Norbert Watzinger

The potential of contrast‐enhanced magnetic resonance imaging for predicting left ventricular remodeling

To determine whether the myocardial injury size on day 2 measured after gadolinium (Gd)‐mesoporphyrin and Gd‐diethylenetriamine‐pentaacetic acid (DTPA) administration can be used for predicting left ventricular (LV) remodeling 8 weeks later, and to monitor the structural and functional changes in the infarct, peri‐infarct rim, and remote myocardium in reperfused infarction using contrast‐enhanced and functional magnetic resonance imaging (MRI)

Comparison of late enhancement cardiovascular magnetic resonance and thallium SPECT in patients with coronary disease and left ventricular dysfunction.

PURPOSEnLate enhancement magnetic resonance imaging (MRI) was compared with thallium-201 rest-redistribution single photon emission computed tomography (SPECT) in patients with reduced left ventricular (LV) function and prior myocardial infarction (MI).nnnBACKGROUNDnHyperenhancement on contrast cardiac MRI using gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) has been reported to identify nonviable myocardium. Comparisons of MRI and thallium-201 SPECT have recently been reported. This study focuses on the comparison of these modalities specifically in patients with ischemic heart failure, where viability determination is most clinically relevant.nnnMETHODSnFifteen patients with LV dysfunction and prior MI [mean ejection fraction (EF) 35 +/- 11%] underwent thallium-201 rest-redistribution scintigraphy and contrast MRI on separate days. Each short axis slice was divided into six 60-degree segments, and correlations between MRI and scintigraphy were made on viability detection for each segment. For SPECT, the mean uptake score was calculated from the average of all percent relative activity values throughout each segment. Areas with < 50% of maximal thallium uptake were considered nonviable. On MRI, regions with increased signal intensity after an injection of 0.1 mmol/kg Gd-DPTA were considered nonviable.nnnRESULTSnA total of 558 segments were analyzed. Overall, there was a strong inverse relationship between the area of hyperenhancement on MRI and diminished thallium-201 uptake on SPECT (r = -0.51, P < 0.001). There was a significant correlation between the imaging methods for each individual segment, except for the inferior-septal segment (r = -0.38, P < 0.08).nnnCONCLUSIONSnIn patients with LV dysfunction and prior MI, our data suggest MRI hyperenhancement significantly correlates with myocardial nonviability by thallium-201 SPECT. Correlations were weaker in the inferior-septal region, which may be due to SPECT attenuation artifact.

Myocardial blood flow in patients with dilated cardiomyopathy: quantitative assessment with velocity-encoded cine magnetic resonance imaging of the coronary sinus.

To quantify global myocardial perfusion using magnetic resonance imaging (MRI) in patients with heart failure due to idiopathic dilated cardiomyopathy (IDC) and to compare myocardial perfusion and microvascular reactivity with healthy subjects.

MR contrast media for myocardial viability, microvascular integrity and perfusion

Cardiovascular imaging requires an appreciation of rapidly evolving MR imaging sequences as well as careful utilization of intravascular, extracellular and intracellular MR contrast media. At the present time, clinical studies are restricted to the use of extracellular MR contrast media. MR imaging has the potential to noninvasively measure multiple parameters of the cardiovascular system in a single imaging session. Recent advances in fast and ultrafast MR imaging have considerably enhanced the capability of this technique, beyond the assessment of left ventricular wall motion and morphology into visualization of the coronary arteries and measurement of blood flow. During the course of the last several years, multiple strategies for imaging viable myocardium have been developed and validated using MR contrast media. Contrast enhanced dynamic MR imaging provides information regarding microvascular integrity and perfusion. Because these information can be provided noninvasively by MR imaging, repeated measurements can be performed in longitudinal studies to monitor the progression or regression of myocardial injury. Similar studies are needed to examine the effects of newly developed cardioprotective therapeutics. Development of suitable intravascular MR contrast medium may be essential for visualization of the coronary arteries and interventional therapies. MR imaging may emerge as one-stop-shop for evaluating the heart and coronary system. This capability will make MR imaging cost-effective in the first decade of this millennium.

