Dobutamine stress magnetic resonance imaging for detection of coronary artery disease.

OBJECTIVES: The clinical value of cine magnetic resonance imaging (MRI) during dobutamine stress for detection of coronary artery disease was evaluated in 45 patients with chest pain who were admitted for coronary arteriography. BACKGROUND: Development of stress-induced wall motion asynergy is considered an early and reliable sign of myocardial ischemia preceding electrocardiographic (ECG) changes and angina. As physical exercise during MRI is difficult because of motion artifacts and space restriction, dobutamine infusion was used to induce cardiovascular stress. METHODS: Cine MRI tomograms were obtained in six adjacent short-axis planes. After baseline acquisition, dobutamine was administered to a maximal dose of 20 micrograms/kg per min. Both at rest and during peak dobutamine stress, magnetic resonance images were displayed in a cinematographic loop to assess regional wall motion qualitatively. Results of dobutamine MRI were considered positive for coronary artery disease if any new or worsening wall motion abnormality developed. Immediately after MRI at peak dobutamine infusion, dobutamine electrocardiography was performed outside the magnetic environment. In addition, all patients performed symptom-limited exercise electrocardiography. RESULTS: Significant coronary artery disease (> 50% diameter stenosis) was present in 37 patients. During peak dobutamine stress, wall motion asynergy developed or worsened in 30 patients, yielding an overall sensitivity for detection of coronary artery disease of 81% and a specificity of 100%. Corresponding data were 51% and 63% for dobutamine electrocardiography and 70% and 63% for exercise electrocardiography. The sensitivity of dobutamine MRI for the detection of coronary artery disease in patients with single-, double- and triple-vessel disease was 75% (15 of 20 patients), 80% (8 of 10) and 100% (7 of 7), respectively. CONCLUSION: Dobutamine MRI is an accurate nonexercise-dependent method for the assessment of myocardial ischemia in patients with coronary artery disease.

Subcutaneous single-incision implantation of cardioverter-defibrillators under local anesthesia by electrophysiologists in the electrophysiology laboratory.

Implantable cardioverter-defibrillators (ICDs) have traditionally been implanted at the operating room under general anesthesia. Endocardial lead systems and downsized devices allowed implantation by electrophysiologists in the pectoral region. The present study evaluates the safety and efficacy of subcutaneous ICD implantation performed entirely by electrophysiologists using a single-incision approach for lead insertion and device placement under local anesthesia. Between June 1996 and May 1997, 51 of 52 consecutive patients (41 men and 10 women, mean age 58 +/- 9 years) underwent ICD implantation at the electrophysiology laboratory. Local anesthesia and intravenous sedation were administered to all patients. After transvenous lead positioning by either venotomy of the left cephalic vein (n = 16) or puncture of the left subclavian vein (n = 35), all ICDs were implanted subcutaneously at the left subclavicular region. Fifty procedures (98%) were successful at first attempt. The mean implantation time was 76 +/- 22 minutes and the mean fluoroscopy time was 7.5 +/- 5.2 minutes. Patients received ICD devices generating biphasic waveforms. The mean defibrillation threshold was 11 +/- 3 J. Procedure-related complications occurred in 5 patients (10%): 1 lead dislocation, 2 pocket hematomas, and 2 pneumothorax requiring drainage. Mean time from implantation to hospital discharge was 1.8 +/- 1.2 days. During follow-up (38 +/- 14 weeks), all devices were operating appropriately and no major complications occurred. In conclusion, this report demonstrates that a single-incision subcutaneous technique for ICD implantation can be safely and successfully performed by electrophysiologists using local anesthesia and intravenous sedation. The high success rate, low complication occurrence, and short implantation and fluoroscopy times make this cost-effective technique in the electrophysiology laboratory the method of choice.

Usefulness of ultrafast magnetic resonance imaging in healed myocardial infarction.

