Stress-related variations in left ventricular function as assessed with gated myocardial perfusion SPECT

BACKGROUND

There is inconsistency in reported patient characteristics associated with differences in basal and poststress left ventricular function (delta ejection fraction [DeltaEF]) assessed by gated single photon emission computed tomography (SPECT). This inconsistency may therefore hamper adequate interpretation. In this study we first determined the reproducibility of serial gated SPECT-assessed left ventricular function. Second, we determined whether left ventricular ejection fraction (LVEF) assessed directly after stress reflects basal LVEF and, if not, what patient characteristics were associated with this discrepancy in LVEF.

METHODS AND RESULTS

Serial reproducibility of technetium 99m tetrofosmin gated SPECT-assessed LVEF in 22 patients showed a mean difference between two sequential measurements at rest of 0.09% EF units, with a 95% limit of agreement (2 SDs) at 5.8% EF units. In 229 patients Tc-99m tetrofosmin gated SPECT was performed after stress and at rest. Independent predictors of DeltaEF were the presence of scintigraphically proven ischemia (standardized coefficient, -1.256; P =.003) and difference in heart rate at the time of acquisition (standardized coefficient, 0.121; P =.001).

CONCLUSIONS

Gated SPECT-assessed LVEF at rest is reproducible under standard clinical conditions. However, LVEF assessed after stress does not represent LVEF at rest in patients with scintigraphically proven ischemia and in patients with increased heart rate after stress compared with heart rate at rest.

125I-BMIPP and 18F-FDG uptake in a transgenic mouse model of stunned myocardium

Reported metabolic patterns in myocardial stunning are not uniform. We investigated relative myocardial perfusion, glucose and fatty acid uptake using a technetium-99 hexakis-2-methoxyisobutyl-isonitrile (MIBI), fluorine-18 2-fluoro-2-deoxyglucose (FDG) and iodine-125 15-(p-iodo-phenyl)-3(R,S)-methylpentadecanoic acid (BMIPP) mixture, in a recently developed transgenic (TR) mouse model which mimics stunned myocardium. Twenty-seven mice - 14 TR and 13 age-matched wild type controls (C) - were divided into four groups: TR-fed, TR-fasted, C-fed and C-fasted. Animals were sacrificed 2 h after injection, tissue samples counted and percent-injected dose/gram tissue (% id/g) calculated for each radioisotope. Tissues were also Folch extracted and 125I incorporation into the various lipid pools (TG, triglycerides; DG, diglycerides; FFA, free fatty acids; PL, phospholipids) was determined by thin-layer chromatography (TLC). The pooled data for each of the four groups (TR-fed vs C-fed and TR-fed vs C-fasted) showed no differences in myocardial blood flow (% MIBI id/g), glucose uptake (% FDG id/g) or fatty acid uptake (% BMIPP id/g). Only minor differences were observed in the incorporation of 125I-BMIPP into the myocardial TG, DG, FFA and PL lipid pools. However, significantly decreased myocardial FDG uptake was observed in a subset of fasted mice - four out of ten TR-fasted mice (3.4% vs 20.5% id/g) and three out of nine C-fasted mice (5.5% vs 30.6% id/g). The transgenic mouse model of stunned myocardium shows normal myocardial perfusion and overall intact myocardial glucose and myocardial fatty acid uptake as determined with clinically applicable radiolabelled analogues. These data are in line with the hypothesis that the contractile inefficiency in stunned myocardium is not linked to metabolic alterations but is associated with an insufficient chemical to mechanical energy coupling.

Beneficial effects of metoprolol on myocardial sympathetic function: Evidence from a randomized, placebo-controlled study in patients with congestive heart failure

BACKGROUND

We sought to investigate whether beta-blockers exert a presynaptic effect in the myocardium as measured by 123I-metaiodobenzylguanidine.

METHODS

The study comprised 59 patients with congestive heart failure, New York Heart Association class II or III, and left ventricular ejection fraction <35%. After an open label titration phase, patients were randomized to their maximal tolerable dose of metoprolol or placebo. Myocardial MIBG uptake was measured before the titration phase and after 6 months of treatment. Other parameters were maximal oxygen consumption, 6-minute walking test, plasma neurohormones, and echocardiographic parameters.

