New directions in myocardial perfusion imaging

In recent years, substantial progress has been made in the field of nuclear cardiology. Pharmacologic stress perfusion imaging with intravenous administration of dipyridamole or adenosine provides comparable sensitivity and specificity values for detection of coronary artery disease (CAD) as exercise imaging and has been employed successfully for risk stratification prior to peripheral vascular or aortic surgery and after myocardial infarction. Detection of myocardial viability can be enhanced utilizing reinjection of a second dose of thallium-201 (Tl-201) at rest after acquisition of redistribution images with the single photon emission computerized tomography (SPECT) technique. Imaging solely in the resting state with Tl-201 can also provide information concerning presence of viable myocardium in asynergic regions that are stunned or hibernating. New technetium-99m (Tc-99m) perfusion agents have emerged in the clinical setting and have provided excellent predictive value for detection of CAD in patients with chest pain and permit simultaneous assessment of function and regional blood flow. Tc-99m Sestamibi, one of these agents, is also a valid marker of viability when assessing myocardial salvage after coronary reperfusion in acute myocardial infarction.     

Non-atherosclerotic acute myocardial infarction

AIM: The aim of the study is to analyse the benefits and risks of PEE in patients, cared for by a team with many years experience. PATIENTS AND METHODS: From 16. 2. 1988 until 31. 12. 1993 246 PEEs (229 gastrostomies, 6 duodenostomies, 7 jejunostomies, 4 attempts) were performed on 234 patients (56% male, 44% female, mean age 68.3 years). 117 patients had tumorous and 117 neurological diseases. We used the pull technique with the Fresenius Freka PEG-system. Analysis was performed using a standardised documentation sheet which was filled out until the end of tube feeding. In total, we registered 39,678 days of tube feeding, 4513 of which were in hospitalized patients. RESULTS: The mean intubation time was 192.6 days (maximum 1496). In 8 cases, the tube could be explanted before the patient was discharged; 68 patients were discharged to a nursing home and 71 patients were allowed to go home. The tube-independent hospital lethality was 36.64%. A PEE-specific lethality had not been registered. Complications arose in a total of 37 patients (15.04%), 4 of which were severe (1.63%) Fifty-nine patients (25.43%) reported short-term feelings of ill health (vomiting, diarrhoea, pain). CONCLUSION: PEE is an effective and low-risk method of long-term nutrition. The advantages are simple insertion, safe handling by patients and relatives/nursing staff and the low cost.     

Alpha-adrenergic blockade improves recovery of myocardial perfusion and function after coronary stenting in patients with acute myocardial infarction

BACKGROUND: AMI reperfusion by thrombolysis does not improve TIMI flow and LV function. The role of infarct-related artery (IRA) stenosis and superimposed changes in coronary vasomotor tone in maintaining LV dysfunction must be elucidated. METHODS AND RESULTS: Forty patients underwent diagnostic angiography 24 hours after thrombolysis. Seventy-two hours after thrombolysis, the culprit lesion was dilated with coronary stenting. During angioplasty, LV function was monitored by transesophageal echocardiography. Percent regional systolic thickening was quantitatively assessed before PTCA, soon after stenting, 15 minutes after stenting, and after phentolamine 12 microg/kg IC (n=10), the alpha1-blocker urapidil 600 microg/kg IV (n=10), or saline (n=10). Ten patients pretreated with beta-blockers received urapidil 10 mg IC. Coronary stenting significantly improved thickening in IRA-dependent and in non-IRA-dependent myocardium (from 27+/-15% to 38+/-16% and from 40+/-15% to 45+/-15%, respectively). Simultaneously, TIMI frame count decreased from 39+/-11 and 40+/-11 in the IRA and non-IRA, respectively, to 23+/-10 and 25+/-7 (P<0.05). Fifteen minutes after stenting, thickening worsened in both IRA- and non-IRA-dependent myocardium (to 19+/-14% and 28+/-14%, P<0.05), and TIMI frame count returned, in both the IRA and non-IRA, to the values obtained before stenting. Phentolamine and urapidil increased thickening to 36+/-17% and 41+/-14% in IRA and to 48+/-11% and 49+/-17% in non-IRA myocardium respectively, and TIMI frame count decreased to 16+/-6 and to 17+/-5, respectively. Changes were attenuated with beta-blocker pretreatment. CONCLUSIONS: Our finding that alpha-adrenergic blockade attenuates vasoconstriction and postischemic LV dysfunction supports the hypothesis of an important role of neural mechanisms in this phenomenon.     

