Reperfusion of the infarct-related coronary artery limits left ventricular expansion beyond myocardial salvage

The assessment of septal wall motion in patients undergoing CABG by myocardial perfusion-gated SPECT

PURPOSE

In this study, we aimed to assess the presence and prevalence of paradoxical septal motion (PSM) by myocardial perfusion-gated single-photon emission computed tomography (SPECT) imaging in patients undergoing coronary artery bypass grafting (CABG).

METHODS

A total of 172 patients (145 men and 27 women, with a mean age of 64.81 ± 8.93 years) undergoing CABG surgery were included in the study. All selected scintigraphic studies of the patients undergoing CABG were reprocessed. Semiquantitative interpretation of septal perfusion, wall motion, and wall thickening was performed with QPS and QGS programs. Phase analysis parameters were also obtained using the Emory Cardiac Toolbox. According to myocardial perfusion-gated SPECT results, the patients were trichotomized as follows: group 1 (nonischemic PSM): regular perfusion and thickening of the septal wall and abnormal motion of the septal wall; group 2 (ischemic PSM): abnormal perfusion, motion, and thickening of the septal wall; group 3 (non-PSM): normal perfusion, motion, and thickening of the septal wall. The data in each of the three groups were compared using Student's t-test and one-way analysis of variance.

RESULTS

No PSM (normal perfusion, motion, and thickening of the septal wall) was observed in 19.2% of patients undergoing CABG, whereas nonischemic PSM (regular perfusion and thickening of the septal wall and abnormal motion of the septal wall) was observed in 60.5% of patients and ischemic PSM (abnormal perfusion, motion and thickening of the septal wall) was seen in 20.3% of patients.

CONCLUSION

According to our study results, PSM is fairly common in patients undergoing CABG. It will be beneficial to use myocardial perfusion scintigraphy-gated SPECT, which is a noninvasive examination method, to identify the presence of PSM and investigate whether it is accompanied by ischemia or infarction.

Predictors of early and late ventricular remodeling after acute myocardial infarction

BACKGROUND

The determinants of the early and late stages of the ventricular remodeling process after infarction are not well defined.

HYPOTHESIS

The study was undertaken to evaluate the factors that condition the time course of left ventricular dilation during the first 6 months after infarction.

METHODS

The study group consisted of 74 patients with a first intermediate-large (> or = 4 Q waves) acute myocardial infarction. Contrast left ventricular and coronary angiograms were performed at 7 +/- 1 and 175 +/- 25 days after infarction. Left ventricular volumes, regional function and infarction artery status were quantified. Percutaneous transluminal coronary angioplasty (PTCA) was performed in the early angiogram in 31 patients.

RESULTS

In the early angiogram, 13 patients showed ventricular remodeling (end-diastolic volume > 90 ml/m2). A larger extent of dysfunction was the only predictor (p < 0.002) of early remodeling. At 6 months, a smaller, early end-diastolic volume (p < 0.0001) and a poorer regional function recovery (p < 0.05) were independently related to late diastolic enlargement, and a poorer regional function recovery (p < 0.0001) and a smaller, early end-systolic volume (p < 0.009) were independently related to late systolic enlargement. One patient with compared with 20 patients without early remodeling (p < 0.04) presented with late remodeling (increment of the end-diastolic volume > 20% at 6 months). In patients with early remodeling, the end-diastolic volume did not change significantly (101 +/- 13 vs. 94 +/- 22 ml/m2, NS) at 6 months; despite this, they maintained larger diastolic volumes than patients with late remodeling (81 +/- 12 ml/m2, p < 0.04) at 6 months. Infarction artery status did not influence the evolution of ventricular volumes and regional function.

CONCLUSIONS

(1) A large infarct size is the main determinant of postinfarction remodeling. (2) Such infarct size-dependent ventricular dilation occurs early and does not tend to increase in late stage; in contrast, some cases of intermediate-large size infarcts without early remodeling exhibit late remodeling associated with a poor late recovery of regional function. (3) Recovery of regional function (indicating myocardial viability) rather than infarction artery status plays a role in the late ventricular remodeling process.

