Acute myocardial infarction in two adolescent males

Acute myocardial infarction in previously healthy children is rare in the absence of congenital anomalies. We describe two cases of acute anterior myocardial infarction in adolescent males with no congenital heart disease, without prior history of or risk factors for coronary heart disease, and with no history of drug abuse. These cases illustrate that myocardial infarction in the absence of systemic illness or coronary anomalies can occur in an adolescent population.

Myocardial blood flow and flow reserve in response to short-term cyclical hormone replacement therapy in postmenopausal women

OBJECTIVES

To measure the effects of combined cyclical hormone replacement therapy (HRT) on myocardial blood flow (MBF) in postmenopausal women at high risk for coronary heart disease (CHD) and in women with documented CHD.

BACKGROUND

Estrogen restores endothelium-dependent vasodilation in response to acetylcholine in postmenopausal women, and it has a direct, endothelium-independent vasodilatory effect on coronary arteries.

METHODS

To determine whether coronary microcirculation can be affected by short-term, combined HRT, we performed positron emission tomography (PET) in two groups of women without previous HRT. Group I (n = 10) had one or more risk factors for CHD; group II (n = 8) had documented CHD and previous myocardial infarction. Group II was older (54 +/- 4 vs 59 +/- 5 y, P = .03) and had lower total cholesterol levels at baseline because of lipid-lowering therapy (244 +/- 31 vs 203 +/- 40 mg/dL, P = .03). Patients underwent baseline dynamic PET with N-13 ammonia at rest and during maximal adenosine-induced hyperemia to assess MBF. Each then began taking HRT (conjugated equine estrogen alone or with medroxyprogesterone acetate (MPA), administered in cyclical fashion), and returned for follow-up PET 46 +/- 12 days later.

RESULTS

There was no difference in resting MBF between groups I and II prior to starting therapy or at follow-up. Stress MBF and flow reserve (FR) tended to be higher in group I patients at baseline. MBF values remained unchanged at follow-up and resulted in similar FR values at baseline and during HRT for both groups. Women using only estrogen (n = 6) tended to show higher FR values after estrogen therapy, however.

CONCLUSIONS

Short-term HRT in postmenopausal women did not lead to improvements in MBF or FR. Combined cyclical HRT may not exert measurable effects on coronary microcirculation. MPA may attenuate estrogen effects on the coronaries, which may be largely endothelium-dependent.

Improved detection of left main coronary artery disease with attenuation-corrected SPECT

BACKGROUND

Myocardial perfusion imaging has demonstrated a limited sensitivity as a means of accurately identifying left main (LM) coronary disease. Because regional quantitative perfusion biases are eliminated with attenuation corrected (AC) single photon emission computed tomography (SPECT), as compared with uncorrected (NC) SPECT, we hypothesized that AC SPECT would demonstrate increased diagnostic accuracy for the detection of significant LM coronary stenosis.

METHODS AND RESULTS

We studied 28 patients (23 men, 5 women; mean age, 66+/-9 years) with significant LM stenoses (> or =50%) and 34 control patients (27 men, 7 women; mean age, 65+/-11 years) with 2-vessel coronary disease. Rest thallium-201 and stress technetium 99m sestamibi SPECT imaging with and without AC were performed, as described earlier. Both AC and NC images were analyzed visually and quantitatively in comparison with corresponding normal databases. A greater sensitivity for detection of an LM defect pattern (64% vs. 7%, P = .0009) with equivalent specificity (94% vs. 100%, P = not significant) was demonstrated by means of visual analysis of AC SPECT images. More disease was demonstrated in a greater number of territories with AC SPECT images than with NC images (2.14+/-0.97 for AC images vs. 1.43+/-0.84 for NC images, P = .0001). Similar improvement in the detection of LM disease was shown by means of automated quantitative analysis (57% for AC SPECT vs 14% for NC SPECT, P = .0005), again with no loss in specificity.

CONCLUSIONS

AC SPECT with the University of Michigan method in consecutive patients with LM stenoses and a select control population with severity matched multivessel coronary disease significantly improved the diagnostic accuracy of myocardial perfusion imaging for the identification of LM coronary disease, compared with uncorrected SPECT.

Gender differences in myocardial blood flow dynamics: lipid profile and hemodynamic effects

OBJECTIVES

The purpose of the study was to compare myocardial blood flow (MBF) in hyperlipidemic postmenopausal women and age-matched hyperlipidemic men, and to analyze the relationship between cholesterol subfractions and myocardial blood flow in men and women.

BACKGROUND

Women are protected from coronary artery disease (CAD) events until well after menopause, in part due to gender-specific differences in lipid profiles.

