Angiotensin II reduces infarct size and has no effect on post-ischaemic contractile dysfunction in isolated rat hearts

1. In order to test the hypothesis that angiotensin II exacerbates myocardial ischaemia-reperfusion (IR) injury, we examined the effects of graded angiotension II concentrations of angiotensin II on IR injury in both working and non-working (Langendorff) isolated rat hearts. 2. Non-working hearts were subjected to 30 min aerobic perfusion (baseline) then 25 min of global, no-flow ischaemia followed by 30 min of reperfusion either in the absence (control, n=7) or presence of 1 (n=6) or 10 nM (n=5) angiotensin II). Recoveries of LV developed pressure and coronary flow after 30 min reperfusion in control hearts (58+/-9 and 40+/-8% of baseline levels, respectively) were no different from hearts treated with 1 or 10 nM angiotensin II. Infarct size (determined at the end of reperfusion by triphenyltetrazolium chloride staining) was reduced by angiotensin II in a concentration-dependent manner (from a control value of 27+/-3 to 18+/-4% and 9+/-3% of the LV, respectively). 3. Working hearts were subjected to 50 min pre-ischaemic (pre-I) aerobic perfusion then 30 min of global, no-flow ischaemia followed by 30 min of reperfusion either in the absence (control, n=14) or presence of 1 (n=8), 10 (n=7) or 100 nM (n=7) angiotensin II). In controls, post-ischaemic (post-I) left ventricular (LV) work and efficiency of oxygen consumption were depressed (43+/-9 and 42+/-10% of pre-I levels, respectively). The presence of angiotensin II throughout IR had no effect on LV work compared with control. 4. Thus, angiotensin II reduces infarct size in a concentration-dependent manner but has no effect on contractile stunning associated with IR in isolated rat hearts.

Enhanced regional AT(2)-receptor and PKC(epsilon) expression during cardioprotection induced by AT(1)-receptor blockade after reperfused myocardial infarction

We assessed the effects of the angiotensin II (Ang II) type 1 receptor (AT1-receptor) blocker, candesartan, (CN, 1 mg/kg i.v. over 30 minutes pre-ischaemia) alone or after intracoronary administration of Ang II type 2 receptor (AT2-receptor) blocker (PD 123319), protein kinase C (PKC) inhibitor (chelerythrine), endothelial nitric oxide (NO) synthase inhibitor (N(G)-monomethyl-L-arginine or L-NMMA), and bradykinin (BK) -B2 receptor inhibitor (HOE140) on in vivo left ventricular (LV) function and remodelling (echocardiograms/Doppler) and haemodynamics in 30 dogs with reperfused anterior infarction (90 minutes ischaemia, 120 minutes reperfusion), and ex vivo infarct size, AT1-receptor/AT2-receptor proteins and PKC(epsilon) (immunoblots), and cyclic guanosine 3', 5' monophosphate (cGMP, immunoassay). Compared with controls, CN inhibited the Ang II pressor response, reduced LV preload, improved LV systolic and diastolic function, limited LV remodelling, decreased infarct size, and increased AT2-receptor and PKC(epsilon) proteins in the infarct zone (IZ), and these responses were abrogated by PD 123319, chelerythrine, L-NMMA and HOE140. In addition, the increase in LV cGMP with CN was attenuated by PD 123319, L-NMMA and HOE140. The overall results suggest that AT2-receptor activation and signalling via BK, PKC(epsilon) and cGMP contribute to cardioprotection associated with AT1-receptor blockade during ischaemia-reperfusion injury.

Postischemic apoptosis and functional recovery after angiotensin II type 1 receptor blockade in isolated working rat hearts

OBJECTIVE

To determine whether chronic angiotensin (AngII) type I receptor (AT1R) blockade inhibits cardiomyocyte (CM) apoptosis and attenuates left ventricular (LV) dysfunction after ischemia-reperfusion (IR) in the isolated working rat heart.

METHODS

Postischemic recovery of LV developed pressure, the apoptotic index (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP in situ nick end labeling or TUNEL assay), and changes in expression of apoptotic markers Bcl-2, Bax, p53 and caspase-3 (Western immunoblots) were measured after IR (50 min aerobic perfusion; 25 min global ischemia; 40 min reperfusion) in working rat hearts that were randomized to five groups of six each along 1 week or 3 week pretreatment arms: sham (no drug, no perfusion); no drug, aerobic perfusion; and oral AT1R blockers losartan (30 mg/kg per day) or UP269-6 (3 mg/kg per day), or no drug before IR.

RESULTS

Compared to the no drug group after IR, losartan (not UP269-6) preserved functional recovery in 1 and 3 week groups. However, both losartan and UP269-6 reduced the apoptotic index and normalized the increase in Bax, decrease in Bcl-2 and increase in p53 and caspase-3 after IR. A bell-shaped relation between apoptosis and functional recovery after IR was flattened by AT1R blockade.

CONCLUSION

The results indicate that IR is associated with LV dysfunction and CM apoptosis involving activation of p53, caspase-3, and increased Bax/Bcl-2 ratio in the working rat heart. Importantly, chronic AT1R blockade inhibited the apoptosis and changes in expression of the markers without improving functional recovery, implying that decrease in apoptosis does not necessarily translate into decreased LV dysfunction.

Effect of chronic AT(1) receptor antagonism on postischemic functional recovery and AT(1)/AT(2) receptor proteins in isolated working rat hearts

To determine whether chronic angiotensin II (Ang II) type I receptor (AT(1)R) antagonism improves recovery of left ventricular (LV) function after ischemia-reperfusion (IR) and increases AT(1)R and Ang II type 2 receptor (AT(2)R) protein expression in isolated working rat hearts, rats were randomized to pretreatment with either losartan (30 mg/kg/day) or UP269-6 (3 mg/kg/day), or no drug (control), for 1 week or 3 weeks before IR (50 min perfusion, 25 min ischemia, 40 min reperfusion). In vitro LV work and power and ex vivo AT(1)R and AT(2)R proteins (immunoblots) were measured. Compared to baseline perfusion, LV work and power showed variable recovery in control, losartan, and UP269-6 groups. Compared to control, losartan preserved recovery of LV work and power while UP269-6 showed less recovery after IR at both 1 week and 3 weeks. Both antagonists increased AT(2)R but not AT(1)R protein. The duration of pretreatment did not affect the expression of AT(1)R or AT(2)R proteins. The results indicate that chronic AT(1)R blockade over 1 or 3 weeks increases AT(2)R (not AT(1)R) protein expression and may preserve but not improve postischemic functional recovery compared to controls in isolated working rat hearts.

Differential morphometric and ultrastructural remodelling in the left atrium and left ventricle in rapid ventricular pacing-induced heart failure

BACKGROUND

Heart failure induced by rapid ventricular pacing (RVP) is associated with left atrial (LA) but not left ventricular (LV) hypertrophy.

OBJECTIVE

To determine whether differences in wall tension correlate with the differential ultrastructural remodelling in the LA and LV chambers, changes in ultrastructure, systolic function and wall tension (an index of wall stress) were compared in dogs after RVP (n=7) and with no RVP (n=9).

RESULTS

Compared with dogs with no RVP (controls), dogs with RVP had increased collagen volume fraction (5.3% versus 8.3%), myocyte cross-sectional area (245 versus 366 microm(2)) and hydroxyproline (222 versus 323 microg/mg protein) in the LA (all P<0.05), but not in the LV. The increase in systolic wall tension produced by RVP was greater in the LA (five versus 43 units, P<0.0004) than in the LV (227 versus 290 units, P<0.01) chambers and correlated closely with the collagen volume fraction (r=0.87), which in turn correlated with myocyte cross-sectional area (r=0.98). In the left atrium, wall tension correlated with wall stress (r=0.99).

CONCLUSIONS

The results suggest that differential wall tension may provide the stimulus for differential ultrastructural remodelling (with more hypertrophy and collagen) between LA and LV chambers in RVP-induced cardiomyopathy.