Determinants of left ventricular systolic function after acute myocardial infarction: the role of residual myocardial ischaemia

BACKGROUND

Left ventricular systolic function (LVSF) is one of the major determinants of survival after acute myocardial infarction (AMI). Some factors such as the infarct size and localization, and the patency of the infarct-related artery are known determinants of LVSF. However, the long-term effect of myocardial ischaemia on LVSF has been poorly studied in clinical settings.

OBJECTIVES

To assess the acute and long-term effects of myocardial ischaemia on LVSF in patients recovering from an AMI.

METHODS

A cohort of 74 patients recovering from AMI was studied. Myocardial ischaemia was detected by means of ambulatory electrocardiogram (ECG) monitoring at recruitment (4+/-2 days after AMI), exercise ECG test and stress echocardiography at discharge (7+/-4 days after AMI). LVSF was studied by means of two-dimensional echocardiography at recruitment, at discharge, and at 1, 3, 6 and 12 months after AMI.

RESULTS

Patients with myocardial ischaemia on ambulatory ECG monitoring and stress echocardiography had worse LVSF at recruitment than those without ischaemia. The presence of myocardial ischaemia on ambulatory ECG monitoring was an independent determinant of LVSF at recruitment together with infarct localization and size (assessed by creatine kinase MB isoenzyme (CK-MB) levels). Patients with signs of myocardial ischaemia on ambulatory ECG monitoring and stress echocardiography had a progressive left ventricular dysfunction compared with those without ischaemia.

CONCLUSIONS

Residual ischaemia is an independent determinant of LVSF after AMI and its presence implied a progressive worsening of the LVSF. Because left ventricular systolic dysfunction is a major determinant of survival after AMI, its precursors, among them residual myocardial ischaemia, should be identified. Treatment of ischaemia is known to be associated with improved prognosis and improved LVSF.

Temporal dissociation of left ventricular function and remodeling following experimental myocardial infarction in rats

BACKGROUND

Left ventricular function early after myocardial infarction (MI) predicts subsequent clinical outcome. Nevertheless, the relationship between early changes in left ventricular function and subsequent left ventricular remodeling has not been well defined.

METHODS AND RESULTS

To explore the temporal relationship between left ventricular function and remodeling after MI, rats (n = 63) underwent coronary artery ligation with and without reperfusion at 45 or 180 minutes or a sham operation. All animals were followed up by serial echocardiography preligation; 4, 24, and 48 hours; and 1, 2, 3, 4, 6, and 9 weeks after MI. Measures of global left ventricular size and function and regional wall motion were obtained at physiological heart rates. Histological infarct sizes (range, 0% to 52%) were determined in all animals. Within 4 hours of MI, fractional area change (FAC) decreased dramatically in association with an increase in left ventricular systolic cavity area, whereas diastolic area increased more gradually. Early FAC was related to infarct size (r = -0.82; P < .000), predicted the extent of left ventricular enlargement (P = .0001), and remained depressed throughout the duration of follow-up. Regional wall motion excursion and systolic wall thickness decreased in the infarcted and noninfarcted regions in animals with large infarctions.

CONCLUSIONS

The rate of left ventricular dilatation after MI in rats is proportional to initial left ventricular function, although left ventricular function remains relatively constant as the ventricle progressively enlarges. Regional myocardial function after a large MI is abnormal in noninfarcted as well as infarcted regions.

