Effects of dobutamine on myocardial blood flow, contractile function, and bioenergetic responses distal to coronary stenosis: implications with regard to dobutamine stress testing

Transmurally differentiated measurement of ATP hydrolysis rates in the in vivo porcine hearts

PURPOSE

Compare the transmural distribution of forward creatine kinase reaction (kf,CK ) and ATP hydrolysis rate (kr,ATPase ) in the myocardium of normal porcine heart. Rate constants were extracted from partially relaxed spectra by applying the T1nom method, effectively reducing data acquisition time by up to an order of magnitude.

THEORY AND METHODS

T1nom method for double saturation of PCr and Pi is introduced and validated through simulations. Bioenergetics was measured in vivo utilizing one-dimensional chemical shift imaging (1D-CSI) magnetic resonance (31) P spectroscopy.

RESULTS

At basal conditions, there was no significant difference between subepicardial layers (EPI) vs. the subendocardial layers (ENDO) for both fluxf,CK and fluxr,ATPase . At high cardiac workload (HWL), where the rate pressure product increased 2.6-fold, PCr/ATP ratio and fluxf,CK showed no significant change in both EPI and ENDO layers, while fluxr,ATPase increased significantly (baseline: 1.11 ± 0.12 and 1.12 ± 0.13 μmol/g/s, EPI and ENDO, respectively; to HWL: 2.35 ± 0.27 and 2.21 ± 0.08 μmol/g/s, EPI and ENDO, respectively, each P < 0.01 vs. baseline).

CONCLUSION

In the normal heart, increase of cardiac work state is accompanied by an increase in ATP hydrolysis rate with no changes in CK flux rate. There are no significant differences between EPI vs. ENDO concerning the ATP hydrolysis rate or CK flux rate in both baseline and high cardiac work states.

Long-term preservation of myocardial energetic in chronic hibernating myocardium

We previously reported that the myocardial energetic state, as defined by the ratio of phosphocreatine to ATP (PCr/ATP), was preserved at baseline (BL) in a swine model of chronic myocardial ischemia with mild reduction of myocardial blood flow (MBF) 10 wk after the placement of an external constrictor on the left anterior descending coronary artery. It remains to be seen whether this stable energetic state is maintained at a longer-term follow-up. Hibernating myocardium (HB) was created in minipigs (n = 7) by the placement of an external constrictor (1.25 mm internal diameter) on the left anterior descending coronary artery. Function was assessed with MRI at regular intervals until 6 mo. At 6 mo, myocardial energetic in the HB was assessed by (31)P-magnetic resonance spectrometry and myocardial oxygenation was examined from the deoxymyoglobin signal using (1)H-magnetic resonance spectrometry during BL, coronary vasodilation with adenosine, and high cardiac workload with dopamine and dobutamine (DpDb). MBF was measured with radiolabeled microspheres. At BL, systolic thickening fraction was significantly lower in the HB compared with remote region (34.4 ± 9.4 vs. 50.1 ± 10.7, P = 0.006). This was associated with a decreased MBF in the HB compared with the remote region (0.73 ± 0.08 vs. 0.97 ± 0.07 ml · min(-1) · g, P = 0.03). The HB PCr/ATP at BL was normal. DpDb resulted in a significant increase in rate pressure product, which caused a twofold increase in MBF in the HB and a threefold increase in the remote region. The systolic thickening fraction increased with DpDb, which was significantly higher in the remote region than HB (P < 0.05). The high cardiac workload was associated with a significant reduction in the HB PCr/ATP (P < 0.02), but this response was similar to normal myocardium. Thus HB has stable BL myocardial energetic despite the reduction MBF and regional left ventricular function. More importantly, HB has a reduced contractile reserve but has a similar energetic response to high cardiac workload like normal myocardium.

Pyruvate-enhanced cardioprotection during surgery with cardiopulmonary bypass

OBJECTIVES

To determine whether pyruvate-fortified cardioplegia solution provides cardioprotection superior to lactate-based cardioplegia solutions in patients undergoing elective coronary revascularization, with specific attention to post-surgical recovery of left ventricular performance as well as biochemical markers of ischemic injury.

DESIGN

Prospective, randomized, semi-blinded human trial.

SETTING

Community-based academic medical center.

PARTICIPANTS

Thirty adult patients undergoing elective coronary artery bypass graft surgery.

