Myocardial mechanics in young adult patients with diabetes mellitus: effects of altered load, inotropic state and dynamic exercise

The disease entity "diabetic cardiomyopathy" has been extensively described in young patients with diabetes in the absence of ischemic, hypertensive or valvular heart disease. The most convincing data have been a 30% to 40% incidence of decreased radionuclide angiographic left ventricular ejection fraction response to dynamic exercise. In the current study, the hypothesis was tested that this abnormal ejection fraction response was due to alterations in ventricular loading conditions or cardiac autonomic innervation (extrinsic factors), or both, rather than to abnormalities in intrinsic ventricular systolic fiber function (contractility). Twenty normotensive patients with diabetes (mean age 30 +/- 5 years, mean duration 15 +/- 6 years) and 20 age-matched normal subjects were studied. All patients with diabetes had a normal treadmill exercise tolerance test without evidence of myocardial ischemia. By radionuclide angiography, all normal subjects increased ejection fraction with exercise (62 +/- 4% to 69 +/- 6%; p less than 0.001). In contrast, 11 (55%) of 20 patients with diabetes maintained or increased ejection fraction with exercise (group 1; 62 +/- 4% to 69 +/- 6%; p less than 0.001) and 9 (45%) of 20 showed an exercise-induced decrease (group 2; 73 +/- 4% to 66 +/- 6%; p less than 0.001). No difference in the incidence of microangiopathy, as noted by funduscopic examination, was present between the diabetic groups. Despite the abnormal ejection fraction response to exercise in the group 2 patients with diabetes, all patients with diabetes had a normal response to afterload manipulation, normal baseline ventricular contractility as assessed by load- and heart rate-independent end-systolic indexes and normal contractile reserve as assessed with dobutamine challenge. Autonomic dysfunction did not explain the disparate results between the group 2 patients' radionuclide angiographic data and their load-independent tests of ventricular contractility and reserve. In addition, the high ejection fraction at rest in group 2 patients (73 +/- 4% versus 62 +/- 4% for normal subjects; p less than 0.001) was not related to the abnormal tests of autonomic function. Thus, when left ventricular systolic performance was assessed by load- and rate-independent indexes, there was no evidence for cardiomyopathy in young adult patients with diabetes who have normal blood pressure and no ischemic heart disease.

Parasympathetically modulated antiarrhythmic action of lidocaine in atrial fibrillation

Clinical experience has shown that the antiarrhythmic effect of lidocaine on atrial arrhythmias, and specifically for the conversion of atrial fibrillation to normal sinus rhythm, is minimal. This study summarizes our experience in 30 dogs in which atrial fibrillation was initiated and sustained (greater than or equal to 15 minutes) under increased vagal tone achieved by either alpha-chloralose anesthesia (26 dogs) or pentobarbital sodium anesthesia combined with direct external electrical vagal stimulation (four dogs). Under increased vagal tone (regardless of the procedure), an intravenous bolus of lidocaine (2 to 3 mg/kg) was 100% effective (101 of 101 episodes) in pharmacologically converting atrial fibrillation to normal sinus rhythm. This was associated with marked slowing of intra-atrial electrical activity, as shown by fast Fourier analysis of intra-atrial electrograms. Over a period of 3 to 5 minutes, lidocaine progressively shifted the peak frequency content from 84 +/- 18 mV2/Hz in the 10 to 20 Hz frequency band during the pre-lidocaine phase to 110 +/- 34 mV2/Hz in the 0 to 10 Hz frequency band immediately prior to conversion to normal sinus rhythm. When atropine was administered or electrical vagal stimulation was discontinued, the conversion of atrial fibrillation to normal sinus rhythm followed a similar electrophysiologic pattern. When isoproterenol was infused, it was difficult to induce atrial fibrillation; when the arrhythmia was initiated, it could not be sustained even with concomitant electrical vagal stimulation. Thus in this model of parasympathetically sustained atrial fibrillation, lidocaine was 100% effective in converting atrial fibrillation to normal sinus rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of Doppler indexes of left ventricular diastolic function with simultaneous high fidelity left atrial and ventricular pressures in idiopathic dilated cardiomyopathy