Heterogeneous fate of perfusion and contraction after anterior wall acute myocardial infarction and effects on left ventricular remodeling

After acute myocardial infarction, patency of infarct vessel and extent of left venticular (LV) dysfunction are major determinants of ventricular remodeling. Spontaneous, delayed reperfusion in the infarct zone occurs in a sizeable number of patients well after the subacute phase. The aim of this study was to determine the relation between the occurrence of this spontaneous, delayed reperfusion and LV remodeling. In 84 patients, resting LV volumes, topography, regional function, and perfusion were quantitatively evaluated by 2-dimensional echocardiography and sestamibi tomography 5 weeks (study 1) and 7 months (study 2) after anterior Q-wave infarction. At study 2, LV end-diastolic volume increased by > 15% in 17 patients (20%, LV remodeling); they had already had at study 1 significantly larger LV volumes, more severe hypoperfusion and wall motion abnormalities, and greater regional dilation than patients with stable LV volumes. Delayed reperfusion occurred in 8 of 17 patients with and in 42 of 67 patients without LV remodeling (47% vs 63%; p=NS). At study 2, LV regional dilation and end-diastolic volumes were stable in patients with, but increased in patients without, spontaneous reperfusion (from 25+/-24% to 29+/-26% at study 2 [p<0.05] and from 65+/-14 to 68+/-18 ml/m2 [p <0.05]). At multivariate analysis, however, regional ventricular dilation at study 1 was the sole predictor of further LV remodeling. Thus, after acute myocardial infarction, spontaneous reperfusion occurring after 5 weeks plays only a minor role in influencing LV remodeling. Benefits from delayed reperfusion seem limited to patients with preserved LV volumes; patients with an enlarged left ventricle 5 weeks after acute infarction are prone to further LV remodeling, irrespective of delayed reperfusion.

Increased intensity of contrast material immediately after late angioplasty of infarct-related coronary artery is associated with reduced ventricular volumes at six months

To assess the contribution of residual muscle perfusion in the infarcted territory to prevent ventricular remodeling, 24 patients with 1-vessel disease underwent coronary angiography and angioplasty of a critical left anterior descending coronary stenosis 18+/-11 days after a first anterior myocardial infarction. The degree of stenosis was assessed using biplane quantitative angiography, whereas ventricular volumes, together with regional wall motion, were computed from single-plane ventriculography. Patients were reevaluated at 6 months after they had been subdivided according to the videointensity of the territory of the culprit vessel, as assessed from images obtained during main stem dye contrast injections before and immediately after angioplasty using a subtraction technique (group A, increased intensity [n= 15]; group B, no change [n=9]), assuming that higher peak intensities reflect greater myocardial blood volume. There was a significant time group interaction for ventricular volumes (diastolic, -13+/-12% for group A vs +20+/-24% for group B, p=0.008; systolic, -15+/-19% for group A vs +18+/-36% for group B, p=0.017), although no interaction was evident for the degree of resolution of coronary stenosis or the extent of recovery of regional dysfunction. The effects on volumes were paralleled by changes in ventricular end-diastolic pressure (-3+/-7 mm Hg in group A vs +5+/-6 mm Hg in group B, p=0.006), although baseline clinical characteristics and medical regimen over the 6-month period were quite comparable between the 2 groups. In conclusion, despite late angioplasty of the culprit vessel, ventricular remodeling is prevented mainly when the procedure guarantees improved perfusion at the muscular level. The result is not necessarily mediated by recovery of regional systolic function.

Left ventricular size and function in patients with noninsulin-dependent diabetes and postinfarction total or subtotal coronary occlusions

The aim of this study was to establish the effects of postinfarction total or subtotal coronary occlusion on left ventricular remodeling in patients with noninsulin-dependent diabetes (NIDD) compared with the effects in postinfarct nondiabetic patients. The authors selected 100 patients submitted to coronary angiography between 1 and 5 weeks after acute myocardial infarction (T0: 20.5+/-15.4 days) and classified into three groups: G1: NIDD with coronary occlusion/subocclusion (n=24), G2: controls with coronary occlusion/subocclusion (n=43), G3: controls without coronary occlusion/subocclusion (n=33). At time zero (T0) the following parameters were evaluated: end-systolic and end-diastolic volume indexes (ESVi, EDVi), ejection fraction (EF), echocardiographic wall motion score index (WMI), presence of left ventricular aneurysm, and triple-vessel coronary disease. The frequencies of major cardiovascular events were recorded during follow-up. Significantly greater ESVi and EDVi were noted in G2 compared with G3 (P<0.0001), while no significant differences were observed between NIDD patients and controls. Although left ventricular global and segmental dysfunctions were increased in diabetics, controls with coronary occlusion/subocclusion presented more pronounced EF reduction (P<0.0001 G2 vs G3) and higher elevation in WMI (P<0.005 G2 vs G3). Cardiac events during follow-up were elevated in G1 and G2, particularly as regards the occurrence of congestive heart failure. The authors conclude that NIDD seems to influence in a positive way left ventricular remodeling associated with postinfarct total or subtotal coronary occlusion.

