Pharmacological stress agents for evaluation of ischemic heart disease

Characterization of the Human Coronary Microvascular Response to Multiple Hyperaemic Agents

Background

It is unclear whether the coronary microvascular responses to multiple, mechanistically distinct hyperaemic agents exert similar dilatory responses or share common clinical predictors. This study therefore sought to characterize the index of microvascular resistance (IMR) response to multiple hyperaemic agents in the human coronary circulation.

Methods

Thermodilution-derived IMR was determined during intravenous adenosine, intracoronary acetylcholine, and intravenous dobutamine in patients with ischemic symptoms and nonobstructive coronary angiograms. A total of 128 patients were studied (44 with adenosine and acetylcholine, and 84 with all agents). Adenosine IMR >25, acetylcholine IMR >31, and dobutamine IMR >29 were used to define elevated responses.

Results

IMR responses demonstrated weak-to-moderate association (adenosine vs acetylcholine IMR: ρ = 0.33; adenosine vs dobutamine IMR: ρ = 0.51; acetylcholine vs dobutamine IMR: ρ = 0.28; all P < 0.01). Logistic regression analyses revealed that: (1) elevated adenosine IMR was associated with increasing age and left ventricle hypertrophy (odds ratio [OR] = 1.27 and 1.58; both P < 0.05, respectively), (2) elevated acetylcholine IMR was associated with increasing plasma uric acid (OR = 1.09; P < 0.05), and (3) elevated dobutamine IMR was associated with hypertension and left atrial volume index (OR = 3.99 and 1.07; both P < 0.05, respectively). Subset analyses to evaluate clinical utility of the acetylcholine and dobutamine IMR, independent of abnormal adenosine IMR, revealed that elevated acetylcholine and/or dobutamine IMR were associated with higher risk exercise stress tests, left atrial volumes, and burden of exertional chest pain.

Conclusions

Microvascular-specific IMR responses to different hyperaemic agents are only moderately associated, whereas the predictors for agent-specific IMR responses varied, suggesting that multiple pharmacologic agents interrogate different microvascular control mechanisms.

Myocardial strain indices and coronary flow reserve are only mildly affected in healthy hypertensive patients

To investigate changes in two-dimensional myocardial strain echocardiography (2DSTE) indices following a dipyridamole stress test (DIPSE) in relatively healthy hypertensive patients and healthy controls. Forty-seven male hypertensive patients (aged 57±9 years) with normal ejection fraction and without left ventricular (LV) hypertrophy and 20 healthy male subjects were studied with conventional and 2DSTE echocardiography at rest and post DIPSE. Coronary flow reserve (CFR) in the left anterior descending artery following DIPSE was also evaluated. Global longitudinal strain (GLS) and TWIST were higher while UNTWIST rate was lower in hypertensives versus controls (p < 0.05 for all); TWIST remained higher in hypertensives (p = 0.021) after adjustment for differences in age and body mass index (BMI) between the groups. CFR was higher in controls compared to hypertensives even after adjustment for confounders (4.14 vs. 2.53, p = 0.001). DIPSE-induced changes did not differ between the groups after adjustment for age and BMI (p > 0.05 for all). DIPSE-induced improvement in GLS was associated with higher CFR only in hypertensive patients (r - 0.372, p = 0.010). The current study showed that well controlled hypertensive patients have only mild echocardiographic differences compared to controls; some of these differences appear to depend on age and BMI. A 'hyper-rotation' phenomenon (i.e. higher TWIST) early in hypertension may be a compensatory mechanism to preserve global systolic LV function. Coronary microcirculatory function was impaired in hypertensive patients, albeit within normal range, and was associated with DIPSE-induced changes in myocardial long-axis systolic function.

The prognostic role of myocardial strain indices and dipyridamole stress test in renal transplantation patients

INTRODUCTION

Renal transplantation (RT) increases survival in end-stage kidney disease patients but cardiovascular diseases remain the leading cause of morbidity and mortality. We evaluated the role of myocardial strain (2DSTE) indices and dipyridamole-induced (DIPSE) changes in echocardiographic parameters at baseline for the prediction of clinical events and echocardiographically assessed deterioration of cardiac function in a RT population.

METHODS

Forty-five RT patients underwent an echocardiographic study at baseline including 2DSTE and DIPSE. If no cardiovascular/renal event occurred, patients were investigated at 3-year follow-up; eight patients presented a clinical event while 37 patients were re-evaluated.