Doppler echocardiographic indexes of ventricular inflow have been used clinically to characterize left ventricular (LV) diastolic function. The reliability of these indexes as markers for intrinsic myocardial diastolic properties has been questioned. Micro-manometer left atrial (LA) and LV pressures as well as transmitral Doppler flow velocity signals and M-mode and 2-dimensional echocardiograms were simultaneously recorded. These unique measurements were acquired in patients with dilated cardiomyopathy under baseline conditions and during infusion of high dose amrinone. The response to amrinone was chosen as a hemodynamic model because this drug has previously been described as having beneficial effects on overall LV systolic and diastolic performance. At peak amrinone effect, LV contractility increased (as assessed using load independent end-systolic indexes) and early diastolic relaxation improved whereas passive chamber stiffness, heart rate and stroke volume were unchanged. There was a significant decrease in LV end-diastolic pressure as well as a parallel downward shift of the entire LV diastolic pressure-dimension relation. These findings, which indicated an improvement in overall LV diastolic properties, probably represent the combination of more rapid early diastolic relaxation in conjunction with a reduction in venous return, the relief of pericardial restraint or the reduction in right ventricular-LV interaction. In contrast, the ratios of Doppler-determined peak transmitral early-to-late flow velocities and early-to-late diastolic flow velocity integrals decreased with amrinone infusion, thereby suggesting a drug-induced decrease in LV diastolic compliance. Thus, in patients with idiopathic dilated cardiomyopathy, administration of amrinone has a complex effect on LV diastolic properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological mechanisms for calcium-induced changes in systemic arterial pressure in stable dialysis patients

The mechanisms by which variations in blood ionized calcium (Ca2+) influence systemic arterial pressures independent of changes in extracellular fluid volume, pH, and electrolytes are unknown. To study this issue, we dialyzed eight stable hemodialysis patients on three separate occasions during 1 week with dialysates differing only in calcium concentration. Ultrafiltration was adjusted to achieve the patient's estimated dry weight. Postdialysis Ca2+ was measured, as were arterial blood gases, electrolytes, magnesium, blood urea nitrogen, creatinine, and hematocrit. Blood pressures and two-dimensional, targeted M-mode echocardiograms were recorded with the patient in the supine position after 15 minutes of rest. Postdialysis, three different levels of Ca2+ were achieved. Other measured biochemical variables and body weight did not differ among the three study periods. Changes in Ca2+ correlated directly with changes in systolic, diastolic, and mean blood pressures, left ventricular stroke volume, and cardiac output. In contrast, heart rate, left ventricular end-diastolic dimension, and total systemic vascular resistance were not altered significantly by changes in Ca2+. Thus, alterations in Ca2+ within the physiological range affect systemic blood pressure primarily through changes in left ventricular output rather than in peripheral vascular tone in stable dialysis patients.

Role of the beta 2 adrenoceptor in mediating positive inotropic activity in the failing heart and its relation to the hemodynamic actions of dopexamine hydrochloride

In patients with severe congestive heart failure, it has been suggested that since myocardial beta 1 adrenoceptors are selectively down-regulated, activation of beta 2 receptors may be a preferable approach to augmenting contractility. Accordingly, dopexamine hydrochloride (1, 2 and 4 micrograms/kg/min) and dopamine (2 and 4 micrograms/kg/min) were administered to 8 patients with dilated cardiomyopathy. Left ventricular (LV) dimensions, thicknesses and pressures were obtained using simultaneous high-fidelity pressure measurements and echocardiographic recordings. LV contractility was assessed using the load-independent relation between LV end-systolic wall stress and rate-corrected velocity of fiber shortening. Cardiac index increased in a dose-related manner with both drugs, and was accompanied by a decline in systemic vascular resistance, a measure of peripheral arteriolar tone. LV end-diastolic pressure was unaltered except for a decrease from 29 +/- 6 to 19 +/- 5 mm Hg (p less than 0.017) at the highest dose of dopexamine hydrochloride. Heart rate was unchanged during the infusion of dopamine but increased significantly with dopexamine hydrochloride. LV end-systolic wall stress, a measure of LV internal load, decreased with both drugs. With dopamine, a dose-dependent positive inotropic effect was observed. Dopexamine hydrochloride, at the 4 micrograms/kg/min infusion dose, exerted a mild positive inotropic effect comparable to that noted with dopamine at 2 micrograms/kg/min. Thus, dopamine and dopexamine hydrochloride improved overall LV performance. With dopamine, a substantial positive inotropic effect occurred in association with a reduction in LV afterload. The increased cardiac index observed with dopexamine hydrochloride was due primarily to peripheral vasodilatation and a positive chronotropic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dopamine on left ventricular afterload and contractile state in heart failure: relation to the activation of beta 1-adrenoceptors and dopamine receptors