Echocardiography to understand remodeling and to assess prognosis after acute myocardial infarction

Ventricular remodeling indicates a dynamic process, starting with and after acute myocardial infarction, as a result of structural and functional modifications which involve acutely and chronically both the infarcted and noninfarcted zones of the left ventricle. The most effective way to prevent or minimize post-MI cardiac remodeling is to limit the extent of the initial insult. This can be partly achieved by early myocardial reperfusion obtained by different strategies including thrombolysis. In 6405 patients of the GISSI-3 trial, 2D echocardiographic studies were available at predischarge, at 6 weeks and at 6 months after the infarction. The increase in left ventricular volumes over time was reduced by 6-week lisinopril treatment. Patients randomized to lisinopril had smaller volume also at 6 months, after withdrawal of treatment at 6 weeks. Important prognostic indications can also be derived from predischarge echocardiography, since larger quartiles of left ventricular volumes and lower quartile of ejection fraction indicates higher risk of mortality and non-fatal congestive heart failure in the 6 months after the index event, even in the relatively low risk general population of infarcts of the GISSI-3.

Asynergy of the noninfarcted left ventricular inferior wall in anterior wall acute myocardial infarction secondary to isolated occlusion of the left anterior descending artery

There are patients in whom left ventricular (LV) wall motion decreases in the noninfarcted region and LV systolic function declines globally despite the presence of a localized myocardial infarct attributable to narrowing or occlusion of a single coronary artery. This study examines angiographic characteristics of patients with chronic hypokinesia of noninfarcted myocardium after anterior wall acute myocardial infarction (AMI) due to narrowing of a single coronary artery, namely, the left anterior descending (LAD) artery. The LV ejection fraction, abnormalities in the motion of the noninfarcted LV inferior wall (SD/chord value by Sheehan's technique), the angiographic characteristics of the infarct-related coronary artery, the effect of acute reperfusion therapy, and presence of coronary risk factors were examined in 85 consecutive patients. The SD/chord value in the noninfarcted region showed a positive correlation with the LV ejection fraction (r = 0.505, p <0.0001). By multivariate analysis, hypertension (odds ratio = 0.53, 95% confidence interval [CI] 0.36 to 0.80), an infarct-related narrowing proximal to the origin of the first diagonal branch (odds ratio = 0.56, 95% CI 0.38 to 0.84), and patency of the infarct-related lesion during AMI (odds ratio = 1.56, 95% CI 1.03 to 2.30) were independent predictors of wall motion in the noninfarct region. In some patients with single-vessel anterior wall AMI, the motion of the noninfarcted inferior LV wall decreases during the chronic stage and cardiac function declines severely. In most of these patients, the infarct-related narrowing or occlusion is proximal to the origin of the first diagonal branch of the LAD artery.