RESULTS

Coronary flow reserve (CFR) was abnormal in 24% of the population. DIPSE induced improvements in classic and 2DSTE systolic and diastolic echocardiographic indices including TWIST, UNTWIST, global longitudinal strain (GLS), and circumferential strain (P < .05 for all). Compared to baseline, deteriorations in E/E', LVEF, E', and TWIST were observed at follow-up (P < .05 for all). DIPSE-induced changes in GLS, global radial strain, and LVEF were associated with changes in these indices at follow-up (P < .05 for all). Higher LV mass index, E/E', and lower MAPSE, E', and CFR at baseline were associated with the occurrence of clinical events at follow-up (P < .05 for all).

CONCLUSIONS

In RT patients, coronary vascular dysfunction (ie, low CFR) was associated with the occurrence of adverse events. DIPSE-induced changes in myocardial strain and classic echocardiographic indices could identify individuals with a subclinical deterioration in cardiac function at follow-up. This may indicate that DIPSE could serve as a means to assess myocardial reserve in this population.

Quantitative magnetic resonance imaging can distinguish remodeling mechanisms after acute myocardial infarction based on the severity of ischemic insult

The type and extent of myocardial infarction encountered clinically is primarily determined by the severity of the initial ischemic insult. The purpose of the study was to differentiate longitudinal fluctuations in remodeling mechanisms in porcine myocardium following different ischemic insult durations. Animals (N = 8) were subjected to coronary balloon occlusion for either 90 or 45 min, followed by reperfusion. Imaging was performed on a 3 T MRI scanner between day-2 and week-6 postinfarction with edema quantified by T2, hemorrhage by T2*, vasodilatory function by blood-oxygenation-level-dependent T2 alterations and infarction/microvascular obstruction by contrast-enhanced imaging. The 90-min model produced large transmural infarcts with hemorrhage and microvascular obstruction, while the 45 min produced small nontransmural and nonhemorrhagic infarction. In the 90-min group, elevation of end-diastolic-volume, reduced cardiac function, persistence of edema, and prolonged vasodilatory dysfunction were all indicative of adverse remodeling; in contrast, the 45-min group showed no signs of adverse remodeling. The 45- and 90-min porcine models seem to be ideal for representing the low- and high-risk patient groups, respectively, commonly encountered in the clinic. Such in vivo characterization will be a key in predicting functional recovery and may potentially allow evaluation of novel therapies targeted to alleviate ischemic injury and prevent microvascular obstruction/hemorrhage.

The adverse events and hemodynamic effects of adenosine-based cardiac MRI

OBJECTIVE

We wanted to prospectively assess the adverse events and hemodynamic effects associated with an intravenous adenosine infusion in patients with suspected or known coronary artery disease and who were undergoing cardiac MRI.

MATERIALS AND METHODS

One hundred and sixty-eight patients (64 ± 9 years) received adenosine (140 µg/kg/min) during cardiac MRI. Before and during the administration, the heart rate, systemic blood pressure, and oxygen saturation were monitored using a MRI-compatible system. We documented any signs and symptoms of potential adverse events.

RESULTS

In total, 47 out of 168 patients (28%) experienced adverse effects, which were mostly mild or moderate. In 13 patients (8%), the adenosine infusion was discontinued due to intolerable dyspnea or chest pain. No high grade atrioventricular block, bronchospasm or other life-threatening adverse events occurred. The hemodynamic measurements showed a significant increase in the heart rate during adenosine infusion (69.3 ± 11.7 versus 82.4 ± 13.0 beats/min, respectively; p < 0.001). A significant but clinically irrelevant increase in oxygen saturation occurred during adenosine infusion (96 ± 1.9% versus 97 ± 1.3%, respectively; p < 0.001). The blood pressure did not significantly change during adenosine infusion (systolic: 142.8 ± 24.0 versus 140.9 ± 25.7 mmHg; diastolic: 80.2 ± 12.5 mmHg versus 78.9 ± 15.6, respectively).

CONCLUSION

This study confirms the safety of adenosine infusion during cardiac MRI. A considerable proportion of all patients will experience minor adverse effects and some patients will not tolerate adenosine infusion. However, all adverse events can be successfully managed by a radiologist. The increased heart rate during adenosine infusion highlights the need to individually adjust the settings according to the patient, e.g., the number of slices of myocardial perfusion imaging.

Dipyridamole with low-dose aspirin augments the infarct size-limiting effects of simvastatin

PURPOSE

Statins protect against ischemia-reperfusion injury and limit myocardial infarct size (IS). This effect is dependent on increased generation of adenosine by ecto-5' nucleotidase and downstream activation of cyclooxygenase-2 (COX2). Dipyridamole (DIP) augments the IS-limiting effects of statins by blocking the cellular reuptake of adenosine; whereas aspirin (ASA) attenuates the effect by inhibiting COX2. We studied the effect of acute administration of DIP, ASA and their combination on the IS-limiting effect of simvastatin (SIM).

