MRI of weight bearing and movement.

Conventional, static magnetic resonance imaging (MRI) is able to provide a vast amount of information regarding the anatomy and pathology of the musculoskeletal system. However, patients, especially those whose pain is position dependent or elucidated by movement, may benefit from more advanced imaging techniques that allow for the acquisition of functional information. This manuscript reviews a variety of advancements in MRI techniques that are used to image the musculoskeletal system dynamically, while in motion or under load. The methodologies, advantages and drawbacks of stress MRI, cine-phase contrast MRI and real-time MRI are discussed as each has helped to advance the field by providing a scientific basis for understanding normal and pathological musculoskeletal anatomy and function. Advancements in dynamic MR imaging will certainly lead to improvements in the understanding, prevention, diagnosis and treatment of musculoskeletal disorders. It is difficult to anticipate that dynamic MRI will replace conventional MRI, however, dynamic MRI may provide additional valuable information to findings of conventional MRI.

Heterogeneity of chondrocyte mitochondria. A study of the Ca2+ concentration and density banding characteristics of normal and rachitic cartilage.

Previous morphological studies of the mineralizing epiphysis suggested that some mitochondria were concerned with Ca2+ accumulation while others were associated with cellular energetics and metabolism. To determine if there was mitochondrial heterogeneity in chondrocytes of the epiphyseal growth plate, mitochondria were isolated from four different regions of the plate and subjected to continuous sucrose gradient centrifugation. Centrifugation of the organelles in a narrow density sucrose gradient (1.5--2.0 M) in the presence of inhibitors of Ca2+ transport (ruthenium red and 5,5'-dithiobis-(2-nitrobenzoic acid)) revealed that considerable heterogeneity existed. In the least calcified zone 20% of the mitochondria formed a low density band of low Ca2+ concentration (309 nmol/mg protein). Organelles isolated from more calcified tissue zones showed a concomitant increase in Ca2+ concentration (up to 5700 nmol/mg protein) as well as an increase in the total percentage of mitochondria sedimenting in 2.0 M sucrose. The banding patterns of mitochondria isolated from rachitic and hypertrophic cartilage were similar. In addition, similarities were also noted in the Ca2+ concentration and the cytochrome oxidase activities of mitochondria of these tissues. During recovery from the rachitic condition, there was a change in the density centrifugation characteristics of this tissue and a substantial increase was noted in the proportion of mitochondria sedimenting in 2.0 M sucrose. The Ca2+ concentration of mitochondria of this rapidly calcifying tissue suggested that the critical Ca2+ concentration necessary for initiation of the calcification mechanism was 4 mumol/mg protein.

Distribution of left ventricular hypertrophy in hypertrophic cardiomyopathy: a two-dimensional echocardiographic study.

The distribution of left ventricular hypertrophy was assessed by M-mode and two-dimensional echocardiography in 89 patients with hypertrophic cardiomyopathy. Myocardial thickness was measured in the septum and the free and posterior wall in both the proximal and distal left ventricle. All patients had at least one myocardial region that was hypertrophied. The predominant pattern of hypertrophy was defined as symmetric (31%), asymmetric septal (55%) and distal ventricular (14%). The spectrum of wall thickness measurements between patients with symmetric hypertrophy was wide (1.5 to 4.5 cm) and was not related to age. In patients with asymmetric septal hypertrophy, the distribution of hypertrophy conformed to previously described patterns; hypertrophy was localized to the anterior septum (14%) or the anterior and posterior septum (35%) or involved both the septum and the left ventricular free wall (51%). The patients with distal ventricular hypertrophy had marked papillary muscle thickening, and only 1 of 12 patients could be correctly diagnosed using M-mode echocardiography. The proportion of patients with symmetric and distal ventricular hypertrophy was greater than that reported when patients are selected on the basis of M-mode diagnostic criteria. This reflects the limitations of the M-mode technique in the assessment of left ventricular hypertrophy and suggests that the recognition and understanding of hypertrophic cardiomyopathy have been biased by patients with asymmetric septal hypertrophy who previously were most readily identified.