Myocardial salvage by reperfusion 12 hours after coronary ligation in dogs

It is not clear why late reperfusion therapy in patients with acute myocardial infarction is effective. An investigation was carried out as to whether or not reperfusion conducted 12 h after coronary occlusion causes myocardial salvage in dogs. Coronary arteries were occluded in 11 mongrel dogs and a portion of the occlusion (late reperfusion area; LR area) reperfused 12 h later; the other part was left occluded (permanent occlusion area; PO area). The dogs were maintained for 4 weeks after reperfusion. Regional myocardial blood flow (Qm) was measured by the non-radioactive colored microsphere method. In both areas, the transmurality of necrosis was measured by triphenyl tetrazolium chloride staining, and the amount of viable myocardium and the extent of fibrosis was determined by Azan-Mallory staining. Qm decreased markedly after coronary occlusion to similar levels in both areas until 12 h. Qm transiently increased in the LR area only following reperfusion after 12 h. The transmurality of necrosis in the PO area was 83.8+/-10.5%, but that in the LR area was 58.7+/-21.3%, a significant decrease (p<0.01). In the outer layer, the amount of viable myocardium was significantly greater, and the extent of myocardial fibrosis was significantly less in the LR area. Evaluation in the same heart of dogs confirmed the myocardial salvage effects of late reperfusion (12 h after coronary occlusion).

Role of infarction artery status in left ventricular remodeling after acute myocardial infarction

The aim of this study was to evaluate the relation between the infarction artery status and left ventricular volumes, independently of regional ventricular dysfunction, at 4-6 weeks after a first myocardial infarction. The study group consisted of 100 patients, of whom 80 received thrombolytic treatment. Coronary and contrast left ventricular angiograms were performed at 36+/-5 days postinfarction. Left ventricular end-diastolic and end-systolic volumes were measured. The centerline chord motion method was used to calculate the extent of wall motion abnormality (percentage of chords with hypokinetic motion) and its severity (maximum units of S.D. below the normal wall motion reference). Minimum lumen diameter, patency and collateral flow in the infarction artery were also analyzed. Eight patients (group I) showed occlusion with poor collateral flow in the infarction artery, 22 patients (group II) occlusion with good collateral flow, 38 patients (group III) severe residual stenosis (minimum lumen diameter < or = 1 mm), and 32 patients (group IV) non-severe residual stenosis (minimum lumen diameter > 1 mm). Patients from group I presented greater wall motion abnormality in terms of both extent (P=0.005) and severity (P=0.007), and greater end-diastolic (P=0.07) and end-systolic (P=0.0008) volumes; there were no differences among groups II, III and IV. By stepwise multivariate regression analysis, the extent of wall motion abnormality was the main determinant of end-diastolic (P=0.0001) and end-systolic (P=0.0001) volumes; occlusion with poor collateral flow was also a significant independent factor for end-systolic volume (P=0.03). Total occlusion (including both with and without collaterals) and the minimum lumen diameter did not correlate with end-diastolic and end-systolic volumes. We concluded that (A) the extent of regional dysfunction is the primary determinant of left ventricular volumes at 4-6 weeks postinfarction. (B) The status of the infarction artery is a weak predictor of end-diastolic volume, which is the best descriptor of ventricular remodeling, although occlusion with poor collateral flow is associated to larger end-systolic volume.

Long-term implications of reocclusion on left ventricular size and function after successful thrombolysis for first anterior myocardial infarction

BACKGROUND

Successful thrombolysis can prevent left ventricular dilatation after acute myocardial infarction. However, in almost 30% of patients, reocclusion occurs. The aim of this study was to assess the long-term implications of reocclusion on left ventricular size and function.

