Effect of intracoronary nitroglycerin administration on phasic pattern and transmural distribution of flow during coronary artery stenosis

Postpartum coronary vasospasm with literature review

Acute myocardial infarction during pregnancy or the postpartum period is rare. We report a case of a 39-year-old postpartum woman who developed non-ST-elevation myocardial infarction due to severe diffuse coronary vasospasm. To our knowledge, this is the first case of angiographically evidenced coronary vasospasm, in a postpartum woman, with resistance to intracoronary nitroglycerin.

Nitroglycerin-induced heterogeneous subendocardial myocardial blood flow observed by cardioscopy in patients with coronary artery disease

It is controversial as to whether or not nitroglycerin (NTG) increases subendocardial myocardial blood flow (SMBF), and if it does, whether arterial or venous blood flow is increased in patients with coronary artery disease. This study was performed to examine NTG-induced changes in SMBF.Changes in SMBF induced by NTG (200 µg, i.v.) were examined by cardioscopy in 58 left ventricular wall segments of 58 patients with coronary artery disease. NTG-induced red and purple endocardial colors were defined as increased arterial and venous SMBF, respectively. Endocardial color before NTG administration was classified into brown, light brown, pale and white. Endomyocardial biopsy of the observed portion and (201)Tl scintigraphy were performed in 40 of these patients immediately after cardioscopy and several days after cardioscopy, respectively.Upon administration of NTG, SMBF increased in 48 of 58 wall segments; arterial SMBF in 34 and venous SMBF in 12 wall segments; arterial SMBF in all 24 brown to light brown segments; venous SMBF, arterial SMBF and no change in 12, 10 and 5 of pale segments, respectively; and no change in all 10 white wall segments. (201)Tl-scintigraphy and endomyocardial biopsy revealed that brown, light brown, pale and white endocardial color represented no ischemia, mild ischemia, severe ischemia and fibrosis, respectively.NTG caused an increase in either arterial or venous SMBF depending on control endocardial color, wall motion and severity of coronary stenosis.

Coronary endothelial dysfunction is associated with a reduction in coronary artery compliance and an increase in wall shear stress

OBJECTIVE

Endothelial dysfunction is associated with arterial stiffness in large arteries. The purpose of this study was to investigate the association between coronary endothelial dysfunction, coronary artery compliance and wall shear stress in patients with early atherosclerosis.

METHODS

Coronary endothelial function was assessed according to responses to intracoronary acetylcholine in 120 patients without significant coronary stenosis. Acceleration of peak velocity (ACC), which is inversely related to coronary artery compliance, was derived from coronary flow velocity spectra, and wall shear rate (WSR) was calculated. Measurements were performed at baseline and after intracoronary nitroglycerin in order to eliminate the contribution of vascular smooth muscle tone to coronary artery compliance.

RESULTS

In all patients, heart rate significantly increased (72+/-1 to 77+/-1 bpm, p<0.01) and mean arterial pressure decreased (97+/-2 to 93+/-1 mm Hg, p<0.01) after nitroglycerin. Coronary blood flow (CBF) and resistance were not significantly changed, but the diastolic to systolic velocity ratio increased significantly (2.15+/-0.08 to 5.36+/-0.61, p<0.01). Patients with abnormal endothelial function (n=70) had a higher WSR at baseline (559+/-41 vs 440+/-26 s(-1), p<0.05) and after nitroglycerin (457+/-41 vs 339+/-29 s(-1), p<0.05), and a higher ACC after nitroglycerin (3.9+/-0.4 vs 2.8+/-0.4 m/s(2), p<0.05) than patients with normal function (n=50).

CONCLUSIONS

The current study demonstrates that intracoronary nitroglycerin does not contribute to an increase of CBF but alters the phasic coronary flow pattern. Furthermore, early coronary atherosclerosis characterised by endothelial dysfunction is associated with a decrease in coronary artery compliance and an increase in wall shear stress. Therefore, coronary wall properties are affected early in the atherosclerosis process.

Intracoronary administration of isosorbide dinitrate induced severely slow flow and transient ST-segment elevation

Nitroglycerin is one of the most widely used drugs in the treatment of angina. However, nitroglycerin fails to relieve angina in patients with syndrome X who have microvessel dysfunction. Microvessel function is impaired in several diseases. In this article, the authors report that despite normal coronary angiograms at control, intracoronary administration of isosorbide dinitrate induced severe coronary slow flow and transient ST-segment elevation with mild chest pain in a patient with congestive heart failure. The authors speculated that functional stenosis and a delay in the dilatation of microvessels less than 100 microm in diameter because of their dysfunction resulted in a severely slow flow after intracoronary administration of isosorbide dinitrate.