Coronary flow reserve improves after aortic valve replacement for aortic stenosis: an adenosine transthoracic echocardiography study.

OBJECTIVES: The goal of this study was to assess coronary flow reserve (CFR) before and after aortic valve replacement (AVR). BACKGROUND: Coronary flow reserve is impaired under conditions of left ventricular (LV) hypertrophy. It is not known whether CFR improves with regression of LV hypertrophy in humans. METHODS: We investigated 35 patients with pure aortic stenosis, LV hypertrophy and normal coronary arteriograms. Patients underwent adenosine transthoracic echocardiography on two occasions--immediately before AVR and six months postoperatively. Left ventricular mass, distal left anterior descending coronary artery (LAD) diameter, flow and CFR were assessed on each occasion. RESULTS: Distal LAD diameter was successfully imaged in 30 patients (86%), and blood flow was successfully imaged in 27 (77%). Paired data were subsequently available in 24 patients, of whom 14 were men, mean age 68.1+/-12.5 years, body mass index 24.5+/-2.0 kg/m2, aortic valve gradient 93+/-32 mm Hg. Pre- to post-AVR a significant decrease was seen in LV mass (271+/-38 vs. 236+/-32g, p<0.01) and LV mass index (154+/-21 vs. 134+/-21 g/m2, p< 0.01). Distal LAD diameter fell from 2.27+/-0.37 to 2.23+/-0.35 mm, p = 0.08). Pre- to post-AVR there was no significant change in resting parameters of peak diastolic velocity (0.43+/-0.16 vs. 0.41+/-0.11 m/s), distal LAD flow 23.3+/-10.1 vs. 20.9+/-5.2 ml/min or distal LAD flow scaled for LV mass (8.7+/-3.8 vs. 9.0+/-2.5 ml/min/100 g LV mass), but there was significant increase in hyperemic peak diastolic velocity (0.71+/-0.26 vs. 1.08+/-0.24 m/s; p<0.01), distal LAD flow (37.8+/-11.3 vs. 53.5+/-16.1 ml/min; p<0.01) and distal LAD flow scaled for LV mass (14.3+/-5.0 vs. 23.3+/-8.5 ml/min/100 g LV mass; p<0.01). Coronary flow reserve, therefore, increased from 1.76+/-0.5 to 2.61+/-0.7. CONCLUSIONS: Coronary flow reserve increases after AVR for aortic stenosis. This increase occurs in tandem with regression of LV hypertrophy.

Measurement of isovolumic relaxation: comparison of echocardiographic mitral valve opening and Doppler mitral valve flow.

The relation between mitral valve opening and transmitral blood flow was investigated by M-mode echocardiography and Doppler ultrasound in 50 normal subjects to allow the measurement of the timing of the end of isovolumic relaxation. Standard parasternal M-mode echocardiograms of the mitral valve to show the onset of cusp separation were recorded with a simultaneous electrocardiogram and phonocardiogram. Pulse wave Doppler ultrasound using both amplitude and spectral analysis was recorded with a transducer at the apex, and the initial diastolic blood flow towards the transducer was taken as the onset of flow. For each subject five cardiac cycles of similar length were measured using the three methods. Isovolumic relaxation could be measured with a high degree of reliability (retest reliability coefficient greater than 0.94). The echocardiographic measurement of isovolumic relaxation ranged from 52 to 82 ms (mean(SD) 67(9) ms). Isovolumic relaxation measured by Doppler was 52-83 ms (mean(SD) 67(9) ms) using amplitude analysis and 54-89 ms (mean(SD) 72(11) ms) using spectral analysis. There was a strong correlation between the echocardiographic isovolumic relaxation and measurements made using spectral analysis (r = 0.93, slope 0.97) and amplitude analysis (r = 0.97, slope 0.98). Therefore in normal subjects the end of isovolumic relaxation can be reliably measured by echocardiographic and Doppler methods, and whereas the amplitude signal is coincidental with that measured by echocardiography that measured by spectral analysis is delayed by approximately 5 ms.

A comparison of the effects of intermittent and continuous nasogastric feeding on the oxygen consumption and nitrogen balance of patients after major head and neck surgery.