METHODS AND RESULTS

Fifty-six patients were studied with two-dimensional echocardiography at baseline (2 +/- 1.6 days) and 5.0 +/- 1.4 years after first anterior myocardial infarction. All patients (a subset of those enrolled in the APRICOT trial) had a patent infarct-related artery when studied < 48 hours after thrombolysis and underwent repeat coronary angiography at 3 months. Baseline characteristics were comparable in patients with (n = 17) and without reocclusion (n = 39). Left ventricular volume indexes were stable in patients without reocclusion. Patients with reocclusion, however, showed a significant increase in end-diastolic volume index (EDVI; P = .008) and end-systolic volume index (ESVI; P = .039). Furthermore, patients without reocclusion demonstrated improvement in wall motion score index (WMSI; P = .0001) and ejection fraction (EF; P = .016), whereas patients with reocclusion did not. After 5 years, patients with reocclusion had significantly larger volume indexes (EDVI, 99 +/- 41 versus 76 +/- 22 mL/m2, P = .007; ESVI, 59 +/- 40 versus 39 +/- 20 mL/m2, P = .017) and more compromised left ventricular function (WMSI, 1.63 +/- 0.33 versus 1.39 +/- 0.32, P = .013; EF, 45 +/- 13% versus 51 +/- 11%, P = .077) than patients without reocclusion. Multivariate analysis identified baseline WMSI and reocclusion as significant independent predictors of left ventricular dilatation.

CONCLUSIONS

Reocclusion of the infarct-related artery within 3 months of successful thrombolysis is associated with left ventricular dilatation and is detrimental to functional recovery of left ventricular function 5 years after first anterior myocardial infarction.

Early identification of patients at risk for significant left ventricular dilation one year after myocardial infarction

We prospectively investigated criteria to identify patients in the early phase of acute myocardial infarction at risk for significant left ventricular (LV) dilation 1 year after myocardial infarction. In 54 patients receiving thrombolysis within 4 hours after onset of symptoms, the end-diastolic volume index (EDVI) and the end-systolic volume index were assessed by two-dimensional echocardiography initially (within 23 +/- 21 hours) and 1 year after myocardial infarction. After 1 year, LV dilation occurred in 51 patients (94%) and was significant (> mean normal value + 2 SDs) in 14 patients (26%). Significant univariate predictors (p < 0.05) for LV dilation were age, anterior myocardial infarction, initial EDVI and end-systolic volume index, enzymatic infarct size, LV end-diastolic pressure, and mitral regurgitation. No other variables obtained from clinical information, two-dimensional echocardiography, or angiography, including residual coronary perfusion or stenosis, had predictive value. The optimal multivariate predictive model was the combination of the initial EDVI and the enzymatic infarct size, which correctly predicted significant LV dilation in 12 of 14 patients and falsely in eight of 39 patients (sensitivity 86%; specificity 79%). Patients at risk for significant LV dilation 1 year after myocardial infarction were identified adequately 3 days after myocardial infarction by the combination of the initial echocardiographic assessment of EDVI and the enzymatic infarct size. Thus a simple method could facilitate the selection of patients for intervention after acute myocardial infarction.

Reperfusion reduces left ventricular dilatation by preventing infarct expansion in the acute and chronic phases of myocardial infarction

Reperfusion reduces left ventricular dilatation in patients with acute myocardial infarction, but it is unclear to what extent this is a primary effect or only a consequence of the limiting effect of reperfusion on infarct size. To address this issue, 56 consecutive patients were examined by means of two-dimensional echocardiography on day 1, on day 3, before discharge, and at 6 months after an acute myocardial infarction. From this population two groups of 12 patients each, perfectly matched for site of myocardial infarction, extent of ventricular asynergy at two-dimensional echocardiography (akinesis + dyskinesis), and clinical characteristics were identified according to the creatine kinase (CK) time to peak, which was regarded as a marker of spontaneous or induced reperfusion: (1) CK time to peak of 12 hours or less (reperfused patients, n = 12), and (2) CK time to peak of more than 12 hours (nonreperfused patients, n = 12). In these two groups of patients end-diastolic and end-systolic left ventricular volumes and endocardial lengths of asynergic and normal ventricular segments, imaged in a cross-sectional view at the level of the papillary muscles, were then computed. At the first examination end-diastolic volume, end-systolic volume, and endocardial segment lengths of normal and asynergic segments were similar in the two groups of patients. Patients with late CK time to peak, however, showed a progressive increase in left ventricular systolic volumes and in asynergic endocardial segment lengths between the first and third (predischarge) examinations (p < 0.05 for both), with no change in systolic length of the normal myocardium. The left ventricular end-systolic volume and the asynergic endocardial segment length of patients with early CK time to peak, however, did not increase during hospitalization. The increment in end-systolic volume and in systolic infarct segment length from the first to the third examinations was higher in nonreperfused patients (p = 0.018 and p = 0.04, respectively). Changes similar to those detected in systole were found for diastolic volume and diastolic infarcted and noninfarcted segment length in both groups, but they did not reach statistical significance. After 6 months, an increases in volume and endocardial length were found in both groups of patients. Relative to the first examination, however, the increase in systolic volume and in asynergic systolic endocardial lengths remained greater for nonreperfused patients (p = 0.077 and p = 0.01, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Frequency of predischarge ventricular arrhythmias in postmyocardial infarction patients depends on residual left ventricular pump performance and is independent of the occurrence of acute reperfusion. The GISSI-2 Investigators