Effect of oral nitroglycerin and cold stress on myocardial perfusion in areas subtended by stenosed and nonstenosed coronary arteries

Physical obstruction and coronary vasoconstriction mediated by adrenergic stress are believed to be responsible for episodes of myocardial hypoperfusion and angina. Nitroglycerin relieves symptoms by reducing preload and dilating epicardial vessels. The net perfusion change and relation to stenosis severity of nitroglycerin and adrenergic stress have been debated. This study aimed to evaluate whether oral nitroglycerin and adrenergic stress alters perfusion in myocardial segments subtended by stenosed and nonstenosed coronary arteries. Myocardial perfusion was quantified (using N-13-ammonia positron emission tomography [PET]) at rest, after oral nitroglycerin 400 microg, and after cold stress in 25 patients with coronary artery disease (62 +/- 9 years, 21 men) and in 30 controls (34 +/- 9 years, 22 men). Myocardial perfusion was quantified in areas supplied by stenosed (>70%) and nonstenosed (<30%) coronary arteries. The cold pressor test did not significantly alter myocardial perfusion in any of the groups. However, when normalized for rate-pressure product, the response in stenosed areas showed a significantly more pronounced reduction compared with nonstenosed areas (0.78 +/- 0.18 vs 0.64 +/- 0.19 ml/g/min, p <0.005 and 0.86 +/- 0.19 vs 0.73 +/- 0.24 ml/g/min, p <0.05, p <0.05) for intergroup comparison. In both stenosed areas and nonstenosed areas nitroglycerin increased perfusion (0.51 +/- 0.14 vs 0.60 +/- 0.17 ml/g/min, p <0.05 and 0.56 +/- 0.14 vs 0.61 +/- 0.17 ml/g/min, p <0.05). Nitroglycerin did not alter myocardial perfusion in the control group. There was a negative correlation between the cold pressor test response and stenosis severity (r(2) = 0.17, p <0.046), whereas this was not the case for nitroglycerin. In patients with coronary artery disease, myocardial segments supplied by stenosed coronary arteries showed an altered perfusion response to adrenergic stress. Oral nitroglycerin increased myocardial perfusion irrespective of the presence of a stenosis.

Vasodilator responses of coronary conduit and resistance arteries to continuous nitroglycerin infusion in humans: a Doppler guide wire study

To examine the responses of coronary conduit and resistance arteries to the continuous i.v. administration of nitroglycerin in 15 patients with atypical chest pain, we measured coronary blood flow velocity in the left anterior descending coronary artery using a Doppler guide wire and the lumen diameter and cross-sectional area by quantitative coronary angiography. Systolic flow, diastolic flow, total coronary flow, and coronary vascular resistance were calculated. Stepwise increases in dose of nitroglycerin resulted in significant dose-dependent decrease in mean aortic pressure (p < 0.01) and increase in lumen diameter (p < 0.05). After nitroglycerin administration of 0.5 microg/kg/min, systolic flow decreased significantly by 89.9+/-15.7% (p < 0.01), and diastolic flow increased significantly by 74.2+/-37.1% (p < 0.05). Total coronary flow did not change significantly with the various doses of nitroglycerin. However, coronary vascular resistance decreased significantly at concentrations greater than 0.5 microg/kg/min nitroglycerin. Continuous nitroglycerin infusion did not reduce either diastolic or total coronary blood flow despite a significant reduction in coronary perfusion pressure. These results indicate that subendocardial blood flow might be maintained during continuous i.v. infusion of nitroglycerin within the clinical dose range.

