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Biomedical subjects

R H Marcus

Publications and source records attributed to R H Marcus.

At least 37 records · Page 2Linked to original sources
PubMed1993

Ultrasonic backscatter system for automated on-line endocardial boundary detection: evaluation by ultrafast computed tomography.

OBJECTIVES: The purpose of this study was to evaluate the accuracy of the recently developed echocardiographic on-line endocardial border detection system using ultrafast computed tomography, an independent and proved tomographic imaging modality. BACKGROUND: The automated system for on-line endocardial border detection identifies the blood-tissue interface by acoustic quantification of the ultrasonic backscatter signal. METHODS: Eighteen subjects were screened by conventional echocardiography and acoustic quantification. Ten of these, with high quality echocardiographic images, were also examined by ultrafast computed tomography. Comparable image planes at the midpapillary level were analyzed. Measurements of left ventricular cavity area were compared at end-diastole and end-systole and time course analyses of cavity area during the cardiac cycle were performed. RESULTS: There was good correlation between values for left ventricular end-diastolic area (r = 0.99), end-systolic area (r = 0.93) and fractional area change (r = 0.91) using the two methods. The on-line backscatter system underestimated end-diastolic area (p < 0.001), but the negative bias was small (-1.6 cm2) and the 95% confidence intervals were narrow (-3.6 cm2 to +0.4 cm2). In contrast, the backscatter system overestimated end-systolic area (p < 0.02); the positive bias for this variable was also small (+2.6 cm2) but the confidence intervals were relatively wide (+7.9 to -2.8 cm2). The negative bias of backscatter values for cavity area was fairly constant during diastole and early systole (range -5% to -10%), but during the second half of systole, backscatter values increased progressively relative to computed tomographic values. Real time values for fractional area change measured by the backscatter system were 13% smaller than those determined by ultrafast computed tomography (p < 0.001), with wide confidence intervals (+3% to -30%). Absolute peak rates of area change during systole and diastole were lower by 39% (p < 0.001) and 41% (p < 0.01), respectively, using the on-line ultrasonic backscatter system. Time course analyses revealed the errors to be consistent with cardiac cycle-dependent alterations in gain sensitivity of the ultrasonic backscatter system. CONCLUSIONS: The ultrasonic backscatter system is associated with cyclic cavity area measurement errors that need to be addressed if its early promise for on-line assessment of ventricular function is to be fulfilled. Incorporation of an electrocardiographically triggered time-varying gain control may improve accuracy for on-line analysis of ventricular performance.

Echocardiography↗
PubMed1992

Effects of simultaneous alterations in preload and afterload on measurements of left ventricular contractility in patients with dilated cardiomyopathy: comparisons of ejection phase, isovolumetric and end-systolic force-velocity indexes.

OBJECTIVES: The study was designed to critically evaluate the clinical utility of ejection phase and nonejection phase indexes of contractile state in patients with severe left ventricular dysfunction. BACKGROUND: Ejection phase indexes of left ventricular systolic performance are unable to differentiate contractility changes from alterations in loading conditions. Isovolumetric and end-systolic force-velocity indexes have been proposed as alternative measurements of contractile state that are load independent. METHODS: Seventeen patients with nonischemic dilated cardiomyopathy were studied during cardiac catheterization. High fidelity central aortic and left ventricular pressure measurements were made with simultaneous echocardiographic recordings of chamber minor- and long-axis dimensions and wall thickness. Data were acquired under control conditions, during nitroprusside infusion and with dopamine (6 micrograms/kg per min). RESULTS: Patients were classified into those without (group 1, n = 10) and those with (group 2, n = 7) a decrease in end-diastolic circumferential wall stress in response to dopamine. There were no baseline differences between the groups in functional class, left ventricular chamber geometry or cardiovascular hemodynamics. Ejection phase indexes were variably altered by changes in preload, afterload and heart rate, thereby complicating physiologic interpretation of data. Dopamine increased the commonly used isovolumetric index, maximal rate of rise in left ventricular pressure (dP/dtmax), by 64% for group 1 but by only 16% for group 2 (p less than 0.001), resulting in an underestimation of contractile state change in 41% of patients. In contrast, the left ventricular end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation, which incorporates afterload, ventricular wall mass and heart rate in its analysis, was a sensitive contractility measurement that was preload independent and equally augmented by dopamine for both groups. CONCLUSIONS: Of the left ventricular contractility indexes evaluated, the end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation was the most physiologically appropriate for assessing pharmacologically induced changes in inotropic state that were accompanied by complex alterations in loading conditions in patients with dilated cardiomyopathy.