OBJECTIVES

To test whether acute reperfusion of the infarct-related vessel after an acute myocardial infarction is associated with a subsequent reduction in spontaneous ventricular arrhythmias that is independent of ventricular ejection fraction, 1,944 patients from the GISSI-2 study population were studied. The patients were selected on the basis of a first myocardial infarction and the availability of two-dimensional echocardiographic ejection fraction and data on the number of premature ventricular contractions per hour on Holter monitoring.

BACKGROUND

It has been suggested that postthrombolytic reperfusion of the culprit vessel may be associated with an increased electrical stability of the infarcted heart, irrespective of its residual pump performance.

METHODS

The predischarge relation between ejection fraction and number of premature ventricular contractions per hour was plotted according to the occurrence (1,309 patients) or not (635 patients) of acute reperfusion, identified noninvasively according to the modifications of the ST segment in serial electrocardiograms obtained in the first 24 h after infarction.

RESULTS

The frequency of premature ventricular contractions increased in a linear fashion with decreasing ejection fraction in both cohorts (p < 0.005 and p < 0.0001); however, there was no significant difference between the slopes and the intercepts of the two regression lines, so that the relation between ejection fraction and number of premature ventricular contractions per hour could be adequately described by a single equation: y (number of premature ventricular contractions) = 33.0-0.42x (ejection fraction) (r = -0.107, p < 0.0001). The results were the same even when differences between group characteristics were accounted for in a multiple regression model.

CONCLUSIONS

It is concluded that 1) the number of premature ventricular contractions per hour after an acute myocardial infarction is dependent in a linear, inverse fashion on the residual ventricular ejection fraction, and 2) this relation is independent of the occurrence of reperfusion in the acute phase of infarction.

Ventricular remodeling and infarct expansion

Infarct expansion, defined as an alteration in the ventricular topography due to thinning and lengthening of the infarcted segment, develops within the first few hours of the acute symptoms, mostly in patients with a large, transmural, anterior myocardial infarction. Shape changes, peculiar to risk region location and due to disparity in regional ventricular architecture, could be posited as the first step in the process of infarct expansion, with various cellular mechanisms contributing to subsequent continued early and late ventricular dilation. Because the increase in left ventricular volume is expected to be linearly dependent on the extent of the infarction, limiting infarct size, by thrombolysis, would proportionally reduce enlargement of the cavity. The effect of thrombolysis on left ventricular volume, however, seems not to be completely accounted for by the lessening effect of reperfusion on infarct size, because data suggest a restraining effect of reperfusion on the process of ventricular dilation in addition to the lessening effect on infarct size. If this turns out to be true, then the achievement of a patent vessel even beyond the time period when that patency may be expected to salvage myocardium would be further justified. Theoretical predictions substantiate the potential effectiveness in restraining ventricular dilation of stiffening of the necrotic region alone, independently of myocardial salvage in infarcted patients. The process of progressive ventricular dilation involves not only a primary alteration in function of the infarcted region, but also a time-dependent secondary change in the noninfarcted tissue itself, finalized to restore stroke volume despite a persistently depressed ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)