Limited clinical diagnostic specificity of technetium-99m stannous pyrophosphate myocardial imaging in acute myocardial infarction

To test the sensitivity and specificity of technetium-99m stannous pyrophosphate myocardial imaging in the diagnosis of acute myocardial infarction, myocardial scintigrams were performed in 115 patients. Positive scintigrams were found in all 48 patients with acute myocardial infarction; uptake was localized in 29 patients with transmural infarction and diffuse in 2 patients with transmural infarction and in the remaining 17 patients with subendocardial myocardial infarction. Positive scintigrams were also found in 31 of 67 patients without clinical evidence of acute myocardial infarction. Diffusely positive scintigrams were found in 3 of 3 patients with unstable angina pectoris, 7 of 30 patients with stable angina pectoris, 4 of 13 patients who had undergone aortocoronary bypass surgery, 4 of 4 patients with congestive cardiomyopathy and 1 patient studied 1 day after direct current cardioversion. Localized uptake of 99mTc-pyrophosphate was found in 9 of 10 patients with left ventricular aneurysm and in 3 of 13 patients after aortocoronary bypass surgery. All four patients with atypical chest pain and two patients with pericarditis had normal scintigrams. Our data confirm the previously reported sensitivity of 99mTc-pyrophosphate imaging in detection of acute myocardial infarction but indicate that positive scintigrams are not specific for this entity.     

Myocardial perfusion imaging in the setting of coronary artery stenosis and acute myocardial infarction using venous injection of a second-generation echocardiographic contrast agent

BACKGROUND: We hypothesized that by producing excellent myocardial opacification, venous injection of FS-069 coupled with intermittent harmonic imaging (IHI) can be used to determine the presence and severity of coronary stenoses during hyperemia, the size of the risk area during coronary occlusion, and the extent of myocardial salvage after reperfusion. METHODS AND RESULTS: Twelve dogs were imaged both continuously and intermittently (every end systole) in the fundamental (2 MHz) and harmonic (transmit at 2 and receive at 4 MHz) modes. FS-069 (1 mL) was injected intravenously for all stages and modes of imaging. Myocardial video intensity was severalfold (P<.01) higher during IHI than all other modes of imaging. Perfusion defects were difficult to measure during continuous and intermittent fundamental imaging and during continuous harmonic imaging. In comparison, the defects were clearly demarcated during IHI. When this mode was used, the magnitude of perfusion mismatch during hyperemia in the presence of a coronary stenosis correlated closely with the magnitude of flow mismatch when radiolabeled microspheres were used (r=.94). The perfusion defect sizes during coronary occlusion and reperfusion also correlated closely with postmortem risk area (r=.89) and infarct size (r=.96), respectively. CONCLUSIONS: Venous injection of FS-069 coupled with IHI produces excellent myocardial opacification. This approach can be used to determine the severity of coronary stenoses during hyperemia, the size of the risk area during coronary occlusion, and the extent of myocardial salvage after reperfusion. This approach, therefore, holds promise in the clinical setting.     

Thrombolysis for acute myocardial infarction

Thrombolytic therapy has been a major advance in the management of acute myocardial infarction. Unfortunately, it continues to be underused or is administered later than is optimal. Thrombolytic therapy works by lysing infarct artery thrombi and achieving reperfusion, thereby reducing infarct size, preserving left ventricular function, and improving survival. The most effective thrombolytic regimens achieve angiographic epicardial infarct-artery patency in only approximately 50% of patients within 90 minutes. Bleeding requiring transfusion occurs in approximately 5% of patients and stroke in approximately 1.8% with these regimens, which include adjunctive aspirin and intravenous heparin. There are several ways in which reperfusion rates and thus patient outcomes might be improved, such as different dosing regimens of established agents; combinations of different agents; improved adjunctive therapy such as direct antithrombin agents, low-molecular-weight heparin, or glycoprotein IIb/IIIa receptor antagonists; or the development of novel thrombolytic agents with enhanced fibrin specificity, resistance to native inhibitors, or prolonged half-lives allowing bolus administration. All of these strategies are being tested in clinical trials. The best approach currently is to administer thrombolytic therapy as soon as possible to all patients without contraindications who present within 12 hours of symptom onset and have ST-segment elevation on the ECG or new-onset left bundle-branch block, unless an alternative reperfusion strategy is planned.     