Although long-term therapy with oral beta-adrenoceptor agonists in patients with heart failure is generally associated with the development of diminished pharmacologic efficacy, the ingestion of levodopa, which is decarboxylated endogenously to dopamine, is associated with a sustained improvement in cardiac function. The beneficial hemodynamic actions of dopamine in patients with heart failure have been attributed to a positive inotropic effect that is mediated through activation of beta 1-adrenoceptors. However, a reduction in left ventricular afterload resulting from the activation of dopamine receptors may also lead to an improvement in the performance of the failing heart. To ascertain the relative importance of the positive inotropic and afterload-reducing effects of dopamine in patients with heart failure, dopamine (2, 4, 6 micrograms/kg per min), dobutamine (2, 6, 10 micrograms/kg per min) and nitroprusside (0.125 to 2.0 micrograms/kg per min) were administered to 13 patients with dilated cardiomyopathy while monitoring left ventricular wall thickness and dimensions by echocardiography and left ventricular and aortic pressures with a micromanometer-tipped catheter. Altering left ventricular afterload, quantified as end-systolic circumferential wall stress, with nitroprusside allowed generation of the left ventricular end-systolic circumferential wall stress-velocity of fiber shortening relation that represented the baseline contractile state of the myocardium. Left ventricular velocity of fiber shortening was elevated during the administration of dobutamine and dopamine when compared with measurements obtained with nitroprusside at the same left ventricular end-systolic circumferential wall stress. Furthermore, left ventricular end-systolic wall stress decreased with dopamine but not with dobutamine. Thus, the beta 1-adrenoceptor activity of dopamine and dobutamine augmented the contractile state of the myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical utility of exercise, pacing, and pharmacologic stress testing for the noninvasive determination of myocardial contractility and reserve

The ability of the left ventricle to modulate its performance is an important and integral component in the cardiovascular system's adaptive response to increased workload. Abnormalities in ventricular contractility can blunt this response and thus significantly limit the patient's functional capacity. The accurate determination and quantitation of cardiac contractility and reserve is a difficult task in the symmetrically contracting ventricle and more so when regional contraction abnormalities are present. Moreover, derangements in other physiologic variables, such as ventricular loading conditions, heart rate, systemic vascular tone, cardiac autonomic function, and pulmonary gas exchange, can diminish cardiopulmonary reserve. This report relates the determinants of myocardial oxygen demand and efficiency to the currently available forms of exercise, pacing, and pharmacologic stress testing. Within this framework, commonly used as well as newer approaches to the noninvasive assessment of stress-induced changes in left ventricular performance and contractility are addressed. In addition, several examples are presented in which noninvasive techniques for assessing intracardiac structures, pressures, and flows (eg, echo/Doppler, radionuclide angiography, rapid acquisition computed tomography, and magnetic resonance imaging) are combined with various cardiovascular stress tests to achieve more reliable measures of myocardial contractility and reserve.

Role of adrenoceptors and dopamine receptors in modulating left ventricular diastolic function

Although both dopamine and dobutamine are potent positive inotropic agents, multiple studies indicate that dopamine may produce a rise in left ventricular (LV) filling pressure, while dobutamine often has the opposite effect. To ascertain the pharmacological and hemodynamic mechanisms responsible for the elevation in LV filling pressure observed with dopamine, we administered incremental infusions (2, 4, and 6 micrograms/kg/min) of dopamine to 18 open-chest, anesthetized dogs in the presence and absence of rauwolscine (selective alpha 2-adrenoceptor antagonist) (n = 7), terazosin (selective alpha 1-antagonist) (n = 6), and domperidone (selective dopamine2 antagonist) (n = 5), while measuring pressures in the LV and left atrium and changes in dimension in the LV short-axis (with ultrasonic piezo crystals). Dobutamine (2, 4, and 6 micrograms/kg/min) was infused in five additional dogs before and after administration of rauwolscine. The time constant of isovolumic pressure decay, peak lengthening rate (mm/sec), LV end-diastolic pressure, and diastolic pressure-dimension relation were computed. A significant elevation in LV end-diastolic pressure and a parallel increase in LV end-diastolic chamber size was observed with dopamine, while a decline in LV end-diastolic pressure occurred with dobutamine. Yet both dopamine and dobutamine caused a dose-related acceleration of pressure decay and augmentation of peak lengthening rate. Furthermore, heart rate declined during the administration of dopamine but rose with dobutamine. In the presence of either rauwolscine or terazosin, dopamine infusion resulted in a positive chronotropic effect and dose-dependent reductions in LV end-diastolic pressure and end-diastolic chamber dimension; arterial pressure fell only after terazosin administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular contractility varies directly with blood ionized calcium

