always reflect changes in myocardial blood flow.

Spatial distribution of [14C]-lidocaine and blood flow in transmural and lateral border zones of ischemic canine myocardium

The purpose of this study was to determine the spatial distribution of lidocaine relative to blood flow in ischemic, normal and border zone canine myocardium. Ischemic zone tissue was distinguished from normal zone tissue by a special microsphere technique in adjacent sections 4 to 5 mm wide from the center to the lateral border of the ischemic region in 14 open chest dogs. Gamma-labeled microspheres were separated by a special technique from carbon-14 ([14C])-lidocaine in the same tissue sample. Blood flow (mean value +/- 1 standard deviation) was reduced to 46 +/- 25 percent of normal in the ischemic subepicardium and 17 +/- 18 percent of normal in the subendocardium. [14C]-lidocaine was 0.56 +/- 0.12 microgram/g in normal myocardium 10 minutes after bolus injection of [14C]-lidocaine; it was reduced to 91 +/- 15 percent of normal in ischemic subepicardium and 58 +/- 12 percent of normal in the subendocardium. Blood flow and lidocaine concentration were uniformly lowest in gross samples from the central and intermediate ischemic zones, and highest in the gross samples from the border normal zone (p less than 0.05). The values for flow and lidocaine in samples from the border ischemic zone were intermediate, that is, higher than values from central ischemic (p less than 0.05) and lower than values from border normal zone samples (p less than 0.05). However, the labeling technique for normal zone tissue revealed that the values of blood flow and lidocaine in the gross samples from the lateral border of the ischemic zone were intermediate between those of adjacent ischemic and normal samples because of the mixture of overlapping normal and ischemic tissues components--not because of a unique mildly ischemic region. Both blood flow and lidocaine concentration were lower in the subendocardial third than in the subepicardial third of the ischemic zone (p less than 0.05) even after the contribution of normal zone tissue was subtracted, suggesting a gradient of ischemia across the transmural border zone. In conclusion, lidocaine is distributed uniformly in ischemic components from the center to the lateral border of the ischemic zone, but there is an endocardial to epicardial gradient. Both lateral and transmural border zone distributions must be considered to understand the mechanisms of drug effects in myocardial ischemia.

The effects of nifedipine on myocardial blood flow and contraction during ischemia in the dog

Nifedipine has been proposed as an agent to preserve viability and function of ischemic myocardium. We studied 23 open-chest dogs that underwent carotid-to-left anterior coronary artery perfusion with flow probe and perfusion pressure monitoring. Segment length was measured with ultrasonic crystals in the ischemic and nonischemic endocardium. Myocardial blood flow was measured with radioactive microspheres. Partial coronary occlusion was performed to 25 mm Hg diastolic perfusion pressure. Ten dogs received intracoronary nifedipine, 10 micrograms, and 13 dogs received i.v. nifedipine, 3 micrograms/kg/min. Nifedipine resulted in an increase in segmental shortening in both groups, but nonischemic zone shortening did not change in either group. Nifedipine did not affect myocardial blood flow in the ischemic zone, but increased flow in the nonischemic zone in the group that received i.v. nifedipine. Thus, nifedipine appears to have a direct beneficial effect on ischemic myocardium.

Variable effect of nifedipine on myocardial blood flow at three grades of coronary occlusion in the dog

The effect of nifedipine on myocardial blood flow at various grades of coronary stenosis is unknown, Thus 22 open-chest dogs underwent carotid to left anterior descending perfusion with flow and perfusion pressure monitoring. Grades of coronary occlusion were defined by minimum diastolic perfusion pressure. six dogs (group 1) underwent moderate occlusion to 50 to 55 mm Hg diastolic perfusion pressure; (group 2), severe occlusion to 40 mm Hg perfusion pressure; and six (group 3), more severe occlusion at 25 mm Hg. Regional myocardial blood flow was measured with radioactive microspheres before and after the intracoronary injection of 10 microgram of nifedipine. In group 1, nifedipine induced epicardial hyperemia and little change in endocardial flow in the ischemic zone. In group 2, nifedipine induced epicardial hyperemia from 1.06 to 1.39 mg/g per min, but endocardial flow decreased from 0.70 to 0.60 ml/g per min. In group 3, there was no change in blood flow. Thus the effect of nifedipine on myocardial blood flow depends on the extent of occlusion. Furthermore for certain degrees of occlusion, redistribution of blood flow from endocardium to epicardium has been shown to occur.

The relationship between myocardial blood flow and contraction by myocardial layer in the canine left ventricle during ischemia

We investigated the relationship between regional myocardial blood flow (MBF) and segmental shortening in 17 open-chest dogs. The left anterior descending coronary artery was cannulated and perfused from the left carotid while measuring perfusion pressure. Graded occlusion was produced by a screw clamp. Extent of occlusion was monitored by perfusion pressure. Percent systolic shortening (% delta L) was measured using ultrasonic crystals implanted in normal and ischemic endocardium and ischemic epicardium. MBF was measured in ischemic and normal endocardium and epicardium with tracer microspheres. Dogs underwent 1 to 4 grades of coronary stenosis. Myocardial blood flow both to endocardium and epicardium was found to be linearly related to diastolic perfusion pressure below 50 mmHg (r = 0.803 and 0.748, respectively). Normalized % delta L (N% delta L) was best related to fraction normal zone MBF in the endocardium by the sigmoidal equation, N% delta L = e9.01 MBF-4.03/1 + e9.01 MBF-4.03. % delta L was only weakly related to myocardial blood flow in the epicardium (r = 0.584), and, in four dogs, % delta L was zero in the epicardium despite normal regional blood flow. However, % delta L in the epicardium was linearly related to % delta L in the endocardium (r = 0.78). Thus, endocardial wall motion is related to MBF by a sigmoidal relationship while epicardial wall motion is tethered to endocardial wall motion.