Ten patients were fed by nasogastric tube for 5 days after major surgery of the head and neck. Five were fed by continuous infusion 24 h/day using an enteral nutrition pump and five were fed comparable quantities by 2-h bolus administration between 0600 and 2200 h. Those fed by bolus had lower resting oxygen consumption on the 4th and 5th postoperative days and better cumulative nitrogen balance over the 5 days than the continuously fed group. It appears that metabolically it may be better to use an intermittent feeding regimen than a continuous one when feeding patients postoperatively via a nasogastric tube.

Transthoracic high-frequency two-dimensional echocardiography, Doppler and color flow mapping to determine anatomy and blood flow patterns in the distal left anterior descending coronary artery.

Combined high-frequency transthoracic ultrasound, pulsed Doppler and color flow mapping were used to image and assess blood flow velocity in the distal left anterior descending artery (LAD) in 56 consecutive patients. All patients subsequently underwent coronary angiography. The LAD was imaged in 19 patients (34%), and the diameter was measured in 12 with high-quality images (mean diameter 1.8 mm +/- 0.08). In 1 patient, the penetrating branches of the LAD were imaged. The distal LAD appeared normal by ultrasound in 18 patients, and a significant stenosis was detected in 1; angiography confirmed the ultrasound findings. There were no false negative results. Characteristic biphasic flow with higher velocities in diastole were noted in all 19 patients. Color flow mapping demonstrated normal laminar flow, except in the patient with a distal stenosis. Pulsed Doppler confirmed an increased velocity distal to the stenosis in this patient. This study is the first transthoracic evaluation of the hemodynamic effects of a coronary artery stenosis, and the first in vivo description of blood flow disturbance at a distal coronary stenosis in humans. The clinical use of this technique is limited, because only the distal portion of the LAD is visualized. However, it may provide a noninvasive means of assessing distal LAD diameter and blood flow, and changes in these parameters under a variety of physiologic, pharmacologic and interventional stimuli.

Analysis of phasic flow velocity dynamics in the left anterior descending coronary artery before and after angioplasty using transthoracic echocardiography in patients with stable angina pectoris.

High-frequency transthoracic Doppler echocardiography was used to determine the effects of significant stenosis on distal coronary blood flow velocity profiles. Before coronary angioplasty there was a reduction in diastolic and systolic flow and diastolic/systolic peak velocity ratio. After successful angioplasty velocity ratios returned to normal.

Transient ST-segment changes associated with mitral valvuloplasty using the Inoue balloon.

We describe unexplained transient inferior ST-segment elevation on the electrocardiogram during Inoue mitral valvuloplasty in 8 patients from a series of 108. Electrocardiographic changes were associated with chest pain in 7 patients, and although the clinical features were suggestive of myocardial ischemia, no cause for this could be found.

Pulmonary capillary wedge pressure in mitral stenosis accurately reflects mean left atrial pressure but overestimates transmitral gradient.

Current opinion varies as to whether pulmonary capillary wedge pressure assessment of transmitral gradient in mitral stenosis is accurate; we therefore compared transmitral gradient in 36 patients awaiting balloon valvuloplasty using both pulmonary capillary wedge pressure and direct left atrial pressure. Mean pulmonary capillary wedge pressure correlated well with mean left atrial pressure (limits of agreement -1.5 to +3.7 mm Hg), but mean diastolic mitral gradient calculated using pulmonary capillary wedge pressure differed significantly from that calculated using left atrial pressure (limits of agreement -1.2 to +9.8 mm Hg): wedge pressure-assessed transmitral gradient is therefore misleading, routinely overestimating stenosis severity.

Radial versus femoral approach for diagnostic coronary angiography in stable angina pectoris.

We compared coronary angiography of the radial artery using 6Fr catheters in 116 patients with that of the femoral artery in 100 case controls. We showed that transradial coronary angiography offers a useful alternative to the femoral route and can be performed without resorting to 5Fr catheters.

Comparison of central venous and inferior vena caval pressures.

Inferior vena caval pressures were measured in 60 patients undergoing cardiac catheterization and compared with central venous pressure from within the right atrium. Mean pressures within the abdominal inferior vena cava were essentially the same as mean right atrial pressure, suggesting that the inferior vena cava provides a useful safe alternative for measuring central venous pressure.