Cardiac Catheterization↗
PubMed1992

A time-course study of the effects of pentobarbital, fentanyl, and morphine chloralose on myocardial mechanics.

Cardiovascular physiological studies in anesthetized animals may be confounded by the hemodynamic actions of the anesthetic agents themselves. To identify an anesthetic regimen that does not significantly influence cardiovascular physiology, the hemodynamic responses of 28 dogs were studied. Animals were equally divided among groups with 1) no anesthesia (i.e., trained conscious preparation), 2) pentobarbital sodium, 3) fentanyl citrate, and 4) a combination of morphine sulfate and alpha-chloralose. Anesthesia was maintained for 3 h. Data were acquired with the use of ultrasound imaging of the heart in conjunction with invasive pressure measurements. Left ventricular ejection phase indexes and end-systolic force-velocity relations were used to evaluate the effects of each anesthetic agent on overall systolic performance and myocardial contractility. Compared with the conscious animals, pentobarbital profoundly depressed systolic performance (P less than 0.05 vs. control) because of a reduction in myocardial contractility (P less than 0.01) and an increase in left ventricular afterload (end-systolic wall stress, P less than 0.05). Fentanyl increased myocardial contractility (P less than 0.05) but also tended to increase afterload with the net result that overall systolic performance remained unchanged. Morphine-chloralose did not affect overall ventricular systolic performance or its individual determinants. Pentobarbital and fentanyl also caused progressive time-dependent deteriorations in all parameters of systolic function during prolonged anesthesia. In contrast, cardiac function was stable for greater than or equal to 3 h after induction of morphine-chloralose anesthesia. The hemodynamic profile of dogs anesthetized with morphine-chloralose most closely resembled that of the conscious animals. Morphine-chloralose is recommended when prolonged anesthesia is required for studies of cardiovascular physiology.

Anesthetics↗
PubMed1991

Beneficial effect of atrial pacing in severe acute aortic regurgitation and role of M-mode echocardiography in determining the optimal pacing interval.

The effect of atrial pacing on cardiac performance was assessed in 11 men (aged 20 to 64 years) with recent-onset severe aortic regurgitation (AR), all of whom had diastolic closure of the mitral valve on the echocardiogram. Thermodilution cardiac outputs were determined, and aortic, left ventricular and pulmonary arterial wedge pressures recorded. Once baseline recordings were completed, the pacing rate was increased by increments of 10 beats/min (70, 80, 90...) to a maximal rate of 140 beats/min. The optimal pacing interval, obtained from hemodynamic data, was defined as that at which the lowest filling pressure was associated with the highest cardiac index. This was then compared with a pacing interval derived from the R wave of the electrocardiogram to the diastolic mitral closing point on the M-mode echocardiogram. Such an interval would shorten diastole without affecting forward mitral flow. Atrial pacing improved the overall hemodynamic state in all patients; the most favorable hemodynamics were achieved at heart rates between 110 and 130 beats/min (mean: 120 +/- 8). At the optimal rate, left ventricular end-diastolic pressure decreased from 46 +/- 7 to 23 +/- 12 mm Hg (p less than 0.001), and the pulmonary arterial wedge pressure from 28 +/- 8 to 16 +/- 7 mm Hg (p less than 0.001), while the cardiac index increased from 2.34 +/- 0.46 to 2.63 +/- 0.49 liters/min/m2 (p less than 0.01). The mean difference between the optimal pacing interval determined from the hemodynamic data and the interval derived from the echocardiogram was 18 +/- 21 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1991

A physiological approach to drug therapy in dilated cardiomyopathy. Echo-Doppler evaluation of cardiac mechanics, myocardial energetics, and ventriculo-vascular coupling.

Cardiac ultrasound imaging can be used in conjunction with calibrated external pulse recordings to provide detailed information regarding cardiovascular hemodynamics. This review establishes a physiological framework for the echo-Doppler assessment of cardiac mechanics, left ventricular energetics, and ventriculo-systemic vascular coupling in patients with dilated cardiomyopathy. The section on cardiac mechanics concerns the evaluation of overall cardiac performance and its individual determinants. Particular emphasis is placed upon the use of noninvasive methodology to identify the relative contributions of altered loading conditions and intrinsic myocardial contractility to cardiac performance. The noninvasive evaluation of left ventricular energetics is based on the physiological premise that myocardial oxygen consumption is a function of three major determinants, i.e., heart rate, contractility, and the integral of left ventricular systolic load (or wall stress). Following a brief discussion of the vascular properties that determine the relationship between pressure and flow in the systemic circulation, noninvasive methods for determination of systemic vascular resistance and arterial compliance are described. At the end of each section, practical clinical applications of these techniques to the evaluation and management of patients with dilated cardiomyopathy are presented.

