Mechanisms of transient augmentation of myocardial contraction after a brief coronary occlusion

The purpose of this study was 1) to clarify whether augmented myocardial contraction after a brief coronary occlusion, i.e. post-ischemic hypercontraction, depends on a transient increase in coronary blood flow or preceding myocardial ischemia, and 2) to identify the role of catecholamines or calcium flux in this phenomenon. Sixteen mongrel dogs were examined in open-chest anesthetized condition. One-minute reperfusion after two-minute total coronary occlusion of the left anterior descending artery resulted in a transient increase in segment shortening. Intracoronary administration of adenosine caused hyperemia without any changes in segment shortening. Two minutes of total coronary occlusion with adenosine caused post-ischemic hypercontraction to the same degree, but without any additional hyperemia. Two minutes of partial occlusion with 75% flow reduction caused less post-ischemic hypercontraction. Post-ischemic hypercontraction did not occur after partial occlusion with 50% flow reduction, irrespective of hyperemia with adenosine during reperfusion. Propranolol or verapamil did not prevent this phenomenon. Thus, post-ischemic hypercontraction is not dependent on the transient increase in coronary blood flow, but is related to the preceding myocardial ischemia. Local release of catecholamines is not likely to be the cause. A calcium antagonist, verapamil, did not modify this phenomenon. The precise mechanism of this phenomenon is still uncertain, although some alterations in cellular hemostasis, such as ionic changes, are likely to be the cause.

[Recurrent ischemia after acute myocardial infarction: clinical profile and significance of electrocardiographic ST changes during the attacks]

This study investigated the clinical characteristics of acute myocardial infarction (AMI) complicated by recurrent ischemia, especially relating to the electrocardiographic ST changes during the attacks. Fifty-six patients with AMI were complicated by recurrent ischemia (ischemia group), and 238 were not (non-ischemia group). The ischemia group was preceded by prior episodes of angina or myocardial infarction in 88%, as compared with 65% in the non-ischemia group (p less than 0.05). There were non Q wave infarction in 45% of the ischemia group, and 24% of the non-ischemia group (p less than 0.05). The overall in-hospital mortality rate was similar in the ischemia group (13%) and in the non-ischemia group (17%), although the causes were predominantly pump failure in the former and cardiac rupture in the latter. ST segment elevation occurred in 29 patients and ST depression occurred in 26 patients of the ischemia group during the attacks. Multivessel coronary arterial lesions were more frequently present in the latter subgroup than the former (38% vs 79%, p less than 0.05). The in-hospital cardiac deaths were also more frequently noted in the latter subgroup. Recurrent ischemia after AMI with concomitant electrocardiographic ST depression is a high risk subgroup, and, therefore, aggressive revascularization procedures may be indicated in such cases if suitable.

Left ventricular ejection performance in mitral stenosis, and effects of successful percutaneous transvenous mitral commissurotomy

Impaired left ventricular ejection performance was reported in pure mitral stenosis. The speculative mechanisms included insufficient preload, increased wall stress, high right ventricular pressure and unknown myocardial factors, but no definitive mechanism has been established. Fifteen patients with tight mitral stenosis who underwent successful percutaneous transvenous mitral commissurotomy were studied to ascertain whether ejection performance would improve with sufficient blood filling. The indexes of preload (end-diastolic volume) and ejection performance (stroke volume, ejection fraction, and mean systolic and mean normalized ejection rates) were calculated angiographically before and immediately after mitral commissurotomy. Improved blood filling (the result of successful mitral commissurotomy) produced an increase in end-diastolic volume (mean +/- SD 99.0 +/- 30.2 to 112.1 +/- 30.1 ml/m2; p less than 0.05). All 4 indexes of ejection performance also improved. There was good correlation between end-diastolic and stroke volumes before intervention (stroke volume = 0.476 x end-diastolic volume + 16.77; r = 0.76), and the relation between them showed no change even after mitral commissurotomy. It is concluded that both left ventricular preload and ejection performance improved after successful percutaneous transvenous mitral commissurotomy. Insufficient preload could affect ejection performance in patients with tight mitral stenosis.