METHODS

Rats received oral SIM (10 mg/kg/d) or vehicle for 3 days. Rats underwent 30 min of coronary artery occlusion and 4 h reperfusion. After 5 min of ischemia rats received i.v. DIP (5 mg/kg), ASA (20 mg/kg or 2 mg/kg) or DIP+ASA (2 mg/kg) or vehicle alone. Ischemia area at risk (AR) was assessed by blue dye and IS by TTC. Myocardial samples were analyzed for the activation of Akt, ERK 1/2, endothelial nitric oxide synthase (eNOS), and cyclic-AMP-response-element-binding-protein (CREB).

RESULTS

SIM limited IS. High- or low-dose ASA alone had no effect on IS. DIP alone or with low-dose ASA significantly reduced IS. Low-dose ASA did not attenuate the SIM effect, whereas high-dose ASA completely blocked the effect. The combination of DIP+low-dose ASA+SIM resulted in the smallest IS. Both SIM and DIP+low-dose ASA augmented Akt phosphorylation and their effect was additive. Both SIM and DIP+low-dose ASA augmented eNOS, ERK 1/2 and CREB phosphorylation.

CONCLUSIONS

During acute myocardial ischemia, DIP alone or with low-dose ASA limits IS and does not attenuate the IS-limiting effect of SIM as high-dose ASA.

Head-to-head comparison of first-pass MR perfusion imaging during adenosine and high-dose dobutamine/atropine stress

To directly compare the stressor capabilities of adenosine and high-dose dobutamine/atropine using first pass myocardial perfusion magnetic resonance imaging. Fourty-one patients with suspected or known coronary artery disease underwent cardiac magnetic resonance (CMR) perfusion imaging at 1.5 Tesla on two consecutive days prior to invasive coronary angiography. On day 1 a standard CMR perfusion protocol during adenosine stress was carried out (adenosine infusion with 140 μg/kg/min, 0.1 mmol/kg Gd-DTPA). On day 2, the identical CMR perfusion sequence was repeated during a standard high-dose dobutamine/atropine stress protocol at rest and during target heart rate (85% of maximum age-predicted heart rate). Stress-inducible perfusion deficits were evaluated visually regarding presence and transmural extent. Quantitative coronary angiography served as the reference standard with significant stenosis defined as ≥50% luminal diameter reduction. Twenty-five patients (61%) had significant coronary stenoses. Adenosine and dobutamine stress CMR perfusion imaging resulted in an equally high sensitivity and specificity for the stenosis detection on a per patient basis (92 and 75% for both stressors, respectively). Agreement of both stressors with regard to the presence or absence of stress-inducible perfusion deficits was nearly perfect using patient- and segment based analysis (kappa 1.0 and 0.92, respectively). Adenosine and dobutamine/atropine stress CMR perfusion imaging are equally capable to identify stress inducible deficits and resulted in an almost identical extent of ischemic reactions. Though adenosine stress CMR perfusion imaging is widely employed, dobutamine stress CMR perfusion represents a valid alternative and may be particularly useful in patients with contraindications to vasodilator testing.

The quantification of dipyridamole induced changes in regional deformation in normal, stunned or infarcted myocardium as measured by strain and strain rate: an experimental study

Strain rate imaging (SRI) during dobutamine stress-echocardiography (DSE) has been shown to differentiate between ischemic substrates based on the segmental response. Dipyridamole stress echo (DIPSE) is currently used as an alternative to DSE in detecting coronary artery disease. The aim of this study was: (a) to determine the normal response in peak-systolic myocardial strain (S) and strain-rate (SR) during DIPSE and (b) to compare the S and SR responses of DSE and DIPSE in the same chronically ischemic/infarcted segments in the setting of single vessel disease.

METHODS

The deformation response to DIPSE was studied in 7 normal pigs and in an additional 18 pigs, with a spectrum of ischemic substrates. S and SR data were extracted from a posterior wall "at risk" segment at baseline and during both DSE and DIPSE. The animals were divided into different ischemic substrate (stunning, non-transmural and transmural infarction), based on the DSE response as previously suggested.

RESULTS

In normal myocardium, dipyridamole induced no changes in regional systolic deformation neither during nor after the infusion. Furthermore there was no detectable response in S and SR in segments with either a non-transmural or a transmural infarction. However, in myocardial segments with a DSE "stunning response", both end systolic S and peak-systolic SR tended to "normalize" at peak dipyridamole dose.

CONCLUSIONS

These results suggest that dipyridamole does not induce changes in regional deformation in normal or (partially) infarcted myocardium. Only in stunned myocardium (in the setting of single-vessel disease), dipyridamole tends to normalize deformation.