STUDY OBJECTIVE

To determine the effect of variations in blood ionized calcium (Ca2+) on myocardial contractility independent of changes in loading conditions and other biochemical variables.

DESIGN

Hemodialysis done in a randomized, double-blind manner with dialysates differing in calcium concentration only. Left ventricular contractility was assessed using the load- and heart rate-independent relationship between end-systolic wall stress (sigma es) and rate-corrected velocity of fiber shortening (Vcfc).

SETTING

In-hospital dialysis unit and echocardiography laboratory of a university medical center.

PATIENTS

Seven patients with stable, chronic renal failure maintained on regular hemodialysis.

INTERVENTIONS

Each patient was hemodialyzed three times within 1 week with dialysates differing in calcium concentration only. Ultrafiltration was adjusted to achieve the same postdialysis weight. Immediately after dialysis, two-dimensionally targeted M-mode echocardiographic and calibrated carotid pulse tracings were recorded over a wide range of left ventricular end-systolic wall stress values (a measure of left ventricular afterload) generated by either methoxamine or nitroprusside.

MEASUREMENTS AND MAIN RESULTS

After dialysis, three statistically distinct levels of Ca2+ were achieved. When Ca2+ was 1.34 +/- 0.03 mmol/L, Vcfc, calculated at a common level of afterload (sigma es = 50 g/cm2), was 1.01 +/- 0.05 cir/sec; at low Ca2+ (1.02 +/- 0.02 mmol/L), Vcfc fell to 0.89 +/- 0.04 cir/sec (P less than 0.001 compared with medium); at high Ca2+ (1.68 +/- 0.07 mmol/L) Vcfc rose to 1.10 +/- 0.03 circ/sec (P less than 0.001 compared with medium and low).

CONCLUSION

Variations in Ca2+ are directly correlated with clinically significant changes in myocardial contractility.

Physiologic mechanisms governing hemodynamic responses to positive inotropic therapy in patients with dilated cardiomyopathy

Clinical trials in patients with dilated cardiomyopathy (DCM) have shown a wide disparity in the hemodynamic responses to positive inotropic therapy. In addition, the response of the failing left ventricle to positive inotropic agents reflects the net interaction of multiple factors, including the magnitude of contractile abnormality and compensatory mechanisms. In the current study, left ventricular geometry, loading conditions, and contractile state were assessed in 13 patients with nonischemic DCM with the use of simultaneous high-fidelity pressure measurements and echocardiographic recordings. Comparisons were made with echocardiographic and calibrated carotid pulse data acquired in nine age-matched normal subjects. The patients with DCM were divided according to the left ventricular end-diastolic wall thickness-to-dimension ratio into groups with "appropriate" hypertrophy (i.e., less than or equal to 2 SDs from mean normal; n = 5; group 1) and "inadequate" hypertrophy (i.e., greater than 2 SDs from mean normal; n = 8; group 2). Age, New York Heart Association functional class, left ventricular wall mass index, and left ventricular end-diastolic pressure and dimension were similar for the DCM groups. Baseline left ventricular afterload (defined as circumferential end-systolic wall stress, sigma es) was 168% and 203% greater than normal in groups 1 and 2, respectively. The administration of the beta-adrenoceptor agonist dobutamine decreased left ventricular afterload by 12% in the normal subjects and by 10% in group 1 patients, while augmenting afterload by 5% in group 2 patients. The latter response occurred despite a 17% fall in systemic vascular resistance. Overall left ventricular performance, as assessed by the rate-corrected mean velocity of fiber shortening (Vcfc), was related to left ventricular afterload (i.e., sigma es). The resultant sigma es -Vcfc relationship, a sensitive measure of left ventricular contractility, was determined over a wide range of afterload conditions generated by methoxamine (normal subjects) or nitroprusside (DCM). Baseline left ventricular contractile state was 61% of normal for group 1 and 44% of normal for group 2. The contractile response to dobutamine infusion was 52% of normal for group 1 and only 22% of normal for group 2. Thus, positive inotropic therapy with dobutamine in patients with DCM is limited by (1) an attenuated contractile response and (2) elevated left ventricular afterload, which may be augmented further during its administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Contrast echocardiography during coronary arteriography in humans: perfusion and anatomic studies