The value of ultrafast magnetic resonance imaging (MRI) in the assessment of dynamic contrast enhancement and myocardial perfusion abnormalities was evaluated in 20 patients with healed myocardial infarction, who also underwent 2-dimensional echocardiography. At baseline and after bolus injection of the paramagnetic contrast agent gadolinium-diethylenetriaminepentaacetic acid (DTPA) (0.04 mmol/kg body weight), single-level short-axis MRI was performed every third RR interval with an acquisition time of 500 ms. Myocardial signal intensities were measured in transmural myocardial regions of interest. After gadolinium-DTPA injection, infarcted and normal myocardium demonstrated a signal intensity enhancement of 50 and 134%, respectively (p < 0.001). A signal intensity of normal relative to infarcted myocardium increased from 1.25 +/- 0.22 (SD) before to 1.91 +/- 0.41 after gadolinium-DTPA (p < 0.001). The rate of signal increase in the infarcted and normal myocardium was 5.17 +/- 2.22 and 18.99 +/- 9.96 s-1 (p < 0.001), respectively. Ultrafast MRI using gadolinium-DTPA bolus administration clearly identifies myocardial perfusion abnormalities in patients with healed myocardial infarction. The infarct site on MRI corresponded with the location of wall motion asynergy determined by echocardiography. It is concluded that gadolinium-DTPA-enhanced ultrafast MRI provides noninvasive assessment of myocardial perfusion in patients with proven coronary artery disease.

Alternative stress methods for the diagnosis of coronary artery disease.

Bicycle exercise and treadmill exercise are the commonest devices used in the evaluation of coronary artery disease. However, not all patients are capable of performing a maximal exercise test due to orthopaedic, vascular or pulmonary disease, poor physical condition and motivation. Alternative tests as a reliable substitute for the more conventional methods have been proposed, such as right atrial pacing, arm ergometry, handgrip test, cold pressure test, and inotropic stimulation. In particular, pharmacological stress testing with dipyridamole (and recently with adenosine and dobutamine) in combination with radionuclide techniques has gained much interest. This review will consider the usefulness and role of alternative stress testing to provoke myocardial ischaemia, with emphasis on pharmacological stress testing in conjunction with thallium-201 myocardial perfusion scintigraphy.

Endocardial activation mapping of ventricular tachycardia in patients : first application of a 32-site bipolar mapping electrode catheter.

BACKGROUND: Localization of early activated endocardial areas during ventricular tachycardia (VT) is mandatory for performance of surgical or radiofrequency catheter interventions. The use of a multielectrode catheter may shorten the procedure time and increase the accuracy of the procedure compared with single-electrode mapping techniques. This study was performed to evaluate the safety and efficacy of a 32-bipolar-electrode mapping catheter in patients. METHODS AND RESULTS: The basket-shaped mapping catheter (BMC), integrated with a computerized mapping system, allowed on-line reconstruction of endocardial activation maps. Twenty patients with VT were studied before surgery (n=4) or radiofrequency catheter ablation (n=16). End-diastolic left ventricular (LV) volume was 280+/-120 mL, with an LV ejection fraction of 33+/-14%. The volume encompassed by the BMC was 164+/-27 mL (130 to 200 mL); the deployment time was 46+/-11 minutes. Endocardial activation time during sinus rhythm was 105+/-34 ms; 14+/-5 electrodes could be used to stimulate the heart. Cycle length of VT was 325+/-83 ms. Earliest endocardial activation was recorded 58+/-42 ms before the onset of the surface ECG. Complications were pericardial effusion (n=2) and transient cerebral disorientation (n=1). CONCLUSIONS: Percutaneous multielectrode endocardial mapping in patients with VT is feasible and relatively safe. The use of this technique shortens the time patients have to endure VT.

New developments in pharmacologic stress imaging.