Enhanced cardioprotection against ischemia-reperfusion injury with a dipyridamole and low-dose atorvastatin combination

Atorvastatin (ATV) limits infarct size (IS) by activating Akt and ecto-5-nucleotidase, which generates adenosine. Activated Akt and adenosine activate endothelial nitric oxide synthase (eNOS). When given orally, high doses (10 mg/kg) are needed to achieve full protection. We determined whether dipyridamole (DIP), by preventing the reuptake of adenosine, has a synergistic effect with ATV in reducing myocardial IS. In this study, rats received 3-days of the following: water, ATV (2 mg·kg−1·day−1), DIP (6 mg·kg−1·day−1), or ATV + DIP. In addition, rats received 3-days of the following: aminophylline (Ami; 10 mg·kg−1·day−1) or Ami + ATV + DIP. Rats underwent 30 min of myocardial ischemia followed by 4 h of reperfusion (IS protocol), or hearts were explanted for immunoblotting. As a result, IS in the controls was 34.0 ± 2.8% of the area at risk. ATV (33.1 ± 2.1%) and DIP (30.5 ± 1.5%) did not affect IS, whereas ATV + DIP reduced IS (12.2 ± 0.5%; P < 0.001 vs. each of the other groups). There was no difference in IS between the Ami alone (48.1 ± 0.8%) and the Ami + ATV + DIP (45.8 ± 2.9%) group ( P = 0.422), suggesting that Ami completely blocked the protective effect. Myocardial adenosine level in the controls was 30.6 ± 3.6 pg/μl. ATV (51.0 ± 4.9 pg/μl) and DIP (51.5 ± 6.8 pg/μl) caused a small increase in adenosine levels, whereas ATV + DIP caused a greater increase in adenosine levels (66.4 ± 3.1 pg/μl). ATV and DIP alone did not affect myocardial Ser473 phosphorylated-Akt and Ser1177 phosphorylated-eNOS levels, whereas ATV + DIP significantly increased them. In conclusion, low-dose ATV and DIP had synergistic effects in reducing myocardial IS and activation of Akt and eNOS. This combination may have a potential benefit in augmenting the eNOS-mediated pleiotropic effects of statins.

Myocardial perfusion imaging in the elderly: a review

Coronary artery disease is a major cause of morbidity and mortality in the elderly population. As a result of ageing of the population and better medical, interventional and surgical treatment of patients with coronary artery disease, more and more elderly patients are referred to the cardiology department for diagnostic work-up. Stress testing, in combination with myocardial perfusion imaging, is routinely used in elderly patients, a population in which the diagnosis of significant coronary artery disease is often challenging because of atypical symptomatology. Since the introduction of technetium-99m ligands for myocardial perfusion imaging, it is possible to perform electrocardiogram-gated perfusion imaging. This not only improves the specificity of the test for coronary artery disease detection, but also enables the simultaneous assessment of left ventricular functional parameters. This article briefly overviews the possible stress modalities, diagnostic accuracy and prognostic value of myocardial perfusion imaging in elderly patients.

Dipyridamole protects the liver against warm ischemia and reperfusion injury

BACKGROUND

Adenosine, a metabolite of adenosine triphosphate degradation during ischemia, is reported to attenuate ischemia and reperfusion injury in several tissues. Dipyridamole is a nucleoside transport inhibitor that augments endogenous adenosine. In this study, we tested whether dipyridamole would attenuate hepatic I/R injury. For this purpose, dipyridamole was applied to a 2-hour total hepatic vascular exclusion model in dogs.

STUDY DESIGN

Dipyridamole (DYP) was given by continuous intravenous infusion for 1 hour before ischemia at a dose of 0.25 mg/kg (high-DYP, n = 6), 0.1 mg/kg (medium-DYP, n = 6), or 0.05 mg/kg (low-DYP, n = 6). Nontreated animals were used as ischemic controls (CT, n = 12). Two-week survival, systemic and hepatic hemodynamics, liver function tests, energy metabolism, adenosine 3', 5'-cyclic monophosphate (cyclic AMP) levels, platelet numbers, arachidonic acid metabolites, and histopathology were analyzed.

RESULTS

Two-week animal survival was 25% in CT, 17% in high-DYP, 100% in medium-DYP, and 17% in low-DYP. Dipyridamole significantly improved postreperfusion hepatic blood flow and energy metabolism, attenuated liver enzyme release and purine catabolite production, and augmented cyclic AMP levels. The medium dose of dipyridamole lessened platelet aggregation, thromboxane B2 production, and polymorphonuclear neutrophil infiltration, and improved survival.

CONCLUSIONS

We demonstrated marked hepatoprotective effects of dipyridamole against severe ischemia and reperfusion injury in canine livers. Dipyridamole is a promising agent for liver surgery and transplantation.