Hisashi Shimoyama

Effects of long-term monotherapy with enalapril, metoprolol, and digoxin on the progression of left ventricular dysfunction and dilation in dogs with reduced ejection fraction.

BACKGROUND Recent clinical trials have suggested that therapy with angiotensin-converting enzyme inhibitors in asymptomatic patients with reduced left ventricular (LV) function can significantly reduce the incidence of congestive heart failure compared with patients receiving placebo. In the present study, we examined the effects of long-term monotherapy with enalapril, metoprolol, and digoxin on the progression of LV systolic dysfunction and LV chamber enlargement in dogs with reduced LV ejection fraction (EF). METHODS AND RESULTS LV dysfunction was produced in 28 dogs by multiple sequential intracoronary microembolizations. Embolizations were discontinued when LVEF was 30% to 40%. Three weeks after the last embolization, dogs were randomized to 3 months of oral therapy with enalapril (10 mg twice daily, n = 7), metoprolol (25 mg twice daily, n = 7), digoxin (0.25 mg once daily, n = 7), or no treatment (control, n = 7). As expected, in untreated dogs, LVEF decreased (36 +/- 1% versus 26 +/- 1%, P < .001) and LV end-systolic volume (ESV) and end-diastolic volume (EDV) increased during the 3-month follow-up period (39 +/- 4 versus 57 +/- 6 mL, P < .001, and 61 +/- 6 versus 78 +/- 8 mL, P < .002, respectively). In dogs treated with enalapril or metoprolol, LVEF remained unchanged or increased after therapy compared with before therapy (35 +/- 1% versus 38 +/- 3% and 35 +/- 1% versus 40 +/- 3%, respectively, P < .05), whereas ESV and EDV remained essentially unchanged. In dogs treated with digoxin, EF remained unchanged but ESV and EDV increased significantly. CONCLUSIONS In dogs with reduced LVEF, long-term therapy with enalapril or metoprolol prevents the progression of LV systolic dysfunction and LV chamber dilation. Therapy with digoxin maintains LV systolic function but does not prevent progressive LV enlargement.

Effects of ACE inhibition on cardiomyocyte apoptosis in dogs with heart failure

Cardiomyocyte apoptosis or programmed cell death has been shown to occur in end-stage explanted failed human hearts and in dogs with chronic heart failure (HF). We tested the hypothesis that early long-term monotherapy with an angiotensin-converting enzyme (ACE) inhibitor attenuates cardiomyocyte apoptosis in dogs with moderate HF. Left ventricular (LV) dysfunction (ejection fraction 30-40%) was produced in dogs by multiple sequential intracoronary microembolizations. Dogs were randomized to 3 mo of therapy with enalapril (Ena, 10 mg twice daily, n = 7) or to no therapy at all (control, n = 7). After 3 mo of therapy, dogs were euthanized and the hearts removed. Presence of nuclear DNA fragmentation (nDNAf), a marker of apoptosis, was assessed in frozen LV sections using the immunohistochemical deoxynucleotidal transferase-mediated dUTP-digoxigenin nick-end labeling (TUNEL) method. Sections were also stained with ventricular anti-myosin antibody to identify cells of cardiocyte origin. From each dog, 80 fields (×40) were selected at random, 40 from LV regions bordering old infarcts and 40 from LV regions remote from any infarcts, for quantifying the number of cardiomyocyte nDNAf events per 1,000 cardiomyocytes. The average number of cardiomyocyte nDNAf events per 1,000 cardiomyocytes was significantly lower in Ena-treated dogs compared with controls (0.81 ± 0.13 vs. 2.65 ± 0.81, P < 0.029). This difference was due to a significantly lower incidence of cardiomyocyte nDNAf events in LV regions bordering scarred tissue (infarcts) in Ena-treated dogs compared with controls. We conclude that early long-term Ena therapy attenuates cardiomyocyte apoptosis in dogs with moderate HF. Attenuation of cardiomyocyte apoptosis may be one mechanism by which ACE inhibitors preserve global LV function in HF.