Enhanced expression of angiotensin II type 2 receptor, inositol 1,4, 5-trisphosphate receptor, and protein kinase cepsilon during cardioprotection induced by angiotensin II type 2 receptor blockade

We hypothesized that the cardioprotective effect of angiotensin II type 2 receptor (AT(2)R) blockade with PD 123,319 (PD) on the recovery of left ventricular (LV) mechanical function after ischemia/reperfusion (IR) in the isolated working rat heart is associated with the enhanced expression of AT(2)R protein and mRNA as well as an increase in inositol 1,4,5-trisphosphate type 2 receptor (IP(3)R) and protein kinase Cepsilon (PKCepsilon) proteins. We assessed AT(2)R, angiotensin II type 1 receptor (AT(1)R), IP(3)R, and PKCepsilon protein expression (Western blots) and AT(2)R mRNA levels (Northern blots) in myocardium from isolated working rat hearts that were subjected to global ischemia (30 minutes) followed by reperfusion (30 minutes). Groups of adult rat hearts (n=6) were exposed to no IR, no IR+PD (0.3 micromol/L), IR, and IR+PD. Compared with no IR and no IR+PD, IR decreased (P<0.05) functional recovery and AT(2)R mRNA and protein, as well as AT(1)R mRNA (not protein) and IP(3)R and PKCepsilon proteins. Compared with IR, PD+IR improved LV functional recovery (P<0.05) and markedly increased AT(2)R mRNA and protein (P<0.001). However, PD did not change AT(1)R mRNA or protein. More importantly, PD+IR markedly increased IP(3)R and PKCepsilon proteins. The downregulation of AT(2)R mRNA and protein with IR and their upregulation with PD indicate that the effects of PD are AT(2)R specific. The overall results suggest that the cardioprotective effect of acute PD treatment on LV functional recovery after IR in the isolated working rat heart is specifically due to AT(2)R blockade and is associated with enhanced downstream IP(3)R and PKCepsilon signaling.

Cardioprotection induced by AT1R blockade after reperfused myocardial infarction: association with regional increase in AT2R, IP3R and PKCepsilon proteins and cGMP

BACKGROUND

We hypothesized that the cardioprotective effect of angiotensin II (AngII) type 1 receptor (AT(1)R) blockade during in vivo ischemia-reperfusion (IR) might be associated with an increase in AngII type 2 receptor (AT(2)R) protein, as well as 1,4,5-inositol trisphosphate type 2 receptor (IP(3)R) and protein kinase C(epsilon) (PKC(epsilon)) proteins and cyclic guanosine 3',5' monophosphate (cGMP).

METHODS AND RESULTS

We studied the effects of the AT(1)R blocker, candesartan, on in vivo left ventricular (LV) systolic and diastolic function and remodeling (echocardiogram/Doppler) and hemodynamics during canine reperfused anterior infarction (90-minute ischemia, 120-minute reperfusion), and ex vivo infarct size and AT(1)R/AT(2)R, IP(3)R, and PKC(epsilon) proteins (immunoblots), and cGMP (enzyme immunoassay). Compared with controls, candesartan (1 mg/kg intravenously over 30-minute preischemia) inhibited the AngII pressor response, decreased preload and afterload, improved LV systolic and diastolic function, limited LV remodeling, decreased infarct size (55% vs 27% risk; P <.000003), markedly increased AT(2)R, IP(3)R, and PKC(epsilon) proteins in the infarct zone, but not the AT(1)R protein, and increased infarct more than noninfarct cGMP.

CONCLUSIONS

The overall results suggest that cardioprotective effects of AT(1)R blockade on acute IR injury might involve AT(2)R activation and downstream signaling via IP(3)R, PKC(epsilon), and cGMP.

Cardiac tamponade as the first clinical manifestation of metastatic adenocarcinoma of the lung

A 62-year-old woman presented in the emergency department with new onset of dyspnea and clinical signs of cardiac tamponade. She had a history of cigarette smoking and a family history of adenocarcinoma, pancreatic and breast carcinoma. An emergency two-dimensional echocardiogram confirmed the diagnosis of cardiac tamponade. Therapeutic pericardiocentesis resulted in prompt relief. Cytology confirmed malignant glandular cells, consistent with a metastatic adenocarcinoma. Computerized chest tomography confirmed pulmonary involvement.

Characterization of cardioprotection mediated by AT2 receptor antagonism after ischemia-reperfusion in isolated working rat hearts

BACKGROUND

Whether cardioprotection induced by the angiotensin II (AngII) type 2 receptor (AT(2)R) antagonist PD123,319 (PD) after ischemia-reperfusion (IR) is influenced by the concentration of PD, presence of AngII, timing of exposure, or inhibition of proton production from glucose metabolism is not known.

METHODS AND RESULTS

We examined these factors in isolated working rat hearts subjected to IR injury, no treatment (control), or treatment with N(6)-cyclohexyl adenosine (CHA, 0.5 micromol/L), an adenosine A(1) receptor agonist that induces cardioprotection by decreasing protons ("positive" control). Compared with control, 1 micromol/L PD present throughout IR improved recovery of left ventricular work (73 +/- 5 vs. 40 +/- 8%) to the level with CHA (82 +/- 5%), but 0.1 micromol/L PD did not (58 +/- 6 vs. 40 +/- 8%). AngII (1 nmol/L) did not effect postischemic recovery associated with 1 micromol/L PD (73 +/- 7%) but improved that associated with 0.1 micromol/L PD (86 +/- 3%). PD (1 micromol/L), present solely during reperfusion, enhanced postischemic left ventricular recovery to 72 +/- 5%. Also, PD (1 micromol/L) did not affect glycolytic rates or proton production in nonischemic or IR hearts.

CONCLUSION

PD-induced cardioprotection is 1) PD concentration-dependent, 2) AngII-sensitive, 3) mediated during reperfusion, and 4) independent of proton production, suggesting that reduction in IR injury and indirect AT(1)R stimulation might be involved.

Cardioprotection after angiotensin II type 1 blockade involves angiotensin II type 2 receptor expression and activation of protein kinase C-epsilon in acutely reperfused myocardial infarction in the dog. Effect of UP269-6 and losartan on AT1 and AT2-receptor expression and IP3 receptor and PKCepsilon proteins

To determine whether cardioprotection after chronic angiotensin II (Ang II) type 1 (AT(1)) receptor blockade involves Ang II type 2 (AT(2)) receptor expression and protein kinase C-epsilon (PKC(epsilon)) activation, we measured in vivo haemodynamics and left ventricular (LV) remodelling and dysfunction (echocardiogram/ Doppler) and ex vivo AT(1)/AT(2)-receptor expression, IP(3)R (1, 4, 5-inositol trisphosphate type 2 receptor) and PKC(epsilon) proteins in dogs with acutely reperfused (90 minutes ischaemia, 90 minutes reperfusion) myocardial infarction (MI) following seven days of AT(1)-receptor blockade with oral losartan or UP269-6. The animals were randomised to sham; sham + losartan or UP269-6; MI alone; MI + losartan; MI + UP269-6. More marked AT(1)-receptor blockade with UP269-6 (greater inhibition of Ang II pressor responses) was associated with a smaller increase in preload, less systolic and diastolic dysfunction, less infarct expansion, and smaller LV diastolic and systolic volumes. However, both AT(1)-receptor antagonists decreased infarct size. Importantly, MI decreased AT(1)-receptor and AT(2)-receptor expression while MI after AT(1)-receptor antagonism increased AT(1)-receptor (mRNA, not protein) and AT(2)-receptor (mRNA and protein) expression as well as IP(3)R and PKC(epsilon) proteins and cyclic guanosine 3', 5' monophosphate (cGMP). These results suggest that cardioprotection induced by chronic AT(1)-receptor antagonism involves enhanced AT(2)-receptor expression and possibly downstream signalling through IP(3)R, PKC(epsilon) and cGMP.

Opposite effects of amlodipine and enalapril on infarct collagen and remodelling during healing after reperfused myocardial infarction

OBJECTIVES

To compare the effects of the calcium channel blocker amlodipine versus the angiotensin-converting enzyme inhibitor enalapril with or without reperfusion on infarct collagen and remodelling during healing after anterior myocardial infarction (MI).

ANIMALS AND METHODS

In vivo left ventricular (LV) remodelling and function (by quantitative echocardiography) and hemodynamics were measured over six weeks in dogs that were randomized 24 h after reperfusion (2 h after anterior MI) or no reperfusion to oral amlodipine (5 mg bid, n=6), enalapril (5 mg bid, n=6), placebo (bid, n=6) or sham surgery (n=6) for six weeks. Ex vivo infarct size, infarct collagen (hydroxyproline), collagen volume fraction and LV topography were measured at six weeks.

RESULTS

Compared with placebo controls without reperfusion over six weeks in vivo, enalapril or amlodipine with or without reperfusion produced LV unloading and preserved volumes, shape and function, but enalapril limited LV hypertrophy more than amlodipine. However, compared with no reperfusion, amlodipine preserved infarct wall thickness and shape while enalapril decreased infarct wall thickness and increased the shape index. Ex vivo at six weeks, scar size as a percentage of risk was similar in the MI groups. Importantly, enalapril decreased infarct collagen already lowered by reperfusion, while amlodipine preserved infarct collagen after reperfusion and increased collagen volume fraction in spared myocardium.

CONCLUSIONS

Preservation of infarct collagen limits infarct remodelling during healing after reperfused MI and preserves LV shape. Amlodipine and enalapril exert opposite effects on infarct collagen and remodelling after reperfused MI.