INTERVENTIONS

Patients were randomized to two 4:1 blood cardioplegia solutions, one pyruvate enhanced and the other lactate based. Hemodynamic and laboratory variables were measured in all patients at pre-cross-clamp, post-cross-clamp, and 4, 6, 8, and 12 hours after bypass.

MEASUREMENTS AND MAIN RESULTS

Relative to lactate-based cardioplegia, pyruvate-fortified cardioplegia sharply increased left ventricular stroke work at 4 to 12 hours after bypass (p < 0.001), lowered coronary sinus troponin I and creatine phosphokinase-MB activities 67% (p < 0.001) and 53% (p < 0.01), respectively, and increased coronary sinus hemoglobin O(2) saturation 18% (p < 0.001). Ten patients treated with lactate cardioplegia required beta-adrenergic inotropic support postbypass, but only 4 pyruvate-treated patients required beta-adrenergic support (p = 0.067). Pyruvate cardioplegia shortened postsurgery hospitalization from 6.3 +/- 0.3 to 5.2 +/- 0.1 days (p < 0.002).

CONCLUSIONS

Pyruvate-fortified cardioplegia mitigated myocardial injury during coronary artery bypass surgery and facilitated postsurgical recovery of cardiac performance. Thus, pyruvate-enhanced cardioplegia may provide cardioprotection superior to lactate-based solutions during surgical cardiac arrest.

Noninvasive measurements of transmural myocardial metabolites using 3-D (31)P NMR spectroscopy

A completely noninvasive three-dimensional (3-D) static magnetic field magnitude spatially localized (31)P spectroscopy technique has been developed and applied to study the in vivo canine myocardium at 9.4 T. The technique incorporates both Fourier series windows and selective Fourier transform methods utilizing all three orthogonal gradients for 3-D phase encoding. The number of data acquisitions for each phase-encoding step was weighted according to the Fourier coefficients to define cylindrical voxels. Spatially localized (31)P spectra can be generated for voxels of desired location within the field of view as a postprocessing step. The quality of localization was first demonstrated by using a three-compartment phantom. The technique was then applied to in vivo canine models and yielded (31)P cardiac spectra with an excellent signal-to-noise ratio. The in vivo validation experiments, using an implanted 2-phosphoenolpyruvate-containing marker, demonstrated that the technique is capable of measuring at least two transmural layers of left ventricular myocardium representing the subepicardium and subendocardium.

Dobutamine enhances both contractile function and energy reserves in hypoperfused canine right ventricle

Although the beta(1)-adrenergic agent dobutamine is used clinically to provide inotropic support to the failing myocardium, it could jeopardize the myocardium by depleting energy reserves. This investigation delineated the contractile and energetic effects of low versus high dobutamine doses in the hypoperfused right ventricular (RV) myocardium. The right coronary artery (RCA) of anesthetized dogs was cannulated for controlled perfusion with arterial blood, and regional RV contractile function was measured. RCA perfusion pressure was lowered from 100 mmHg baseline to 40 mmHg, and flow fell by 54%. At 15-min hypoperfusion, dobutamine was infused into the RCA at either 0.01 (low-dose dobutamine) or 0.06 microgram. kg(-1). min(-1) (high-dose dobutamine) for 15 min. Regional power (systolic segment shortening x isometric developed force x heart rate) stabilized at 63% of baseline during hypoperfusion. Low-dose dobutamine restored power to baseline but did not increase RV myocardial O(2) consumption (MVO(2)) and thus increased myocardial O(2) utilization efficiency (O(2)UE:power/MVO(2)). At 5 min, high-dose dobutamine enhancement of power was similar to that of low-dose dobutamine, but by 15 min, power and O(2)UE fell to untreated levels. Remarkably, low-dose dobutamine tripled cytosolic phosphorylation potential; in contrast, high-dose dobutamine lowered phosphorylation potential to 45% of the untreated value. Analyses of glucose uptake and glycolytic intermediates revealed sustained enhancement of glycolysis by low-dose dobutamine, but glycolysis became limited at glyceraldehyde 3-phosphate dehydrogenase during high-dose dobutamine treatment. In summary, low-dose dobutamine improved mechanical performance and efficiency of the hypoperfused RV myocardium while increasing myocardial energy reserves, but high-dose dobutamine failed to sustain improved function and depleted energy reserves. Dobutamine is capable of improving both contractile function and cellular energetics in the hypoperfused RV myocardium, but dosage should be carefully selected.