Comparison of radial versus brachial approaches for diagnostic coronary angiography when the femoral approach is contraindicated.

One hundred patients with contraindications to the femoral approach were randomized to undergo diagnostic coronary angiography via percutaneous radial puncture or brachial artery cutdown. Procedure duration, fluoroscopy time, and total radiation dose were significantly less via the radial route, whereas procedural success, complication rates, and pain scores were comparable; we conclude that the radial technique should be the arm approach of choice for new trainees, although there will be occasions when radial access fails and a brachial approach is required.

Hemodynamic evaluation of the Monostrut and spherical disc Björk-Shiley aortic valve prosthesis with Doppler echocardiography.

A Doppler echocardiographic study was performed to assess whether the Monostrut model of the Björk-Shiley valve (Shiley, Inc., Irvine, Calif.) had an improved hemodynamic performance in comparison with the spherical disc model in the aortic position. Twenty retrospectively randomly selected patients were studied, 10 with each valve type. Within each valve type two sizes of valve were studied, 21 and 23 mm. The two groups were comparable with respect to age, postoperative time, fractional shortening, New York Heart Association functional class preoperatively, and body surface area. Pulsed and continuous wave Doppler measurements were recorded at rest. Continuous wave Doppler recordings were performed every 2 minutes after exercise with supine bicycle ergometry until 10 minutes after exercise. Peak and mean gradients across the aortic valve prostheses were estimated. Both groups achieved a significant and comparable rise in heart rate with exercise. The mean gradients +/- standard error of the mean at rest and 2 minutes after exercise were 19.7 +/- 1.9 mm Hg and 30.9 +/- 2.2 mm Hg, respectively in the spherical disc group compared with 14.9 +/- 1.1 mm Hg and 23.6 +/- 1.7 mm Hg in the Monostrut group (p < 0.05 and p < 0.025, respectively). Peak transvalvular gradient at rest was 30.7 +/- 2.7 mm Hg in the spherical group compared with 23.9 +/- 1.9 mm Hg in the Monostrut group (p < 0.05). We conclude that the Monostrut Björk-Shiley valve prosthesis has better hemodynamic performance than the spherical disc model in the aortic position.

Conservative operation for infective endocarditis of the mitral valve.

BACKGROUND: Subvalvular preservation is necessary to maintain left ventricular function, but accidental retention of infected tissue could cause postoperative endocarditis. METHODS: We examined 71 consecutive patients who underwent operation for mitral endocarditis. Endocarditis was uncontrolled and active in 24 patients, partially treated (unfinished antibiotic course) in 17, and healed in 30. RESULTS: Valves were repaired in 17% versus 59% versus 63% and replaced with subvalvular preservation in 25% versus 6% versus 3% of the uncontrolled active, partially treated, and healed groups, respectively. Thirty-day mortality was 29% versus 0% versus 3.3% (p=0.003), total mortality was 46% versus 18% versus 17% (p=0.035), and complications-related mortality was 38% versus 11% versus 13% (p=0.054), respectively. There was a trend toward lower complications-related mortality with subvalvular preservation than without. Postoperative endocarditis occurred in 3 of 30 patients without and 1 of 41 patients with subvalvular preservation. CONCLUSIONS: Postoperative mortality in uncontrolled active mitral endocarditis remains high, but results are good with partially treated or healed endocarditis. Subvalvular preservation improves outcome, does not increase postoperative endocarditis rates, and should be performed whenever feasible.

Midterm results of mitral valve repair with the Sculptor annuloplasty ring.