Efficacy of pretreatment with the angiotensin II type 1 receptor blocker UP269-6 and losartan in the dog: effect on hemodynamics and ischemia-reperfusion

BACKGROUND

Whether pretreatment with the novel oral angiotensin II (AngII) type 1 receptor (AT(1)R) antagonist UP269-6 (UP) can produce more effective AT(1)R blockade than losartan (LN) for cardioprotection during ischemia-reperfusion (IR) in the dog has not been determined.

METHODS AND MATERIALS

We compared the effect of UP (n = 5) and LN (n = 5) on serial in vivo hemodynamics, AngII pressor responses, and left ventricular (LV) volumes and function (echocardiograms) during escalation to optimal oral dosage over 7 days (day 0 to day 6), and acute IR (15 minutes ischemia, 30 minutes reperfusion) and ex vivo AT(1)R protein (Western immunoblots) with additional sham (n = 5) and IR (n = 5) controls on day 6. Compared with LN, UP produced greater vasodepression and decrease in diastolic volume during dose escalation and greater inhibition of the AngII pressor response over the range of escalating concentrations (0.05, 0.10, 0.25, and 0.50 microg/kg) on day 6. Acute IR after UP pretreatment resulted in less increase in LV filling pressure and LV diastolic and systolic volumes and greater ejection fraction, although UP and LN had similar effects on AT(1)R protein.

CONCLUSION

Pretreatment with UP269-6 over 7 days produces more effective pharmacological AT(1)R blockade and cardioprotection after acute IR than LN in the dog.

Electrophysiologic properties and ventricular fibrillation in normal and myopathic hearts

This study tests the hypothesis that moderate myocardial dysfunction is associated with altered myocardial anisotropic properties and structurally altered ventricular fibrillation (VF). Mongrel dogs were randomized to either a control group or a group that was rapidly paced at 250 beats/min until the left ventricular ejection fraction was < or = 40%. Changes in anisotropic properties and the electrical characteristics of VF associated with the development of moderate myocardial dysfunction were assessed by microminiature epicardial mapping studies. In vivo conduction, refractory periods, and repolarization times were prolonged in both longitudinal and transverse directions in myopathic animals versus controls. VF was different in myopathic versus control animals. There were significantly more conducted deflections during VF in normal hearts compared with myopathic hearts. Propagated deflection-to-deflection intervals during VF were significantly longer in myopathic hearts compared with controls (125.5 +/- 49.06 versus 103.4 +/- 32.9 ms, p = 0.009). There were no abnormalities in cell size, cell shape, or the number of intercellular gap junctions and there was no detectable change in the expression of the gap junction proteins Cx43 and Cx45. Moderate myocardial dysfunction is associated with significant electrophysiological abnormalities in the absence of changes in myocardial cell morphology or intercellular connections, suggesting a functional abnormality in cell-to-cell communication.

Inhibition of apoptosis after ischemia-reperfusion in rat myocardium by cycloheximide

Macromolecular synthesis inhibitors protect cells from apoptosis in many systems. To determine whether the protein synthesis inhibitor cycloheximide (CHX) might inhibit apoptosis and protect the myocardium during ischemia-reperfusion, we subjected isovolumic isolated perfused rat hearts to 25 min of normothermic global ischemia followed by reperfusion. We monitored coronary flow, end-diastolic pressure and rate-pressure product (RPP) throughout and assessed apoptosis by terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL). Regardless of the treatment regimen (only before ischemia; only during reperfusion; or both before ischemia and during reperfusion), CHX significantly improved functional recovery during reperfusion. These effects were most pronounced when CHX was present during reperfusion. When hearts were treated with CHX only during reperfusion the recovery of sinus rhythm was more frequent in the CHX-treated hearts than control hearts (80% v 53%) and earlier for CHX-treated than control hearts: 6.4 +/- 2 v 19.4 +/- 4.7 min of reperfusion. The maximal RPP recoveries for the CHX-treated hearts were 45 +/- 4.0% (P=0.005) of pre-ischemic values, compared to 26 +/- 3% for controls. In control hearts reperfused for 2 h, TUNEL identified 49.5 +/- 10 intact nuclei and 7.5 +/- 2 fragmented nuclei per 1000 nuclei counted. A significantly lower incidence of labeled nuclei with or without fragmentation was observed in CHX treated hearts: 7.6 +/- 3.4 (P=0.009) intact labeled nuclei and 1.8 +/- 0.7/10(3)fragmented labeled nuclei. Our results suggest that CHX-induced inhibition of apoptosis in reperfused myocardium is cardioprotective and promotes functional recovery in vitro.

Intrinsic ANG II type 1 receptor stimulation contributes to recovery of postischemic mechanical function

To determine whether intrinsic angiotensin II (ANG II) type 1 receptor (AT1-R) stimulation modulates recovery of postischemic mechanical function, we studied the effects of selective AT1-R blockade with losartan on proton production from glucose metabolism and recovery of function in isolated working rat hearts perfused with Krebs-Henseleit buffer containing palmitate, glucose, and insulin. Aerobic perfusion (50 min) was followed by global, no-flow ischemia (30 min) and reperfusion (30 min) in the presence (n = 10) or absence (n = 14) of losartan (1 mumol/l) or the cardioprotective adenosine A1 receptor agonist N6-cyclohexyladenosine (CHA, 0.5 mumol/l, n = 11). During reperfusion in untreated hearts (controls), left ventricular (LV) minute work partially recovered to 38% of aerobic baseline, whereas proton production increased to 155%. Compared with controls, CHA improved recovery of LV work to 79% and reduced proton production to 44%. Losartan depressed recovery of LV work to 0% without altering proton production. However, exogenous ANG II (1-100 nmol/l) in combination with losartan restored recovery of LV work during reperfusion in a concentration-dependent manner, suggesting that postischemic recovery of function depends on intrinsic AT1-R stimulation.

Limitation of left ventricular hypertrophy and dysfunction by ACE inhibition after anterior Q-wave myocardial infarction

To determine whether limitation of left ventricular (LV) hypertrophy with angiotensin-converting enzyme inhibition after myocardial infarction (MI) is associated with improved systolic and diastolic function, quantitative two-dimensional echocardiograms and Doppler of 40 patients, who were randomized on day 3 after a first Q-wave anterior MI to receive therapy with captopril (12.5 mg t.i.d.) or placebo for 6 weeks, were analyzed for LV volumes (Simpson's rule) and mass (3D reconstruction), remodeling parameters and peak early (E) and late (A) transmitral flow velocities and deceleration times (DT) at 3 days, 6 weeks, 6 months and 1 year. Compared to placebo over 1 year, captopril limited (p < 0.001) the increase in diastolic volume and mass, increased LV ejection fraction and diastolic E/A ratio, and decreased DT, the frequency of E and A reversal, infarct expansion and aneurysm frequency but volume/ mass ratio was unchanged. Captopril over the first 6 weeks after a first Q-wave anterior MI limited LV remodeling and hypertrophy and improved both systolic and diastolic function up to 1 year.

Effect of the novel angiotensin II type 1 receptor antagonist L-158,809 on acute infarct expansion and acute anterior myocardial infarction in the dog

OBJECTIVES

To assess the effect of the angiotensin II type 1 receptor (AT1-R) antagonist L-158,809 on acute infarct expansion and left ventricular (LV) function during acute anterior myocardial infarction.

METHODS

Dogs were randomized to receive intravenous L-158,809 (0.1 mg/kg bolus and 0.6 microgram/kg/min infusion) or vehicle beginning 1 h after permanent left anterior descending coronary artery ligation and continued for 48 h. In vivo LV remodelling and function (quantitative echocardiography) and hemodynamics over 48 h, and postmortem remodelling after 48 h were measured.

RESULTS

L-158,809 produced 90% to 100% inhibition of the angiotensin II pressor response during the infusions. With respect to percentage changes over the 48 h in vivo, compared with vehicle controls, L-158,809 decreased mean arterial pressure (-20 +/- 4 versus -9 +/- 2%, P = 0.03) and left atrial pressure (-38 +/- 5 versus 25 +/- 6%, P < 0.0001) but did not change heart rate. These unloading effects were associated with a smaller percentage increase in infarct expansion index (-5 +/- 7% versus 27 +/- 2%, P = 0.001) and LV diastolic volume (11 +/- 11% versus 52 +/- 6%, P = 0.008), less shape deformation, fewer apical aneurysms (0 versus 100%, P = 0.0003), better global ejection fraction (49 +/- 2% versus 39 +/- 2%, P = 0.005), less ST segment elevation and fewer Q waves. Also compared with vehicle controls, with L-158,809 postmortem infarct size (19.8 +/- 2.4% versus 50.4 +/- 4.7% of risk region, P = 0.0002) and expansion index (2.06 +/- 0.09 versus 2.76 +/- 0.18, P = 0.006) were less and thinning ratio greater (0.92 +/- 0.02 versus 0.60 +/- 0.05, P = 0.0001).