Response to incremental doses of dobutamine early after reperfusion is predictive of the degree of myocardial salvage in dogs with experimental acute myocardial infarction

OBJECTIVES

We sought to determine whether the inotropic response to dobutamine might be useful for estimating the extent of viable myocardium soon after reperfusion.

BACKGROUND

Early identification of viable myocardium in the presence of severe left ventricular dysfunction after reperfusion is important for clinical decision making.

METHODS

Nine open-chest dogs had left anterior descending coronary artery occlusion for 40 to 180 min, followed by gradual reperfusion. The systolic thickening response to incremental dobutamine doses was measured with ultrasonic crystals and regional flow by microspheres.

RESULTS

Dogs were divided into two groups based on triphenyl tetralozium chloride infarct size (group 1: 9.3 +/- 3.0% risk area; group 2: 51.1 +/- 4.8%). In group 2 dogs with larger infarcts, regional flow during peak dobutamine was lower than it was in group 1 in endocardial (1.15 +/- 0.22 vs. 2.64 +/- 0.33 mL x min(-1) x g(-1)) and midwall (1.47 +/- 0.32 vs. 2.92 +/- 0.36 mL x min(-1) x g(-1)) layers, and endocardial flow in group 2 failed to increase from baseline (0.96 +/- 0.07 vs. 1.15 +/- 0.22 mL x min(-1) x g(-1)). Group 1 dogs demonstrated a dose dependent increase in systolic thickening with dobutamine versus a blunted response in group 2. The inotropic response to only 10 microg x kg(-1) x min(-1) of dobutamine was predictive of the degree of myocardial salvage.

CONCLUSIONS

In the early postischemic stunning phase of reperfusion, the inotropic response to dobutamine is predictive of the degree of myocardial salvage and ultimate infarct size. The ability to distinguish between stunned versus necrotic myocardium early after reperfusion was most likely due to the presence of subendocardial flow reserve during dobutamine in dogs with predominantly salvaged myocardium.

Intracoronary flow velocity measurements in adjacent stenotic and normal coronary arteries during incremental intravenous dobutamine stress and intracoronary adenosine injection

To investigate the concomitant coronary flow and hemodynamic changes induced by dobutamine and adenosine in the catheterization laboratory, we studied stenotic and adjacent normal coronary arteries in 20 patients using paired Doppler Flowires. Coronary flow velocity and hemodynamics were measured sequentially after intracoronary (ic) adenosine, during incremental iv dobutamine infusion, and after the addition of ic adenosine during sustained peak dobutamine stress (adenosine on dobutamine). Distal to stenotic arteries, average peak velocity (APV) increased significantly (from 11 +/- 5 to 16 +/- 7 cm/sec, P < 0.001) at an intermediate dose of dobutamine (20 microg/kg/min, Dobutamine20) but did not change further thereafter to peak dobutamine stress (17 +/- 7 cm/sec), despite the significant further increase in rate-pressure product (RPP). Peak stress APV did not change with adenosine on dobutamine (to 18 +/- 7 cm/sec). In normal arteries, APV increased at Dobutamine20 (from 20 +/- 7.5 to 30 +/- 12 cm/sec, P < 0.01) and further at peak dobutamine stress (to 42 +/- 10 cm/sec, P < 0.0001) always exceeding the concomitant significant increases in RPP. Peak stress APV increased further with adenosine on dobutamine (to 53 +/- 13 cm/sec, P < 0.001). Our data demonstrate that at peak dobutamine stress there is supply/demand mismatch only in stenotic arteries where coronary flow reserve is exhausted at an intermediate dobutamine dose. Furthermore, adenosine on dobutamine potentiates coronary flow heterogeneity between stenotic and normal adjacent arteries. Cathet. Cardiovasc. Intervent. 48:1-9, 1999.