RESULTS

We found a 21.9% increase in mean myocardial MIBG uptake after 6 months of treatment with metoprolol. In contrast, MIBG uptake decreased by 7.8% in the placebo group (P = 0.03 compared with metoprolol). Left ventricular end-diastolic diameter decreased from 74 +/- 11 mm to 67 +/- 10 mm (P <.05, within-group comparison) and LVEF increased from 25.3% +/- 7.4% to 32.6% +/- 9.6% (P <.05, within-group comparison) in the metoprolol group. Placebo-treated patients showed no significant changes. Comparison of changes in left ventricular end-diastolic diameter and LVEF between metoprolol and placebo did not reach statistical significance (P = 0.2).

CONCLUSIONS

This randomized, placebo-controlled study demonstrates that metoprolol has a presynaptic effect as measured by myocardial MIBG scintigraphy in both ischemic and nonischemic cardiomyopathy.

Hyperemic stenosis resistance index for evaluation of functional coronary lesion severity

BACKGROUND

Both coronary blood flow velocity reserve (CFVR) and myocardial fractional flow reserve (FFR) are used to evaluate the hemodynamic severity of coronary lesions. However, discordant results between CFVR and FFR have been observed in 25% to 30% of intermediate coronary lesions. An index of stenosis resistance based on a combination of intracoronary pressure and flow velocity may improve the assessment of functional coronary lesion severity.

METHODS AND RESULTS

Single photon emission computed tomography (SPECT) was performed in 151 patients with angina to determine reversible perfusion defects within one-week before cardiac catheterization. Coronary pressure and flow velocity was measured distal to 181 single coronary lesions with a mean diameter stenosis of 56% (range: 32% to 85%). Maximum hyperemia was induced by 15 to 20 microg IC adenosine to determine CFVR, FFR, and the hyperemic stenosis resistance index (h-SRv), defined as the ratio of hyperemic stenosis pressure gradient (mean aorta pressure-mean distal pressure) and hyperemic average peak-flow velocity. Receiver-operating-characteristic curves of CFVR, FFR, and h-SRv were calculated to evaluate the predictive value for presence of reversible perfusion defects on SPECT with the use of the area under curve (AUC). The AUC was significantly higher for h-SRv (0.90+/-0.03) compared with those for CFVR (0.80+/-0.04; P=0.024) and FFR (0.82+/-0.03; P=0.018), respectively. Agreement with SPECT was particularly higher (73%) than for CFVR (49%, P=0.022) or FFR (51%, P=0.037) in the group of lesions showing discordant results between CFVR and FFR CONCLUSION: These results indicate that hyperemic stenosis resistance index is a more powerful predictor of reversible perfusion defects than CFVR or FFR.

Prognostic value of coronary blood flow velocity and myocardial perfusion in intermediate coronary narrowings and multivessel disease

OBJECTIVES

This study aimed to investigate the roles of intracoronary derived coronary flow velocity reserve (CFVR) and myocardial perfusion scintigraphy (single photon emission computed tomography, or SPECT) for management of an intermediate lesion in patients with multivessel coronary artery disease.

BACKGROUND

Evaluation of the functional significance of intermediate coronary narrowings (40% to 70% diameter stenosis) is important for clinical decision making and risk stratification.

METHODS

In a prospective, multicenter study, SPECT was performed in 191 patients with stable angina and multivessel disease and scheduled for angioplasty (percutaneous transluminal coronary angioplasty, or PTCA) of a severe coronary narrowing. Coronary flow velocity reserve was determined selectively distal to an intermediate lesion in another artery using a Doppler guidewire. Percutaneous transluminal coronary angioplasty of the intermediate lesion was deferred when SPECT was negative or CFVR greater-than-or-equal 2.0. Patients were followed for one year to document major cardiac events (death, infarction, revascularization), related to the intermediate lesion.