CONCLUSIONS

The novel AT1-R antagonist L-158,809 produces significant AT1-R blockade, reduces LV loading, and effectively limits acute infarct expansion and early LV remodelling during canine myocardial infarction.

Effects of amlodipine versus enalapril on left ventricular remodelling after reperfused anterior myocardial canine infarction

OBJECTIVE

To compare the effects of the calcium channel blocker amlodipine with those of the angiotensin-converting enzyme (ACE) inhibitor enalapril on left ventricular (LV) remodelling and dysfunction during healing after reperfused anterior myocardial infarction (MI). ACE inhibitors and reperfusion are known to limit LV remodelling after MI. However, the effects of ACE inhibitors and calcium channel blockers on LV remodelling after reperfused MI have not been compared.

METHODS

Changes in LV topography and function (quantitative echocardiograms) and hemodynamics were measured over six weeks in dogs that were randomized 24 h after reperfusion, done after 2 h of anterior MI, to oral amlodipine (5 mg bid; n = 7), enalapril (5 mg bid; n = 6) or no drug (controls; n = 6) for six weeks. Postmortem LV topography was measured at six weeks.

RESULTS

Scar sizes after six weeks were similar in the three groups. Both enalapril and amlodipine reduced the rate pressure product, but decreases in mean arterial and left atrial pressures were more sustained over six weeks with enalapril. Compared with controls over six weeks, both enalapril and amlodipine preserved LV volumes, global ejection fraction, regional function and infarct segment length, but enalapril blocked the increase in non-infarct wall thickness, attenuated the infarct wall thickness, preserved shape and decreased global LV mass more than amlodipine. Sham-operated dogs (n = 3) showed no significant structural changes.

CONCLUSIONS

Both enalapril and amlodipine preserve LV volumes and function during healing after reperfused MI, but enalapril more effectively limits hypertrophy, attenuates infarct wall thickness and preserves shape.

Changes in myocardial density during postinfarction healing: effect on estimation of in vivo left ventricular mass by echocardiographic imaging

To determine whether changes in density (rho) of infarct and noninfarct zones during healing and remodeling after myocardial infarction influence estimates of left ventricular mass and detection of temporal changes by imaging, we measured weights (g) and volumes (mL) of infarct, noninfarct, and mixed tissue in hearts removed 1 to 42 days after anterior infarction in three groups of dogs: nonreperfused infarction treated with placebo or captopril, or infarcts reperfused after 2 h. In vivo mass was calculated from in vivo diastolic myocardial volumes (echocardiograms) and an assumed density of 1.05 g/mL or actual values derived from tissue weights and volumes. Over the 42 days, actual density deviated more from the assumed value of 1.05 in infarct than noninfarct zones, and the overall density was higher for reperfused than nonreperfused ventricles (1.09 vs. 1.06 g/mL, p < 0.01). Correction for density improved the correlation between absolute in vivo and postmortem mass slightly but not the detection of relative changes in mass in control, captopril, or reperfusion groups. These findings suggest that (i) densities of infarct and noninfarct zones differ and change during healing, especially after reperfusion, and (ii) correction for density provides more accurate estimates of volume-derived mass in reperfused hearts.

Effect of angiotensin-converting enzyme inhibition on infarct collagen deposition and remodelling during healing after transmural canine myocardial infarction

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibition for six weeks after myocardial infarction (MI) lowers the collagen content of infarct scars in dogs. However, temporal changes in collagen content of the infarct zone (IZ) with ACE inhibition during healing over six weeks after MI and their possible relation to IZ remodelling have not been determined.

METHODS

IZ collagen (hydroxyproline) was measured over six to seven weeks in dogs treated with captopril (50 mg bid), enalapril (2.5 mg bid) or placebo, beginning on the second day following transmural anterior MI (or sham). In vivo changes in IZ and global left ventricular (LV) remodelling, mass and function (echocardiograms) and hemodynamics among six-week survivors were also measured.

RESULTS

Compared with placebo, both inhibitors decreased IZ collagen (P < 0.001) over the seven weeks. Among the six-week survivors, both inhibitors lowered IZ collagen (P < or = 0.001) and increased the collagen type I:III ratio. However, preload was lower, increase in diastolic volume and mass were less and systolic function improved. Although the doses of captopril (but no enalapril) decreased afterload, inhibition of IZ collagen was less, IZ bulging and global LV dilation were less and systolic function was better with captopril than with enalapril. In all three MI groups, deaths over the seven weeks correlated with greater infarct size, LV volume and dysfunction and lower IZ collagen.

CONCLUSIONS

ACE inhibition suppresses the temporal increase in IZ collagen and attenuates IZ expansion, thinning and bulging, and LV enlargement and aneurysm formation during healing after MI.

Effect of reperfusion on ventricular mass, topography, and function during healing of anterior infarction

The effect of reperfusion performed 2 h after left anterior descending coronary artery occlusion on in vivo changes (echocardiograms) in ventricular mass, topography, and function during postinfarction healing over 6 wk and postmortem topography (planimetry) and collagen (hydroxyproline) content at 6 wk were measured in dogs randomized to reperfusion (n = 12) and no reperfusion (n = 12). Compared with no reperfusion over the 6 wk, reperfusion resulted in less increase in systolic and diastolic volumes, less increase in ventricular mass, less infarct wall thinning, and mild improvement in global ejection fraction without any change in regional asynergy. Although reperfusion decreased the infarct collagen content at 6 wk, it reduced the in vivo expansion of the endocardial surface area; the elongation, diastolic bulge, echogenicity, and systolic thinning of the infarct zone; and the global shape index and aneurysm frequency. Thus reperfusion after 2 h attenuates regional and global dilation and produces less increase in mass during postinfarct healing than no reperfusion, so that the improvement in global systolic function cannot be attributed to global hypertrophy.

Prompt improvement of left ventricular function and preservation of topography with combined reperfusion and intravenous nitroglycerin in acute myocardial infarction

Reperfusion alone during acute myocardial infarction (AMI) preserves left ventricular (LV) topography but causes 'stunning', with delayed or no recovery of function. To determine whether adjunctive intravenous nitroglycerin (NTG) accelerates functional recovery, we prospectively measured function and topography by repeated two-dimensional echocardiography between 1 day and 6 months in 5 groups of patients (n = 73) with a first AMI: placebo (group 1), NTG alone (group 2), NTG combined with successful reperfusion after 4 h (group 3) or failed reperfusion (group 4), and successful reperfusion alone (group 5). Asynergy decreased promptly (p < 0.001) and ejection fraction improved (p < 0.001) between day 1 and 6 months in groups 2 and 3 compared to baseline and groups 1, 4 and 5. Infarct expansion and thinning found in group 1 were prevented in groups 2, 3, 4 and 5. Diastolic volume increased in the anterior subgroup 1 but not 2, 3, 4 and 5. This is the first demonstration that reperfusion combined with adjunctive NTG produces earlier, greater and persistent recovery of LV function in addition to attenuation of remodeling in patients after AMI.

Opposite effects of angiotensin AT1 and AT2 receptor antagonists on recovery of mechanical function after ischemia-reperfusion in isolated working rat hearts

BACKGROUND

Angiotensin II type 1 (AT1) receptor antagonists, when given over the long term, reduce the deleterious consequences of ischemia-reperfusion injury. Whether short-term administration of AT1 or angiotensin II type 2 (AT2) receptor antagonists is cardioprotective has not been investigated.

METHODS AND RESULTS

The effects of short-term administration of selective AT1 and AT2 receptor antagonists on the recovery of mechanical function during reperfusion after 30 minutes of global, no-flow ischemia were studied in left atrium-perfused isolated working rat hearts. Control hearts (n = 8) showed incomplete recovery of left ventricular minute work (LV work) and cardiac efficiency during reperfusion to 51 +/- 15% and 61 +/- 19% of preischemic levels, respectively. Compared with control hearts, the selective AT2 receptor antagonist PD123,319 (0.3 mumol/L) given before ischemia (n = 7) improved the recovery of LV work and efficiency to 82 +/- 4% and 98 +/- 7% of preischemic levels, respectively (P < .01). In contrast, the selective AT1 antagonist losartan (1 mumol/L) blocked the recovery of LV work and depressed efficiency to 0 +/- 0% and 1 +/- 0% (n = 7) of preischemic levels, respectively (P < .01; n = 7). Neither antagonist altered coronary vascular conductance.

CONCLUSIONS

This is the first demonstration that short-term treatment with a selective AT1 versus AT2 antagonist exerts different effects on recovery of mechanical function after ischemia-reperfusion: the AT2 antagonist was cardioprotective, whereas the AT1 antagonist was not. These data suggest that AT2 antagonists and AT1 agonists may offer novel approaches for the treatment of mechanical dysfunction after ischemia-reperfusion.