Relation between ST-segment changes and myocardial perfusion evaluated by myocardial contrast echocardiography in patients with acute myocardial infarction treated with direct angioplasty

The aim of this study was to evaluate the relation between myocardial perfusion and ST-segment changes in patients with acute myocardial infarction treated with successful direct angioplasty. Thirty-seven patients, successfully treated with direct angioplasty, underwent myocardial contrast echocardiography before and after angioplasty. The sum of ST-segment elevation divided by the number of the leads involved (ST-segment elevation index) was calculated at 1, 5, 10, 20, and 30 minutes after restoration of a Thrombolysis In Myocardial Infarction trial grade 3 flow. After recanalization, myocardial reperfusion within the risk area was observed in 26 patients, whereas a no-reflow phenomenon occurred in 11. In patients with myocardial reperfusion, the ST-segment elevation index progressively declined, whereas in patients with no reflow, no significant change was observed. Reduction of > or = 50% in the ST-segment elevation index occurred in 20 of the 26 patients with reflow and in 1 of the 11 with no reflow (p = 0.0002). An additional increase of > or = 30% in the ST-segment elevation index occurred in 3 patients with reflow and in 7 with no reflow (p = 0.003). Sensitivity, specificity, positive and negative predictive values, and accuracy of the reduction in the ST-segment elevation index for predicting microvascular reflow were 77%, 91%, 95%, 62%, and 81%, respectively. The corresponding values of the increase in ST-segment elevation index for predicting no reflow were 64%, 88%, 70%, 85%, and 81%, respectively. In conclusion, after successful angioplasty, different patterns of myocardial perfusion are associated with different ST-segment changes. Analysis of ST-segment changes predicts the degree of myocardial reperfusion.     

Primary angioplasty for acute myocardial infarction

The comparative stability of eight different triplexes constituted with 16-mer pyrimidine-modified oligodeoxynucleotides (wild-type ODN, PS-ODN, alpha-ODN, or alpha-PS-ODN) or oligoribonucleotides (wild-type ORN, alpha-ORN, 4'-thio-ORN, or 2'-O-MeORN) and a DNA hairpin, termed H36, was studied in five different buffers by UV melting curve analysis. The composition of buffers varied in pH (5.5 and 6.5), in salt concentration (100 mM and 1 M Na+), and in the presence or absence of divalent cation (0 or 3 mM Mg2+) or spermine (0 or 1 mM). At pH 5.5, the eight triplexes are formed with Tm values ranging from 24.7 degrees C to 50.9 degrees C (delta G298K between -8.1 and -16.8 kcal/mol). At pH 6.5, the triplexes are less stable, and thus 4'-thio-ORN and PS-ODN showed broad transitions that did not allow us to conclude triplex formation. An increase of salt concentration or the presence of spermine stabilizes the triplexes, whereas Mg2+ has a destabilizing effect (excepted for alpha-ORN). In general ORN:H36 and 2'-O-MeORN:H36 triplexes were the most stable. Finally, introduction of alpha-anomeric nucleosides led to an alpha-ORN analog that showed low binding with H36 and to alpha-ODN and alpha-PS-ODN analogs. Triplexes formed with alpha-ODN were slightly less stable than those formed with unmodified ODN. Surprisingly, introduction of phosphorothioate in an alpha analog led only to a low destabilization.     

Tricuspid regurgitation and acute myocardial infarction

A 71-year-old man had a right ventricular infarct complicated with hypotension and transient complete atrioventricular block. The patient was found to have tricuspid regurgitation, which was corrected with a prosthetic tricuspid valve. After correction, there was dramatic improvement in his clinical status, with correction of persistent hypotension and weakness and early discharge home to full activity. Tricuspid regurgitation is a mechanical defect of acute myocardial infarction that benefits greatly from surgical correction. This therapy should be considered in any individual in whom tricuspid regurgitation complicates acute right ventricular infarction.     

Diabetes mellitus and acute myocardial infarction

A series of 597 consecutive patients with acute myocardial infarction (AMI) have been screened for diabetes mellitus (DM). Six per cent of the series had DM, which is exactly the frequency of DM in an age-matched population. This finding corresponds with results of other investigators, indicating that treated diabetics do not have an increased risk of AMI. Diabetics suffering from AMI do not have an increased mortality, nor do patients treated with oral antidiabetics have a higher mortality than those treated with insulin.