Transmural metabolic heterogeneity at high cardiac work states

This study compared the transmural distribution of high-energy phosphate (HEP) depletion during oxidative stress induced by pacing- and dobutamine-induced tachycardia in myocardium perfused by a flow-limiting coronary stenosis. Myocardial blood flow (MBF) was measured with radioactive microspheres. Creatine phosphate (CrP), ATP, and P(i) were measured with transmurally localized (31)P NMR spectroscopy. In normal dogs a hydraulic occluder was used to produce a left anterior descending coronary artery stenosis, which maintained constant flow measured with a Doppler probe. Tachycardia was induced by rapid pacing (200 beats/min, n = 11) or by dobutamine infusion (20 micrograms . kg(-1). min(-1) iv, n = 13) to produce a similar heart rate. In the presence of stenosis, pacing and dobutamine caused similar reductions of subendocardial (Endo)-to-subepicardial (Epi) MBF ratios (0.66 +/- 0.06 vs. 0.63 +/- 0.08, respectively). Stenosis plus pacing caused a decrease of the CrP-to-ATP ratio (CrP/ATP) in Endo from 2.00 +/- 0.07 to 1.65 +/- 0. 08 (P < 0.05) with no significant change in Epi. Stenosis plus dobutamine caused HEP changes across the left ventricular wall, which were most marked in the outer myocardial layer (Epi CrP/ATP decreased from 2.33 +/- 0.11 to 1.67 +/- 0.12; Endo CrP/ATP decreased from 1.99 +/- 0.09 to 1.64 +/- 0.12). Thus HEP changes during oxidative stress that are produced by pacing parallel the pattern of hypoperfusion and are most severe in the subendocardium. In contrast, in response to inotropic stimulation, the transmural metabolic changes did not correspond to the pattern of the hypoperfusion.

Recovery of contractility of viable myocardium during inotropic stimulation is not dependent on an increase of myocardial blood flow in the absence of collateral filling

OBJECTIVES

The purpose of this study was to determine whether contractile recovery induced by dobutamine in dysfunctioning viable myocardium supplied by nearly occluded vessels is related to an increase in blood flow in the absence of collaterals.

BACKGROUND

Dobutamine is used to improve contractility in ventricular dysfunction during acute myocardial infarction. However, it is unclear whether a significant increase in regional blood flow may be involved in dobutamine effect.

METHODS

Twenty patients with 5- to 10-day old anterior infarction and > or =90% left anterior descending coronary artery stenosis underwent 99mTc-Sestamibi tomography (to assess myocardial perfusion) at rest and during low dose (5 to 10 microg/kg/min) dobutamine echocardiography. Rest echocardiography and scintigraphy were repeated >1 month after revascularization. Nine patients had collaterals to the infarcted territory (group A), and 11 did not (group B).

RESULTS

Baseline wall motion score was similar in both groups (score 15.9+/-1.3 vs. 17.4+/-2.0, p = NS), whereas significant changes at dobutamine and postrevascularization studies were detected (F[2,30] = 409.79, p < 0.0001). Wall motion score improved significantly (p < 0.001) in group A both at dobutamine (-5.3+/-2.2) and at postrevascularization study (-5.5+/-1.9), as well as in group B (-3.9+/-2.8 and -4.5+/-2.4, respectively). Baseline 99mTc-Sestamibi uptake was similar in both groups (62.9+/-9.7% vs. 60.3+/-10.4%, p = NS), whereas at dobutamine and postrevascularization studies a significant change (F[2,30] = 65.17, p < 0.0001) and interaction between the two groups (F[2,30] = 33.14, p < 0.0001) were present. Tracer uptake increased significantly in group A both at dobutamine (+ 10.9+/-7.9%, p < 0.001) and at postrevascularization study (12.1+/-8.7%, p < 0.001). Conversely, group B patients showed no change in tracer uptake after dobutamine test (-0.4+/-5.8, p = NS), but only after revascularization (+8.8+/-7.2%, p < 0.001).

CONCLUSIONS

The increase in contractility induced by low dose dobutamine infusion in dysfunctional viable myocardium supplied by nearly occluded vessels occurs even in the absence of a significant increase in blood flow.

Comparison of 2 myocardial velocity gradient assessment methods during dobutamine infusion with Doppler myocardial imaging