METHODS

To examine the effect of these influences on coronary microcirculation, MBF was quantitated with N-13 ammonia/PET (positron emission tomography) at rest and during adenosine hyperemia in 15 women and 15 men, all nondiabetic, who were matched for age and total cholesterol levels (53+/-4 vs. 50+/-8 years, p = NS, 6.44+/-1.1 vs. 6.31+/-0.85 mmol/liter, or 249+/-41 vs. 244+/-33 mg/dl, p = NS).

RESULTS

Women had significantly higher high density lipoprotein (HDL) and lower triglyceride (Tg) levels than did men, and they showed significantly higher resting MBF and stress MBF levels. Significant correlations were found between resting and hyperemic MBF and HDL and Tg levels (r = 0.44, p < 0.02 for stress MBF vs. HDL; r = 0.48, p < 0.007 for stress MBF vs. Tg). Gender was the strongest predictor of hyperemic MBF in multivariate analysis. Women responded to adenosine hyperemia with a significantly higher heart rate than did men, and hemodynamic factors correlated significantly with blood flow both at rest and during stress.

CONCLUSIONS

These data suggest that the favorable lipid profile seen in women may be associated with preserved maximal blood flow in the myocardium.

Myocardial blood flow and coronary flow reserve late after anatomical correction of transposition of the great arteries

OBJECTIVES

Myocardial blood flow (MBF) in children late after arterial switch operation (ASO) was investigated quantitatively by positron emission tomography (PET).

BACKGROUND

In children with transposition of the great arteries (TGA), ASO is widely accepted as the management of choice. The long-term patency of coronary arteries after surgical transfer to the neo-aorta, however, remains a concern.

METHODS

Twenty-two normally developed, symptom-free children were investigated by PET with nitrogen-13 ammonia at rest and during adenosine vasodilation 10+/-1 years after ASO. A subgroup of 15 children (9+/-1 years; group A) had simple TGA and underwent ASO within 20 days after birth while 7 (13+/-3 years; group B) had complex TGA and underwent ASO and correction of associated anomalies later after birth. Ten young, healthy adults (26+/-6 years) served as the control group.

RESULTS

Resting MBF was not different between groups. After correction for the rate-pressure product as an index of cardiac work, younger children of group A had significantly higher MBF at rest compared to healthy adults (102+/-29 vs. 77+/-6 ml/100 g/min; p = 0.012) while flow in group B was not different from the other groups (85+/-22 ml/100 g/min; p = NS). Hyperemic blood flows were significantly lower in both groups after ASO compared to normals (290+/-42 ml/100 g/min for group A, 240+/-28 for group B, 340+/-57 for normals; p < 0.01); thus, coronary flow reserve was significantly lower in both groups after ASO compared to healthy adults (3.0+/-0.6 for group A, 2.9+/-0.6 for group B, 4.6+/-0.9 for normals; p < 0.01).

CONCLUSIONS

Blood flow measurements suggest decreased coronary reserve in the absence of ischemic symptoms in children late after arterial switch repair of TGA. The global impairment of stress flow dynamics may indicate altered vasoreactivity; however, the prognostic significance of these findings needs to be determined.

The role of nitrogen 13 ammonia positron emission tomography in predicting functional outcome after coronary revascularization

BACKGROUND

We sought to evaluate the predictive value of positron emission tomography (PET) by using blood flow imaging with semiquantitative data analysis techniques for predicting recovery of regional function after revascularization. Positron emission tomography in combination with fluorodeoxyglucose (FDG) has been shown to predict tissue recovery after revascularization. Previous studies have suggested a quantitative threshold for perfusion as evaluated by PET that separates scar from viable tissue.

METHODS AND RESULTS

In a group of 25 patients with impaired regional wall motion at baseline as measured by radionuclide ventriculography, we examined the relationship between myocardial blood flow and functional outcome of myocardial segments in patients who underwent coronary revascularization within 2 months after PET. Regional wall motion was graded on a 5-point scale, from normal to dyskinetic. Regional nitrogen 13 (N-13) ammonia uptake values were expressed as a percentage of maximal myocardial N-13 ammonia uptake and compared with values obtained from healthy volunteers. Results were displayed as polar maps, on which regions of interest were placed corresponding to revascularized vascular territories. We were able to show a statistically significant relationship between regional wall motion abnormalities and decreasing blood flow by N-13 ammonia uptake. An N-13 ammonia uptake of greater than 80% for any given segment was highly accurate in predicting normal or nearly normal postoperative regional wall motion, whereas severely decreased ammonia uptake less than 40% showed normalization of regional wall motion in only 13% of segments.

CONCLUSIONS

Relative ammonia uptake of greater than 80% and less than 40% preoperatively had excellent predictive value for functional outcome, but intermediate quantitative ammonia uptake (between 40% to 80%) necessitates additional information to accurately predict functional recovery.