Recently published studies reflect the versatility of cardiac MR, multislice CT, rubidium-82 PET/CT, and stress echocardiography for shedding diagnostic light on various aspects of coronary artery disease and other cardiac conditions.

Cardiac arrhythmia

Infarct tissue heterogeneity by magnetic resonance imaging identifies enhanced cardiac arrhythmia susceptibility in patients with left ventricular dysfunction
Circulation 2007;115:2006-2014
Preliminary research from the cardiology department at Johns Hopkins University adds substance to the argument that myocardial infarct heterogeneity and a patient's susceptibility to cardiac arrhythmia are interrelated. Working under the supervision of Dr. Katherine Wu, Dr. Andrá Schmidt and colleagues found evidence of this connection by examining 47 patients with known left ventricular systolic function. Cine and contrast-enhanced MRI were performed prior to placement of implantable cardioverter defibrillators. No significant differences were seen in LV function, volumes, mass, and infarct size among patients with or without inducible sustained monomorphic ventricular tachycardia. But a strong correlation was observed between the quantification of tissue heterogeneity at the infarct periphery and the inducibility for monomorphic ventricular tachycardia (P = 0.015).

Acute coronary syndrome

Usefulness of 64-slice cardiac computed tomographic angiography for diagnosing acute coronary syndromes and predicting clinical outcomes in emergency department patients with chest pain of uncertain origin
Circulation 2007;115:1762-1768
Dr. Nathan Peled and colleagues from the Lady Davis Carmel Medical Center in Haifa, Israel, demonstrated the potential of 64-slice cardiac CTA as an initial screening instrument for patients who arrive in emergency rooms with chest pain that suggests the presence of acute coronary syndrome. The group prospectively studied 58 patients who underwent 64-slice CTA after arriving in the ER with chest pain without showing new ECG changes or elevated biomarkers. Contrast-enhanced MSCT found normal coronary arteries in 15 patients, nonobstructive plaque in 20, and obstructive coronary disease in 23. For that final category, 20 of 23 patients were subsequently diagnosed with acute coronary syndrome. In the next 15 months, no deaths or myocardial infarctions were recorded for 35 patients discharged from the emergency room after initial triage and MSCT findings. One patient underwent a late percutaneous coronary intervention. Overall, the sensitivity and specificity of emergency room MSCT for predicting major adverse cardiovascular events were 92% and 76% respectively. Positive and negative predictive values were 52% and 97% respectively. These encouraging findings are leading researchers to design larger multicenter trials to gain more confidence in the diagnostic power of this approach.

Infarct size prediction

Early prediction of infarct size by strain Doppler echocardiography after coronary reperfusion
J Am Coll Cardiol 2007;49:1715-1721
Norwegian cardiologists found that strain Doppler echocardiography performed immediately after percutaneous coronary revascularization stacks up well against contrast-enhanced MRI for measures of global strain and infarct size among patients treated for severe coronary artery disease. Working in the cardiology lab of Dr. Thor Edvardsen, Dr. Trond Vartdal and colleagues at Rikshospitalet University Hospital in Oslo, Norway, compared the two techniques performed on 30 patients who received percutaneous interventions for acute anterior myocardial infarction. Doppler ultrasound measuring longitudinal strain was performed 1.5 hours after revascularization. Delayed-enhancement MRI was performed nine months later to measure the extent of scarring. A strong correlation was found between echo and DE-MRI for global strain and total infarct size (R = 0.77, p <0.00001). A clear inverse relationship was found between segmental strain and the transmural extent of infarction in each of 16 myocardial segments (R = 0.67, p <0.0001).

Myocardial viability

Acute myocardial infarction early viability assessment by 64-slice computed tomography immediately after coronary angiography: comparison with low-dose dobutamine echocardiography
J Am Coll Cardiol 2007;49:1178-1185
A preliminary study of 36 patients admitted for a first acute myocardial infarction documented the promise of 64-slice CT for evaluating viable myocardium after coronary angiography. Dr. Michel Habis and colleagues under the supervision of cardiologist Dr. Jean Francois Paul at the Centre Chirurgical Marie Lannelongue in Le Plessis-Robinson, France, conducted the trial. They performed coronary angiograms soon after admission followed by MSCT without contrast reinjection. Sixteen segments of the left ventricle from the CT exams were then graded for no, subendocardial, or transmural hyperenhancement. The contractility of the same segments was evaluated two to four weeks later. A disagreement between x-ray angiography and CT perfusion arose for only 16 of 576 segments, producing 64-slice CT sensitivity and specificity rates of 98% and 94%, respectively, for detecting viable myocardial infarction at a very early stage of infarction. On a per patient basis, the sensitivity and specificity rates were 92% and 100% respectively.

Vasodilator left ventricular ejection fraction reserve

Value of vasodilator left ventricular ejection fraction reserve in evaluating the magnitude of myocardium at risk and the extent of angiographic coronary artery disease: an Rb-82 PET/CT study
Journal of Nuclear Medicine 2007;48(3):349-358
Dr. Sharmila Dorbala and colleagues in Dr. Marcelo Di Carli's lab at Brigham and Women's Hospital studied 510 consecutive patients with suspected myocardial infarction to determine the value of vasodilator left ventricular ejection fraction reserve for evaluating the volume of heart muscle at risk and the anatomic extent of severe coronary artery disease. Patients underwent gated rest and vasodilator stress Rb-82 PET/CT. A subgroup of 68 patients who also received coronary angiography was categorized as having 0-vessel, 1-vessel, 2-vessel, or left main/3-vessel disease. Dorbala found that high left ventricular ejection fraction reserve appears to be an excellent tool for noninvasively excluding left main/3-vessel disease. During Rb-82 PET/CT, left ventricular ejection fraction increases with vasodilator stress in patients without significant stress-induced perfusion defects or severe left main/3-vessel coronary artery disease.

Myocardial bridge

Myocardial bridge: evaluation on MDCT
AJR 2007;188:1069-1073
Myocardial bridge, an intramural segment of a coronary artery that normally courses epicardially, should be considered an anatomic risk factor when evaluating coronary artery disease, according to a study of 300 consecutive subjects examined by Adbel-Rauf Zeina and colleagues at the Bnai Zion Medical Center in Haifa Israel. Myocardial bridge proved to be fairly common, appearing in 26% of the subjects examined with 16-slice coronary CTA. A mid left anterior descending artery was the most common artery involved with bridging. Zeina identified a significant difference between the LAD myocardial bridge group and control subjects regarding the presence of atheromatous changes in a similar LAD segment proximal to the myocardial bridge and in the severity of atheromatous changes in those segments. The presence of stenosis in the LAD proximal to the myocardial bridge correlated with the thickness and length of the bridge.

Pulmonary arterial hypertension

Pulmonary arterial hypertension: noninvasive detection with phase-contrast MR Imaging
Radiology 2007;243:70-79
Phase-contrast MRI and right-sided heart catheterization of 59 patients with known or suspected pulmonary arterial hypertension (PAH) found that average blood velocity throughout the cardiac cycle is strongly correlated with pulmonary pressures and resistance. Working in Dr. Michael Poon's lab at the Mount Sinai School of Medicine in New York, Dr. Javier Sanz and colleagues measured numerous indicators of arterial function. Of these, average blood velocity provided the best correlation with mean pulmonary artery pressure, systolic pulmonary artery pressure, and pulmonary vascular resistance index. Average blood velocity, with a cutoff value of 11.7 cm/sec, reveals PAH with a sensitivity of 92.9% and specificity of 82.4%. The sensitivity and specificity for the minimum pulmonary arterial areas were 92.9% and 88.2% respectively.