Rate of collagen deposition during healing and ventricular remodeling after myocardial infarction in rat and dog models

BACKGROUND

We hypothesized that the rate and amount of infarct collagen deposition during healing after myocardial infarction might influence ventricular remodeling in rat and dog models. The purpose of this study was to compare rates of infarct collagen deposition and ventricular remodeling in the two models.

METHODS AND RESULTS

Infarcted rat and dog hearts were removed at fixed time intervals between 1 and 50 days for measuring remodeling parameters and infarct and noninfarct collagen content (mg/g hydroxyproline). Collagen was less in sham rat (n=29) than dog (n=30) ventricles (3.32 versus 4.57 mg/g, P<.001) and markedly lower in the rat (n=48) than dog (n=59) infarcts throughout healing and by 50 days (9.98 versus 56.74 mg/g, P<.0001). Infarct collagen leveled off earlier and healing (histology) was completed sooner in the rat. Infarct scars were also thinner in the rat, with more (P<.0001) thinning and bulging (mm/g), and greater increase in ventricular volume. Although the mass to volume ratio decreased (P<.001) in both models, global remodeling was different, with greater transverse axis widening and globularity in the dog. Although infarct size, transmurality, heart rate, filling pressure, and blood pressure were greater in the rat, infarcts 10% to 30% in size in both models showed similar differences in infarct collagen and remodeling.

CONCLUSIONS

Compared with dog infarcts, rat infarcts exhibited faster healing and infarct collagen deposition and markedly lower infarct collagen. In addition to larger, more transmural, and thinner infarcts, and greater hemodynamic load, the lower infarct collagen in that model might be an important factor in the greater regional remodeling.

Effect of prolonged inotropic stimulation on ventricular remodeling during healing after myocardial infarction in the dog: mechanistic insights

OBJECTIVES

We hypothesized that positive inotropic stimulation during healing after myocardial infarction might increase contractile pull on the infarct segment, increase expansion and promote ventricular dilation.

BACKGROUND

The effect of prolonged inotropic stimulation on left ventricular remodeling during healing after myocardial infarction has not been studied.

METHODS

The effects of 6 weeks of inotropic stimulation on in vivo changes in left ventricular topography, function and mass (serial two-dimensional echocardiograms), hemodynamic variables, postmortem topography (planimetry) and collagen (hydroxyproline content) were studied in 36 chronically instrumented dogs randomized, 2 days after small anterior infarction, to digoxin (0.125 mg daily) and no digoxin (control group).

RESULTS

Heart rate and arterial and left atrial pressures were similar in the two groups, but the first derivative of left ventricular pressure (peak dP/dt), systolic thickening of the noninfarct wall and systolic thinning of the infarct wall were higher in the digoxin group during the 6 weeks. At 6 weeks, infarct scar size and collagen content were similar in both groups, but the digoxin group had more infarct expansion and thinning. Between 2 days and 6 weeks, the digoxin group showed more in vivo diastolic infarct expansion, thinning and bulging; more aneurysm but less global dilation and increase in mass; and no change in ejection fraction. The effects of inotropic stimulation on remodeling were more marked in infarcts with 100% than 85% transmurality.

CONCLUSIONS

Prolonged inotropic stimulation with digoxin during healing after small anterior infarction increases infarct bulging without decreasing infarct collagen content and preserves global ventricular size, mass and systolic function.

Effect of nitrates on myocardial remodeling after acute myocardial infarction

Nitrates are effective for the therapy of acute coronary syndromes, including acute myocardial infarction. Their application in acute infarction has established that vasodilators are beneficial provided hypotension is avoided. Nitrates limit early ventricular remodeling in infarction. New dosing strategies and formulations that permit chronic use after infarction with less tolerance might limit late remodeling. Over the last decade, the demonstrated effectiveness of angiotensin-converting enzyme (ACE) inhibitors in limiting ventricular dilation postinfarction has generated controversy over the usefulness of nitrates for that indication. The uncertainty has been intensified by 2 large mortality trials that tested both agents as adjuncts to conventional therapy. These trials were not designed to test whether nitrates might limit remodeling. Mechanistic experimental and clinical studies that tested whether nitrates or ACE inhibitors could effectively limit ventricular remodeling showed that both improved remodeling endpoints. However, experimental studies raise some concern about the decrease in infarct collagen associated with ACE inhibition and emphasize the fact that final outcome represents a balance of effects. That nitrates do not decrease infarct collagen could be important. Nitrate-induced early recruitment of ventricular function after late reperfusion of acute infarction might also be important. In the mortality trials, >50% of patients received open-label nitrates as per indication. Thus, the trial results to date do not suggest that nitrates are ineffective for remodeling, but rather that ACE inhibitors can confer added benefit. There has been no large clinical trial to test the efficacy of nitrates for remodeling as there has been for ACE inhibitors.

Impact of left ventricular unloading after late reperfusion of canine anterior myocardial infarction on remodeling and function using isosorbide-5-mononitrate

BACKGROUND

Late reperfusion during acute myocardial infarction results in delayed recovery of ventricular function and less remodeling, whereas ventricular unloading with nitrates improves function and attenuates remodeling. Whether late reperfusion combined with prolonged unloading with isosorbide-5-mononitrate (ISMN) might produce greater functional recovery and less remodeling than late reperfusion alone is not known.

METHODS AND RESULTS

In vivo left ventricular function and topography (echocardiograms), postmortem topography (planimetry), and collagen (hydroxyproline) were measured in dogs that were randomized to reperfusion 2 hours after left anterior descending coronary artery ligation, and ISMN (n = 12) or placebo (n = 12) was given as 25 mg IV over 4 hours followed by 50 mg PO QID for 6 weeks. Compared with placebo, the ISMN group had similar heart rate but lower left atrial pressure, mean arterial pressure, and rate-pressure products. Although in vivo baseline remodeling and functional parameters were similar in the two groups, by 6 weeks the ISMN group had smaller (P < or = .05) infarct and noninfarct segment lengths, ventricular volumes, and mass; less (P < .001) asynergy; and greater (P < .001) ejection fraction. More important, by 2 days, ejection fraction was 18% greater (P < .025) and asynergy 26% less (P < .05) with ISMN. At 6 weeks, ISMN showed less (P < or = .05) scar size, scar collagen, cavity dilation, noninfarct wall thickness, and apical bulging than placebo. In another 4 dogs, acute ISMN produced less improvement in function and remodeling than prolonged ISMN.

CONCLUSIONS

Late reperfusion of acute anterior myocardial infarction combined with prolonged ISMN unloading results in greater and earlier recovery of ventricular function and less remodeling than late reperfusion alone.

Effect of captopril and enalapril on left ventricular geometry, function and collagen during healing after anterior and inferior myocardial infarction in a dog model

OBJECTIVES

This study compared the effects of captopril and enalapril on left ventricular geometry, function and mass and on scar collagen and topography during healing after anterior and inferior myocardial infarction in a canine model.

BACKGROUND

The beneficial effect of prolonged angiotensin-converting enzyme inhibitor therapy on remodeling during healing after myocardial infarction might be greater in anterior than inferior infarcts and more effective with captopril than enalapril therapy.

METHODS

The effects of 6 weeks of therapy with captopril (50 mg twice a day), enalapril (2.5 mg twice a day) or placebo on in vivo variables of left ventricular remodeling, function and mass (by echocardiography), hemodynamic function, postmortem topography (by planimetry) and collagen (hydroxyproline levels) were studied in 36 instrumented dogs randomized to receive therapy 48 h after left anterior descending or left circumflex coronary artery occlusion.

RESULTS

Compared with placebo therapy, both captopril and enalapril decreased infarct expansion and thinning, progressive ventricular dilation, ventricular mass and asynergy and infarct collagen levels in anterior and inferior infarcts. Despite similar small scar sizes, the effects on remodeling and dysfunction were greater in anterior than inferior infarcts. In addition, captopril produced greater attenuation of infarct expansion and ventricular enlargement, greater improvement in volume ejection fraction and less decrease in infarct collagen levels than enalapril.

CONCLUSIONS

On balance, captopril and enalapril attenuated left ventricular remodeling and preserved function in small anterior and inferior infarcts despite differences in the effects of the drugs on individual remodeling variables. Further studies will be needed to determine whether inhibition of infarct collagen might be harmful, or differences between captopril and enalapril therapy important, in large transmural infarctions.

Combined captopril and isosorbide dinitrate during healing after myocardial infarction. Effect on ventricular remodeling, function, mass and collagen

OBJECTIVES

We sought to compare the effects of captopril plus isosorbide dinitrate versus monotherapy on infarct collagen content and left ventricular remodeling and function during healing after myocardial infarction.

BACKGROUND

Captopril or isosorbide dinitrate monotherapy can limit postinfarction dilation. Whether captopril inhibits infarct collagen content, or whether captopril plus isosorbide dinitrate might be more beneficial, is not known.

