Pharmacologic stress echocardiography in the assessment of coronary artery disease

The Hypoxia-Adenosine Link during Myocardial Ischemia-Reperfusion Injury

Despite increasing availability and more successful interventional approaches to restore coronary reperfusion, myocardial ischemia-reperfusion injury is a substantial cause of morbidity and mortality worldwide. During myocardial ischemia, the myocardium becomes profoundly hypoxic, thus causing stabilization of hypoxia-inducible transcription factors (HIF). Stabilization of HIF leads to a transcriptional program that promotes adaptation to hypoxia and cellular survival. Transcriptional consequences of HIF stabilization include increases in extracellular production and signaling effects of adenosine. Extracellular adenosine functions as a signaling molecule via the activation of adenosine receptors. Several studies implicated adenosine signaling in cardioprotection, particularly through the activation of the Adora2a and Adora2b receptors. Adenosine receptor activation can lead to metabolic adaptation to enhance ischemia tolerance or dampen myocardial reperfusion injury via signaling events on immune cells. Many studies highlight that clinical strategies to target the hypoxia-adenosine link could be considered for clinical trials. This could be achieved by using pharmacologic HIF activators or by directly enhancing extracellular adenosine production or signaling as a therapy for patients with acute myocardial infarction, or undergoing cardiac surgery.

Coordination of ENT2-dependent adenosine transport and signaling dampens mucosal inflammation

Intestinal epithelial barrier repair is vital for remission in inflammatory bowel disease (IBD). Extracellular adenosine signaling has been implicated in promoting restoration of epithelial barrier function. Currently, no clinically approved agents target this pathway. Adenosine signaling is terminated by uptake from the extracellular space via equilibrative nucleoside transporters (ENTs). We hypothesized that ENT inhibition could dampen intestinal inflammation. Initial studies demonstrated transcriptional repression of ENT1 and ENT2 in IBD biopsies or in murine IBD models. Subsequent studies in mice with global Ent1 or Ent2 deletion revealed selective protection of Ent2-/- mice. Elevated intestinal adenosine levels in conjunction with abolished protection following pharmacologic blockade of A2B adenosine receptors implicate adenosine signaling as the mechanism of gut protection in Ent2-/- mice. Additional studies in mice with tissue-specific deletion of Ent2 uncovered epithelial Ent2 as the target. Moreover, intestinal protection provided by a selective Ent2 inhibitor was abolished in mice with epithelium-specific deletion of Ent2 or the A2B adenosine receptor. Taken together, these findings indicate that increased mucosal A2B signaling following repression or deletion of epithelial Ent2 coordinates the resolution of intestinal inflammation. This study suggests the presence of a targetable purinergic network within the intestinal epithelium designed to limit tissue inflammation.

Biological implications of extracellular adenosine in hepatic ischemia and reperfusion injury

The purine nucleoside adenosine is clinically employed in the treatment of supraventricular tachycardia. In addition, it has direct coronary vasodilatory effects, and may influence platelet aggregation. Experimental observations mechanistically link extracellular adenosine to cellular adaptation to hypoxia. Adenosine generation has been implicated in several pathophysiologic processes including angiogenesis, tumor defenses and neurodegeneration. In solid organ transplantation, prolonged tissue ischemia and subsequent reperfusion injury may lead to profound graft dysfunction. Importantly, conditions of limited oxygen availability are associated with increased production of extracellular adenosine and subsequent tissue protection. Within the rapidly expanding field of adenosine biology, several enzymatic steps in adenosine production have been characterized and multiple receptor subtypes have been identified. In this review, we briefly examine the biologic steps involved in adenosine generation and chronicle the current state of adenosine signaling in hepatic ischemia and reperfusion injury.

Adenosine and hypoxia-inducible factor signaling in intestinal injury and recovery

The gastrointestinal mucosa has proven to be an interesting tissue in which to investigate disease-related metabolism. In this review, we outline some of the evidence that implicates hypoxia-mediated adenosine signaling as an important signature within both healthy and diseased mucosa. Studies derived from cultured cell systems, animal models, and human patients have revealed that hypoxia is a significant component of the inflammatory microenvironment. These studies have revealed a prominent role for hypoxia-induced factor (HIF) and hypoxia signaling at several steps along the adenine nucleotide metabolism and adenosine receptor signaling pathways. Likewise, studies to date in animal models of intestinal inflammation have demonstrated an almost uniformly beneficial influence of HIF stabilization on disease outcomes. Ongoing studies to define potential similarities with and differences between innate and adaptive immune responses will continue to teach us important lessons about the complexity of the gastrointestinal tract. Such information has provided new insights into disease pathogenesis and, importantly, will provide insights into new therapeutic targets.

