Effects of increasing left ventricular filling. Pressure in patients with acute myocardial infarction

Myocardial stretch-induced compliance is abrogated under ischemic conditions and restored by cGMP/PKG-related pathways

Introduction: Management of acute myocardial infarction (MI) mandates careful optimization of volemia, which can be challenging due to the inherent risk of congestion. Increased myocardial compliance in response to stretching, known as stretch-induced compliance (SIC), has been recently characterized and partly ascribed to cGMP/cGMP-dependent protein kinase (PKG)-related pathways. We hypothesized that SIC would be impaired in MI but restored by activation of PKG, thereby enabling a better response to volume loading in MI. Methods: We conducted experiments in ex vivo rabbit right ventricular papillary muscles under ischemic and non-ischemic conditions as well as pressure-volume hemodynamic evaluations in experimental in vivo MI induced by left anterior descending artery ligation in rats. Results: Acutely stretching muscles ex vivo yielded increased compliance over the next 15 min, but not under ischemic conditions. PKG agonists, but not PKC agonists, were able to partially restore SIC in ischemic muscles. A similar effect was observed with phosphodiesterase-5 inhibitor (PDE5i) sildenafil, which was amplified by joint B-type natriuretic peptide or nitric oxide donor administration. In vivo translation revealed that volume loading after MI only increased cardiac output in rats infused with PDE5i. Contrarily to vehicle, sildenafil-treated rats showed a clear increase in myocardial compliance upon volume loading. Discussion: Our results suggest that ischemia impairs the adaptive myocardial response to acute stretching and that this may be partly prevented by pharmacological manipulation of the cGMP/PKG pathway, namely, with PDE5i. Further studies are warranted to further elucidate the potential of this intervention in the clinical setting of acute myocardial ischemia.

Understanding preload and preload reserve within the conceptual framework of a limited range of possible left ventricular end-diastolic volumes

Preload has been variously defined, but if there is to be a direct relationship with activity of the Frank-Starling mechanism in its action to increase the force and extent of contraction, preload must directly reflect myocardial stretch. The Frank-Starling mechanism is activated during any stretch of a cardiac chamber beyond its resting size, which is present immediately before contraction. Every left ventricle has an intrinsic and limited range of possible volumes at end diastole. There is a curvilinear relationship between left ventricular (LV) end-diastolic pressure (LVEDP) and LV end-diastolic volume (LVEDV), and, at maximal or near maximal LVEDV, there will be a high LVEDP. Within the possible range, the LVEDV will be determined by the extent of filling, any change in LVEDV will result in changed activity of the Frank-Starling mechanism, and change in LVEDV might, therefore, be considered to represent change in preload. On the other hand, it is the difference between the current and the maximal possible LVEDV (or the preload reserve) that may be of the most clinical relevance. There is a reciprocal relationship between preload and preload reserve, with minor or absent LV preload reserve indicating that there will be either minimal or no increase in stroke volume following intravenous fluid administration. As left atrial pressure can remain within the normal range when the LVEDP is elevated, it is LVEDP, and not left atrial pressure, that provides the most reliable guide to preload reserve in an individual at a specific period in time.

Reliability of updated left ventricular diastolic function recommendations in predicting elevated left ventricular filling pressure and prognosis

An updated 2016 echocardiographic algorithm for diagnosing left ventricular (LV) diastolic dysfunction (DD) was recently proposed. We aimed to assess the reliability of the 2016 echocardiographic LVDD grading algorithm in predicting elevated LV filling pressure and clinical outcomes compared to the 2009 version.

METHODS

We retrospectively identified 460 consecutive patients without atrial fibrillation or significant mitral valve disease who underwent transthoracic echocardiography within 24 hours of elective heart catheterization. LV end-diastolic pressure (LVEDP) and the time constant of isovolumic pressure decay (Tau) were determined. The association between DD grading by 2009 LVDD Recommendations and 2016 Recommendations with hemodynamic parameters and all-cause mortality were compared.

RESULTS

The 2009 LVDD Recommendations classified 55 patients (12%) as having normal, 132 (29%) as grade 1, 156 (34%) as grade 2, and 117 (25%) as grade 3 DD. Based on 2016 Recommendations, 177 patients (38%) were normal, 50 (11%) were indeterminate, 124 (27%) patients were grade 1, 75 (16%) were grade 2, 26 (6%) were grade 3 DD, and 8 (2%) were cannot determine. The 2016 Recommendations had superior discriminatory accuracy in predicting LVEDP (P<.001) but were not superior in predicting Tau. During median follow-up of 416 days (interquartile range: 5 to 2004 days), 54 patients (12%) died. Significant DD by 2016 Recommendations was associated with higher risk of mortality (P=.039, subdistribution HR1.85 [95% CI, 1.03-3.33]) in multivariable competing risk regression.

CONCLUSIONS

The grading algorithm proposed by the 2016 LV diastolic dysfunction Recommendations detects elevated LVEDP and poor prognosis better than the 2009 Recommendations.

