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Mark Doyle

Publications and source records attributed to Mark Doyle.

16 recordsLinked to original sources
PubMed2005

Physiologic compensation is supranormal in compensated aortic stenosis: does it return to normal after aortic valve replacement or is it blunted by coexistent coronary artery disease? An intramyocardial magnetic resonance imaging study.

BACKGROUND: In compensated aortic stenosis (AS), cardiac performance measured at the ventricular chamber is typically supranormal, whereas measurements at the myocardium are often impaired. We investigated intramyocardial mechanics after aortic valve replacement (AVR) and the effects relative to the presence or absence of coronary artery disease (CAD+ or CAD-), respectively. METHODS AND RESULTS: Twenty-nine patients (46 to 91 years, 10 female) with late but not decompensated AS underwent cardiovascular MRI before AVR (PRE), with follow-up at 6+/-1 (EARLY) and 13+/-2 months (LATE) to determine radiofrequency tissue-tagged left ventricle (LV) transmural circumferential strain, torsion, structure, and function. At the myocardial level, concentric LV hypertrophy regressed 18% LATE (93+/-22 versus 77+/-17 g/m2; P<0.0001), whereas at the LV chamber level, ejection fraction was supranormal PRE, 67+/-6% (ranging as high as 83%) decreasing to 59+/-6% LATE (P<0.05), representing not dysfunction but a return to more normal LV physiology. Between the CAD+ and CAD- groups, intramyocardial strain was similar PRE (19+/-10 versus 20+/-10) but different LATE, with dichotomization specifically related to the CAD state. In the CAD- patients, strain increased to 23+/-10% (+20%), whereas in CAD+ patients it fell to 16+/-11% (-26%), representing a nearly 50% decline after AVR (P<0.05). This was particularly evident at the apex, where CAD- strain LATE improved 17%, whereas for CAD+ it decreased 2.5-fold. Transmural strain and myocardial torsion followed a similar pattern, critically dependent on CAD. AVR impacted LV geometry and mitral apparatus, resulting in decreased mitral regurgitation, negating the double valve consideration. CONCLUSIONS: In AS patients after AVR, reverse remodeling of the supranormal systolic function parallels improvement in cardiovascular MRI-derived regression of LV hypertrophy and LV intramyocardial strain. However, discordant effects are evident after AVR, driven by CAD status, suggesting that the typical AVR benefits are experienced disproportionately by those without CAD and not by those obliged to undergo concomitant coronary artery bypass grafting/AVR.

Adaptation, Physiological↗
PubMed2005

Extension of rapid phase-contrast magnetic resonance imaging using BRISK in multidirectional flow.

We developed BRISK-CON-VPS, a rapid phase-contrast cine approach that is a hybrid of the BRISK-VPS (Block Regional Interpolation Scheme for k-space) and conventional (CONV-VPS) scanning employing k-space views per segment (VPS). BRISK-CON-VPS allows data acquisition approximately four times faster than CONV-VPS imaging and has the advantage compared to BRISK-VPS that it can potentially be incorporated into real-time applications. In BRISK-CON-VPS contiguous regions of k-space are sampled using a views per segment factor that is varied as a function of distance from the k-space center. Computational fluid dynamics (CFD) data were used to simulate CONV-VPS, BRISK-VPS, and BRISK-CON-VPS. BRISK-CON-VPS was simulated by incrementing the VPS progressively with increasing distance from the k-space origin while BRISK-VPS was simulated using a uniform VPS applied to the sparse sampling scheme. Simulations showed that up to a base VPS of 5, both BRISK-CON-VPS and BRISK-VPS retained excellent axial-velocity accuracy. Secondary in-plane velocity flow fields were well represented with BRISK-CON-VPS and BRISK-VPS up to a base VPS of 3. CONV-VPS, BRISK-CON-VPS, and BRISK-VPS were applied in vivo and shown to provide comparable quantitative flow data. BRISK-CON-VPS accomplishes breath-hold acquisitions as efficiently as BRISK-VPS, but without requiring data interpolation or under-sampling k-space.

Animals↗
PubMed2005

Magnetic resonance imaging in the assessment of coronary artery disease.