Cardiomyopathy, Dilated↗
PubMed1991

Venous air embolism. Diagnosis by spontaneous right-sided contrast echocardiography.

This report describes the definitive diagnosis of venous air-embolism by documentation of spontaneous echo contrast in the right cardiac chambers following removal of a jugular venous catheter in a patient with hepatic failure. This complication was potentiated by the presence of concurrent hepatic coagulopathy which prejudiced effective hemostasis at the central venous puncture site.

Catheterization, Central Venous↗
PubMed1990

Comparison of intravenous amrinone and dobutamine in congestive heart failure due to idiopathic dilated cardiomyopathy.

A prospective randomized study was performed in 46 consecutive patients with refractory congestive heart failure (CHF) due to idiopathic dilated cardiomyopathy to compare the hemodynamic responses to 48-hour infusions of amrinone and dobutamine. Both drugs substantially reduced pulmonary arterial wedge pressure, right atrial pressure and systemic vascular resistance and increased cardiac index. Amrinone caused a greater decrease in right atrial pressure than dobutamine (p less than 0.02) and had a positive chronotropic effect not observed with dobutamine (p less than 0.01). The increase in heart rate produced by amrinone correlated inversely with the changes in right atrial and pulmonary arterial wedge pressures, suggesting a baroreceptor response to reduced preload. Dobutamine produced a larger increase in stroke volume index than amrinone (p less than 0.01). Ninety-one percent of patients receiving amrinone and only 65% receiving dobutamine had reduction of greater than or equal to 30% in pulmonary arterial wedge pressure (p less than 0.05). Cardiac index increased greater than or equal to 30% in similar numbers of patients given amrinone (74%) and dobutamine (65%). Negative fluid balance was recorded in all patients receiving amrinone and in 78% of patients receiving dobutamine (p less than 0.05). Target hemodynamic criteria were achieved in 83% of patients receiving 10 micrograms/kg/min of amrinone. The effective maintenance dose of dobutamine was extremely variable. No clinically important adverse effects were observed with either drug regimen. Both amrinone and dobutamine are effective and safe agents for short-term parenteral therapy of patients with dilated cardiomyopathy in severe CHF that is unresponsive to oral medication.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Mechanisms and management of heart failure in active rheumatic carditis.

Fulminating active rheumatic carditis has been observed for over three decades in this environment with no recent alteration in either the incidence or the pattern of presentation. Heart failure (in this context defined as 'an inadequate circulation at rest together with a raised pulmonary venous pressure, with or without an associated high systemic venous pressure in the absence of haemodynamically significant tricuspid valve disease or pericardial effusion') is prevalent but occurs only when a haemodynamically important left-sided valve lesion supervenes. Regurgitation is the predominant valve lesion and involves principally the mitral valve. Mitral annular dilatation is marked and predisposes to lengthening--or rupture--of chordae tendineae and prolapse of the anterior leaflet. The resultant cardiac work-overload apparently perpetuates or aggravates the rheumatic activity. Heart failure, as defined, whether caused by or associated with active rheumatic carditis, makes surgical management of the valve lesion mandatory as a life-saving measure. Aggressive medical therapy for heart failure, which should include vasodilator drugs and especially angiotensin-converting enzyme inhibitors, provides temporary improvement only. Contrary to ongoing doctrine, treatment with steroid drugs in this context is neither life-saving nor beneficial.

Adolescent↗
PubMed1989

Maternal and fetal sequelae of anticoagulation during pregnancy in patients with mechanical heart valve prostheses.