"Left ventricular filling pressure(s)" - Ambiguous and misleading terminology, best abandoned

The use of the terms "left ventricular filling pressure" and "left ventricular filling pressures" is widespread in the cardiology literature, but the meanings ascribed to these terms have not been consistent. Left ventricular end-diastolic pressure (LVEDP) and mean left atrial pressure (LAP) cannot be used interchangeably as they will often differ in magnitude in the presence of cardiac disease and they also have different clinical significance. LVEDP is the best pressure to use when considering left ventricular function, whereas mean LAP is the most relevant pressure when considering the tendency to pulmonary congestion. The mean LAP is also the most relevant pressure for determining whether pulmonary hypertension has a left heart (post-capillary) component. If only a left ventricular pressure tracing is available then a technique to measure the mean left ventricular diastolic pressure is the best option for estimating the mean LAP. If only right heart pressures are available then the pulmonary artery end-diastolic pressure will provide a reasonable estimate of LVEDP, but only when the heart and pulmonary circulation are normal. If there is mitral valve disease, left ventricular disease or pulmonary hypertension the LVEDP cannot be estimated from right heart pressures. The problem of the ambiguity of "filling pressure (s)" is readily solved by the abandonment of this term and the use of either LVEDP or mean LAP as appropriate.

Theodore E. Woodward Award: Coming in out of the rain. Relieving congestion in heart failure

Heart failure decompensation is dominated by congestive symptoms from elevated pulmonary and systemic venous pressures. In dilated heart failure, forward flow is optimal at near-normal filling pressures, with minimized mitral regurgitation. Tailored therapy to reduce filling pressures improves symptoms acutely. However, monitored reduction of filling pressures during hospitalization did not translate into improved outcome during the ESCAPE trial. Data recently analyzed from the COMPASS trial indicates that 1) ambulatory filling pressures are far higher than clinically suspected, 2) filling pressures begin to increase over 3 weeks before heart failure events, and 3) events occurring during weight-based management show mismatch between changes in weight and changes in filling pressures. Accumulated days of high filling pressures increases risk continuously above left-sided filling pressures of 15 mmHg. The challenge is to intensify not only acute management of heart failure but ambulatory surveillance to allow early intervention and reduce re-hospitalization.

Subjective assessment of left ventricular preload using transesophageal echocardiography: corresponding pulmonary artery occlusion pressures

OBJECTIVE

To record pulmonary artery occlusion pressures (PAOPs) in patients whose left ventricular preload reserve was subjectively determined using transesophageal echocardiography (TEE).

DESIGN

Prospective, blinded, nonrandomized.

SETTING

University hospital.

PARTICIPANTS

Twenty-three patients with well-preserved left ventricular function during nonemergent cardiac surgery.

INTERVENTIONS

After separation from cardiopulmonary bypass, patients received repeated boluses of fluid volume through the aortic inflow cannula while being monitored with TEE. The endpoint for this fluid administration was a plateau in left ventricular fractional area change and end-diastolic area. This point at which additional fluid failed to cause noticeable increases in left ventricular end-diastolic area and fractional area change was defined as the preload reserve volume. After reaching the preload reserve volume, the PAOP was measured, as were the systolic blood pressure, left ventricular fractional area change, and end-diastolic area.

MEASUREMENTS AND MAIN RESULTS

The mean PAOP for all patients at the time of achieving preload reserve volume was 18.6 +/- 2.9 mmHg. In 8 patients, the PAOP corresponding to preload reserve volume was elevated (20 to 25 mmHg). The remaining 15 patients had PAOPs ranging from 13 to 19 mmHg. When these 2 groups were compared with respect to left ventricular end-diastolic area, fractional area change, and systolic blood pressure, there were no significant differences between groups. The left ventricular wall thickness was significantly greater, however, in the group with elevated PAOP (1.37 +/- 0.04 cm) when compared with the group with normal ventricular filling pressures (1.05 +/- 0.15 cm) (p = 0.001).

CONCLUSIONS

In patients with well-preserved left ventricular function and normal wall thickness, preload reserve volumes subjectively determined by TEE corresponded to a range of filling pressures historically targeted to maximize cardiac performance (13 to 19 mmHg). In a subset of patients with increased wall thickness, however, subjective determination of preload reserve was associated with filling pressures that were higher than traditionally considered optimal (20 to 25 mmHg). Similarities in left ventricular fractional area change and end-diastolic area between these 2 groups suggest that patients with elevated filling pressures had decreased ventricular compliance and were managed correctly with higher than usual PAOPs.

Sustained hemodynamic efficacy of therapy tailored to reduce filling pressures in survivors with advanced heart failure

BACKGROUND

During therapy to relieve congestion in advanced heart failure, cardiac filling pressures can frequently be reduced to near-normal levels with improved cardiac output. It is not known whether the early hemodynamic improvement and drug response can be maintained long term.