Magnetic resonance imaging (MRI) is gaining importance in cardiology as the noninvasive test of choice for patients with a multitude of cardiovascular problems. Recently, cardiovascular MRI has emerged as an important noninvasive diagnostic modality in the assessment of coronary artery disease. Because of its superior spatial resolution, integration of qualitative and quantitative methodology, and excellent reproducibility, MRI has advantages over conventional noninvasive modalities currently used in the evaluation of coronary artery disease. This article reviews the rapidly expanding recent literature that has now established cardiovascular MRI as an ideal choice in the evaluation of myocardial ischemia (including dobutamine cine MRI and vasodilator perfusion MRI techniques). We further discuss the role of delayed contrast-enhanced MRI and low-dose dobutamine cine MRI for evaluation of myocardial viability. Comparisons with more established techniques, such as dobutamine stress echocardiography, single-photon emission computed tomography perfusion imaging, and positron emission tomography, are reviewed.

Coronary Artery Disease↗
PubMed2005

Exercise treadmill testing using a modified exercise protocol in women with suspected myocardial ischemia: findings from the National Heart, Lung and Blood Institute-sponsored Women's Ischemia Syndrome Evaluation (WISE).

BACKGROUND: Exercise testing, a major diagnostic modality in individuals with suspected coronary artery disease (CAD), has in general demonstrated less overall diagnostic accuracy in women compared to men. As part of the WISE, a modified protocol was examined with the intention of improving reliability of exercise testing. METHODS: Criteria for entry in the WISE study include clinically indicated coronary angiography. Exercise testing was performed using a protocol modified to be more appropriate for women. The study population consisted of 96 women, mean age of 55.8 y (range 34-77), who completed exercise treadmill test (ETT). Most (78%) were postmenopausal; 96% had >or =2 risk factors for CAD. RESULTS: By core laboratory angiography, 29/96 women had stenosis > or =50% in at least one coronary artery. Of these 29 women, 9 had abnormal ETT, yielding overall sensitivity of 31%. The remaining 20 women had normal (12/29, 41%) or nondiagnostic (8/29, 28%) studies. Among the 67 women with minimal or no coronary stenosis, 35 had no ischemic ST-segment changes during ETT, yielding overall specificity of 52%. Analysis with exclusion of women with nondiagnostic studies yielded sensitivity and specificity of 43% and 66%, respectively. The presence of coronary artery stenosis and inability to perform ETT, but not results of testing, predicted the outcomes of myocardial infarction, heart failure, and death. CONCLUSIONS: Exercise treadmill test appears to be of limited diagnostic value in women with suspected myocardial ischemia referred for coronary angiography. Sensitivity and specificity remain poor even with modified exercise protocol and core laboratory angiographic analysis. These findings merit consideration in view of current guidelines that recommend exercise testing in women with suspected CAD.

Adult↗
PubMed2005

Coronary artery fistula; non-invasive diagnosis by cardiovascular magnetic resonance imaging.

Coronary arteriovenous fistulas are among rare anomalies of coronary arteries. Role of X-ray angiography is well established in identification and characterization of these anomalies, however there accurate course and termination is often not defined. We demonstrate role of routine cardiovascular MRI in non-invasively diagnosing and characterizing the course and termination of these anomalous coronary branches.

Adult↗
PubMed2004

Prognosis in women with myocardial ischemia in the absence of obstructive coronary disease: results from the National Institutes of Health-National Heart, Lung, and Blood Institute-Sponsored Women's Ischemia Syndrome Evaluation (WISE).

BACKGROUND: We previously reported that 20% of women with chest pain but without obstructive coronary artery disease (CAD) had stress-induced reduction in myocardial phosphocreatine-adenosine triphosphate ratio by phosphorus-31 nuclear magnetic resonance spectroscopy (abnormal MRS), consistent with myocardial ischemia. The prognostic implications of these findings are unknown. METHODS AND RESULTS: Women referred for coronary angiography for suspected myocardial ischemia underwent MRS handgrip stress testing and follow-up evaluation. These included (1) n=60 with no CAD/normal MRS, (2) n=14 with no CAD/abnormal MRS, and (3) n=352 a reference group with CAD. Cardiovascular events were death, myocardial infarction, heart failure, stroke, other vascular events, and hospitalization for unstable angina. Cumulative freedom from events at 3 years was 87%, 57%, and 52% for women with no CAD/normal MRS, no CAD/abnormal MRS, and CAD, respectively (P<0.01). After adjusting for CAD and cardiac risk factors, a phosphocreatine-adenosine triphosphate ratio decrease of 1% increased the risk of a cardiovascular event by 4% (P=0.02). The higher event rate in women with no CAD/abnormal MRS was primarily due to hospitalization for unstable angina, which is associated with repeat catheterization and higher healthcare costs. CONCLUSIONS: Among women without CAD, abnormal MRS consistent with myocardial ischemia predicted cardiovascular outcome, notably higher rates of anginal hospitalization, repeat catheterization, and greater treatment costs. Further evaluation into the underlying pathophysiology and possible treatment options for women with evidence of myocardial ischemia but without CAD is indicated.