Myocardial velocity gradient (MVG) has been shown to be the best quantitative parameter for the detection of ischemic myocardium during dobutamine infusion with the use of Doppler myocardial imaging. MVG has been previously assessed by velocity measurements across the thickness of the myocardium at the time of visually selected maximal color brightness (thickness-velocity plot method). We hypothesized that MVG could be assessed by velocity measurements throughout the cardiac cycle in the subendocardium parallel to the endocardial boundary to the left ventricular cavity and in the subepicardium parallel to the epicardial boundary (time-velocity plot method). This study was designed to compare MVG obtained from the thickness-velocity plot method and from the time-velocity plot method in quantifying dobutamine-induced changes in myocardial wall motion in 8 phases of the cardiac cycle on color M-mode Doppler myocardial imaging recordings of the left ventricular posterior wall performed in 8 conscious dogs at baseline and at steady state during dobutamine infusion (10 microg/kg per minute). For both methods, MVG was considered present if its mean value was significantly different from zero and if endocardial and epicardial velocities were significantly different. There was close agreement between the 2 methods. MVG was present during the preejection period, systole, rapid ventricular filling, and atrial contraction. Dobutamine induced a significant increase in MVG during the preejection period (from 2.64 +/- 0.83 to 4.05 +/- 0.81 seconds-1 ), systole (from 2.14 +/- 0.59 to 6.08 +/- 2.20 seconds-1 in early systole, from 1.90 +/- 1.06 to 5.31 +/- 2.95 seconds-1 in mid systole, from 1.37 +/- 0.57 to 2.44 +/- 0.53 seconds-1 in end systole), and rapid ventricular filling (from 3.06 +/- 1.12 to 7.82 +/- 2.58 seconds-1 ), related to a greater rise in endocardial than in epicardial velocities. The time-velocity plot method showed that ejection and diastole were 11% and 28% decreased during dobutamine infusion, respectively, as heart rate was 31% increased. Thus according to our quantitative criteria, both MVG assessment procedures enabled objective interpretation of dobutamine effects on left ventricular wall motion. In addition, the time-velocity plot method provided automatic detection of peak velocity, timing, and duration of wall velocity changes over time.

Relative role of coronary stenosis severity and morphology in determining pharmacologic stress echo positivity

Angiographically assessed plaque morphology, not only plaque severity, may affect myocardial vulnerability to ischemia during stress testing. The aim of this study was to evaluate directly, in a head-to-head comparison, the relation between coronary stenosis severity and morphology and pharmacologic stress echo response. From our inpatients echo databank, we selected 68 patients (62 men, mean age 57 +/- 9 years) who had undergone high-dose dipyridamole and high-dose dobutamine-atropine echocardiography, performed within 1 week and in random order, before coronary angiography that showed significant coronary artery disease by selection. There were altogether 121 vessels with visually assessed stenosis >50% in 68 patients. Thirty-three had complex-type and 56 simple-type lesions (according to the Ambrose classification), whereas 32 vessels were occluded. During dobutamine echocardiography there were 51 dyssynergic regions of the left ventricle fed by different coronary arteries in 50 patients and dipyridamole stress was able to induce ischemia in 45 separate regions in 44 patients. The overall agreement between the 2 tests in recognizing ischemia was 76%. Induced ischemia was associated with greater quantitatively assessed stenosis severity for both dipyridamole (positive, 70 +/- 12% vs negative, 63 +/- 12% area reduction; p <0.05) and dobutamine (positive, 68 +/- 12% vs negative, 63 +/- 12% area reduction; p <0.05). The simple-type stenosis was more frequently identified with dobutamine (46%) versus dipyridamole (21%, [p <0.01]), whereas the complex-type stenosis was associated with a trend toward more frequent positivity of dipyridamole (55%) versus dobutamine (36%), p = 0.13. Adenosinergic stress positivity is affected not only by plaque severity, but also by plaque morphology, whereas adrenergic stress positivity is affected by plaque severity, not by plaque morphology.

Does dobutamine stress echocardiography induce damage during viability diagnosis of patients with chronic regional dysfunction after myocardial infarction?

Experimental hibernating-model investigations of animals have shown that myocardial necrosis can be induced by longer-term intracoronary dobutamine infusion. This study was designed to determine whether myocardial infarction could be ascertained in patients with chronic regional wall motion abnormalities and greater than 75% stenosis in the supplying coronary artery through dobutamine stress echocardiography. Twenty patients with coronary artery disease and regional resting wall motion abnormalities were examined with a standard dobutamine protocol (5 to 50 microg/kg/min). Exclusion criteria were an acute coronary syndrome, severe heart failure, and severe hypertension. Creatine kinase (CK, CKMB), myoglobin, and troponine-I were measured before and at each of the first 7 hours after beginning of infusion. Fourteen of these 20 patients exhibited viable myocardium. The serum markers CK, CKMB, myoglobin, and troponin-I demonstrated no increase beyond the reference range, suggesting that with this protocol, no myocardial necrosis was induced.