METHODS

In vivo remodeling variables and function (echocardiography), hemodynamic variables, postmortem topography (planimetry) and collagen content (hydroxyproline) were measured in 48 chronically instrumented dogs that were randomized 2 days after left anterior descending coronary artery ligation to 6 weeks of therapy with captopril, isosorbide dinitrate, captopril plus isosorbide dinitrate or placebo.

RESULTS

Compared with placebo, the three active therapies decreased blood pressure and left atrial pressure; limited infarct expansion, infarct thinning, noninfarct wall stretching and thickening; limited left ventricular dilation and increase in left ventricular mass; and decreased regional bulging, aneurysm frequency and left ventricular dysfunction. However, the decrease in asynergy and increase in volume ejection fraction were less with captopril or captopril plus isosorbide dinitrate than with isosorbide dinitrate. Infarct thinning and bulging at 6 weeks was also less with isosorbide dinitrate than with captopril. Although initial left ventricular asynergy, final scar sizes and noninfarct collagen content at 6 weeks were similar among the groups, collagen in the center of the infarct scar was less with captopril or captopril plus isosorbide dinitrate than with placebo or isosorbide dinitrate.

CONCLUSIONS

Monotherapy with captopril or isosorbide dinitrate, or their combination, improved all remodeling variables, but isosorbide dinitrate improved function more than captopril or captopril plus isosorbide dinitrate. Inhibition of infarct collagen content by captopril suggests that benefits with captopril represent a balance between positive and negative effects, and its combination with isosorbide dinitrate might be advantageous.

Effect of enalapril on ventricular remodeling and function during healing after anterior myocardial infarction in the dog

BACKGROUND

Ventricular remodeling after myocardial infarction involves changes in ventricular size, shape, structure, and matrix that impact on function. Prolonged angiotensin-converting enzyme inhibition after infarction with captopril reduces ventricular enlargement and improves clinical outcome, but whether enalapril produces similar benefits is controversial.

METHODS AND RESULTS

The effect of enalapril during healing between 1 day and 6 weeks after myocardial infarction on in vivo changes in ventricular size, shape, mass, and function (asynergy, or akinesis and dyskinesis, and ejection fraction), as determined by serial two-dimensional echocardiography, hemodynamics, postmortem topography (planimetered short- and long-axis ventricular contours), and collagen content (determined by levels of hydroxyproline, a marker for collagen), was measured in 25 instrumented dogs. The dogs were randomized 1 day after left anterior descending coronary artery ligation to a control group (no treatment) and a group receiving oral enalapril (2.5 mg BID). Compared with no treatment, enalapril produced a sustained lowering of left atrial pressure but no difference in heart rate and mean blood pressure over the 6 weeks. Also compared with no treatment, enalapril modified in vivo remodeling parameters between 1 day and 6 weeks, with less elongation of the asynergy-containing segment, a lower expansion index (ratio of endocardial lengths of infarct to non-infarct-containing segments demarcated by papillary muscle landmarks), less scar wall thinning, a lower thinning ratio (ratio of average thickness of infarcted wall to average thickness of the normal wall), smaller ventricular volume, less regional bulging and aneurysm frequency, prevention of the increase in ventricular mass, less total extent of asynergy, and higher volume ejection fraction. At postmortem examination, scar mass was similar in the two groups, but topographic maps with enalapril revealed less infarct bulging, flatter infarct scars, and less noninfarct wall thickness. In addition, postmortem collagen content was similar in noninfarct zones of the two groups but lower in infarct zones of the dogs given enalapril.

CONCLUSIONS

Prolonged enalapril therapy, in a dose that did not lower blood pressure, during healing after anterior infarction produced prolonged reduction of left ventricular preload in dogs. This diastolic unloading was associated with limitation of remodeling parameters (infarct expansion and thinning, progressive ventricular dilation and hypertrophy, and regional bulging), less total asynergy, and improved left ventricular ejection fraction. Although angiotensin-converting enzyme inhibition was associated with lower collagen content in the infarct area and altered scar topography, these effects did not impact negatively on overall remodeling and function.

Laser-induced fluorescence: III. Quantitative analysis of atherosclerotic plaque content

BACKGROUND AND OBJECTIVE

Laser-induced fluorescence (LF) spectroscopic analysis of the chemical composition of atherosclerotic plaque was examined.

STUDY DESIGN/MATERIALS AND METHODS

The intima of 18 dog aortas was injected with chemical compounds found in atherosclerotic plaque. Spectra were recorded in air prior to and after injection of collagens I, III and IV, elastin, cholesterol, triglyceride, and beta-nicotinamide adenine dinucleotide (NADH).

RESULTS

Significant changes in LF intensity were detected after injection of collagens I and III, cholesterol and elastin in thoracic aorta (P < 0.001), but not with triglyceride or NADH. Minor changes were detected in abdominal aorta. Multiple regression analysis of LF intensity ratios demonstrated a clear correlation with the quantity of injected collagens I (R2 = 0.90-0.99) and III (R2 = 0.84-1.0), cholesterol (R2 = 0.72-0.76), and triglyceride (R2 = 0.68-0.80) in both thoracic and abdominal aorta. The correlation between LF and atherosclerotic plaque composition was confirmed in a rooster model of atherosclerosis where multiple regression analysis predicted the measured aortic cholesterol (R2 = 0.78) and triglyceride content (R2 = 0.96).

CONCLUSIONS

(1) Fluorescence spectra recorded from dog aorta were significantly altered by injection of collagens I and III, cholesterol, and elastin. (2) LF may allow quantitative assessment of plaque chemical content.

Nitrates in myocardial infarction

Until two decades ago nitroglycerin was contraindicated in acute myocardial infarction (MI). Studies in the canine model demonstrated that low-dose intravenous (i.v.) infusion, carefully titrated to decrease mean blood pressure by 10% but not below 80 mmHg, during early stages of acute MI produced marked reduction of left ventricular (LV) preload, improvement in regional perfusion, and limitation of infarct size and remodeling. However, more i.v. nitroglycerin to decrease blood pressure further resulted in a paradoxical J-curve effect, with hypoperfusion and increased infarct size. Clinical studies have confirmed that low-dose i.v. nitroglycerin infusion for the first 48 hours after acute MI is safe, not only for improving performance in LV failure, but also for limiting ischemic injury, infarct size, remodeling, and infarct-related complications, including deaths in-hospital and up to 1 year. Recent studies suggest that more prolonged therapy with nitrates spanning the healing phase of acute anterior Q-wave MI can further limit LV remodeling and preserve function. Preliminary results of the recently completed ISIS-4 megatrial suggest, however, that long-term nitrate in patients with suspected MI in the 1990s does not improve survival significantly.

Effect of prolonged nitrate therapy on left ventricular remodeling after canine acute myocardial infarction

BACKGROUND

Prolonged nitrate therapy during healing between 2 days and 6 weeks after anterior myocardial infarction has the potential for limiting further left ventricular remodeling (or changes in topography) and preserving function. Longterm therapy throughout healing over 6 weeks might be more beneficial than short-term therapy over the first 2 weeks after infarction.

METHODS AND RESULTS

The effect of prolonged nitrate therapy between 2 days and 6 weeks during healing after infarction on serial parameters of ventricular remodeling (scar expansion, scar thinning, ventricular dilation, and hypertrophy) and function (asynergy or akinesis plus dyskinesis and ejection fraction) by serial two-dimensional echocardiography, hemodynamics, postmortem topography (computerized planimetry, geometric maps, and radiographs), and collagen content (hydroxyproline) was studied in 64 instrumented dogs randomized 2 days after left anterior descending coronary artery ligation to various nitrate regimens (n = 32) over the first 2 weeks (subgroup 1: 2% transdermal nitroglycerin at 8 AM and 4 PM, n = 6; subgroup 2: 2% transdermal nitroglycerin plus 2.6 mg of sustained-release oral nitroglycerin at 8 AM, 3 PM, and 10 PM, n = 5; subgroup 3: oral isosorbide dinitrate, 30 mg at 8 AM and 4 PM, n = 11) or 6 weeks (subgroup 4: isosorbide dinitrate, n = 10) and in matching controls (n = 32). Nitrate therapy reduced left atrial pressure, mean arterial pressure, and the rate-pressure product compared with controls over the 6 weeks. Postmortem scar mass and hydroxyproline were similar in control and nitrate groups. However, scar stretching and thinning, cavity dilation, noninfarct wall hypertrophy, and apical bulging were less with nitrates, especially in the long-term subgroup 4. In vivo remodeling parameters between 2 days and 6 weeks after ligation showed that, compared with controls, nitrate therapy prevented further stretching of the asynergic segment, decreased the expansion index, decreased further scar thinning, prevented the increase in ventricular volumes, reduced the frequency of ventricular aneurysm, prevented the increase in ventricular mass, reduced the extent of asynergy, and improved ejection fraction. Although the beneficial effect on topography and function was seen in all nitrate subgroups, the overall benefit was greater with long-term therapy over 6 weeks (subgroup 4) than short-term therapy confined to the first 2 weeks (subgroups 1, 2, and 3).