[Left ventricular blood filling in patients with severe mitral stenosis: comparisons before and soon after percutaneous transluminal mitral commissurotomy]

To clarify the effects of mitral obstruction on left ventricular (LV) diastolic blood filling, 15 patients with tight mitral stenosis (each mitral valve area was less than 1.5 cm2) were studied. Each selected patient underwent successful percutaneous transluminal mitral commissurotomy (PTMC), which resulted in a 1.5 fold increase in each mitral valve area. LV pressure, left atrial (LA) pressure and cardiac output were measured before and immediately after PTMC. Left ventriculography was performed before and immediately after PTMC. The ventriculogram was traced frame by frame for one cardiac cycle. The LV volume curve was obtained from the traced image using a computer. The LV end-diastolic and end-systolic volumes (EDVI, ESVI), and ejection fraction in the subsequent cardiac cycle were calculated. The diastolic filling period was divided into 3 equal parts: namely, early, mid-, and late diastole. The blood volume entering the LV during early, mid-, and late diastole, which indicated the filling properties of each part, were calculated. After successful PTMC, both the mitral valve area (1.1 +/- 0.3 cm2 to 1.9 +/- 0.6 cm2, p < 0.01) and the cardiac index (3.2 +/- 0.8 l/min/m2 to 3.6 +/- 1.1 l/min/m2, p < 0.05) increased with the decreases in the mean diastolic pressure gradients between the LA and LV (13.4 +/- 4.5 mmHg to 5.9 +/- 2.6 mmHg, p < 0.01). The blood volume entering the LV during early diastole increased significantly without significant change in the blood volume entering the LV during mid- and late diastole.(ABSTRACT TRUNCATED AT 250 WORDS)

Diastolic pressure-volume relationship during handgrip exercise in patients with coronary artery disease

There is some controversy regarding the mechanisms of an upward shift in the left ventricular diastolic pressure-volume curve during ischemia. The effects of handgrip exercise on the pressure-volume curve were examined in 21 patients with coronary artery disease and in 6 control subjects. Pressure-volume curves were constructed from digitized left ventricular pressure and volume derived from biplane left ventriculogram. Diastolic pressure-volume curve shifted upward in 12 patients with coronary artery disease during handgrip exercise (Group 1), but not in the other 9 patients who were similarly afflicted (Group 2). The upward shift did not occur in any control subject. No difference was observed in rate-pressure product gain during exercise. In Group 1, left ventricular end-diastolic pressure increased (p less than 0.01) and ejection fraction was reduced (p less than 0.01), although it did not change in Group 2. In Group 1, the time constant was prolonged (p less than 0.01) with no change in the coefficient for elastic modulus. In Group 2, these parameters remained unchanged. Group 1 was accompanied by more extensive asynergy than Group 2. Thus, isometric handgrip exercise resulted in an upward shift in the diastolic pressure-volume curve in patients with coronary artery disease. Incomplete relaxation and/or the viscoelastic properties of the left ventricle associated with ischemia could be responsible for this phenomenon.

Variations in myocardial contraction sequence under various hypoxic conditions

Hypokinetic myocardial segment motion is observed in various pathophysiologic conditions. The aim of this study was to clarify the mechanisms involved in differences in segment motion of hypokinesis. Nineteen open-chest dogs were studied with regard to myocardial segment length, left ventricular pressure, and internal minor-axis diameter. Sequential instantaneous myocardial elastance [alpha(t) curve] was calculated under 4 different hypoxic conditions: complete coronary occlusion and reperfusion, partial coronary occlusion, coronary microembolization, and anoxic perfusion. The alpha(t) curve peaked at end-systole in the case of normal contraction; but it was almost totally flat when complete bulging occurred. The hypokinesis which occurred during development of the complete systolic bulge immediately after complete coronary occlusion had an earlier alpha(t) peak curve than the hypokinesis resulting from partial coronary stenosis (209.5 +/- 35.6 ms after end-diastole vs. 261.9 +/- 18.2 ms; p less than 0.02), microsphere injection into the coronary artery (243.2 +/- 24.5 ms vs. 289.3 +/- 15.4 ms; p less than 0.05), or anoxic perfusion (213.4 +/- 40.2 vs. 275.6 +/- 28.3 ms; p less than 0.05). The early alpha(t) peak resulted in a late-systolic bulge in segment length motion. In conclusion, hypokinetic segment motion differed depending on whether the coronary blood flow was present or not. A late-systolic bulge only developed immediately after complete coronary occlusion, and resulted from an abrupt decrease in myocardial stiffness during the cardiac cycle, which is closely related to the abrupt cessation of coronary blood flow.