Adenosine Triphosphate↗
PubMed2004

Future prospects in magnetic resonance imaging.

Cardiovascular magnetic resonance (CMR) is widely regarded as capable of providing a cornucopia of detailed diagnostic information. However, of that information, very little is truly unique, and can be obtained by a combination of alternate diagnostic modalities. Given this, it is anticipated that in the short term (1-5 years) CMR will find use primarily as a modality to service patients whose diagnosis is inaccessible to established technologies such as ultrasound and radionuclide imaging. Due to the evolving emphasis on finding new and more efficient approaches to disease detection and prevention, as outlined in a policy-setting speech given by the director of the National Institutes of Health, it is anticipated that the scientific and clinical trial communities will adopt CMR at a more rapid pace due to its inherent dimensional accuracy and comprehensive nature. CMR is particularly well suited to participate in the approaching explosion of nanoparticle technologies, as they are applied to diagnostic and therapeutic approaches. In the longer term (5-10 years), as paradigms of disease detection likely expand beyond evaluation of symptoms and risk factors, the comprehensive nature of information provided by CMR will drive the increase of its use as a primary, first-tier, diagnostic modality. In summary, the use of CMR will become increasingly common, and as understanding of disease processes expand, it will emerge as a diagnostic modality that provides an abundance of unique information.

Cardiovascular Diseases↗
PubMed2004

Improving Door-to-Drug time and ST segment resolution in AMI by moving thrombolysis administration to the Emergency Department.

BACKGROUND: We describe a combination of measures to reduce Door-to-Drug (DTD) time and improve the Emergency Department (ED) management of ST elevation MI (STEMI): appointment of a Cardiology Nurse Specialist, application of the American College of Cardiology and the American Heart Association (ACC/AHA) guidelines, changing the site of thrombolysis from the CCU to the ED, the introduction of a single bolus thrombolytic agent. METHODS: The 12-month period before and after the introduction of the measures were retrospectively reviewed. One hundred and sixty patients were discharged from the CCU with the diagnosis of myocardial infarction confirmed by ECG and enzyme criteria. Eighty patients had STEMI and fulfilled criteria for thrombolytic therapy at the time of presentation to hospital. A full data set was available on 35/38 of patients in the 12 months prior to the measures (Year 1), and 39/42 in the 12 months subsequent (Year 2). RESULTS: Median DTD time fell from 80 to 22 min after institution of the measures. Median Pain-to-Drug time also fell from 270 to 140 min. Thrombolytic agent given in the ED rose from 3% in Year 1, to 72% in Year 2. IV beta-blocker administered in the ED rose from 12% to 79%, resulting in median time to receiving IV beta-blocker falling from 63 to 19 min. Elevated ST segments resolved by >/=70% in <2 h in 53% of Year 2 patients, compared with 23% of Year 1 patients. Combined major in-hospital adverse clinical events were reduced from 49% to 15%. CONCLUSION: This combination of measures reduces DTD time, improves speed to delivery of important concomitant medications, and significantly improves the time to ST segment resolution and outcome in STEMI.

Adult↗
PubMed2004

Alternative control volume geometries for measuring regurgitant flow through a valve.

Control-volume (CV) methods applied to magnetic resonance velocity-encoded cine images of the convergent proximal flow field of a regurgitant valve have been shown to measure reverse blood flow volume accurately. Spatial and temporal averaging are known to affect accuracy, but the effects of slice thickness and orientation relative to the flow field have not been systematically studied, nor have CV configurations requiring fewer scans been explored. Further, surface area calculations at the intersection of CV walls are a previously unrecognized source of error. Using a computational fluid dynamics model of steady flow through an orifice, we evaluated five different CV configurations in terms of accuracy, time costs, and clinical potential. CVs incorporating a basal wall were affected by blurring of axial velocity gradients near the orifice, and voxel grid alignment relative to the orifice was the most significant source of inaccuracy. Errors in surface area calculations at plane intersections produced deviations of 7-20%, depending on configuration. A CV formed by slices parallel to the orifice plane was deemed clinically unusable, while a cylindrical CV yielded good accuracy in simulated tests and showed potential for practical implementation based on scan time, ease of view selection, and visualization of the flow field.