Short-term Hemodynamic Effects of Endothelin Receptor Blockade in Dogs With Chronic Heart Failure

BACKGROUND Plasma endothelin levels are increased in heart failure and may contribute to the increased peripheral vasoconstriction that characterizes this disease state. In the present study, we examined the effects of intravenous bosentan, a nonpeptide, competitive endothelin-1 receptor antagonist, on hemodynamics in dogs with chronic heart failure. METHODS AND RESULTS Chronic heart failure was produced in 11 dogs by multiple sequential intracoronary microembolization. At the time of study, left ventricular (LV) ejection fraction was 25 +/- 2%. Hemodynamic and echocardiographic measurements were made at baseline and at 15, 30, and 60 minutes after a bolus injection of bosentan (10 mg/kg). Bosentan had no significant effect on heart rate or mean aortic blood pressure. At 60 minutes, bosentan reduced LV end-diastolic pressure (17 +/- 2 versus 11 +/- 2 mm Hg; P < .05) and systemic vascular resistance (3891 +/- 379 versus 3071 +/- 346 dyne .s. cm-5; P < .05) compared with baseline and increased cardiac output (2.63 +/- 0.29 versus 3.33 +/- 0.46 L/min; P < .05), peak rate of change of LV pressure during isovolumic contraction and relaxation (1751 +/- 92 versus 2197 +/- 170 mm Hg/s; P < .05), and LV fractional shortening determined by echocardiography (30 +/- 2% versus 36 +/- 2%; P < .05). CONCLUSIONS Short-term intravenous bosentan reduced systemic vascular resistance and improved overall LV performance in dogs with chronic heart failure. These results suggest that endothelin-1 receptor antagonists may be useful therapeutic agents in the treatment of heart failure.

Abnormalities of cardiocytes in regions bordering fibrous scars of dogs with heart failure

Progressive deterioration of left ventricular function is a characteristic feature of the heart failure state and is often speculated to result from ongoing loss of viable myocytes. We previously showed that in dogs with chronic heart failure, cardiocyte death through apoptosis occurs in the border region of fibrous scars (old infarcts). In the present study we examined the structural integrity of cardiocytes in regions bordering fibrous scars using transmission electron microscopy. Morphometric studies were performed using left ventricular tissue obtained from ten dogs with chronic heart failure produced by intracoronary microembolizations. Mitochondrial number increased significantly with proximity to the scar, while mitochondrial size decreased leading to a gradual decrease in mitochondrial volume fraction. Severe injury to mitochondria was present in only 5% of organelles in myocytes far from the scar but increased markedly to 28-41% in myocytes adjacent to or incorporated within the scar. Similarly, severe myofibrillar abnormalities were present in only 3% of myocytes that were far from the scar but increased significantly to 12-73% in myocytes adjacent to or incorporated within the scar. These results indicate that in dogs with chronic heart failure, constituent myocytes of left ventricular regions bordering fibrous scars manifest heterogeneity in the extent of degeneration. The extent of degeneration is greatest in myocytes closest to the scar and least in myocytes far from the scar. We postulate that this wavefront of myocyte degeneration is a dynamic process that may lead to progressive expansion of the scar through loss of viable myocytes and ultimately may contribute, in part, to the progressive left ventricular dysfunction that characterizes the heart failure state.

Abnormalities of contractile structures in viable myocytes of the failing heart

We examined the incidence and severity of abnormalities of contractile structures of residual viable cardiomyocytes in the left ventricular free wall, septum and right ventricular free wall of 10 dogs with chronic heart failure produced by multiple intracoronary microembolizations and in septal biopsies of 13 patients with chronic heart failure. The abnormalities were evaluated by transmission electron microscopy and classified as either (i) type-1, defined as complete interruption of myofibrils; (ii) type-2, defined as disconnection of end-sarcomeres from the intercalated disc; or (iii) type-3, sarcomere abnormalities defined as Z-bands irregularities and/or focal myofilament disarray. In the left ventricular free wall of dogs, type-1 abnormalities were present in 33 +/- 8% of myocytes, type-2 in 26 +/- 8%, and type-3 in 63 +/- 9%. The incidence of a type-3 abnormality but not type-1 or type-2 was greater in the left ventricular wall compared with the septum and right ventricular wall (P < 0.05). Among abnormal myocytes, 29 +/- 3% of myofibrils were interrupted, 18 +/- 4% of end-sarcomeres were disconnected from the intercalated disc and 12 +/- 2% of sarcomeres were abnormal. The severity of a type-1 but not type-2 or type-3 abnormalities was greater in the left ventricular wall compared with the septum and right ventricular wall. A similarly high incidence of abnormalities was observed in septal myocytes of patients. The results indicate that abnormalities of contractile structures are common among viable myocytes of the failing heart. The incidence of these abnormalities is sufficiently high to warrant serious consideration of their potential role in the progression of left ventricular dysfunction that characterizes the heart failure state.