METHODS AND RESULTS

After referral for cardiac transplantation with initially severe hemodynamic decompensation, 25 patients survived without transplantation to undergo hemodynamic reassessment after 8+/-6 months of treatment tailored to early hemodynamic response. Initial changes included net diuresis, increased ACE inhibitor doses, and frequent addition of nitrates. After 8 months of therapy, early reductions were sustained for pulmonary wedge pressure (24+/-9 to 15+/-5 mm Hg early; 12+/-6 mm Hg late) and systemic vascular resistance (1651+/-369 to 1207+/-281 dynes x s(-1) x cm(-5) early; 1003+/-193 dynes x s(-1) x cm(-5) late). Acute response to doses persisted at reevaluation. Sustained reduction in filling pressures was accompanied by a progressive increase in stroke volume (42+/-10 to 56+/-13 mL early; 79+/-20 mL late), improved functional class, and freedom from resting symptoms. Study design did not control for amiodarone, which was initiated for arrhythmias in 12 patients and associated with greater improvement in cardiac index (1.8 to 3.2 L min(-1) x m(-2) late on amiodarone versus 2.0 to 2.6 L x min(-1) x m(-2), P<.05).

CONCLUSIONS

During chronic therapy tailored to early hemodynamic response in advanced heart failure, acute vasodilator response persists, and near-normal filling pressures can be maintained in patients who survive without transplantation. Stroke volumes at low filling pressures increase further over time. Chronic hemodynamic improvement was accompanied by symptomatic improvement, but the contributions of the monitored hemodynamic approach, increased vasodilator doses, and comprehensive outpatient management have not yet been established.

Mechanism of shock associated with right ventricular infarction

Various mechanisms have been proposed to explain the shock sometimes associated with right ventricular infarction, but only small numbers of patients with clinical shock have been studied. The haemodynamic profiles of seven patients with clinical cardiogenic shock after right ventricular myocardial infarction were studied prospectively. They were selected because all had a stable cardiac rhythm and none had absolute hypovolaemia during the study period. In all of them the mean right atrial pressure exceeded the pulmonary artery occlusion pressure. After treatment with varying combinations of dopamine, dobutamine, and glyceryl trinitrate (titrated to achieve the optimum haemodynamic response) the mean systemic arterial pressure increased, as did the cardiac index. There was an associated increase in the left ventricular stroke work index but the right ventricular stroke work index was unchanged. There was no significant change in heart rate, mean right atrial pressure, or pulmonary artery occlusion pressure. This suggests that the probable mechanism of the shock associated with right ventricular infarction is concomitant severe left ventricular dysfunction.

Effect of preload change on resting and exercise cardiac performance in hypertrophic cardiomyopathy

The purpose of this study was to investigate the hemodynamic responses, at rest and on exercise, of patients with hypertrophic cardiomyopathy to changes in circulating volume. After Swan-Ganz and radial arterial cannulation, 13 patients with hypertrophic cardiomyopathy performed maximal exercise tests after diuretic (frusemide 20 mg intravenously) and after fluid loading (0.9% saline at 10 ml/kg body weight intravenously) on different days. At rest, right atrial and pulmonary capillary wedge pressures increased with volume loading and decreased with a diuretic. There were no significant changes in the resting, supine cardiac or stroke indexes but in the upright position, the cardiac index and stroke index were higher after volume loading (2.5 +/- 0.7 vs 2.2 +/- 0.5 liters/min/m2, p less than 0.05; 33 +/- 11 vs 27 +/- 9 ml/m2, p less than 0.005, respectively). Although the right atrial, pulmonary arterial and pulmonary capillary wedge pressures were higher during exercise after volume loading, there were no significant differences in exercise heart rate, systemic blood pressure, cardiac index, stroke index, systemic vascular resistance index or overall exercise capacity compared to exercise after diuresis. The data show that the cardiac index and stroke index, at supine rest and during upright exercise, were not influenced by the preload changes induced in these patients with hypertrophic cardiomyopathy. The results suggest that these patients are operating on the plateau of left ventricular Frank-Starling function (filling pressure/output) curve.

Measurement of cardiac reserve in cardiogenic shock: implications for prognosis and management

The hypothesis that the prognosis of cardiogenic shock patients is primarily dependent on cardiac pumping reserve was tested in a prospective study of 28 consecutive patients clinically diagnosed to be in cardiogenic shock and treated medically. Haemodynamic function was assessed by thermodilution Swan-Ganz catheters and arterial cannulas. The cardiac pumping reserve was evaluated by the response of the failing heart to graded incremental dobutamine infusion (2.5 to 40 micrograms/kg/min) after optimalising the left ventricular preload. Eleven of the patients survived for more than the one year of follow up and the rest died. Haemodynamic evaluation during the basal resting state was only able to identify unambiguously non-survivors whose cardiac function was most severely compromised. Survivors and non-survivors with higher values were indistinguishable by basal haemodynamic criteria. The response to dobutamine stimulation clearly separated the cardiac pump function of survivors and those who died. All patients with peak cardiac power output of less than 1.0 W or peak left ventricular stroke work index of less than 0.25 J/m2 died whereas all those with higher values lived for more than a year. Thus this study showed that haemodynamic evaluation of cardiac reserve can provide objective criteria for predicting outcome in individual patients with cardiogenic shock. The availability of such a prognostic indicator will be invaluable in formulating management plans for these patients.