Blood Flow Velocity↗
PubMed2003

Future prospects in cardiac magnetic resonance imaging.

To appreciate the impact that key developments will have on the future of cardiovascular magnetic resonance (CMR) imaging, it is instructive to consider its present status. CMR has passed the threshold of being used primarily by innovators, and is now in the early adopter stage. To reach this threshold has taken many years, but its adoption by early majority users is expected to accelerate the growth of CMR. A number of factors govern its natural growth potential, including physician education and credentialing, scanner availability, technology, and reimbursement policies. The intrinsic dimensional accuracy of CMR, coupled with its high level of reproducibility, make it ideal for inclusion in trials, potentially with dramatic reductions in trial duration and the number of subjects required. Clinically, there are a number of applications for which CMR is widely regarded as being the diagnostic test of choice. Software and hardware developments that speed up the basic CMR procedure are being incorporated into scanners, extending the functionality of routine applications such as flow imaging and tag visualization. Exciting areas that are close to routine application include coronary artery imaging, and evaluation of myocardial perfusion and viability status.

Heart Diseases↗
PubMed2003

The impact of myocardial flow reserve on the detection of coronary artery disease by perfusion imaging methods: an NHLBI WISE study.

Myocardial flow reserve (MFR) is not routinely assessed in myocardial perfusion imaging (MPI) studies but has been hypothesized to affect test accuracy when assessing disease severity by coronary vessel lumenography. Magnetic resonance imaging (MRI) is an emerging diagnostic technique that can both perform MPI and assess MFR. We studied women (n = 184) enrolled in the Women's Ischemia Syndrome Evaluation (WISE) study with symptoms suggesting ischemic heart disease. Tests performed were coronary angiography and MPI by both MR and gated radionuclide single photon emission computed tomography (gated-SPECT). The MFR index was calculated using the MR data acquired at baseline and under vasodilation (dipyridamole) conditions. The study was structured with a pilot and an implementation phase. During the pilot phase (n = 46) data were unmasked and an MFR threshold was defined to divide patients into those with an adequate (AMFRI) or inadequate (IMFRI) MFR index. During the implementation phase, the MFR index threshold was prospectively applied to patients (n = 138). In the implementation phase, MPI ischemia detection accuracy compared to severe (> or = 70%) coronary artery diameter narrowing by angiography was higher in the AMFRI vs. the IMFRI group for MRI (86% vs. 70%, p < 0.05) and gated-SPECT (89% vs. 67%, p < 0.01). The IMFRI group (n = 55, 30% of study population) had a higher resting rate-pressure product compared with the AMFRI group (10,599 +/- 2871 vs. 9378 +/- 2447 bpm mm Hg, p < 0.01), consistent with higher resting myocardial flow. When compared with each other, MRI and gated-SPECT MPI showed no difference in accuracy among MFR groups. Myocardial perfusion patterns in the IMFRI group may have resulted in atypical perfusion patterns, which either masked or mimicked epicardial coronary artery disease.

Contrast Media↗
PubMed2002

Effect of contrast agent viscosity and injection flow velocity on bolus injection pressures for peripheral venous injection in first-pass myocardial perfusion studies.

Myocardial perfusion imaging using Gd contrast agents is typically performed with bolus injections of the contrast agent using a power injector to provide for consistent and sufficiently rapid injection rates for all patients. For protocols in which a peripheral venous injection is called for (e.g. antecubital vein) injection catheters of 18 ga are used where vessel geometry permits. In some patients, particularly women with smaller veins, 20 and 22 ga catheters are used. The effect of catheter size and pressure tubing length can result in high injection pressures that occasionally cause leakage or connector failure. The viscosity of the contrast agent also impacts injection pressure. In this study, a simulation of the injection pathway was constructed with time resolved pressures measured at two points in the pathway. Pressure drops were calculated for a typical MR perfusion injection protocol.

Catheterization, Peripheral↗
PubMedDate not supplied

Urinary incontinence in nulliparous women.

Linda Birch and colleagues review the evidence associated with various demographic and behavioural risk factors for the development of urinary incontinence in nulliparous, pre-menopausal women.

Adult↗