Effects of long-term therapy with enalapril on severity of functional mitral regurgitation in dogs with moderate heart failure

OBJECTIVES This study examined the effects of early long-term monotherapy with enalapril on the severity of functional mitral regurgitation in dogs with moderate heart failure. BACKGROUND Functional mitral regurgitation often develops in patients with heart failure and, depending on its severity, can have a marked adverse impact on the stroke output of the failing left ventricle and contribute to progressive deterioration of the heart failure state. METHODS Left ventricular dysfunction (ejection fraction 30% to 40%) was produced in 14 dogs by multiple sequential intracoronary microembolizations. Dogs were randomized to 3 months of therapy with enalapril (10 mg twice daily, n = 7) or no therapy at all (control, n = 7). The severity of functional mitral regurgitation was quantified by Doppler color flow mapping in seven control and six enalapril-treated dogs. Mitral annular diameter was assessed by echocardiography and left ventricular volumes and shape by ventriculography. Measurements were made before initiation and after completion of therapy. RESULTS In control dogs, the severity of mitral regurgitation increased during the follow-up period ([mean +/- SEM] 14 +/- 4 vs. 23 +/- 4%, p < 0.001) and was associated with increased left ventricular end-systolic and end-diastolic volumes. In contrast, the severity of regurgitation was not significantly changed in dogs treated with enalapril (18 +/- 3 vs. 16 +/- 6%, p < 0.59) and was associated with preservation of left ventricular volumes. CONCLUSIONS In dogs with moderate heart failure, early long-term therapy with enalapril prevents progressive worsening of functional mitral regurgitation. This beneficial effect is most likely achieved by prevention of progressive left ventricular dilation.

Relation of left ventricular chamber shape in patients with low (≤40%) ejection fraction to severity of functional mitral regurgitation

Abstract In conclusion, the results of this study indicate that severity of functional MR in patients with low ejection fraction appears to be dictated primarily by increased sphericity of the left ventricle rather than by mitral annular dilatation or LV chamber enlargement.

Effects of AT1-receptor blockade on progression of left ventricular dysfunction in dogs with heart failure.

The objective of the present study was to determine the effects of early long-term monotherapy with the angiotensin II AT1-receptor antagonist valsartan on the progression of left ventricular (LV) dysfunction and remodeling in dogs with moderate heart failure (HF). Studies were performed in 30 dogs with moderate HF produced by multiple sequential intracoronary microembolizations. Embolizations were discontinued when LV ejection fraction was 30-40%. Two weeks after the last embolization, dogs were randomized to 3 mo of oral therapy with low-dose valsartan (400 mg twice daily, n = 10), to high-dose valsartan (800 mg twice daily, n = 10), or to no treatment at all (control, n = 10). Treatment with valsartan significantly reduced mean aortic pressure and LV end-diastolic pressure compared with control. In untreated dogs, LV ejection fraction decreased (37 +/- 1 vs. 29 +/- 1%, P = 0.001) and end-systolic volume (ESV) and end-diastolic volume (EDV) increased (81 +/- 5 vs. 92 +/- 5 ml, P < 0.001; 51 +/- 3 vs. 65 +/- 3 ml, P = 0.001, respectively) after 3 mo of follow-up compared with those levels before follow-up. In dogs treated for 3 mo with low-dose valsartan, ejection fraction was preserved (37 +/- 1 vs. 38 +/- 2%, pretreatment vs. posttreatment) as was ESV but not EDV. In dogs treated for 3 mo with high-dose valsartan, ejection fraction decreased (35 +/- 1 vs. 31 +/- 2%, P = 0.02) and ESV and EDV increased in a manner comparable to those levels in controls. Valsartan had no significant effects on cardiomyocyte hypertrophy or on the extent of interstitial fibrosis. We conclude that, for dogs with moderate HF, early long-term therapy with the AT1-receptor blocker valsartan decreases preload and afterload but has only limited benefits in attenuating the progression of LV dysfunction and chamber remodeling.The objective of the present study was to determine the effects of early long-term monotherapy with the angiotensin II AT1-receptor antagonist valsartan on the progression of left ventricular (LV) dysfunction and remodeling in dogs with moderate heart failure (HF). Studies were performed in 30 dogs with moderate HF produced by multiple sequential intracoronary microembolizations. Embolizations were discontinued when LV ejection fraction was 30-40%. Two weeks after the last embolization, dogs were randomized to 3 mo of oral therapy with low-dose valsartan (400 mg twice daily, n = 10), to high-dose valsartan (800 mg twice daily, n = 10), or to no treatment at all (control, n = 10). Treatment with valsartan significantly reduced mean aortic pressure and LV end-diastolic pressure compared with control. In untreated dogs, LV ejection fraction decreased (37 ± 1 vs. 29 ± 1%, P = 0.001) and end-systolic volume (ESV) and end-diastolic volume (EDV) increased (81 ± 5 vs. 92 ± 5 ml, P < 0.001; 51 ± 3 vs. 65 ± 3 ml, P = 0.001, respectively) after 3 mo of follow-up compared with those levels before follow-up. In dogs treated for 3 mo with low-dose valsartan, ejection fraction was preserved (37 ± 1 vs. 38 ± 2%, pretreatment vs. posttreatment) as was ESV but not EDV. In dogs treated for 3 mo with high-dose valsartan, ejection fraction decreased (35 ± 1 vs. 31 ± 2%, P = 0.02) and ESV and EDV increased in a manner comparable to those levels in controls. Valsartan had no significant effects on cardiomyocyte hypertrophy or on the extent of interstitial fibrosis. We conclude that, for dogs with moderate HF, early long-term therapy with the AT1-receptor blocker valsartan decreases preload and afterload but has only limited benefits in attenuating the progression of LV dysfunction and chamber remodeling.