Comparability of echocardiography and chest X-ray following myocardial infarction

In a group of 23 patients with first-time myocardial infarction (MI) we compared the results of echocardiography and chest X-ray as measured 1 week, 2 months, and 6 months following acute MI. Left ventricular end-diastolic dimension (LVEDd) and left atrial (LA) dimension were measured from the echocardiogram, and the cardiac volume in ml/m2 body surface area (BSA) was calculated from the chest X-ray. A progressive increase in LA dimension was noticed during the 6-month period: a significant increase after 2 months (P less than 0.001) with a further increase at 6 months compared with after 2 months (P less than 0.001). The changes in LA dimension were more pronounced in anterior and Q-wave infarction (P less than 0.001) than in inferior and non-Q-wave infarction (P less than 0.01). On the other hand, LVEDd showed a less conspicuous change: a moderate increase (P less than 0.05) at 2 and 6 months, also with a more pronounced change in anterior wall and Q-wave infarction (P less than 0.01). There was no significant concurrent change in the calculated heart volume in ml/m2 BSA, as measured from the chest X-ray. It is suggested that the observed changes in LA dimension reflect reduced left ventricular compliance after MI.

Depressed left ventricular performance. Response to volume infusion in patients with sepsis and septic shock

Volume infusion, to increase preload and to enhance ventricular performance, is accepted as initial management of septic shock. Recent evidence has demonstrated depressed myocardial function in human septic shock. We analyzed left ventricular performance during volume infusion using serial data from simultaneously obtained pulmonary artery catheter hemodynamic measurements and radionuclide cineangiography. Critically ill control subjects (n = 14), patients with sepsis but without shock (n = 21), and patients with septic shock (n = 21) had prevolume infusion hemodynamic measurements determined and received statistically similar volumes of fluid resulting in similar increases in pulmonary capillary wedge pressure. There was a strong trend (p = 0.004) toward less of a change in left ventricular stroke work index (LVSWI) after volume infusion in patients with sepsis and septic shock compared with control subjects. The LVSWI response after volume infusion was significantly less in patients with septic shock when compared with critically ill control subjects (p less than 0.05). These data demonstrate significantly altered ventricular performance, as measured by LVSWI, in response to volume infusion in patients with septic shock.

Rate and extent of recovery of left ventricular function in patients following acute myocardial infarction

To determine the rate and extent of recovery of left ventricular (LV) performance following acute myocardial infarction (MI), peak aortic blood acceleration was measured serially in 26 patients and in 11 normal volunteers with a continuous wave Doppler placed suprasternally. In patients, Doppler measurements were made 20 +/- 2 hours after the acute onset of chest discomfort and were repeated daily for 6 consecutive days. Infarction patients were divided into two groups. Group I consisted of 15 patients who did not have a previous MI and whose present course was not complicated by congestive heart failure (CHF). Group II consisted of 11 patients who had either a previous MI or developed CHF during the present admission. Peak acceleration in the normal volunteers showed minimal daily variations over a period of 6 days. Peak acceleration in the entire group of 26 MI patients increased from 13 +/- 3 m/sec/sec on the day of admission (day 1) to 18 +/- 6 m/sec/sec on day 6 (p less than 0.001). In group I, peak acceleration increased from 13 +/- 4 to 20 +/- 6 m/sec/sec between day 1 and day 6 (p less than 0.001). In group II, however, peak acceleration was 12 +/- 2 m/sec/sec on day 1 and increased to only 15 +/- 4 m/sec/sec on day 6 (NS). These results indicate that LV performance, based upon peak acceleration of blood in the ascending aorta, improves markedly within 6 days in patients suffering their first MI uncomplicated by CHF.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of acute and chronic cardiac failure

Cardiac (or myocardial) failure, a major health problem, can be defined using physiologic criteria that consider the adequacy of O2 delivery relative to the body's O2 requirements. In clinical terms, cardiac failure may be described in terms of its chronicity or the extent to which signs and symptoms of right- versus left-sided heart failure are dominant. Congestive heart failure is a clinical syndrome that consists of a constellation of signs and symptoms that arise from congested organs and hypoperfused tissues. Acute cardiac failure occurs because of a decrease in myocardial contractility that can be offset by the Frank-Starling mechanism. In chronic cardiac failure dilatation and myocardial hypertrophy serve to restore ventricular function. Other compensatory responses that are invoked include a salt avid kidney, which mediates an expansion of the intravascular space, and the activation of the adrenergic nervous and renin-angiotensin-aldosterone systems and an increase in circulating arginine vasopressin. The management of acute and chronic cardiac failure can be derived from an understanding of the pathophysiologic mechanisms responsible for their appearance and include improving cardiac performance, as well as the distribution of systemic blood flow to tissues based on physiologic priorities and moment to moment variations in O2 requirements.