The clinical usefulness of cardiac imaging modalities that rely upon the detection of perfusion defects and wall motion disturbances requires conditions that provoke a heterogeneity of coronary flow and a myocardial oxygen imbalance, respectively. Traditionally, this has been achieved by exercise stress testing. Many patients cannot perform dynamic exercise sufficiently for various reasons. Pharmacologic stress has been proven to be an attractive alternative for physical exercise. Currently, several stressing agents are used in conjunction with thallium-201 scintigraphy, 2-D echocardiography and, recently, MRI. The most employed agents include vasodilators, such as dipyridamole and adenosine, and catecholamines, such as dobutamine (Table VI). The predominant rationale of thallium-201 perfusion scintigraphy is based on the creation of a flow maldistribution between territories supplied by normal arteries and those supplied by stenotic arteries that does not necessarily require ischemia. Dipyridamole and adenosine, as rather selective coronary vasodilators, are well suited to provoke such a condition and may be classified as the ideal markers of myocardial perfusion. 2-D echocardiography and MRI have the potential to provide noninvasively derived information of cardiac dynamics and regional myocardial function. To assess the functional significance of coronary artery disease, detection of wall motion abnormalities and alterations in ejection fraction require the presence of myocardial ischemia. Dobutamine, as a widely applied inotropic agent in the management of severely depressed left ventricular contractile function, seems to be an appropriate pharmacologic stressor when heart failure is absent. By increasing contractility, heart rate, and systolic arterial pressure, it is capable of inducing an imbalance between myocardial oxygen demand and supply, leading to ischemia in patients with coronary artery disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Ischemic heart disease: value of MR techniques.

BACKGROUND: The cardiovascular applications of magnetic resonance (MR) techniques in coronary artery disease have increased considerably in recent years. Technical advantages of MR imaging are the excellent spatial resolution, the characterization of myocardial tissue, and the potential for three-dimensional imaging. These characteristics allow the accurate assessment of left ventricular mass and volume, the differentiation of infarcted from normal tissue, and the determination of systolic wall thickening and regional wall motion abnormalities. METHODS: In addition to the conventionally used spin-echo and cine-echo techniques, newer techniques such as myocardial tagging, ultrafast MR imaging and MR coronary angiography have been developed. These newer techniques allow a more accurate assessment of ventricular function (tagging), myocardial perfusion (ultrafast imaging), and evaluation of stenosis severity (MR coronary angiography). Particularly early detection and flow assessment of stenosed coronary arteries and bypasses by MR angiography would constitute a major breakthrough in cardiovascular MR imaging. Apart from the MR imaging techniques, cardiac metabolism may be well assessed using MR spectroscopy. This provides unique information on the metabolic behaviour of the myocardium under conditions stress-induced ischemia. However, the definite niche of cardiac MR spectroscopy has still to be settled. CONCLUSION: Currently, MR techniques allow the evaluation of anatomy and function (accepted use), perfusion and viability (development phase), and coronary angiography (experimental phase). A particular strength of MR imaging is that one single MR test may encompass cardiac anatomy, perfusion, function, metabolism and coronary angiography. The replacement of multiple diagnostic tests with one MR test may have major effects on cardiovascular healthcare economics and would outweight the cost inherent to the MR angiography procedure.

Quantitation of global and regional left ventricular function by cine magnetic resonance imaging during dobutamine stress in normal human subjects.

Magnetic resonance imaging (MRI) provides high-resolution images of the heart. However, physical exercise during MRI is difficult due to space restriction and motion artefacts. To evaluate the feasibility of MRI during stress conditions, dobutamine was used as an alternative to exercise. Haemodynamics, ventricular volumes and wall thickening were measured at rest and during peak dobutamine infusion (15 micrograms.kg-1 x min-1) in 23 normal human subjects. To calculate left ventricular volumes, eight short-axis views were obtained encompassing the left ventricle from base to apex. At six levels, percent systolic wall thickening (%WTh) was measured in 18 segments (20 degrees intervals). Heart rate, systolic and diastolic blood pressures, stroke index, cardiac output and left ventricular ejection fraction increased significantly during dobutamine infusion (all P values < 0.001). In addition, %WTh increased significantly (P < 0.001) during dobutamine compared to the control state at all levels except in the apical and low-left ventricular levels. Both in control conditions and during dobutamine, segmental wall motion analysis showed the highest %WTh at the posterolateral area and the lowest %WTh at the septal region (P < 0.05). MRI clearly identifies wall motion dynamics and provides calculations of segmental wall thickening and haemodynamic parameters. Dobutamine is a useful stress agent by virtue of its safety, operator control and its effects which resemble physical exercise.

Comparison of ultrafast dipyridamole magnetic resonance imaging with dipyridamole SestaMIBI SPECT for detection of perfusion abnormalities in patients with one-vessel coronary artery disease: assessment by quantitative model fitting.