In humans, the physiologic relation between myocardial blood flow and epicardial coronary artery anatomy remains poorly defined. With the recent development of sonicated microbubble contrast agents, it is now possible to use contrast echocardiography to assess myocardial perfusion and to correlate blood flow with angiographically identified coronary artery anatomy. The purpose of the current study was to determine myocardial perfusion patterns in patients without significant coronary artery disease. The results may be used as a reference to analyze myocardial blood flow in patients with coronary artery disease. Sonicated meglumine sodium diatrizoate solution (Renografin-76), which contains microbubbles measuring 4.5 +/- 2.8 micrograms in diameter by laser analysis, was used as the echocardiographic contrast agent during elective coronary arterriography in 14 patients without significant coronary artery disease. Patients received intracoronary injections of 1.5 to 2 ml of sonicated Renografin-76 without complications. Perfusion characteristics were studied by visual assessment of the two-dimensional echocardiographic images obtained after individual injections. In patients found to be free of significant coronary artery disease by arteriography, the left coronary system always supplied the anteroseptal, anterior, anterolateral and posterior regions of the left ventricle at the mid-papillary, cross-sectional level. The right coronary artery system perfused the inferior and inferoseptal regions in 89% of the patients identified with a right dominant system. The anterolateral papillary muscle was perfused from the left coronary system in all cases. The posteromedial papillary muscle was perfused from the left coronary system in 58% of the patients and from the right system in 42% of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intracoronary injections of sonicated microbubbles on left ventricular contractility

Despite the recent interest in contrast-enhanced echocardiography as a means of defining myocardial perfusion, the effects of echo contrast agents on left ventricular (LV) contractility in humans remains poorly defined. This is particularly relevant because intracoronary injection of contrast agents used for angiographic visualization of coronary arteries produces significant alterations in LV hemodynamics. The relation of LV end-systolic wall stress (sigma es) to rate-corrected velocity of fiber shortening (Vcfc), a load-independent index of contractility, was studied in 7 patients undergoing elective coronary arteriography. Two-dimensional and targeted M-mode echocardiographic and central aortic pressure tracings were recorded during injections of standard volumes of angiographic (7 to 9 ml of nonsonicated Renografin-76) and echocardiographic (1.5 to 2.0 ml of sonicated Renografin-76) contrast agents into the left main coronary artery. The order in which agents were injected was randomly determined. Myocardial contractility was assessed under control conditions and 5 and 15 seconds after injection. Alterations in contractility relative to control were measured as the change in Vcfc after elimination of afterload (sigma es) as a confounding variable. An injection of Renografin-76 adequate for angiographic imaging of coronary artery anatomy resulted in a significant depression of LV contractility (p less than 0.001) in conjunction with a tendency toward increased afterload (p = 0.12); recovery occurred by 15 seconds after injection. The smaller amounts of sonicated Renografin-76 required to give adequate contrast enhancement of the myocardium did not alter LV contractile state or afterload.(ABSTRACT TRUNCATED AT 250 WORDS)

Echocardiographic contrast agents: effect of microbubbles and carrier solutions on left ventricular contractility