Alpha-adrenergic vasoconstriction reduces systolic retrograde coronary blood flow

There is a paradoxical alpha-adrenoceptor-mediated coronary vasoconstriction whenever there is adrenergic activation of the heart, as during cardiovascular reflexes or exercise. A previous study demonstrated that this paradoxical vasoconstriction helps maintain blood flow to the vulnerable inner layer of the left ventricular wall during exercise, but the mechanism for this effect was not elucidated. The purpose of the present investigation was to test the hypothesis that alpha-adrenoceptor-mediated vasoconstriction lessens the to-and-fro oscillation of blood flow that occurs in the coronary arterial tree during systole and diastole. Septal coronary artery blood velocity was measured in anesthetized open-chest dogs with a 20-MHz pulsed Doppler velocimeter. Systolic retrograde velocity and diastolic forward velocity were compared during norepinephrine infusion before and after alpha-adrenoceptor blockade with phenoxybenzamine. Systolic aortic pressure was held constant by aortic banding; heart rate was controlled by pacing at 80, 140, and 200 beats/min; and maximum left ventricular dP/dt was unchanged by alpha-blockade. At each pacing rate, systolic retrograde velocity was significantly greater after alpha-blockade, indicating that alpha-vasoconstriction reduced systolic retrograde flow by changing coronary vascular impedance. Transmural blood flow was measured with microspheres in a second group of dogs during the same experimental conditions, and flow to the inner layer of the left ventricle was diminished by alpha-adrenoceptor blockade at a heart rate of 250 beats/min, demonstrating a beneficial effect of alpha-vasoconstriction. In conclusion, adrenergic alpha-adrenoceptor-mediated coronary vasoconstriction reduces systolic retrograde coronary flow during norepinephrine infusion. This lessens to-and-fro flow oscillation in the coronary circulation and probably is the mechanism whereby alpha-vasoconstriction helps maintain blood flow to the inner layer of the left ventricle during exercise.

Comparison of coronary flow reserve between focal and diffuse vasoconstriction induced by ergonovine in patients with vasospastic angina

Decreased coronary flow reserve has been reported in patients with ergonovine-induced coronary vasoconstriction by the thermodilution method. To assess the difference of coronary flow reserve between patients with focal and diffuse vasospasm, after the vasospasm is discontinued by injection 3 mg of isosorbide dinitrate, phasic flow velocities of the diseased coronary artery were recorded at rest and during hyperemia (140 microg/kg/min of adenosine infusion intravenously) using a 0.014-inch, 15-MHz Doppler guidewire in 26 patients with ergonovine-induced coronary vasospasm (0.2-mg ergonovine injection intravenously), including 12 patients with focal (>90% stenosis), 14 patients with diffuse vasospasm (>50%), and 11 controls with normal coronary arteries without vasospasm. Although time-averaged peak velocity in cases with diffuse and focal vasospasm was not significantly different compared with that in controls at baseline (22 +/- 7, 18 +/- 5 vs 20 +/- 7 cm/s, respectively, NS), it was significantly lower in patients with diffuse vasospasm than in cases with focal vasospasm and in controls during hyperemia (43 +/- 13 vs 64 +/- 18, 61 +/- 19 cm/s, respectively, p <0.01). As a result, coronary flow reserve obtained from the ratio of hyperemic/baseline time-averaged peak velocity was significantly lower in patients with diffuse vasospasm than that in controls (1.9 +/- 0.4 vs 3.1 +/- 0.4, p <0.01), although it was not significantly different between the subjects with focal vasospasm and controls (3.5 +/- 0.7 vs 3.1 +/- 0.4, NS). Thus, coronary flow reserve is maintained normally in patients with focal vasospasm and limited in those with diffuse vasospasm. Microvascular impairment could exist further in cases with diffuse vasospasm, although similar endothelial dysfunction of the epicardial coronary artery is observed in focal and diffuse vasospasm.

Transthoracic echocardiographic measurement of coronary blood flow and reserve

The objectives of this study were to evaluate the use of high-frequency (5 MHz) transthoracic echocardiography for the noninvasive measurement of coronary blood flow and to test its ability to detect small changes in blood flow that may accompany pharmacologic intervention. High-frequency (5 MHz) transthoracic echocardiography was performed on the distal segment of the left anterior descending coronary artery of 32 consecutive patients (23 men and nine women; mean age 60 +/- 10 years) before and after the administration of 0.4 mg sublingual nitroglycerin. The results were compared with those of 10 patients (eight men and two women; mean age 59 +/- 6 years) in whom the ungrafted left internal mammary artery was studied. Doppler velocity profiles of the left anterior descending coronary artery were detected in 18 (56%) of the 32 Study patients. Left anterior descending coronary artery diameter and blood flow were measured in 14 patients (44%). There was no significant difference in blood flow between the left anterior descending artery (74 +/- 35 ml/min) and the internal mammary artery (52 +/- 25 ml/min). After administration of nitroglycerin, there was a 24% decrease in coronary blood flow from 74 +/- 35 ml/min to 56 +/- 30 ml/min (p < 0.05). This study suggests that high frequency transthoracic echocardiography may allow noninvasive identification of the left anterior descending coronary artery and detection of small changes in blood flow that accompany pharmacologic and mechanical intervention.