Adenosine: an old drug newly discovered

Over decades, anesthesiologists have used intravenous adenosine as mainstay therapy for diagnosing or treating supraventricular tachycardia in the perioperative setting. More recently, specific adenosine receptor therapeutics or gene-targeted mice deficient in extracellular adenosine production or individual adenosine receptors became available. These models enabled physicians and scientists to learn more about the biologic functions of extracellular nucleotide metabolism and adenosine signaling. Such functions include specific signaling effects through adenosine receptors expressed by many mammalian tissues; for example, vascular endothelia, myocytes, hepatocytes, intestinal epithelia, or immune cells. At present, pharmacological approaches to modulate extracellular adenosine signaling are evaluated for their potential use in perioperative medicine, including attenuation of acute lung injury; renal, intestinal, hepatic and myocardial ischemia; or vascular leakage. If these laboratory studies can be translated into clinical practice, adenosine receptor-based therapeutics may become an integral pharmacological component of daily anesthesiology practice.

Early reduction in left ventricular contractile reserve detected by dobutamine stress echo predicts high-dose chemotherapy-induced cardiac toxicity

BACKGROUND

High-dose chemotherapy (HDC) is utilized in high-risk cancer patients. This type of treatment may induce cardiac toxicity which becomes clinically evident weeks or months after HDC. Hence, the possibility of early identification of patients who will develop cardiac impairment is strategic for its clinical implications. The aim of this study was to identify possible early changes of left ventricular contractile reserve (LVCR) in cancer patients undergoing HDC, as well as to evaluate the relevance of such changes as predictors of chemotherapy-induced cardiotoxicity.

METHODS

In forty-nine female patients scheduled for HDC, due to poor-prognosis breast cancer, dobutamine stress echocardiography (DSE) was performed, before each of the three HDC cycles (C1, C2, C3), and 1, 4, and 7 months after the end of chemotherapy. According to rest left ventricular ejection fraction (LVEF) evaluated within 18 months after HDC (f-LVEF), patients were allocated to Group A (LVEF < 50% and >10 absolute units reduction) and to Group B (LVEF > or = 50%).

RESULTS

Rest LVEF didn't show any significant difference between the two groups except at f-LVEF. Peak LVEF and LVCR significantly decreased in Group A only, starting from C3. At C3, a > or = 5 units fall in LVCR was found to be predictive for f-LVEF drop below 50%.

CONCLUSIONS

In patients undergoing HDC, low-dose DSE allows the early identification of patients at a high risk of developing cardiac dysfunction.

Cost-effectiveness analysis of noninvasive strategies to evaluate patients with chest pain

We evaluated clinical and economic outcomes of diagnostic strategies on the basis of pharmacologic stress echocardiography (PhSE) versus exercise electrocardiography test (EET) in 527 patients with chest pain (274 women; age 59 +/- 10 years) who underwent both EET and PhSE. We investigated 3 strategies, ie, coronary angiography: after positive EET (strategy 1); after positive PhSE (strategy 2); or after a positive PhSE performed after a positive EET (strategy 3). A patient was correctly identified if he or she had negative test results and no events, or had positive test results and abnormal coronaries. The cost per patient correctly identified was calculated as the ratio between the cost of each strategy and the number of patients correctly identified. The accuracy in correctly identifying the patients was 78%, 92%, and 91% with strategies 1, 2, and 3, respectively. The cost of each patient correctly identified was 1572 US dollars, 1097 US dollars, and 1081 US dollars with strategies 1, 2, and 3, respectively. In conclusion, PhSE-based strategies are cost-effective versus EET.

Serial motion assessment by reference tracking (SMART): application to detection of local functional impact of chronic myocardial ischemia

PURPOSE

To compare measurements of wall motion and thickening with and without correcting for cardiac twisting and shortening.

METHOD

Inversion recovery Gd-DPTA perfusion and cine motion MRI were performed on 12 pigs with chronic ischemia induced by ameroid occluder. Analyses were based on conventional fixed plane imaging and serial motion assessment by reference tracking (SMART).

RESULTS

Normal motion was 31.3 +/- 1.9%, and normal wall thickening was 41.4 +/- 2.2%. At the maximum perfusion defect, SMART wall motion was 10.5 +/- 2.4% and fixed wall motion was 20.6 +/- 1.7% (p < 0.004), SMART wall thickening was 20.1 +/- 4.4%, and fixed wall thickening was 32 +/- 1.9% (p < 0.03).

CONCLUSION

SMART measurements of wall thickening and motion detect much smaller thickening and motion in ischemic myocardium than fixed radial metrics. SMART data, covering the entire heart, should prove twice as sensitive to abnormalities in motion and thickening, such as any produced by ischemic heart disease or improved by treatment.

Non-invasive prediction of angiographic progression of coronary artery disease by dipyridamole-stress echocardiography

BACKGROUND

Coronary angiography is the currently accepted standard means for assessing progression of coronary artery disease. A dipyridamole-echocardiography test (DET) might provide an alternative non-invasive functional imaging method for this purpose.

OBJECTIVE

To assess whether variations in results of serial DET match variations in angiographic assessments of coronary artery disease.