A case of malignant lymphoma simulating acute myocardial infarction

A patient with malignant lymphoma suddenly collapsed, and ST segment elevation with complete atrioventricular block was observed on his electrocardiogram during an episode resembling acute myocardial infarction. Cardiac cineangiography revealed posterobasal asynergy of the left ventricle with no significant obstruction in the coronary arterial tree. Autopsy revealed diffuse invasion of the myocardium by lymphoma cells. Left ventricular wall motion was preserved even in the area of massive invasion; there was no true necrosis. Myocardial biopsy may be indicated in patients in whom there is a discrepancy between coronary pathoanatomy and wall motion abnormalities.

[Prognosis of patients with primary pulmonary hypertension]

Primary pulmonary hypertension is a rare disease entity. Clinical evaluations of such patients were deemed inadequate during a multi-center study in Japan (1976). The prognoses of our patients in Keio Hospital were evaluated, especially in terms of their clinical pictures and hemodynamic backgrounds. The study group consisted of 15 patients, who fulfilled the clinical criteria of primary pulmonary hypertension according to the Research Committee of the Ministry of Health and Welfare in Japan. There were four males and 11 females, whose age ranged from 16 to 72 years and averaged 34.7 years. Follow-up periods from the onsets were from 15 to 152 months, and they averaged 51 months. Nine of the 15 patients were deceased, and autopsies were performed in eight. The periods from onsets to deaths were between 15 and 152 months, and averaged 53 months (4 years and 5 months). Except for four cases followed for less than 2 years, there were seven who survived over three years and four patients who were deceased in this period, but there were no differences between these groups in terms of their clinical pictures, such as age, sex and symptomatology at onset. Survivors included three patients associated with thyroid disease, one with liver cirrhosis, and one with the Sjögren syndrome. Hemodynamically, heart rates and pulmonary artery pressures did not differ among six survivors more than 2 years after the hemodynamic evaluations and five patients who were deceased within this period. In the deceased group, however, cardiac output was low and arterio-venous differences in oxygen content were high.(ABSTRACT TRUNCATED AT 250 WORDS)

A non-linear elastic model of contraction of ischaemic segments

Previous studies have characterised the motion of the myocardium using a linear time varying elastance model, ie, they have sought to characterise the relationship between left ventricular volume and internal pressure as linear, but with time varying slopes over the cardiac cycle. However, the motion of myocardium during regional ischaemia has not been characterized by such models. Studies of totally ischaemic tissue and of myocardium in diastole have characterised the relationship between tension or stress and segment length as exponential. It is the purpose of this study to present a new model in which myocardial contraction is expressed as an exponential, but time varying elastic relationship. In this model tension, T, is related to segment length according to the formula T = e alpha(t)L + beta, where alpha(t) rises with systole and falls in diastole. This model was applied to the motion of hypokinetic segments noted in a series of conscious dogs studied for other purposes. Hypokinetic segments display early systolic bulging, decreased systolic shortening, and early diastolic recoil. These particular types of segment motion are naturally predicted by this model. Furthermore, the motion of myocardial segments as they become increasingly ischaemic may be predicted, including a gradual shift to the right and narrowing of the tension-length loop. alpha was noted to be independent of loading change, and thus may be viewed as an index of contractility. This model thus predicts the pattern of motion of hypokinetic segments and provides new insight into myocardial contractility.