Effects of intraaortic balloon pumping on septal arterial blood flow velocity waveform during severe left main coronary artery stenosis

OBJECTIVES

We sought to evaluate the effect of intraaortic balloon pumping on the phasic blood velocity waveform into myocardium with severe coronary artery stenosis.

BACKGROUND

In the presence of severe coronary artery stenosis, it is not clear whether intraaortic balloon pumping augments intramyocardial inflow during diastole or changes systolic retrograde blood flow from the myocardium to the extramural coronary arteries.

METHODS

Using anesthetized open chest dogs (n=7), we introduced severe stenosis in the left main coronary artery to reduce the poststenotic pressure to approximately 60 mm Hg (>90% diameter stenosis). Septal arterial blood flow velocities were measured with a 20-MHz, 80-channel ultrasound pulsed Doppler velocimeter. Left anterior descending arterial flow, aortic pressure and poststenotic distal coronary pressure were measured simultaneously. The diastolic anterograde flow integral and systolic retrograde flow integral were compared in the presence and absence of intraaortic balloon pumping.

RESULTS

Although intraaortic balloon pumping augmented diastolic aortic pressure, this pressure increase was not effectively transmitted through stenosis. Septal arterial diastolic flow velocity was not augmented, and left anterior descending arterial flow was unchanged during intraaortic balloon pumping.

CONCLUSIONS

In the presence of severe coronary artery stenosis, intraaortic balloon pumping failed to increase diastolic inflow in the myocardium and did not enhance systolic retrograde flow from the myocardium to the extramural coronary artery. Thus, the major effect of intraaortic balloon pumping on the ischemic heart with severe coronary artery stenosis may be achieved by reducing oxygen demand by systolic unloading.

Evaluation of intramyocardial coronary blood flow waveform during intraaortic balloon pumping in the absence or presence of coronary stenosis

Our aim was to evaluate the effects of intraaortic balloon pumping (IABP) on the blood velocity waveform in the absence or presence of coronary artery stenosis. Using anesthetized open-chest dogs, the septal arterial blood flow velocities were measured with a 20 MHz 80-channel ultrasound pulsed Doppler velocimeter in the absence (n = 5) or presence (n = 3) of left main coronary artery stenosis. The blood velocity waveform was analyzed by calculating the systolic retrograde velocity integral (SR) and the diastolic antegrade velocity integral (DA). A slosh ratio was defined as SR/DA. The left anterior descending arterial flow (CBF), aortic pressure (AoP), and poststenotic distal coronary pressure (DiP) were also measured simultaneously. We compared the effect of IABP on the velocity waveforms in the absence and in the presence of coronary artery stenosis. In the absence of stenosis, IABP increased DiP during diastole and augmented DA while it also increased SR. IABP augmented the net CBF because of the greater increase in DA than SR. In the presence of stenosis, however, IABP did not increase DiP and resulted in no significant effect on the net CBF.

New concepts for interpretation of intracoronary velocity and pressure tracings

The development of quantitative angiography and the introduction of new imaging techniques cannot replace functional methods of assessing the severity of stenosis. Measurement of transstenotic pressure gradient and poststenotic flow velocity using miniaturised sensors with guidewire technology offers an alternative to the conventional non-invasive methods that is immediately applicable in the catheterisation laboratory during interventional procedures. The complexity of the coronary circulation, however, makes it difficult to establish simple cut-off criteria to identify the presence of a flow-limiting stenosis. For intermediate lesions or in the presence of variable haemodynamic conditions, the accuracy of the assessment can be improved by the application of more complex indices proposed and validated in the laboratory animals. Two of these indices are myocardial fractional flow reserve and the slope of the instantaneous relation between pressure or pressure gradient and flow velocity.