The value of ultrafast MRI for detection of myocardial perfusion abnormalities in patients with coronary artery disease (CAD) was assessed in 10 patients with stable angina pectoris and angiographically proven one-vessel CAD using double-level short-axis ultrafast MRI with bolus injection of gadolinium-DTPA and tomographic technetium-99m SestaMIBI imaging (SPECT) during dipyridamole-induced coronary hyperemia. Abnormally perfused regions were assessed with SPECT and MRI in all (100%) patients. Agreement in localization between arteriography and SPECT was 80%; between arteriography and MR, 70%; and between SPECT and MR, 90%. The signal intensity increase after the bolus injection of gadolinium-DTPA using a linear fit, and the slope of gadolinium-DTPA wash-in using double exponential model fitting were significantly different between abnormally and normally perfused regions. These preliminary results demonstrate the potential of dipyridamole ultrafast MR to monitor stress-induced flow maldistribution in patients with single vessel CAD.

Cardiac first-pass and myocardial perfusion in normal subjects assessed by sub-second Gd-DTPA enhanced MR imaging.

To evaluate first pass in the right ventricular (RV) and left ventricular (LV) cavities and myocardial perfusion, subsecond MR imaging was performed in seven normal subjects following intravenous bolus injection of Gd-DTPA. After the baseline scans, sequential ECG-triggered images were obtained every three to four RR intervals. The procedure consisted of an initial presaturation pulse (150 degrees), and the acquisition time for one image was approximately 500 ms with 64 phase-encoding steps. After bolus administration of Gd-DTPA (0.05 mmol/kg body wt), progressively increasing signal intensities were observed in the RV cavity, the LV cavity, and the myocardial wall. Gadolinium DTPA enhanced subsecond MR offers temporal information of the first transit in the cardiac chambers and may provide useful clinical reference data for assessment of myocardial perfusion in patients with coronary artery disease.

Magnetic resonance imaging during dobutamine stress for detection and localization of coronary artery disease. Quantitative wall motion analysis using a modification of the centerline method.

BACKGROUND: Quantitative measurement of wall motion is essential to assess objectively the functional significance of coronary artery disease. We developed a quantitative wall thickening analysis on stress magnetic resonance images. This study was designed to assess the clinical value of magnetic resonance imaging (MRI) during dobutamine stress for detection and localization of myocardial ischemia in patients with suspected coronary artery disease. METHODS AND RESULTS: Thirty-nine consecutive patients with clinically suspected coronary artery disease referred for coronary arteriography and 10 normal volunteers underwent gradient-echo MRI at rest and during peak dobutamine stress (infusion rate, 20 micrograms.kg-1.min-1). MRI was performed in the short-axis plane at four adjacent levels. Display in a cine loop provided a qualitative impression of regional wall motion (cine MRI). A modification of the centerline method was applied for quantitative wall motion analysis by means of calculation of percent systolic wall thickening. Short-axis cine MRI images were analyzed at 100 equally spaced chords constructed perpendicular to a centerline drawn midway between the end-diastolic and end-systolic contours. Dobutamine MRI was considered positive for coronary artery disease if the percent systolic wall thickening of more than four adjacent chords was < 2 SD below the mean values obtained from the normal volunteers. The overall sensitivity of dobutamine MRI for the detection of significant coronary artery disease (diameter stenosis > or = 50%) was 91% (30 of 33), specificity was 80% (5 of 6), and accuracy was 90% (35 of 39). The sensitivity for identifying one-vessel disease was 88% (15 of 17), for two-vessel disease 91% (10 of 11), and for three-vessel disease 100% (5 of 5). The sensitivity for detection of individual coronary artery lesions was 75% for the left anterior descending coronary artery, 87% for the right coronary artery, and 63% for the left circumflex coronary artery. CONCLUSIONS: Dobutamine MRI clearly identifies wall motion abnormalities by quantitative analysis using a modification of the centerline method. Dobutamine MRI is an accurate method for detection and localization of myocardial ischemia and may emerge as a new noninvasive approach for evaluation of patients with known or suspected coronary artery disease.