Recently, there has been a resurgence of interest in the use of contrast-enhanced echocardiography as a means of noninvasively assessing myocardial perfusion. However, if injections of echocardiographic contrast agents are to be used for this purpose it is essential that they are not intrinsically toxic to the heart. In this study, the left ventricular end-systolic wall stress-rate-corrected velocity of fiber shortening relation, a load independent index of contractility, was studied in nine dogs. Two-dimensional and targeted M-mode echocardiographic as well as central aortic pressure tracings were made during echocardiographically gated, pressure- and volume-controlled aortic root injections of nonsonicated and sonicated Renografin-76, saline and dextrose 70% (n = 6), and sonicated and hand-agitated Renografin-76/saline mixture (n = 5). Two of nine dogs received all agents. Off-line computer videodensitometric analysis documented myocardial perfusion. In all cases, data were obtained at control and 5 and 15 seconds after injection. Additional data were collected at 25 seconds after injection for the Renografin-76/saline mixture. Alterations in contractility were measured relative to control as changes in rate-corrected velocity of fiber shortening after afterload (measured as end-systolic wall stress) was eliminated as a confounding variable. Under no condition did saline or Renografin-76 cause alterations in left ventricular contractility. Nonsonicated and sonicated dextrose 70% increased left ventricular contractility at 15 seconds but not at 5 seconds after injection. Hand-agitated Renografin-76/saline mixture induced a negative inotropic effect at 5 and 15 seconds after injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Contrast ultrasonography of the kidney: a new method for evaluation of renal perfusion in vivo

Assessment of the effects of pharmacologic agents on renal blood flow (RBF) is clinically important in many disease states, including hypertension and congestive heart failure. However, because of the complexities of RBF, quantitation in vivo has been technically difficult. This study demonstrates the utility of ultrasound imaging of the kidney combined with injection of a sonicated radiocontrast solution (Renografin-76) for the assessment of regional renal blood flow. The technique uses a suspension of uniform microbubbles (diameter 4.4 +/- 2.8 micron), which when injected directly into the descending aorta are distinctly visualized by renal ultrasound. Five dogs were studied. Catheters were placed in the descending aorta for injection of sonicated Renografin and in the renal artery for drug infusions. Data were collected before and during intrarenal artery infusions of bradykinin and norepinephrine. Total RBF was measured by electromagnetic flowmeter. Video density time curves were generated for comparable segments of the outer renal cortex and fit to a monoexponential decay curve. This allowed calculation of the mean exponential decay index (t1/2). An increase in t1/2 paralleled decreased renal perfusion (i.e., longer washout of contrast material). The opposite was true for a decrease in t1/2. Bradykinin increased RBF from 134 +/- 26 to 249 +/- 19 ml/min (p less than .01 vs control), and norepinephrine decreased RBF from 130 +/- 25 to 51 +/- 17 ml/min (p less than .01 vs control).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute lung injury and anesthesia on left ventricular mechanics

Traditional left ventricular (LV) function curves are frequently depressed in patients with acute lung injury. Similar findings in pentobarbital sodium-anesthetized dogs with oleic acid lung injury (OALI) have been observed. To test the hypothesis that acute OALI produces a significant injury to the heart, the LV mechanics of pentobarbital-anesthetized dogs with (n = 6) and without (n = 6) OALI were evaluated. End-systolic force-length and force-velocity relations determined echocardiographically during afterload manipulation with sodium nitroprusside demonstrated a marked deterioration in LV shortening characteristics over 90 min in both groups of pentobarbital-anesthetized dogs. In contrast, LV mechanics studied using the same protocol in fentanyl-anesthetized dogs were unchanged in both the injured (n = 6) and noninjured (n = 6) lung groups. Comparisons with data acquired over a wide range of LV afterload from six conscious, instrumented dogs showed that LV contractile state was normal to slightly increased with fentanyl and markedly depressed with pentobarbital. Diastolic properties, as assessed by end-diastolic pressure-dimension relations, were essentially unchanged in all anesthetized animals. We conclude that OALI has no effect on LV systolic or diastolic mechanics; the LV dysfunction attributed to OALI in previous studies is due to an acute, severe cardiomyopathy induced by pentobarbital; and unlike pentobarbital, anesthesia with fentanyl has no discernible time-dependent effect on LV mechanics. These findings have important implications for future studies of canine cardiovascular physiology employing anesthetized animal preparations.