Right ventricular myocardial infarction with anterior wall left ventricular infarction: an autopsy study

Right ventricular myocardial infarction has been reported to occur exclusively in association with inferior left ventricular infarction. To determine the frequency of right ventricular myocardial infarction in association with anterior left ventricular myocardial infarction, all hearts with anterior myocardial infarction studied over a 3-year period were examined for evidence of right ventricular necrosis or scar. Of 97 hearts with anterior myocardial infarction, 13 (13%) had anterior right ventricular myocardial infarction. The right ventricular infarcts involved from 10% to 50% (mean 28%) of the circumference of the right ventricular free wall from base to apex. The associated left ventricular infarcts were all anteroseptal and large and involved from 36% to 67% (mean 50%) of the total area of the left ventricular free wall and septum. Nine of the 13 patients underwent equilibrium radionuclide angiography and six had demonstrable right ventricular regional and global dysfunction. Thus, right ventricular myocardial infarction does occur with anterior wall left ventricular infarction, and right ventricular dysfunction may be demonstrable by radionuclide angiography. Further investigation is needed to define the hemodynamic characteristics, clinical importance, and therapeutic implications of anterior right ventricular myocardial infarction.

Maintenance of cardiac output with normal filling pressures in patients with dilated heart failure

Therapy of elevated ventricular filling pressures in patients with dilated heart failure may be limited by concern that cardiac output will be further compromised. Twenty-five patients with severe symptoms and ejection fractions of 25% or less were studied to determine the lowest ventricular filling pressures that could be achieved with vasodilator and diuretic therapy while maintaining cardiac output. In 20 of 25 patients normal pulmonary capillary wedge pressures (PCWs) were achieved (mean 10 mm Hg compared with 30 mm Hg at baseline). Stroke volume was 60 vs 39 ml at baseline. Stroke work index was 30 vs 19 g-m/m2. For each patient, over the range of PCWs, stroke volume and stroke work index were maintained and were often maximal at the lowest PCW achieved. The upright position was well tolerated in patients with normal supine PCW. Normal filling pressures can be achieved in patients with congestive heart failure without compromise of cardiac output. While congestive symptoms should be improved, the feasibility and benefit of maintaining normal filling pressures over a long term must be established.

Hemodynamic abnormalities in acute myocardial infarction

Great strides have been made in the management of patients with acute myocardial infarction since the advent of coronary care units. However, congestive heart failure continues to be the major cause of in-hospital mortality. The accurate diagnosis and classification of hemodynamic abnormalities allow the application of specific therapies for each patient. Because clinicians can now routinely measure left and right ventricular preload, systemic and pulmonary vascular resistance, cardiac output, and arteriovenous oxygen difference, pharmacologic and surgical interventions can be applied in a scientific manner. In addition, mechanical complications can be promptly recognized and aggressively treated. Although the mortality rate for patients with severe left ventricular dysfunction after myocardial infarction remains high, expert management offers an improved prognosis for many patients.

Mechanisms of improving regional and global ventricular function by preload alterations during acute ischemia in the canine left ventricle

We examined the influence of left ventricular end-diastolic pressure (LVEDP) on the mechanical interaction between ischemic and nonischemic areas during acute myocardial ischemia. Circumferentially oriented ultrasonic segment gauges were implanted in the midwall of the anterior apex and posterior apex of the left ventricle in seven anesthetized dogs. Stroke volume was measured with a flow probe around the ascending aorta in five of these animals. We varied LVEDP with vena caval occlusion and dextran infusions to three matched levels (7, 12, and 19 mm Hg) before and 30 min after complete occlusion of the mid left anterior descending coronary artery. With acute ischemia, the anterior apex or ischemic zone demonstrated marked segmental lengthening during isovolumetric systole (end-diastole to aortic valve opening) and akinesis during the ejection phase (aortic valve opening to closure). In the posterior apex or nonischemic area, isovolumetric shortening increased and ejection phase shortening decreased during acute ischemia when compared with those under control conditions at the same LVEDP. Thus, a portion of the shortening generated by the nonischemic area was expended in stretching the ischemic zone during isovolumetric systole, thereby reducing the amount of ejection phase shortening. As LVEDP was increased, there was a parallel decrease in both the amount of isovolumetric lengthening in the ischemic zone and the isovolumetric shortening in the nonischemic area. As a result, acute ischemia produced less of a reduction in ejection phase shortening in the nonischemic area and in stroke volume at high as compared with low LVEDP. We conclude that the ischemic zone imposes a mechanical disadvantage on the nonischemic area, the magnitude of which is directly proportional to the amount of isovolumetric lengthening or bulge in the ischemic zone. An increase in LVEDP during acute ischemia improves regional and global ventricular function by both the Frank-Starling mechanism in the nonischemic (but not the ischemic) area and by reducing the mechanical disadvantage that the ischemic zone imposes on the nonischemic area.