Effects of dobutamine at maximally tolerated dose on myocardial blood flow in humans with ischemic heart disease

BACKGROUND

This study tests the hypothesis in humans with ischemic heart disease that myocardial blood flow response to dobutamine is linearly correlated with blood flow response to adenosine.

METHODS AND RESULTS

PET with [13N]ammonia was used to measure myocardial blood flow at rest and during adenosine and dobutamine at the maximally tolerated dose. Myocardial segments were defined physiologically on the basis of blood flow response to adenosine: normal, > or = 2 mL x min(-1) x g(-1); abnormal, < 2 mL x min(-1) x g(-1); and "steal," decline versus baseline > or = 0.15 mL x min(-1) x g(-1). The patient population consisted of 11 men and 2 women. Dobutamine increased heart rate (79+/-22 to 115+/-28 bpm) and rate-pressure product (9748+/-2862 to 15,157+/-3433 mm Hg/min) significantly (both P<.01). Myocardial blood flow at rest in abnormal segments (0.50+/-0.23 mL x min(-1) x g(-1)) was reduced (P<.001) versus normal (0.90+/-0.45) and steal (0.92+/-0.60). Nevertheless, in abnormal segments, blood flow increased versus rest (P<.001) with dobutamine (0.83+/-0.43) and adenosine (0.90+/-0.49). In steal segments, myocardial blood flow declined versus baseline (P<.001) with dobutamine (0.68+/-0.46) and adenosine (0.50+/-0.45). In normal segments, myocardial blood flow increased (P<.001) with dobutamine (2.16+/-0.99) and adenosine (3.10+/-0.90). Over the range of flows, the correlation between adenosine and dobutamine was good (r=.78, P<.0001). Although flow with dobutamine in normal segments correlated with rate-pressure product (r=.81, P<.05), the slope of the line was 2.7+/-0.8 (P<.02), and normalized blood flow (3.3+/-2.5 x rest) exceeded normalized rate-pressure product (1.9+/-0.8 x rest; P<.05).

CONCLUSIONS

In humans with ischemic heart disease, myocardial blood flow responses to dobutamine and adenosine are linearly correlated over a wide range. The hyperemic response to dobutamine is in excess of that predicted by rate-pressure product and reflects the unmeasured inotropic, oxygen-wasting, and beta2-agonist effects of the drug. Dobutamine induces coronary steal with a frequency approaching that of adenosine.

Effects of dobutamine stress on myocardial blood flow, 99mTc sestamibi uptake, and systolic wall thickening in the presence of coronary artery stenoses: implications for dobutamine stress testing

BACKGROUND

Although dobutamine stress is used with both 99mTc sestamibi (sestamibi) myocardial perfusion imaging and echocardiography for detecting coronary artery stenoses, the impact of stenosis severity on test end points (myocardial sestamibi uptake and systolic thickening, respectively) has not been clearly defined.

METHODS AND RESULTS

In 15 open-chest dogs, dobutamine (2.5 to 30 microg x kg(-1) x min(-1)) was infused after placement of an LAD stenosis that reduced (n=8) or abolished (n=7) flow reserve. In dogs with reduced flow reserve, the stenotic-to-normal sestamibi activity ratio (0.86+/-0.03) significantly underestimated the approximately 2-to-1 dobutamine-induced flow disparity at the time of sestamibi injection (flow ratio, 0.53+/-0.04; P<.001). Stenotic-zone thickening increased at low but not at higher doses of dobutamine (2.9+/-0.4 versus 4.2+/-0.4 mm in normal zone at peak dobutamine; P=.055) but did not fall below baseline (2.7+/-0.3 mm). Similarly, in dogs with absent flow reserve, the sestamibi activity ratio (0.78+/-0.02) underestimated the approximately 2.5-to-1 dobutamine-induced flow disparity (flow ratio, 0.41+/-0.05; P<.001), and failure to increase systolic thickening was observed in the stenotic zone (2.7+/-0.4 versus 4.6+/-0.3 mm in the normal zone at peak stress, P<.01). In both groups of dogs, myocardial sestamibi uptake and image defect magnitudes were less than expected for the dobutamine-induced hyperemia, suggesting that dobutamine adversely affects myocardial sestamibi binding. Finally, a significant reduction in stenotic-zone thickening was seen during postdobutamine recovery, consistent with myocardial stunning.