Systemic vascular resistance: an unreliable index of left ventricular afterload

Systemic vascular resistance (SVR) is a frequently used clinical index of left ventricular afterload. However, SVR may not adequately assess left ventricular afterload (i.e., ventricular internal fiber load during systole) since it reflects only peripheral vasomotor tone. In contrast, left ventricular end-systolic wall stress (sigma es) reflects the combined effects of peripheral loading conditions and left ventricular chamber pressure, dimension, and wall thickness. To determine the relationship between SVR and sigma es, left ventricular afterload and contractility were pharmacologically altered in eight dogs instrumented with central aortic microtip and Swan-Ganz thermodilution catheters. Left ventricular wall thicknesses and dimensions were measured from two-dimensionally targeted M mode echocardiograms. Aortic, right atrial, and left ventricular end-systolic pressures as well as cardiac output were recorded. SVR and sigma es were determined under control conditions as well as during infusions of nitroprusside, methoxamine, dobutamine, and norepinephrine. Control data acquired before each drug infusion were similar. When compared with baseline values, SVR underestimated the magnitude of change in left ventricular sigma es by 22% when afterload alone was decreased (nitroprusside), 54% when afterload alone was increased (methoxamine), and 50% when afterload was decreased and contractility was augmented (dobutamine). Most importantly, when afterload was minimally decreased in association with augmented contractility (norepinephrine), SVR increased by 21% while sigma es fell by 9%. Thus, discordant changes in left ventricular afterload (i.e., sigma es) and SVR can occur during pharmacologic interventions. SVR is an unreliable index of left ventricular afterload, reflecting only peripheral arteriolar tone rather than left ventricular systolic wall force. This emphasizes the fact that a true measure of left ventricular afterload must consider the interaction of factors internal and external to the myocardium.

The differential effects of positive inotropic and vasodilator therapy on diastolic properties in patients with congestive cardiomyopathy

Symptoms of congestive heart failure frequently reflect abnormalities in both systolic and diastolic performance. While much work has been reported regarding the mechanisms by which positive inotropic and vasodilator therapy affect systolic performance, little is known about their effect on diastolic function. In 12 patients with diffuse congestive cardiomyopathy micromanometer left ventricular and aortic pressure measurements were recorded simultaneously with two-dimensionally targeted M mode echocardiograms and thermodilution-determined cardiac output. Each patient received dopamine (2, 4, and 6 micrograms/kg/min), and dobutamine (2, 6, and 10 micrograms/kg/min), and 10 received nitroprusside (0.125 to 2.0 micrograms/kg/min). Baseline hemodynamics were characterized by low cardiac index (2.1 +/- 0.7 liter/min/m2, mean +/- SD), high left ventricular end-diastolic pressure (24 +/- 10 mm Hg), and increased end-diastolic (6.8 +/- 1.0 cm) and end-systolic dimensions (6.0 +/- 1.0 cm). All patients had abnormal left ventricular pressure decay with a prolonged time constant (67 +/- 20 msec) and reduced peak diastolic lengthening rates. Dopamine and dobutamine decreased the time constant of relaxation and increased the peak lengthening rate. Dobutamine also reduced the minimum diastolic pressure from 14 +/- 7 to 10 +/- 9 mm Hg (p less than .01); neither drug reduced end-diastolic pressure. In fact, dopamine elevated end-diastolic pressures in seven patients, despite more rapid pressure decay. Diastolic pressure-dimension relations after dopamine and dobutamine showed a leftward shift with a reduced end-systolic chamber size, but no significant changes in passive chamber stiffness. Nitroprusside decreased left ventricular minimum diastolic pressure by 4 +/- 2 mm Hg and end-diastolic pressure by 7 +/- 4 mm Hg (p less than .01). It did not consistently accelerate left ventricular pressure decay at the doses tested. The decreased end-diastolic pressure with nitroprusside was due to a reduced end-diastolic dimension in five patients. In the other patients, all of whom had elevated right atrial pressures, diastolic pressure-dimension relations showed a parallel downward shift after nitroprusside. Thus, positive inotropic therapy with beta 1-adrenoceptor agonists enhances early diastolic distensibility by accelerating relaxation, augmenting filling, and reducing end-systolic chamber size. Vasodilator therapy is much more effective in lowering diastolic pressures.(ABSTRACT TRUNCATED AT 400 WORDS)

Contrast echocardiography for evaluation of myocardial perfusion: effects of coronary angioplasty