BACKGROUND: The partly flexible Sculptor ring is more physiologic than the rigid Carpentier-Edwards ring and may improve outcome. METHODS: We studied 221 consecutive patients who underwent mitral valve repair for mitral regurgitation. The Sculptor ring was randomly implanted in 30 patients (Sculptor ring group) and the Carpentier-Edwards ring in 36 patients (Carpentier-Edwards ring control group) from 1993 to 1994. Before 1993, 155 patients received the Carpentier-Edwards ring (Carpentier-Edwards ring historical group). Baseline group characteristics were similar. RESULTS: Thirty-day mortality in the Sculptor ring, Carpentier-Edwards ring control, and Carpentier-Edwards ring historical groups was 0.0% versus 2.8% versus 3.2% (p = 0.61), respectively. At 18 months, survival was 86% +/- 6% versus 88% +/- 7% versus 90% +/- 3% (p = 0.89), and freedom from complications was 100% +/- 0% versus 100% +/- 0% versus 98% +/- 1% (p = 0.51) for endocarditis, 90% +/- 6% versus 94% +/- 4% versus 96% +/- 2% (p = 0.47) for severe mitral regurgitation, 93% +/- 5% versus 91% +/- 5% versus 92% +/- 2% (p = 0.91) for thromboembolism, and 77% +/- 8% versus 80% +/- 7% versus 82% +/- 3% (p = 0.49) for myocardial failure, respectively. CONCLUSIONS: The Sculptor ring is a safe alternative to the prosthetic annuloplasty rings in current use. The benefits of its physiologic design are either clinically insignificant or undetectable with a small sample size.

Changing from intensive anticoagulation to treatment with aspirin alone for coronary stents: the experience of one centre in the United Kingdom.

OBJECTIVE: To investigate whether an elective change in the anticoagulation protocol for patients with coronary stents affected clinical outcomes and length of hospital stay. DESIGN: Retrospective observational study of a consecutive series of patients treated with coronary stents over an 18 month period from April 1994 to October 1995. BACKGROUND: Intensive anticoagulation regimens are used in many UK centres to reduce the risk of coronary stent thrombosis. Recent data have called into question the necessity for full anticoagulation and favourable results have been reported with antiplatelet agents alone. The results from a tertiary referral centre were investigated during a period where an elective change in policy was made: an initial 70 patients were treated intensively with intravenous heparin and with warfarin and aspirin; subsequently 94 were treated with aspirin and deployment of a high pressure balloon only. METHODS: Review of case notes, angiograms, and a database of intervention procedures and telephone interview. Classic epidemiological techniques, as well as linear regression and logistic regression, were used to model the outcomes of major procedural complications and length of hospital stay. PATIENTS: 164 patients treated with 196 coronary stents. RESULTS: There were 22 (13.4%) major complications (coronary bypass grafting 11, subacute thrombosis 6, tamponade 2, myocardial infarction 1, death 2). With logistic regression, the risk of major complication was shown not to be affected by anticoagulation (relative risk (RR) 1.03; P = 0.97). Significant determinants of risk included acute vessel closure as an indication for stenting (RR = 80.6; P < 0.001) and sex (male: female RR = 0.19; P = 0.02). The median length of stay (LOS) was 5 days (1-45). Use of a linear regression model showed that anticoagulation added 4.5 days and a major complication added a further 4.5 days to a baseline length of stay of 3.2 days (R2 = 0.32; P < 0.001). CONCLUSION: This is a report of coronary stenting as part of usual clinical practice in one British tertiary referral centre. In this experience, treatment with aspirin alone is probably as safe as intensive anticoagulation, and has the benefit of reducing length of stay by more than 50% to 3.2 days in an uncomplicated case.

Transthoracic Doppler echocardiographic analysis of phasic coronary blood flow velocity in hypertrophic cardiomyopathy.