Myocardial Viability: Magnetic Resonance Assessment of Functional Reserve and Tissue Characterization

The determination of myocardial viability is crucial in patients with left ventricular dysfunction resulting from acute myocardial ischemia or chronic coronary artery disease. Viable myocardium will most likely benefit from revascularization procedures. However, the revascularization of scar tissue will not lead to improvement of ventricularfunction andfurthermore bears unnecessary riskfor the patient. Currently, echocardiographic and radionuclide techniques are the most established methods for the assessment of presence and extent of viable myocardium. Magnetic resonance imaging (MRI) also provides multiple approaches for determining viability of acute ischemically injured and hibernating myocardium. MRI can assess contractile reserve in a manner similar to echocardiography. Additionally, contrast-enhanced MRI can characterize myocardial ischemic injury, including the ability to discriminate viable from nonviable zones. Several new contrast media have been introduced for this purpose. This review addresses the progress toward the goal of defining myocardial viability based on MR techniques and focuses on the current and future role of MR in the assessment of viable myocardium.

Noninvasive assessment of the effects of nicorandil on left ventricular volumes and function in reperfused myocardial infarction

OBJECTIVEnNicorandil, a K-ATP channel opener with a nitrate-like effect, is a potent vasodilator and has favorable hemodynamic effects in heart failure patients. While its cardio-protective properties in the setting of acute ischemia are well known, the long-term effects of oral nicorandil therapy on post-infarction left ventricular (LV) dilatation have not been investigated.nnnMETHODSnMyocardial infarction (MI) was induced in 30 Sprague-Dawley rats by 1 h of coronary artery occlusion followed by reperfusion. After matching for infarction size, animals were randomly assigned to nicorandil treatment (3 mg/kg/day) given in tap water or no treatment (control group). Treatment was started 2 days after MI and continued for 8 weeks. Contrast-enhanced and functional magnetic resonance imaging (MRI) were used to determine infarction size, LV volumes, mass, ejection fraction, and regional wall thickness.nnnRESULTSnNicorandil significantly decreased end-systolic volumes (0.33+/-0.02 ml; P<0.05) and improved LV ejection fraction (37+/-2%; P<0.01) compared to control rats (0.43+/-0.04 ml and 28+/-2%, respectively) 8 weeks after MI. During the study period, the increase in LV mass (DeltaLVM) was significantly greater in control (0.09+/-0.03 g) than in treated animals (0.02+/-0.02 g, P<0.05). Moreover, nicorandil improved systolic wall thickening of the rim of infarction (P<0.001) and remote non-infarcted regions (P<0.01).nnnCONCLUSIONnThese results demonstrate that the long-term oral treatment with nicorandil started 2 days after MI attenuates left ventricular dilatation and improves cardiac function in rats with reperfused MI.

EFFECTS OF IOPROMIDE ON VASOACTIVE PEPTIDES AND ALLERGY-MEDIATED SUBSTANCES IN HEALTHY VOLUNTEERS

RATIONALE AND OBJECTIVES.Little information is available about the direct action of angiographic contrast media on vasoactive peptides and allergy-mediated substances in humans. This study defined the acute effects of iopromide, a nonionic contrast medium (370 mg/mL iodine), on vasoactive peptides, allergy-mediated substances, and hemodynnmic parameters in healthy volunteers. METHODS.Pulmonary digital subtraction angiography was performed in seven healthy volunteers with no cardiovascular or pulmonary disease. Iopromide was administered as a total volume of 100 mL through a 7-Fr catheter inserted in the right femoral vein. The injected volumes and duration of injection (15–20 mL/second) were kept constant. The following hemodynamic parameters were monitored continuously: results of electrocardiogram, heart rate, and phasic and mean pulmonary arterial and peripheral arterial pressures. Blood samples were obtained before and 3 to 5 minutes after injection of contrast media to determine the concentrations of the following vasoactive peptides: renin, angiotensin I-converting enzyme, angiotensin II, aldosterone, atrial natriuretic peptide, antidiuretic hormone, cyclic guanosine monophosphate, and myoglobin; and to allergy-mediated substances such as tryptase, cosinophil protein X, and eosinophil cationic protein, using radioimmunoassay techniques. RESULTS.Iopromide substantially increased atrial natriuretic peptide (48.8 ± 8.9 to 85.8 ± 13.0) and antidiuretic hormone (3.4 ± 0.3 to 4.6 ± 0.5) levels, whereas renin decreased (0.9 ± 0.1 to 0.8 ± 0.2) slightly but not significantly. Iopromide did not induce substantial changes in the other vasoactive peptides or in allergy-mediated substances after the contrast medium was injected. Similarly, cardiovascular parameters (heart rate, pulmonary and systemic blood pressures, and results of electrocardiogram) also remained unchanged after contrast injection. CONCLUSION.Iopromide caused no appreciable hemodynamic alterations associated with the changes in atrial natriuretic peptide and antidiuretic hormone and no evidence of allergy- mediated reactions in all volunteers.