Previous reports indicate an increased risk of thrombotic and embolic events in patients with mechanical heart valve prostheses during pregnancy. We prospectively followed 50 pregnancies in 49 patients with 62 cardiac prostheses from presentation at the antenatal clinic through the remainder of the pregnancy. Of the 60 mechanical prostheses, 39 were Medtronic-Hall, 7 St. Jude Medical, 7 Starr-Edwards and 7 Björk-Shiley. Forty-three patients were in New York Heart Association functional class I or II and 6 were in functional class III or IV. Forty-five patients were in sinus rhythm and 4 had chronic atrial fibrillation. All patients received warfarin during the first and second trimesters. Forty-one pregnancies proceeded beyond 28 weeks. In 23 of these (group I) warfarin was replaced with heparin at 36 weeks gestation. In the remaining 18 (group II) warfarin was not substituted owing to premature onset of labor. The target prothrombin ratio (international normalized ratio) in patients receiving warfarin was 2.0 to 2.5. The partial thromboplastin time was maintained at 1.5 to 2.5 times the control value in patients receiving heparin. Eleven patients received dipyridamole plus warfarin for the duration of pregnancy. There were no maternal thromboembolic complications or deaths associated with pregnancy. Antepartum hemorrhage occurred in 1 patient at 35 weeks gestation. One patient (group I) experienced peripartum hemorrhage. All patients were hemodynamically stable before delivery, but 2 developed pulmonary edema during labor. The mean fetal birth weight was low (2.54 +/- 0.98 kg). There were 9 abortions (18%), 7 stillbirths (14%), 2 neonatal deaths (4%) and 2 instances of warfarin embryopathy (4%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Functional anatomy of severe mitral regurgitation in active rheumatic carditis.

The mechanism of severe mitral regurgitation (MR) due to active rheumatic carditis is ill defined. This study involved 73 patients, aged 7 to 27 years (mean 13), with severe MR and active rheumatic carditis who were subjected to surgery. Sixty-one were studied retrospectively (group 1) and 12 prospectively (group 2). Active rheumatic carditis was diagnosed according to the modified Jones' criteria, morphologic appearances of the heart at operation and histology of the valve. All patients had preoperative 2-dimensional echocardiographic and intraoperative assessment of the mitral valve apparatus. The presence of mitral valve prolapse--defined as failure of leaflet edge coaptation resulting in systolic displacement of the free edge of the involved leaflet toward the left atrium--was determined in all patients. Mitral anular diameter and maximal systolic chordal length were measured at 2-dimensional echocardiography in group 2 patients and compared to values obtained from matched control subjects. Anular and chordal dimensions in 6 of the group 2 patients were correlated with precise measurements obtained at surgery. Mitral valve prolapse involving the anterior leaflet was detected on echocardiography and confirmed at surgery in 69 patients (94%). Mitral anular dilatation was observed at operation in 70 patients (96%). Maximal anular diameter was significantly greater (p less than 0.0001) than in matched control subjects (37 +/- 4 vs 23 +/- 2 mm). The mean anular dimension measured at surgery (36 +/- 3 mm) was similar to that obtained by echocardiography and individual values using the 2 methods correlated well (r = 0.93). Chordal elongation was observed in 66 patients at operation (90%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Pulsed Doppler and two-dimensional echocardiographic findings in coronary arteriovenous fistula complicated by bacterial endocarditis. A case report.

Coronary arteriovenous fistula (CAVF) may occasionally be complicated by bacterial endocarditis. The actual anatomical site of infection has not been clearly defined. A 13-year-old boy with a CAVF and Streptococcus viridans bacteraemia is described. The origin of the fistulous tract and a vegetation in close proximity to the distal drainage site into the right ventricle was demonstrated by Doppler two-dimensional echocardiography.

Adolescent↗
PubMed1989

Aminophylline loading in asthmatic patients: a protocol trial.

We tested an aminophylline loading-dose protocol in which asthmatic patients presenting to an emergency department were given a half (3 mg/kg) IV loading dose based on total body weight (TBW) if they had taken a short-acting or sustained-release theophylline preparation within 12 or 24 hours, respectively, prior to arrival: otherwise, a full (6 mg/kg) loading dose was administered. Of the 28 patients given a full loading dose, 20 (71.4%) achieved a postload therapeutic level (10 to 20 micrograms/mL), and none developed a toxic level (greater than 20 micrograms/mL). Although 34 (60.7%) of 56 patients given a half loading dose attained a postload therapeutic level, 13 patients (23.2%) entered the toxic range. We were able to predict that loading doses of 7.6 mg/kg and 3.8 mg/kg based on ideal body weight (IBW) would have yielded very similar results. The mean change in theophylline level per mg/kg TBW of administered aminophylline was 2.01 micrograms/mL. When calculated on the basis of IBW, the mean change in theophylline level was 1.58 micrograms/mL. Evaluation of the change in theophylline level resulting from aminophylline loading doses based on either TBW or IBW revealed that each dosing method produced changes in blood level with similar variability that were not independent of obesity, indicating that neither dosing method is superior to the other. Thus, patients who report not having taken a theophylline preparation within the above time limits can be given a full aminophylline loading dose of either 6 mg/kg based on TBW or 7.6 mg/kg based on IBW. Other patients, however, require a preload blood level determination to optimize therapy and avoid toxic levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