CONCLUSIONS

In the presence of stenoses that reduced or abolished regional flow reserve, (1) myocardial sestamibi uptake significantly underestimated the dobutamine-induced flow heterogeneity, (2) a "failure to increase systolic thickening" rather than a reduction in thickening was observed during dobutamine stress, and (3) myocardial stunning was observed during postdobutamine recovery.

Can dobutamine echocardiography induce myocardial damage in patients with dysfunctional but viable myocardium supplied by a severely stenotic coronary artery?

In animal experiments, dobutamine infusion was found to impair the oxygen supply-demand balance in hypoperfused areas of hibernating myocardium which may induce myocardial damage. The aim of our study was to assess whether dobutamine echocardiography can induce myocardial damage detected by an increase in the cardiac troponin T level in blood. Twenty seven patients with coronary artery disease and severe stenosis of at least one major coronary artery (> or = 90% of luminal diameter narrowing) supplying dysfunctional myocardial segments underwent dobutamine echocardiography. Dobutamine was infused in 3 min dose increments of 5, 10, 20, 30, and 40 microg per kg body weight per minute with the addition of atropine up to 1 mg if ischemia or an 85% predicted maximal heart rate were not achieved. In 15 patients the protocol with prolonged application of 40 microg per kg per minute of dobutamine for 6 min and for the next 5 min with the addition of atropine was used. To exclude minor myocardial damage, an increase in the cardiac troponin T blood level was assessed qualitatively by the TROP T sensitive Rapid Test 20 h after dobutamine echocardiography. In 20 patients the dysfunctional segments were found to be viable with inducible ischemia exhibiting either continuous worsening in systolic thickening or "biphasic" response characterised by the improvement of their systolic thickening with a small dose and by a worsening of the thickening with a high dose of dobutamine. No patient exhibited positive TROP T sensitive Rapid Test result. In patients with coronary artery disease and severe stenosis of a major coronary artery supplying dysfunctional but viable myocardial segments, dobutamine echocardiography does not induce myocardial damage detectable by an increase in cardiac troponin T level.

Hemodynamic changes, plasma catecholamine responses, and echocardiographically detected contractile reserve during two different dobutamine-infusion protocols

We studied hemodynamic changes, catecholamine responses, and the occurrence of improved wall thickening by echocardiography during two different dobutamine-infusion protocols. Forty-three patients were studied by using a stepwise incremental dobutamine dose-infusion protocol (10-40 microg/kg/min, 3-min intervals); a subgroup of 11 patients also underwent a continuous dobutamine-infusion protocol (10 microg/kg/min for 12 min) in random order. No patient used beta-blockers. At 3-min intervals, blood pressure, heart rate, and plasma concentrations of dobutamine, epinephrine, and norepinephrine were measured. The echocardiographic improvement of wall thickening was analyzed only in paired protocols by visual assessment in left ventricular regions with normal wall motion at rest. The mean heart rate increased in the continuous and stepwise protocols from 73 to 99 and 74 to 132 beats/min. There was no significant change in blood pressure response between the two protocols. The mean plasma dobutamine concentrations during the continuous and stepwise protocols at 0, 3, 6, 9, and 12 min were 0/0; 31/38; 80/203; 106/448; and 120/692 ng/ml, respectively. In each patient, a response curve was constructed for the plasma dobutamine concentration versus heart rate. The heart rate increment and dobutamine concentration at which wall thickening was detected were similar with both protocols (14 +/- 5 vs. 12 +/- 7 beats/min) and (80 +/- 40 vs. 92 +/- 48 ng/ml; mean +/- SD). Wall thickening was noted in two of 11 patients between 0 and 3 min and 11 of 11 patients between 3 and 6 min in both protocols. Catecholamine responses during the continuous and stepwise protocols were epinephrine, 23 versus 28/28 versus 36, and norepinephrine 301 versus 323/347 versus 519. Only norepinephrine plasma concentrations increased significantly during the stepwise protocol. A 6-min dobutamine infusion was sufficient during both protocols to reach an adequate plasma dobutamine concentration, which induced a detectable increase of wall thickening in all patients. There is a significant differences between the two protocols with regard to the plasma catecholamine changes, so some of the hemodynamic effects during the stepwise dobutamine-infusion protocol may be mediated through release of endogenous catecholamines.