Assessment of viable myocardium before and after interventional therapy has become a critical issue in modern cardiology. This report describes a new contrast echocardiographic technique using conventional two-dimensional imaging during direct intracoronary injections of small volumes (1.5 to 2.0 cc) of sonicated Renografin-76. Contrast echocardiography was performed before and after coronary angioplasty in seven patients with single vessel coronary artery disease. Before angioplasty a contrast (that is, perfusion) defect was noted in all seven patients. This defect correlated with the anatomic distribution of the epicardial coronary stenosis. After angioplasty the mean gradient across the stenotic lesion decreased from 52 +/- 11 to 13 +/- 14 mm Hg (p less than 0.01) in association with a fall in the mean diameter of the lesion from 84 +/- 8 to 29 +/- 13% (p less than 0.001). Increased myocardial perfusion to the area of "contrast defect" was demonstrated in only five of the seven patients, despite hemodynamically and angiographically successful angioplasty. Thus, contrast echocardiographic techniques performed during interventional therapy and used in conjunction with standard coronary angiographic procedures may provide additional physiologic information regarding regional myocardial perfusion after attempts at revascularization.

Myocardial mechanics in hyperthyroidism: importance of left ventricular loading conditions, heart rate and contractile state

Hyperthyroidism has been reported to affect all of the major determinants of left ventricular performance in a manner that would augment ventricular shortening characteristics. The hypothesis tested in this study is that reduced afterload in conjunction with increased preload and heart rate, rather than augmented contractility, accounts for much of the increase in left ventricular performance noted previously in these patients. To investigate this hypothesis, 11 hyperthyroid patients were evaluated serially over 4 +/- 2 months. With therapy, serum total thyroxin (T4) decreased significantly (p less than 0.001). Ventricular hemodynamics were assessed by two-dimensional targeted M-mode echocardiograms and calibrated carotid pulse tracings. Ventricular preload was estimated by end-diastolic dimension, whereas afterload was measured as end-systolic wall stress. Overall left ventricular performance was quantitated by the extent and velocity of shortening, whereas myocardial work was assessed by ventricular systolic stress-length relations. With therapy, overall left ventricular performance declined (p less than 0.01). This change was associated with no change in end-diastolic dimension or end-systolic wall stress, and a 24% fall in heart rate (p less than 0.01). This latter finding has been shown previously to have no significant effect on left ventricular contractile state over the range of heart rates encountered in this study. In all cases, the end-systolic stress/rate-corrected shortening velocity relation fell with attainment of normal thyroid status, characteristic of a decline in contractility. There was a strong positive correlation between left ventricular contractility and serum thyroid hormone level (r = 0.83). In addition, ventricular minute work declined with therapy (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Milrinone versus dobutamine: contribution of altered myocardial mechanics and augmented inotropic state to improved left ventricular performance

Milrinone and dobutamine are positive inotropic agents with complex mechanisms of action. Traditional indexes of left ventricular function are unable to determine how much of the improvement in cardiac performance induced by these drugs is due to augmented inotropy and how much is the result of afterload reduction. Recently, the end-systolic wall stress (sigma es)-rate corrected velocity of fiber shortening (Vcfc) relationship has been shown to be a sensitive measure of contractility that is independent of preload while incorporating afterload. This index was measured in two groups of normal subjects (n = 8 per group) over a wide range of aortic pressures generated by administration of methoxamine before and during (1) milrinone or (2) dobutamine infusion. Studies were performed with the use of echocardiographic and calibrated carotid pulse tracings. Milrinone and dobutamine produced similar increases in overall left ventricular performance. Milrinone decrease end-systolic dimension (Des) by 15% and end-systolic pressure (Pes) by 22%, while increasing end-systolic wall thickness (hes) by 14%. This resulted in a 43% decline in left ventricular afterload as measured by sigma es. In contrast, dobutamine decreased Des by 11% while increasing hes by 14% and Pes by 22%. Despite the increase in left ventricular pressure, sigma es fell by 20%. Since afterload reduction alone results in increased left ventricular shortening, analysis of left ventricular performance was performed for both drugs at matched levels of sigma es under control and positive inotropic conditions. Twenty-nine percent of the improvement in Vcfc produced by milrinone was due to a decrease in afterload as compared with 18% of that produced by dobutamine.(ABSTRACT TRUNCATED AT 250 WORDS)