Quantitative sorting of normal and abnormal coronary flow wave form shapes

The normal phasic flow wave form in an epicardial coronary artery has a distinct characteristic shape, which reflects the interaction between the coronary tree, myocardial function and hemodynamic conditions. Since clinical measurements of phasic coronary wave forms are becoming available, determination of abnormal coronary flow wave forms is important. We suggest here an objective and automatic method to discriminate between normal and abnormal flow wave forms based on the Karhunen-Loève Transform (KLT), and experimentally tested it. The normal flow domain was represented by the resting flow waves measured in the left anterior descending arteries in 31 anesthetized dogs. The abnormal flow conditions, imposed and tested experimentally, were varying stenosis severity and severely reduced left ventricular pressure. In addition, the effects of reactive hyperemia on the shape of the flow were examined. The sorting index was based on the mean-square error (MSE) calculated for each flow signal based on a truncated KLT expansion. The results show excellent discrimination between the normal and the abnormal groups. During reactive hyperemia, however, MSE did not change significantly. These results indicate that the shape of abnormal coronary flow wave forms can be identified and discriminated from normal wave forms.

Time of flight quantification of coronary flow with echo-planar MRI

Detection and quantification of flow of the left anterior descending (LAD) coronary artery in healthy volunteers are demonstrated using echo-planar imaging (EPI). A time-of-flight (TOF) model was used to derive coronary flow velocities from wash-in curves, free of cardiac wall motion contamination. Short-axis cardiac studies were performed using a gated, gradient echo EPI technique to limit the effect of cardiac wall motion on coronary vessel imaging. A series of 10 to 20 single or multislice images were acquired within a single breath-hold. Real-time cine series showed the LAD coronary artery with a detectability of 91% (n = 23) and revealed beat-to-beat variability in vessel position of a magnitude equal to or greater than its diameter. Flow velocity was measured in the proximal portion of the artery at rest and during exercise. The data demonstrated the known phasic pattern of LAD flow: Vsystole < or = 5 cm/s and peak Vdiastole = 14 +/- 3 cm/s (n = 11, V = mean laminar flow velocity). During isometric exercise, a LAD flow velocity increase (52 +/- 24%) was detected in eight of nine subjects. The capacity of the EPI TOF method to detect flow velocity changes should prove clinically useful for future assessment of coronary flow reserve.

Assessment of coronary conductance and resistance vessel reactivity in response to nitroglycerin, ergonovine and adenosine: in vivo studies with simultaneous intravascular two-dimensional and Doppler ultrasound

OBJECTIVES

The aim of this study was to determine the differential effects of nitroglycerin, ergonovine and adenosine on the resistance vessels in vivo by using a Doppler-tipped guide wire in combination with an ultrasound imaging catheter.

BACKGROUND

Catheter-based two-dimensional intravascular ultrasound yields images of the coronary arteries from which cross-sectional areas can be measured. Intravascular Doppler ultrasound techniques allow measurement of coronary blood flow velocity. The simultaneous use of the two techniques can yield anatomic and physiologic information on conductance and resistance vessels but has not been tried in the coronary arteries.

METHODS

In 15 dogs, we studied coronary flow and vascular reactivity in response to pharmacologic agents using two approaches: 1) a 30-MHz, 4.3F imaging catheter placed alongside a 0.018-in. (0.046 cm) Doppler wire in the circumflex or left anterior descending coronary artery (n = 5); 2) the ultrasound imaging catheter introduced directly over a 0.014-in. (0.036 cm) Doppler wire (n = 10). Vasodilator and vasoconstrictor responses were studied by using intracoronary nitroglycerin (50, 100 and 200 micrograms), ergonovine (200 micrograms) and adenosine (6 mg).

RESULTS

Nitroglycerin caused a dose-dependent increase in epicardial coronary artery cross-sectional area and, to a lesser extent, in average peak flow velocity, resulting in an increase in volumetric coronary blood flow of 39% and 50% at the doses of 100 and 200 micrograms, respectively. With these doses of nitroglycerin, the decrease in diastolic to systolic velocity ratio and the increased change in cross-sectional area from end-diastole to end-systole suggested an enhanced epicardial coronary artery compliance. With ergonovine, a 12% reduction in epicardial coronary artery cross-sectional area was seen, without a significant change in average peak velocity, resulting in a 15% decrease in volumetric coronary blood flow. Adenosine caused a 270% increase in average peak velocity but no change in epicardial coronary artery cross-sectional area, resulting in a 270% increase in volumetric blood flow.

CONCLUSIONS

This study demonstrates that nitroglycerin and ergonovine predominantly influence coronary conductance arteries whereas adenosine mainly dilates coronary resistance vessels. These findings also demonstrate that the combined use of a two-dimensional and a Doppler ultrasound transducer within one catheter assembly can provide information on the differential effects of vasoactive agents on the epicardial and microvascular coronary circulation.