Factors influencing regional myocardial contractile response to inotropic stimulation. Analysis in humans with stable ischemic heart disease

BACKGROUND

We hypothesized that the response of a myocardial segment to maximal dobutamine reflects not only maximal blood flow but also tethering, metabolic, and beta-blocker status.

METHODS AND RESULTS

Patients with stable ischemic heart disease (n = 27) had positron emission tomographic measurement of blood flow at rest and with adenosine, and echocardiography at rest and with dobutamine. Positron emission tomographic measurement of [18F]fluorodeoxyglucose myocardial distribution also was made. Adenosine blood flow in segments that contracted normally at peak dobutamine was similar to that of segments that became hypokinetic (1.06 +/- 0.72 versus 1.02 +/- 0.77 mL.g-1.min-1). Segments that became akinetic failed to augment blood flow (0.68 +/- 0.30 mL.g-1.min-1). Fluorodeoxyglucose-blood flow mismatch was more common in segments with abnormal wall motion at peak dobutamine (24 of 59, 41%) versus those that contracted normally (63 of 269, 23%; chi 2, 7.40; P < .01). In patients off beta-blockers, segments that contracted normally at peak dobutamine increased blood flow with adenosine (0.70 +/- 0.31 to 0.86 +/- 0.46 mL.g-1.min-1; P < .05), whereas those that became abnormal did not (0.63 +/- 0.24 to 0.65 +/- 0.19 mL.g-1.min-1; P = NS). Segments of patients on beta-blockers that contracted normally at peak dobutamine increased blood flow with adenosine (0.78 +/- 0.31 to 1.10 +/- 0.70 mL.g-1.min-1; P < .05), as did segments that became abnormal (0.74 +/- 0.34 to 1.06 +/- 0.82 mL.g-1.min-1; P = NS). However, segments adjacent to ones with abnormal wall motion at rest had higher frequency of abnormal response at peak dobutamine in groups on (48% versus 16%; chi 2, 14.1; P < .001) and off (51% versus 21%; chi 2, 10.9; P < .01) beta-blockers.

CONCLUSIONS

Augmented contraction at maximal dobutamine depends not only on increased myocardial blood flow but also on tethering, metabolic, and beta-blocker status. Furthermore, impaired flow reserve does not preclude a normal response to maximal dobutamine, since blood flow need not increase greatly to meet demand.

Assessment of reversible dyssynergic segments after acute myocardial infarction: Dobutamine echocardiography versus thallium-201 single photon emission computed tomography

Only a moderate degree of concordance has been reported between stress-redistribution-reinjection thallium-201 single photon emission computed tomography (SPECT) and dobutamine echocardiography for the identification of myocardial viability after acute myocardial infarction. SPECT with rest-reinjection performed 4 hours after exercise testing and digitized two-dimensional (2-D) ultrasound reconstruction of the left ventricle at baseline and after low-dose dobutamine (5 to 10 microg/kg/min) infusion were compared in 50 patients > or = 8 days (12 +/- 7 days) after acute myocardial infarction. Five patients were excluded because of technically inadequate echocardiograms. Both SPECT and dobutamine echocardiography were assessed in a 16-segment model and interpreted in the remaining 45 patients. Digitized 2-D reconstruction of the left ventricle in each wall motion was scored from 1 (normal) to 4 (dyskinesia). Myocardial viability was identified on ultrasound wall-motion improvement of one or more grades from baseline to echocardiography performed > or = 30 days (60 +/- 41 days) after systematic revascularization procedure of the infarct-related artery. Reversible defect under thallium-201 SPECT and wall-motion improvement under dobutamine echocardiography were concordant in 163 (69 percent) of the 235 baseline dyssynergic segments and in 30 (67 percent) patients. Myocardial viability was identified after angioplasty (n=37) or surgery (n=8) in 29 patients and 109 segments. Positive and negative predictive values per patient in the diagnosis of myocardial viability were 86 percent and 57 percent, respectively, for stress thallium-201 SPECT with reinjection, and 100 percent and 62 percent for dobutamine echocardiography. Positive and negative predictive values per segment were 80 percent and 69 percent for the isotopic method and 91 percent and 70 percent for dobutamine echocardiography. We conclude that dobutamine echocardiography and stress thallium-201 SPECT with reinjection have similar accuracies to identify myocardial viability after acute myocardial infarction, with excellent positive but relatively low negative predictive values.