A potential method of correcting intracavitary left ventricular filling pressures for the effects of positive end-expiratory airway pressure

Based on the observation that positive end-expiratory airway pressure (PEEP) causes comparable increments in intrapericardial and right-sided intracardiac pressures, we hypothesized that intracavitary left ventricular filling pressures measured in the presence of PEEP can be corrected for increased intrathoracic pressure by subtracting the effects of PEEP on intracavitary right ventricular filling pressures. Ventricular function curves (aortic blood flow vs intracavitary left ventricular end-diastolic pressure [LVEDP]) were generated with and without 15 cm of water of PEEP in eight dogs. All curves were shifted to the right by PEEP (i.e., intracavitary LVEDP was higher for any submaximal level of aortic blood flow). However, when pressures measured in the presence of PEEP were "corrected" by subtracting the corresponding increment in intracavitary right ventricular end-diastolic pressure caused by PEEP at each level of ventricular filling, control and corrected PEEP data points appeared to fall on the same curve in five dogs, and differed only slightly in three dogs. Mean control and corrected PEEP curves derived by averaging polynomial regression coefficients for each condition differed significantly from uncorrected PEEP curves (p less than .05), but not from each other. Analogous curves based on mean left atrial pressure were corrected equally well by subtracting the effects of PEEP on mean right atrial pressure. We conclude that the increments in intracavitary right heart filling pressures caused by PEEP can be used to correct intracavitary left heart filling pressures for the effects of PEEP on intrathoracic pressure.

Cardiogenic shock

Images

Left ventricular diastolic capacity in man

Plasma volume expansion with 500 ml of low-molecular-weight dextran was used in 27 patients (nine normal subjects, 13 patients with ischemic heart disease, four with aortic stenosis and one with cardiomyopathy) to increase left ventricular end-diastolic pressure (LVEDP) from a control value of 12.4 +/- 7.0 mm Hg (mean +/- SD) to 23.3 +/- 7.0 mm Hg and end-diastolic volume (EDV) from 84.0 +/- 23.8 ml/m2 to 97.6 +/- 22.9 ml/m2. EDV-LVEDP curves constructed for 12 patients from multiple angiograms at progressively increasing LVEDPs during plasma volume expansion showed an initial part where EDV increased in parallel with LVEDP and a final steep or perpendicular part where EDV increased minimally or not at all as LVEDP exceeded 20 mm Hg. Exponential equations were used to fit diastolic volume-pressure data obtained with catheter-tip manometers in seven patients: the exponential constant, k, was 0.012-0.044 ml-1 and was inversely related to EDV (Spearman's rank correlation coefficient = -1). For comparable EDV, there were no differences in k values between normal subjects and patients with a variety of heart diseases.

Circulatory dynamics during surface-induced hypothermia under halothane-ether azeotrope anesthesia

Circulatory dynamics during surface- induced deep hypothermia using the halothane-diethyl ether azeotrope in 100% oxygen (O2) without circulatory arrest and 95% O2 and 5% carbon dioxide (CO2) with and without 60 minutes of arrest were evaluated in 15 adult mongrel dogs. Mean arterial pressure was lower in animals given 5% CO2 than in animals given 100% O2 during cooling. Cardiac output in the 5% CO2 groups increased until 30 degrees C cooling and then gradually decreased to 29% of control at 20 degrees C. Cardiac output in the 100% O2 group progressively decreased to 16% of control at 20 degrees C cooling and was 51 to 77% of the output in the 5% CO2 animals at comparable temperatures throughout the hypothermia procedure. The differences in cardiac output were attributed primarily to changes in stroke volume since heart rates were not significantly different. These changes were probably secondary to differences in systemic vascular resistance, which had increased sixfold in the animals given 100% O2 and had only doubled in the 5% CO2 groups at 20 degrees C during cooling. Hemodynamic variables in animals given 5% CO2 did not reveal significant differences in arrested versus nonarrested animals during early rewarming. However, with further warming, cardiac output, stroke volume, left ventricular stroke work, and mean pulmonary arterial and pulmonary artery wedge pressures were lower, and systemic and pulmonary vascular resistances were higher in the arrest group. We conclude that the improved results with halothane-diethyl ether azeotrope in 95% O2 and 5% CO2 during surface hypothermia are due to a greater cardiac output and reduced peripheral vascular resistance.

Haemodynamic effects of nitroglycerin in comparison with preload and sodium nitroprusside on patients after coronary bypass surgery

To differentiate between the haemodynamic effects of intravenous nitroglycerin (NTG) and preload, left ventricular function curves were constructed for 10 patients with and without a steady NTG-infusion at left ventricular filling pressure (LVFP) levels of between 9 and 17 mmHg eight hours after coronary bypass grafting. The haemodynamic effects of NTG were compared with those caused by sodium nitroprusside (NP) at identical filling pressures. Although NTG as such decreased cardiac index (CI) (p less than 0.05), when systemic vasodilation was induced, CI was 18% greater with than without NTG at constant filling pressures (p less than 0.02). At identical LVFP, mean arterial pressure remained unchanged by NTG, whereas systemic vascular resistance was reduced by 16%. NTG augmented the left ventricular stroke work index (LVSWI) only in patients whose initial LVSWI was below 30 gm-m/m2 (a 20% increase, p less than 0.05). Although NTG relaxes the capacitance vessels more than the resistance vessels, its haemodynamic effects are far superior to the changes that can be induced by preload alteration alone. NTG enhances myocardial performance, especially if LVFP is kept balanced with the reduction of afterload. The increase in left ventricular pumping performance produced by NTG was 45% of the increase produced by NP at identical filling pressures. The results, however, indicate that NTG may affect the myocardial oxygen supply/demand ratio more favourably than NP.