[Contraction of the interventricular septum in right ventricular overload studied by two-dimensional echocardiography]

This study clarified the relationship between right ventricular (RV) overload and contraction of the interventricular septum using two-dimensional echocardiography. Seventeen patients with atrial septal defect (RV systolic pressure: 36 +/- 14 mmHg), 13 with mitral stenosis (49 +/- 19 mmHg), nine with primary pulmonary hypertension (87 +/- 21 mmHg) and 17 normal subjects (23 +/- 3 mmHg) were evaluated using two-dimensional echocardiography and cardiac catheterization. The circumferential lengths of the septum (Civs) and the left ventricular (LV) free wall (Cfw) were measured in the LV short-axis view at the level of the papillary muscles. In normal subjects, Civs was 3.4 +/- 0.5 cm and Civs/Cfw was 0.40 +/- 0.07. All patients with RV overload had longer Civs and greater Civs/Cfw as compared with the normal subjects. There was no significant difference in the Cfw among the cases with mitral stenosis and primary pulmonary hypertension and the normal subjects. Cfw in atrial septal defect was shorter than in the normal subjects. The percent contraction of Civs was decreased in mitral stenosis and primary pulmonary hypertension as compared with the normal subjects. No significant difference was found in the percent contraction of Civs between the normal subjects and the 11 patients with atrial septal defect with normal RV systolic pressure. However, in six patients with atrial septal defect with high RV systolic pressure, the percent contraction of Civs was decreased. There was an inverse correlation between RV systolic pressure and the percent contraction of Civs (r = -0.39, p less than 0.01), and RV ejection fraction (r = -0.52, p less than 0.01) defined by multiplegated equilibrium scintigraphy.(ABSTRACT TRUNCATED AT 250 WORDS)

Absence of coronary vascular reserve in myocardium distal to a fixed coronary stenosis

In a study to test the hypothesis that vascular reserve is exhausted in the setting of a resting blood flow deficit, the left anterior descending or circumflex artery was cannulated and perfused from the left carotid artery. After reactive hyperaemia had been assessed a stenosis was produced with a screw clamp. In the first experiment a moderate stenosis (diastolic perfusion pressure 40 mmHg) was produced in the left anterior descending artery (three dogs) or left circumflex artery (three dogs). Blood pressure was held constant with aortic constriction during intracoronary adenosine infusion (6 mumol.min-1). The stenosis was then adjusted to the preadenosine perfusion pressure. In the second experiment the anterior interventricular coronary vein was also isolated and segment length crystals were placed in the ischaemic and non-ischaemic zones. Severe stenosis (flow reduction of at least 50% and evidence of decreased segmental shortening) was produced in the cannulated left anterior descending artery (eight dogs). Intracoronary adenosine was given with aortic pressure held constant by transfusion and coronary venous drainage. In the first experiment resting coronary flow (ml.min-1) decreased from 41(3) to 29(6) (p less than 0.05) with stenosis. Coronary flow increased from 29(6) to 34(7) (p less than 0.05) with adenosine and to 50(10) (p less than 0.05) with stenosis adjustment. Subendocardial flow (ml.g-1.min-1) decreased from 0.89(0.26) to 0.78(0.23) (p less than 0.05) with adenosine and then increased from 0.94(0.49) with perfusion pressure adjustment. Subepicardial flow tended to increase with adenosine, and increased further with stenosis adjustment.(ABSTRACT TRUNCATED AT 250 WORDS)

The significance of underlying coronary stenosis for recovery of myocardial function after transient ischemia in the dog

The rate of recovery of myocardial function after transient coronary occlusion (CO) has been considered to depend on the duration and frequency of CO. However, underlying coronary stenosis has not been previously demonstrated to be a determinant of the rate of myocardial functional recovery. Thus, 12 open-chest dogs were studied to examine the influence of critical coronary stenosis (CCS) on functional recovery after transient CO. Regional functional recovery following 2-minute CO was examined under two different conditions in eight dogs: patent coronary artery stenosis and fixed CSS that exhausted coronary reserve but did not cause a deficit in resting coronary flow or regional function. Following reperfusion with the coronary artery patent, regional function in the ischemic zone was fully recovered (100 +/- 18.0% of pre-CO value) at 30 seconds and was significantly increased (postischemic hypercontraction) compared to pre-CO value at 1 and at 2 minutes after reperfusion. Following CO and reperfusion in the setting of CCS, regional functional recovery was delayed and regional function remained depressed until 2 minutes after reperfusion. No cumulative effect on functional recovery following repeated 2-minute CO was demonstrated in a control group of four dogs. We conclude that coronary artery patency is a determinant of the rate of myocardial function recovery after a transient ischemic episode, and postischemic hypercontractility was suppressed by the underlying CCS.

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)

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.