CONCLUSIONS

Prolonged nitrate therapy, in various regimens during healing after infarction, effectively reduced left ventricular loading and prevented infarct thinning, further infarct expansion, progressive ventricular dilation, and the increase in mass. These effects were associated with decreased asynergy and improved ejection fraction. The beneficial effects were greater with long-term therapy over 6 weeks than short-term therapy over the first 2 weeks.

Use of nitroglycerin for the treatment of acute myocardial infarction

After a decade of warnings against the use of nitrates in acute myocardial infarction (MI), they are becoming recognized for their potential to salvage left ventricular (LV) myocardium, geometry and function. Low-dose intravenous (IV) nitroglycerin (NTG) infusion for the first 48 h after acute MI, titrated to lower mean blood pressure by 10% to 30%, but not below 80 mmHg, has been shown to be safe, to improve hemodynamics, and to decrease infarct size, infarct expansion, complications, and deaths in a prospective, randomized, single-blind study of 310 patients. In addition, low-dose NTG infusion for the first 48 h, followed by prolonged buccal NTG given during healing after acute MI in an eccentric dose schedule to minimize tolerance, was found to limit further progressive remodeling and preserve LV function. Meta-analysis of nitrate studies in acute MI indicate that they improve survival. Preliminary and ongoing studies suggest that prolonged NTG therapy post MI can produce further benefit.

Overestimation of myocardial infarct size on two-dimensional echocardiograms due to remodelling of the infarct zone

OBJECTIVE

To assess the effect of early regional diastolic shape distortion or bulging of infarct zones due to infarct expansion on estimates of regional left ventricular dysfunction and infarct size by two-dimensional echocardiographic imaging.

DESIGN

Quantitative two-dimensional echocardiograms from patients with a first Q wave myocardial infarction and creatine kinase infarct size data, and normal subjects, were subjected to detailed analysis of regional left ventricular dysfunction and shape distortion in short-axis images by established methods. Regional left ventricular asynergy (akinesis and dyskinesis) and shape distortion indices (eg, peak [Pk]/radius [ri]) were measured on endocardial diastolic outlines of short-axis images in 43 postinfarction patients (28 anterior and 15 inferior, 5.9 h after onset) and 11 normal subjects (controls). In the infarction group, endocardial surface area of asynergy was calculated by three-dimensional reconstruction of the images and infarct size from serial creatine kinase blood levels.

MAIN RESULTS

Diastolic bulging of asynergic zones was found in all infarction patients. The regional shape distortion indices characterizing the area between the 'actual' bulging asynergic segment and the derived 'ideal' circular segment (excluding the bulge) on indexed sections were greater in infarct than control groups (Pk/ri 0.31 versus 0, P < 0.001) and greater in anterior than inferior infarction subgroups (Pk/ri 0.39 versus 0.16, P > 0.001). Importantly, the degree of distortion correlated with overestimation of asynergy (r = 0.89, P < 0.001), and the relation between infarct size and total 'ideal' asynergy showed a leftward shift from that with 'actual' asynergy.

CONCLUSIONS

Early regional diastolic bulging of the infarct zone results in overestimation of regional ventricular dysfunction, especially in patients with anterior infarction. This effect should be considered when assessing effects of therapy on infarct size, remodelling and dysfunction using tomographical imaging.

Effects of nitrate therapy on ventricular remodeling and function

The hypothesis that nitrates might effectively limit left ventricular remodeling and improve function after acute myocardial infarction has been tested in experimental and clinical models, with special attention to the pathophysiologic evolution of remodeling. In 1 clinical study, before the thrombolytic era, the effects of low-dose intravenous nitroglycerin infusion for the first 48 hours during acute myocardial infarction was evaluated in a prospective, randomized, single-blinded, placebo-controlled study of 310 patients (154 nitroglycerin; 156 placebo). Nitroglycerin proved to be safe and produced several benefits compared with placebo: (1) smaller infarct size; (2) less left ventricular dysfunction; (3) less infarct expansion and thinning; (4) better functional status; (5) fewer in-hospital complications such as left ventricular failure, left ventricular thrombus, cardiogenic shock, and infarct extension; and (6) fewer deaths up to 1 year. Two subsequent clinical studies in the thrombolytic era, with low-dose intravenous nitroglycerin infusion during infarction over the first 48 hours followed by buccal nitrate (eccentric dose regimen) or placebo during healing over 6 weeks postinfarction, indicated that prolonged nitrate therapy effectively limited left ventricular remodeling and improved function further compared with placebo.

Intractable ventricular arrhythmias during remodelling and healing after acute myocardial infarction

A patient with extensive myocardial infarction, evidence of early ventricular remodelling, regional left ventricular (LV) dilation and aneurysm formation developed recurrent ventricular tachyarrhythmias and episodes of sudden death. The patient finally died 24 days post infarction despite effective anti-remodelling therapy and appropriate anti-failure and anti-arrhythmic therapies. Remarkable findings at autopsy included normal LV size and a small LV apical aneurysm despite as much as 52% LV necrosis and further right ventricular necrosis. The case underscores the need for aggressive early infarct-limiting therapy to prevent early remodelling, LV aneurysm and possibly fatal ventricular tachyarrhythmias.

Prevention of ventricular remodelling post myocardial infarction: timing and duration of therapy

OBJECTIVE

To review the evidence for the temporal pathophysiological evolution of structural, topographic and functional changes during remodelling post infarction, and how the timing and duration of therapeutic interventions for limiting remodelling might influence outcome.

DATA SOURCES

Published English language literature.

STUDY SELECTION

The focus was on experimental and clinical studies relating to modification of post infarct remodelling as well as pertinent clinical trials with clinical outcome and mortality end-points.

DATA EXTRACTION

An objective determination of the timing and duration of therapy from the indexed infarction, and the rationale for the approach and its possible relation to measured outcome parameters.

DATA SYNTHESIS

Several strategies targeted to salvage ischemic myocardium and unload the left ventricle have proven effective in limiting remodelling. Because remodelling begins very early and is a staged and progressive pathophysiological process, timing and duration of therapy are likely to have a profound effect on outcome. Different outcomes can be expected depending on whether therapy is begun very early (during the infarction process), early (after completion of the infarction process but before significant deposition of infarct collagen has occurred), late (after infarct collagen has peaked and infarct healing is completed) or very late (after healing is completed). Different outcomes can also be expected with therapy that spans one or more of these stages. Maximum benefit might be expected from therapy that is begun very early, spans the entire healing process and extends beyond. Two-dimensional echocardiograms can be used to assess the impact of therapies on remodelling and function. Very early thrombolysis and low dose intravenous nitroglycerin followed by prolonged angiotensin-converting enzyme inhibition and/or nitrate appear to be a very promising algorithm.

CONCLUSIONS

The optimal therapeutic strategy for limiting post infarct remodelling should recognize the pathophysiological staging of the process and be targeted at preventing infarction, early expansion and progressive dilation.

Role of nitrates after acute myocardial infarction

Apart from their ability to relieve myocardial ischemia, nitrates have an important role to play on preservation of left ventricular (LV) geometry and function after acute myocardial infarction (MI). In the first 48 hours after acute MI, intravenous nitroglycerin infusion titrated to a low-dose regimen produces multiple benefits, including smaller infarct size, better regional and global LV function, less remodeling, fewer in-hospital complications, and fewer deaths in-hospital and up to 1 year. This regimen might be an effective adjunct during reperfusion therapy for salvaging ischemic myocardium, LV geometry, and function. Recent studies indicate that prolonged therapy with nitrates during the healing phase after acute MI can effectively further limit progressive LV remodeling (less LV dilation, expansion, thinning, and aneurysm formation) and preserve LV function. Tolerance with chronic therapy is avoided by an eccentric dose regimen to provide a nitrate-free interval.

Functional impact of remodeling during healing after non-Q wave versus Q wave anterior myocardial infarction in the dog

OBJECTIVES

This study was undertaken to compare changes in left ventricular remodeling and function during healing after a first anterior non-Q wave versus a Q wave myocardial infarction in the dog.

BACKGROUND

Whether ventricular remodeling is more severe after anterior Q wave than after anterior non-Q wave infarction has not been studied systematically.

METHODS

Serial remodeling and functional variables (two-dimensional echocardiography), electrocardiography and hemodynamic data were recorded over 6 weeks in 58 instrumented dogs subjected to left anterior descending coronary artery ligation or ligation plus collateral obliteration. Postmortem topography and transmurality (by planimetry) and infarct collagen (hydroxyproline) were measured at 6 weeks.