Sinus arrest in diaphragmatic myocardial infarction: treatment of power failure with atrial pacing

Sinus arrest occurred in a patient with acute diaphragmatic myocardial infarction associated with right ventricular infarction. Cardiac output fell dramatically despite maintenance of a junctional rate of 72. Ventricular pacing at rate 82 and dopamine administration resulted in only slight hemodynamic improvement. Atrial pacing at rate 84 restored normal cardiac output until resumption of sinus node activity. These results suggest that atrial contraction is important for the maintenance of ventricular function in some patients with acute infarction, and may be of particular importance in the presence of right ventricular infarction. Temporary atrial or atrioventricular sequential pacing may be of great hemodynamic benefit in selected patients with conduction defects complicating myocardial infarction.

Normal left ventricular function

The Starling relationship in the normal human ventricle may be different than usually portrayed. In normal, resting, supine man the ventricular function curve is at its peak at a left ventricular end-diastolic pressure of approximately 10 mm Hg. Below this point is a strong direct relation between filling pressure and stroke work, while at higher filling pressures, a plateau occurs. Limitation of ventricular response is related to a sharply rising ventricular pressure-volume curve at a normal level of filling pressure. Thus, in the supine position, the normal heart is not on the active portion of the ventricular function curve, but is in a unique position in which cardiac output is probably controlled by factors other than ventricular filling pressure. In ventricular failure, the peak of the ventricular function curve is displaced to a higher level.

Arterial counterpulsation in severe refractory heart failure complicating acute myocardial infarction

The role of arterial counterpulsation was sought in 100 patients with severe refractory cardiac failure complicating myocardial infarction. Seventy-four were in shock and 26 were not. Average duration of counterpulsation was 7.0 days. Hospital survival was 34 per cent (25/74) in shock (predicted less than 10%) and 65 per cent in patients who were not in shock (predicted less than 50%). Survival at 4 years was 10 +/- 4 per cent in shock and 37 +/- 11 per cent in patients not in shock; functional status was class 1 or 2 in 5 of 9 patients in shock and in 8 of 12 survivors not in shock. Results were best when counterpulsation was started early after onset of symptoms, when ischaemic pain was still present, or when a mechanical defect was corrected surgically. Early coronary artery bypass surgery performed alone in 9 patients did not influence survival or functional status. Complications of counterpulsation occurred in 17 patients in shock and in 2 patients not in shock, all but 6 on the first day; none directly caused death. Counterpulsation is an effective and safe adjunct to medical treatment of complicated infarction provided the intervention is prompt.

Observations on haemodynamic effects of mexiletine

The haemodynamic effects of intravenous mexiletine have been studied in 16 patients with valvular heart disease without clinical evidence of heart failure. A bolus injection of 150 mg administered to 6 of the 16 patients resulted in a mean plasma concentration above the therapeutic range for at least 5 minutes after the drug was given. A small but significant rise in the mean pulmonary artery pressure occurred. In 10 patients, the effects of intravenous mexiletine were compared with those of intravenous saline in a double blind trial. No significant difference was found in the haemodynamic effects, though both saline and mexiletine produced a small rise in the mean pulmonary artery pressure. Mexiletine when administered to patients without heart failure in doses known to be clinically effective did not have important adverse haemodynamic effects.

Hemodynamic monitoring in patients with hypotension after myocardial infarction. The role of the medical center in relation to the community hospital

Patients who develop hypotension after acute myocardial infarction are frequently transferred to medical centers for hemodynamic monitoring. To see if this practice is justified, we reviewed our experience with hemodynamic monitoring over a two-year period. Of 40 patients who underwent hemodynamic monitoring for hypotension, 28 were transferred from other institutions. Eleven (39 percent) of these 28 patients had a pulmonary capillary wedge pressure of 16 mm Hg or less. Ten (91 percent) of these 11 survived, compared with one survivor (8 percent) in the 13 transferred patients with a pulmonary capillary wedge pressure of 17 mm Hg or more (P less than 0.001). The pulmonary capillary wedge pressure did not correlate well with the presence of a third heart sound on physical examination or with chest x-ray films. All hypotensive patients with a low pulmonary capillary wedge pressure received fluids to expand the blood volume as their major form of therapy. Thus, hemodynamic monitoring in patients with hypotension clarifies their status regarding blood volume and identifies those who will benefit from expansion of this volume. Transfer of hypotensive patients for hemodynamic monitoring seems justified, as their status regarding volume of blood is frequently difficult to ascertain by noninvasive means.

Echocardiographic evaluation of cardiac function and drug effects in acute myocardial infarction

The hemodynamic evaluation of patients with acute myocardial infarction (AMI) usually is performed by invasive methods. A prospective echocardiographic study was conducted on 23 AMI patients to determine the feasibility of this technique in evaluating hemodynamics and in measuring the effect of drugs on left ventricular performance. The results showed that: 1) reproducible measurements of left ventricular end-diastolic and end-systolic dimensions can be obtained by echocardiography, and 2) echocardiography can be used in the assessment of the effect of drugs in AMI. As echocardiography is a simple noninvasive procedure, it is well suited for conducting longitudinal studies in patients outside the coronary care unit and in ambulatory AMI patients.