OBJECTIVE: To use transthoracic Doppler echocardiography to assess coronary blood flow non-invasively in patients with hypertrophic cardiomyopathy. DESIGN: High frequency transthoracic Doppler echocardiography was used to assess resting phasic coronary velocity patterns in patients with hypertrophic cardiomyopathy and to define the relation between coronary flow patterns and clinical, echocardiographic, and haemodynamic manifestations of this condition. SETTING: A tertiary referral cardiothoracic centre. METHODS: Fifteen patients (10 men and five women, mean (SD) age 49 (10.3) years) with asymmetric hypertrophic cardiomyopathy underwent high frequency (5 MHz) transthoracic Doppler echocardiographic assessment of the left anterior descending coronary artery. In addition, standard two dimensional echocardiography was performed. The results were compared with 16 normal participants (nine men and seven women, mean age 61.2 (10.7) years) who had no evidence of cardiac disease. RESULTS: Biphasic diastolic predominant coronary artery blood velocity profiles were obtained in all patients and controls. Systolic peak blood velocity and velocity time integral were significantly reduced in the hypertrophic cardiomyopathy group compared with controls (11.3 (15.8) cm/s and 1.09 (1.78) cm v 20.5 (13.1) cm/s and 4.23 (2.80) cm, respectively, P < 0.05). A reversed pattern of systolic blood flow velocity was found in three patients with severe anterior wall and septal hypertrophy. During diastole there was prolongation of the diastolic acceleration (203 (53) ms v 110 (60) ms in controls, P < 0.05) and deceleration times (487 (200) ms v 210 (90) ms in controls, P < 0.05). There was no significant difference between those with and without symptoms or a left ventricular outflow tract gradient. CONCLUSIONS: Patients with hypertrophic cardiomyopathy have abnormal systolic and diastolic coronary flow profiles at rest when measured by transthoracic echocardiography.

Ventricular pacemaker upgrade: experience, complications and recommendations.

OBJECTIVE: To assess outcomes of pacemaker upgrade from single chamber ventricular to dual chamber. DESIGN: Retrospective analysis of patients undergoing the procedure. SETTING: Specialist cardiothoracic unit. PATIENTS: 44 patients (15 female, 29 male), mean (SD) age at upgrade 68.2 (12.9) years. INTERVENTIONS: Upgrade of single chamber ventricular to dual chamber pacemaker. MAIN OUTCOME MEASURES: Procedure duration and complications. RESULTS: Principal indications for upgrade were pacemaker syndrome (17), "opportunistic"--that is, at elective generator replacement (8), heart failure (7), non-specific breathlessness/fatigue (7), and neurally mediated syncope (3). Mean (SD) upgrade procedure duration (82.9 (32.6) minutes) significantly exceeded mean VVI implantation duration (42.9 (13.3) minutes) and mean DDD implantation duration (56.6 (22.7) minutes) (both p < 0.01). Complications included pneumothorax (1), ventricular arrhythmia requiring cardioversion (2), protracted procedure (10), atrial lead repositioning within six weeks (8), haematoma evacuation (1), superficial infection (1), and admission to hospital with chest pain (1); 20 patients (45%) suffered one or more complications including four of the eight who underwent opportunistic upgrade. CONCLUSIONS: Pacemaker upgrade takes longer and has a higher complication rate than either single or dual chamber pacemaker implantation. This suggests that the procedure should be performed by an experienced operator, and should be undertaken only if a firm indication exists. Patients with atrial activity should not be offered single chamber ventricular systems in the belief that the unit can be upgraded later if necessary at minimal risk.

Late complications following permanent pacemaker implantation or elective unit replacement.

OBJECTIVE: To determine the rate of late complications following first implantation or elective unit replacement of a permanent pacemaker system. DESIGN: Analysis of pacemaker data and complications prospectively acquired on a computerised database. Complications were studied over an 11 year period from January 1984 to December 1994. SETTING: Tertiary referral cardiothoracic centre. PATIENTS: Records of 2621 patients were analysed retrospectively. MAIN OUTCOME MEASURES: Complications requiring repeat procedures occurring more than six weeks after pacemaker implantation or elective unit replacement. RESULTS: The overall rate of late complications was significantly lower after first implantation of a permanent pacemaker (34 cases, complication rate 1.4%, 95% confidence interval 0.9% to 1.9%) than after elective unit replacement (16 cases, complication rate 6.5% (3.3% to 9.7%). There were 20 cases of erosion, 18 infections, five electrode problems, and seven miscellaneous problems. Complications were more common with inexperienced operators (18.9% (6.0% to 31.8%)) than with experienced operators (0.9% (0.3% to 1.5%). CONCLUSIONS: The incidence of late complications following pacemaker implantation is low and compares favourably with early complication rates. The majority are caused by erosion and infection. Patients who have undergone elective unit replacement are at particular risk.