Divergent effects of intravenous dobutamine and nitroprusside on left atrial contribution to ventricular filling in dogs with chronic heart failure

The left atrial (LA) contribution to left ventricular (LV) filling is often attenuated in patients with heart failure. It remains uncertain, however, whether therapy with positive inotropic agents or vasodilators improves or further impairs this maladaptation. In the present study, the effects of intravenous dobutamine and nitroprusside on the LA contribution to LV filling was examined in seven dogs with chronic heart failure produced by multiple sequential intracoronary microembolizations. Pulsed Doppler echocardiography was used to measure mitral inflow velocity before and after an intravenous infusion of dobutamine (4 micrograms/kg/min) and an intravenous infusion of nitroprusside (3 micrograms/kg/min). The percent LA contribution to LV filling was calculated as the ratio of the time-velocity integral of the LA component of mitral inflow velocity (Ai) to the time-velocity integral of total diastolic inflow velocity (Ti) times 100. Dobutamine increased LV filling pressure, LV end-diastolic wall stress, LV end-diastolic stiffness, and Ei, but had no effect on Ai or the percent LA contribution to filling (14% +/- 3% vs 12% +/- 2%) (p < 0.34). In contrast, nitroprusside decreased LV filling pressure, LV end-diastolic wall stress, and end-diastolic stiffness, and increased Ei, Ai, and the percent LA contribution to LV filling (12% +/- 2% vs 17% +/- 2%) (p < 0.01). The results indicate that dobutamine and nitroprusside have divergent effects on the LA contribution to LV filling. In dogs with chronic heart failure, dobutamine appears to impair LA contribution to the LV filling by augmenting LA workload, whereas nitroprusside appears to elicit greater LA contribution to LV filling by reducing the LA workload.

Electrophysiologic and electrocardiographic pharmacodynamics of cocaine.

To determine and describe relationships between plasma cocaine concentrations and electrophysiologic and electrocardiographic effects, 10 anesthetized dogs with normal intact hearts received a continuous 3‐hour infusion of cocaine 0.11 mg/kg/minute (total dose 20 mg/kg). Data were collected as part of a randomized, blinded, placebo‐controlled study investigating the effects of cocaine on ventricular fibrillation threshold. Every 30 minutes during infusion of cocaine or placebo and for 3 hours after discontinuation of the infusion, heart rate and mean arterial pressure were determined, effective refractory period (ERP) was measured, and QRS duration and PR, QTc, and JTc intervals were recorded. At the time of each 30‐minute measurement, arterial blood was obtained to determine plasma cocaine concentrations. Hysteresis curves were observed for cocaine‐induced increases in ERP and PR interval. The effects of cocaine on QRS duration and QTc and JTc intervals were not well described by tested models. Pharmacodynamic modeling techniques may be used to describe relationships between plasma cocaine concentrations and specific cardiovascular effects of cocaine. Further study is required to determine applicability of this model for prediction of cocaines cardiovascular effects in humans.