Pulmonary hypertension. Response of vasoactive peptides to a nonionic contrast medium in patients undergoing pulmonary angiography.

RATIONALE AND OBJECTIVES.The degree to which pulmonary angiography may contribute to serious complications in patients with pulmonary hypertension has not been clarified and remains a matter of debate. Accordingly, this study was designed (1) to detect the potential release of vasoactive peptides and (2) to investigate the hemodynamic response after administration of a nonionic contrast medium in patients with pulmonary hypertension undergoing pulmonary angiography. Allergy-mediating substances also were measured to monitor for possible anaphylactoid reactions. METHODS.Pulmonary digital subtraction angiography was performed in 20 patients with pulmonary hypertension (mean pulmonary arterial pressure more than 20 mm Hg). Iopromide was administered as a total of 100 mL via a 7F catheter inserted from the right femoral vein. The injected volume and duration of injection (15 to 20 mL/sec) were kept constant. Hemodynamic parameters were continuously monitored, including electrocardiogram, heart rate, phasic and mean pulmonary arterial and peripheral arterial pressures. Blood samples were obtained before and after administration of contrast media to assay for the concentration of the following vasoactive peptides using radioimmunoassay techniques: renin, angiotensin-I-converting enzyme, angiotensin II, aldosterone, atrial natriuretic peptide, antidiuretic hormone, cyclic-guanosine monophosphate, and myoglobin, as well as allergy-mediating substances such as tryptase, eosinophil protein X, and eosinophil cationic protein. RESULTS.Administration of iopromide caused significant increases in atrial natriuretic peptide (from 61.3 ± 11.8 to 94.0 ± 16.7) and antidiuretic hormone (from 6.6 ± 1.9 to 12.3 ± 3.1), whereas renin significantly decreased (from 3.0 ± 0.6 to 1.3 + 0.5). After administration of contrast media, there were no significant changes in the other measured vasoactive peptides, allergy-mediating substances, and monitored cardiovascular parameters. CONCLUSION. Administration of iopromide for pulmonary angiography in patients with pulmonary hypertension resulted in no appreciable hemodynamic alterations associated with the observed changes in atrial natriuretic peptide, antidiuretic hormone, and renin. No allergy-mediated reactions were observed in these patients.

Myocardial blood flow in patients with dilated cardiomyopathy: Quantitative assessment with velocity-encoded cine magnetic resonance imaging of the coronary sinus

PURPOSEnTo quantify global myocardial perfusion using magnetic resonance imaging (MRI) in patients with heart failure due to idiopathic dilated cardiomyopathy (IDC) and to compare myocardial perfusion and microvascular reactivity with healthy subjects.nnnMATERIALS AND METHODSnA total of 19 subjects (healthy volunteers (N = 12) and IDC patients (N = 7)) were studied using cine MRI to measure left ventricular (LV) mass and a velocity-encoded cine MRI technique to measure coronary sinus flow at rest and after dipyridamole-induced hyperemia. Absolute values of total myocardial blood flow (MBF) were calculated from coronary sinus flow and LV mass.nnnRESULTSnAt baseline, MBF was not significantly different in patients with IDC (0.48 +/- 0.07 mL/minute/g) and healthy subjects (0.55 +/- 0.19 mL/minute/g, P= 0.41). After dipyridamole administration, MBF in IDC patients increased to a level significantly less than that in normal volunteers (1.05 +/- 0.35 mL/minute/g vs. 1.99 +/- 1.05 mL/minute/g, P < 0.05). Consequently, MBF reserve was impaired in patients with IDC (2.19 +/- 0.77) compared to that in healthy subjects (3.51 +/- 1.29, P < 0.05). A moderate correlation was found between MBF reserve and LV ejection fraction (r = 0.48, P < 0.05).nnnCONCLUSIONnMBF reserve is reduced in patients with IDC, indicating that coronary microcirculatory flow is impaired. This integrated MRI approach allows quantitative measurement of global MBF in humans and may have the potential to study the effects of pharmacological interventions on myocardial perfusion.