RESULTS

At 6 weeks, infarct collagen was similarly increased in both groups, but the Q wave group had greater infarct size (7.2% vs. 4.5%, p less than 0.025) and greater transmurality (88% vs. 58%, p less than 0.001), higher left atrial pressures, more infarct expansion (expansion index 2.62 vs. 2.31, p less than 0.001), more thinning (thinning ratio 0.62 vs. 0.72, p less than 0.001), greater cavity dilation (diastolic volume 88 vs. 72 ml, p less than 0.001), more regional bulging in the short-axis view (depth 4.9 vs. 1.9 mm, p less than 0.001), more regional asynergy (18% vs. 7%, p less than 0.001), lower global ejection fraction (40% vs. 48%, p less than 0.001), more endocardial and epicardial bulging in the long-axis view and greater incidence of aneurysm (82% vs. 36%, p less than 0.005), left ventricular thrombus (64% vs. 0%, p less than 0.0005) and ventricular arrhythmias. Echocardiograms obtained during a 6-week period indicated that left ventricular topographic deterioration and dysfunction were present in the earliest postinfarction study at 2 days in both groups but were more frequent in the Q wave group. Regional myocardial blood flow (24 dogs) was lower in the Q wave than in the non-Q wave group. Scanning electron microscopy (10 dogs) revealed preservation of the epicardial collagen matrix in the non-Q wave but not the Q wave group.

CONCLUSIONS

Anterior Q wave infarction is associated with greater transmurality and more postinfarction left ventricular remodeling and dysfunction than is non-Q wave infarction.

Impact of increased infarct transmurality on remodeling and function during healing after anterior myocardial infarction in the dog

To determine the impact of greater infarct transmurality on changes in left ventricular remodeling and function after acute anterior myocardial infarction, serial topographic and functional parameters (two-dimensional echocardiograms) and hemodynamics over 6 weeks, and postmortem topography (planimetry) at 6 weeks, were measured in chronically instrumented dogs randomized to standard coronary artery ligation (group 1) or a modified lower ligation plus collateral obliteration to decrease collateral inflow and increase transmurality (group 2). At 6 weeks, postmortem scar size and collagen were similar in the two groups, but group 2 had greater transmurality associated with more necrosis relative to area at risk, Q waves, infarct expansion, thinning, regional bulging, and cavity dilatation. Over the 6 weeks, group 2 showed more early expansion, late thinning and regional bulging in the short axis, larger diastolic and systolic volumes, and more apical aneurysmal bulging in the long-axis, reflecting more topographic deterioration. More important, group 2 showed greater regional and global left ventricular dysfunction over 6 weeks, lower ejection fraction at 2 days with further decrease over 6 weeks, and more left ventricular thrombus, ventricular arrhythmias, and deaths. In addition, transmurality correlated with the severity of remodeling and dysfunction. The findings indicate that transmurality is a major determinant of remodeling and left ventricular dysfunction during healing after anterior infarction.

Effect of left ventricular unloading with captopril on remodelling and function during healing of anterior transmural myocardial infarction in the dog

OBJECTIVE

To determine whether left ventricular (LV) unloading with captopril between two days and six weeks during healing after transmural anterior acute myocardial infarction might prevent further LV remodelling and preserve function in the canine model.

DESIGN

Serial LV topographic and functional parameters (two-dimensional echocardiograms) and hemodynamics over six weeks and scar topography (planimetry) and collagen (hydroxyproline) at six weeks were measured in 34 chronically instrumented dogs; 24 with anterior transmural acute myocardial infarction (coronary artery ligation and collateral obliteration) that had been randomized at two days post infarction to therapy with oral 50 mg bid placebo (n = 12) or captopril (n = 12) for six weeks, and 10 with sham infarction.

MAIN RESULTS

At six weeks, captopril and placebo groups had similar scar mass (7.7 versus 8.1% LV), infarct hydroxyproline and transmurality but the captopril group showed significantly less (P less than or equal to 0.05) infarct expansion and thinning, cavity dilation, epicardial and endocardial bulge. Between two days and six weeks, captopril decreased mean left atrial and arterial pressures compared to placebo or sham. Echocardiograms at two days showed similar LV asynergy, ejection fraction, infarct expansion and thinning with placebo and captopril. In contrast, echocardiograms between two days and six weeks showed that: further expansion and thinning occurred with placebo but not captopril; LV volumes increased with placebo but decreased with captopril; total LV asynergy was unchanged with placebo but decreased with captopril; and LV ejection fraction was unchanged with placebo but increased with captopril. At six weeks, LV ejection fraction was 10% higher (45 versus 35%, P less than 0.001) and LV aneurysm was less frequent (33 versus 100%, P less than 0.005) with captopril compared to placebo.

CONCLUSIONS

Chronic LV unloading with captopril therapy during healing after canine transmural anterior acute myocardial infarction limits further remodelling, decreases aneurysm formation and improves function.

Effect of long-term captopril therapy on left ventricular remodeling and function during healing of canine myocardial infarction

To determine whether the long-term reduction of preload and afterload by captopril during healing after acute anterior myocardial infarction might attenuate left ventricular remodeling and improve function, 30 chronically instrumented dogs with infarction produced by left anterior descending coronary artery ligation were randomized 2 days later to oral therapy with placebo (n = 15) or captopril, 50 mg twice daily (n = 15), for 6 weeks. Serial hemodynamic as well as topographic and functional variables (two-dimensional echocardiography) were measured over 6 weeks. Scar topography (planimetry), occluded bed size (coronary arteriography) and collagen (hydroxyproline) content were measured at 6 weeks. Between 2 days and 6 weeks, captopril decreased (p less than 0.001) mean arterial pressure and mean left atrial pressure more than did placebo, but it did not influence heart rate. Infarct scar mass, transmurality and collagen content at 6 weeks were similar in the two groups but scars showed less (p less than 0.001) thinning and expansion with captopril than with placebo. Echocardiograms showed similar infarct expansion and thinning in the two groups at 2 days but less aneurysm with captopril at 6 weeks. Between 2 days and 6 weeks, expansion index (infarct-/noninfarct-containing segment length) decreased (p less than 0.001) with captopril but increased (p less than 0.001) with placebo. Also, thinning ratio (infarct/normal wall thickness) decreased (p less than 0.001) with placebo but did not change (p = NS) with captopril. By 6 weeks, left ventricular asynergy and volumes showed a greater decrease (p less than 0.01) and global ejection fraction a greater increase (p less than 0.05) with captopril.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous nitroglycerin unloading in acute myocardial infarction

Low-dose intravenous nitroglycerin infusion can be safely administered during acute myocardial infarction to unload the left ventricle and salvage ischemic myocardium and left ventricular geometry and function. In an experimental conscious dog model, low-dose infusion titrated to decrease mean blood pressure by 10% over the first 6 hours after coronary artery ligation resulted in 51% decrease in infarct size, 54% decrease in preload, and more than 50% increase in collateral blood flow. The same benefits were seen when methoxamine was given to counteract that 10% decrease in blood pressure. Similar short-term nitroglycerin infusion also limited remodeling in the dog model. More important, no myocardial salvage was seen with excessive nitroglycerin-induced hypotension to levels less than 80 mm Hg. Clinically, prolonged low-dose nitroglycerin infusion was evaluated in a prospective, randomized, single-blinded, placebo-controlled study of 310 patients with acute infarction: 154 received nitroglycerin and 156 received placebo. Nitroglycerin was titrated to reduce mean blood pressure by 10% in normotensive patients and up to 30% in hypertensive (blood pressure greater than 140/90 mm Hg) patients, but not to less than 80 mm Hg. Nitroglycerin produced several benefits compared with placebo: (1) smaller creatine kinase infarct size; (2) less regional left ventricular dysfunction, better global ejection fraction, and less infarct expansion and thinning; (3) better clinical functional status and hemodynamics; (4) fewer inhospital complications such as acute left ventricular failure and dilation due to marked infarct expansion, left ventricular thrombus, cardiogenic shock, and infarct extension; and (5) fewer deaths up to 1 year in patients with anterior Q-wave infarction.

Nitrates for myocardial salvage in the 1990s

Low-dose intravenous nitroglycerin infusion for the first 48 h is becoming routine in the management of acute myocardial infarction in North America. It is most widely used as primary therapy in patients admitted more than 6 h after acute infarction. Such therapy has been shown to limit infarct size, infarct complications and remodeling. However, it is being applied increasingly more as an adjunct before, during and after thrombolytic therapy. Several trials are underway to test the effectiveness of more prolonged therapy, with early intravenous nitroglycerin followed by buccal or oral formulations for several weeks, in further limitation of ventricular remodeling, dilatation, aneurysm formation and in preserving function. Nitrates may prove to be a useful adjunct or alternative to angiotensin-converting-enzyme (ACE) inhibitors for long-term therapy.