METHODS

From the Pisa Institute of Clinical Physiology stress-echocardiography data bank (1983-1998), we selected 60 patients satisfying the inclusion criteria of coronary angiography and DET having each been performed and interpreted twice independently and within 1 week. The second angiographic and stress-echocardiographic assessment was performed 45+/-31 months after the initial one. Angiographic progressors were defined a priori as patients with any progression of stenosis to occlusion and those with any stenosis > 30% with > 20% progression of stenosis measured by visual and quantitative coronary angiography. Stress-echocardiography progressors were defined as those patients who had previously had a negative test of a test having a positive result and those patients who had positive results of tests both in initial testing and in a second session of testing with the latter having a peak wall-motion-score index > 0.12 (on a scale of 1, normal to 4, dyskinetic in a 16-segment model) larger than the former.

RESULTS

Of the 60 patients, 44 were angiographic 'progressors' and 16 were 'non progressors'. Stress-echocardiographic responses were concordant with angiographic identification for 39 of 44 progressors and 15 of 16 non-progressors, with an overall concordance of 90%.

CONCLUSIONS

Measurement of dipyridamole-stress-echocardiographic response allows one to separate angiographic progressors and non-progressors efficiently, simply by taking into account the presence, extent and severity of stress-induced abnormalities of wall motion.

Dipyridamole-atropine stress echocardiography versus exercise SPECT scintigraphy for detection of coronary artery disease in hypertensives with positive exercise test

OBJECTIVES

Many different stress echocardiographic and radionuclide perfusion imaging tests have been proposed for detecting epicardial coronary artery disease (CAD) in hypertensive patients. Their relative diagnostic and prognostic value has not been exactly established.

BACKGROUND

A positive exercise electrocardiography test has a low diagnostic specificity in hypertensive patients and warrants for a complementary imaging test to confirm the diagnosis of coronary artery disease.

METHODS

Hypertensive patients (n = 53), (29 males, aged 58 +/- 10 years) with normal left ventricular function detected by echocardiography and previous positive exercise test ( > or = 0.15 mV of ST segment depression on 12 lead electrocardiogram) underwent dipyridamole-atropine stress echocardiography (DASE) and thallium-201 stress/ rest myocardial single-photon emission computed tomography (SPECT). All patients had coronary angiography within 15 days and independently of imaging test results.

RESULTS

Coronary angiogram showed significant ( > or = 50% qualitatively assessed diameter reduction) epicardial coronary artery disease in 23 (43%) patients. Sensitivity for detection of coronary artery disease was significantly higher for scintigraphy (DASE = 78% versus SPECT = 100%, P < 0.05) while specificity was higher for echo (DASE = 100% versus SPECT = 47%, P < 0.00001). Diagnostic accuracy was also higher for echo (DASE = 91% versus SPECT = 70%, P < 0.01).

CONCLUSION

In patients with exercise-nduced ST segment depression, dipyridamole stress echo and SPECT perfusion scintigraphy are both good diagnostic options, with DASE characterized by higher specificity, lower sensitivity, and at least comparable diagnostic accuracy than SPECT.

Preparing the azotemic diabetic patient for surgery

Azotemic diabetic patients have more risk of complications during or after surgery than those without diabetes and azotemia. These complications include infection, excessive bleeding, cardiovascular events, and electrolyte imbalance. The appropriate preoperative evaluation, measures to be taken to avoid the complications, and how to adequately manage blood sugar during surgery is discussed.

Dobutamine stress echocardiography: safety in diagnosing coronary artery disease

Dobutamine stress echocardiography is considered a relatively well-tolerated diagnostic modality, effective in the management of patients with known or suspected coronary artery disease. Adverse effects during testing are relatively frequent, precluding the achievement of a diagnostic end-point in about 5 to 10% of tests. These adverse effects, mostly tachyarrhythmias and arterial hypotension, are usually minor and self limiting. However, severe life-threatening complications, as well as death, also occur. By analysing Medline-quoted literature up to March 1999, we found 35 original studies from a single institution with more than 100 patients, as well as 2 multicentre studies, concerning the feasibility and safety of dobutamine stress echocardiography. In a cumulative total of 26438 tests performed, 79 life-threatening complications (such as acute myocardial infarction, asystole, ventricular fibrillation, sustained ventricular tachycardia or severe symptomatic hypotension) have been reported, giving an incidence of 1 severe adverse reaction per every 335 examinations. In addition, 29 isolated case reports have been published describing life-threatening complications during dobutamine echocardiography. In case reports, 2 deaths have been described, both due to acute cardiac rupture in patients with recent inferior myocardial infarction. Severe adverse reactions during dobutamine echocardiography can be ischaemia independent, and are independent of operator experience and are unpredictable; some complications can be late occurring and long lasting. As a consequence, the procedure must be clearly indicated, written informed consent has to be obtained from the patient, an attending physician must be present during testing, and long term observation of outpatients is useful in order to manage late complications. In conclusion, while the safety of dobutamine stress echocardiography was reported to be outstanding in early reports, further experience presents a substantially more worrying picture. This must be taken into account by both physicians and patients when assessing the risk-benefit profile of the procedure.

Acute cardiac rupture during dobutamine-atropine echocardiography stress test

We report an acute cardiac rupture during dobutamine-atropine echocardiography stress test on the sixth day after admission for an inferoposterior acute myocardial infarction complicated with mild pericardial effusion.