RESULTS

Reversible perfusion defects were documented in the area of the intermediate lesion in 30 (16%) patients; CFVR was positive in 46 (24%) patients. Percutaneous transluminal coronary angioplasty of the intermediate lesion was deferred in 182 patients. During follow-up, 19 events occurred (3 myocardial infarctions, 16 revascularizations). Coronary flow velocity reserve was a more accurate predictor of cardiac events than was SPECT; relative risk: CFVR 3.9 (1.7 to 9.1), p < 0.05; SPECT 0.5 (0.1 to 3.2), p = NS. Multivariate analysis revealed CFVR as the only significant predictor for cardiac events.

CONCLUSIONS

Deferral of PTCA of intermediate lesions in multivessel disease is safe when CFVR greater-than-or-equal 2.0 (event rate 6%). This selective evaluation of coronary lesion severity during cardiac catheterization allows a more accurate risk stratification than does SPECT, which is important for clinical decision making in this patient cohort.

Usefulness of fractional flow reserve for risk stratification of patients with multivessel coronary artery disease and an intermediate stenosis

Intracoronary-derived, pressure-based fractional flow reserve (FFR) is important for clinical decision-making in patients with 1-vessel coronary artery disease (CAD). In the present study, we investigated the prognostic value of FFR in patients with intermediate stenoses and multivessel CAD. Therefore, we analyzed 107 patients with stable angina pectoris who underwent myocardial perfusion scintigraphy and showed no perfusion defects in the region of the intermediate lesion. At angiography, FFR was determined distal to the intermediate lesion. FFR was abnormal (i.e., <0.75) in 15 of 107 stenoses (14%). Angioplasty of the intermediate stenosis was deferred based on the absence of a perfusion defect. Patients were followed for 1 year to document major cardiac events related to the intermediate lesion. At 1-year follow-up, a total of 12 (11%: no deaths, 3 myocardial infarctions, 2 coronary bypass operations, 7 coronary angioplasties) events occurred in the entire group that were related to the intermediate lesion. The event rate was significantly higher when angioplasty was deferred despite FFR <0.75 compared with the group with FFR > or = 0.75 (4 of 15 [27%] vs 8 of 92 [9%]; p <0.041). The relative risk of FFR for predicting cardiac events (mainly revascularization procedures) was 3.1 (95% confidence interval 1.1 to 8.9; p <0.05). In conclusion, deferral of angioplasty of intermediate coronary narrowings is safe based on FFR > or = 0.75 in this patient cohort; this coincides with previous reports in patients with 1-vessel CAD. Furthermore, these results suggest that FFR is more useful than single-photon emission computed tomography for clinical decision-making and risk stratification in patients with multivessel CAD.

Adequate patient selection for coronary revascularization: an overview of current methods used in daily clinical practice

Widely used non-invasive stress modalities, like exercise ECG, MPS and stress-echocardiography, are the tests of first choice for the diagnosis of CAD. It has been shown in numerous studies that non-invasive assessment of perfusion abnormalities is an adequate strategy for risk stratification. Moreover, non-invasive stress testing should be performed before a diagnostic cardiac catheterization to document the presence of myocardial ischemia, as a prerequisite for coronary revascularization. Coronary angiography is the gold standard for identifying CAD; however this technique is limited in assessing functional severity of coronary narrowings ('illusion of luminology'; see also Figure 5). The recently introduced i.c. hemodynamic parameters (CFVR and FFR) can identify functional severity of specific lesions and have shown a good agreement with the results of non-invasive stress test in validation studies. Furthermore, there is accumulating evidence that it is safe to defer a PTCA procedure, based on normal FFR and CFVR values. As these indices are derived during an invasive cardiac catheterization procedure, its use is recommended during a so called 'ad hoc' PTCA setting. Furthermore, they are particularly useful for clinical decision making in patients with documented multivessel CAD, as both indices allow selective evaluation of coronary narrowings in different arteries. Revascularization procedures are costly and always have a potential risk. It is important to be aware that, using above mentioned methods, unnecessary interventions (lacking potential benefit) may be avoided.