Effects of dextran infusion on left ventricular volume and pressure in man

The purpose of this investigation was to quantitate the changes in left ventricular volume and end-diastolic pressure that occur with rapid infusion of 500 ml of low molecular weight dextran, and thus to study left ventricular pressure-volume relationships. Left ventricular pressure and echocardiographic dimensions were recorded before, during, and following dextran infusion in eight patients with normal left ventricular function. With the infusion of dextran, left ventricular end-diastolic pressure rose progressively from 10 +/- 3 mmHg (mean +/- SD) to 24 +/- 5 mmHg, whereas end-diastolic volume increased from 95 +/- 23 ml to 118 +/- 26 ml (24%). These results serve to emphasize the steepness of the left ventricular pressure-volume relationship at end-diastole in subjects with normal ventricular function when in the supine position.

Cardiovascular function during early recovery from acute myocardial infarction

Fifty patients with acute myocardial infarction were studied serially to evaluate the extent and nature of functional cardiovascular impairment and the time course of recovery. Reinfarction or death occurred in six patients. Peak workload during bicycle exercise in a subgroup of 25 patients with maximal initial test and complete follow-up increased from 334 to 409 kpm/min (P less than 0.01) bwtween three and six weeks. There was further significant (P less than 0.01) improvement between three and six months from 438 to 488 kpm/min. The incidence of ischemia at a constant workload decreased between three and six weeks without any significant changes in heart rate or blood pressure. Mean cardiac output during exercise at three months was 6.5 and at six months 7.8 L/min (P less than 0.05). Corresponding values for stroke volume were 61 and 72 ml (P less than 0.05). The data suggest that in clinically stable patients there is an early improvement of the relation between myocardial oxygen supply and demand and a late improvement of functional capacity associated with increased stroke volume and cardiac output.

Left ventricular hemodynamics and function in acute myocardial infarction: studies during the acute phase, convalescence and late recovery

The left ventricular hemodynamics of 70 patients with acute myocardial infarction were determined from measurements of pulmonary arterial end-diastolic pressure, cardiac index, mean arterial pressure and heart rate during the acute phase(first study, 5 hours after admission), 4 to 6 weeks later (second study, during convalescence) and in 35 percent of all subjects 6 to 12 months after the acute infarction (third study). Serial analysis of serum creatine kinase was carried out during the acute phase. The peak CK value normalized for body surface area was used as a rough index of the extent of the acute myocardial necrosis. The condition of all survivors of the acute stage improved. Patients with only slightly reduced left ventricular performance during the acute stage recovered to nearly normal during convalescence. The condition of patients with greatly reduced left ventricular function also improved but remained impaired during convalescence. In all patients the main changes in left ventricular hemodynamics occurred within the first 4 to 6 weeks; there was almost no further alteration during the following 9 months.

Hemodynamic effects of chlorpromazine in patients with acute myocardial infarction and pump failure

The intravenous administration of chlorpromazine in 12 patients with acute myocardial infarction and altered pump function was followed by a significant reduction in systemic vascular resistance (28.4%) and an increased cardiac index (23.0%). The drug also produced a significant decline in mean pulmonary capillary wedge pressure (38.2%), while the heart rate and mean stroke work index did not change significantly. Although the mean blood pressure decreased by 18.3%, the transymocardial pressure gradient was not affected. A significant reduction in the major determinants of myocardial oxygen consumption, such as arterial blood pressure and left ventricular wall tension, suggested a decrease in myocardial demand for oxygen. Improvement of left ventricular performance was associated with a sedative effect in most of the patients. Intravenous administration of chlorpromazine proved to be of benefit in patients with moderate to severe congestive heart failure and cardiogenic shock.

Spontaneous changes in hemodynamics in uncomplicated acute myocardial infarction: a prospective echocardiographic study

Spontaneous changes in heart rate (HR), systolic and diastolic blood pressure, left ventricular end-diastolic dimension (LVEDD), and left ven tricular end-systolic dimension (LVESD) over a 95-minute period were evaluated in 13 patients with uncomplicated myocardial infarction within 48 hours of infarction. The patients were on no medication at the time of their study. ECGs, blood pressures, and echocardiograms were recorded every 1 minute for 5 minutes (control period) and 1, 3, 5, 10, 20, 30, 45, 60, and 90 minutes (study period) after the control measurements.

The mean control LVEDD was 57.4 ± 10.0 mm; the standard deviation (SD) across the control values was 0.9 mm. The mean LVEDD during the 90-minute study period was 57.5 ± 9.7 mm; the SD across the 90-minute study period values was 1.4 mm. The mean control LVESD was 48.3 ± 11.4 mm; the SD across the control value was 1.0 mm. The mean LVESD during the 90-minute study period was 48.9 ± 11.0 mm; the SD across the 90-minute study period was 1.7 mm. No significant differences in HR, systolic or diastolic blood pressure, LVEDD, and LVESD occurred be tween the 5 control values and the 10 values obtained during the 90- minute study period in the 13 patients in this study.

We conclude that (1) reproducible measurements of LVEDD and LVESD can be obtained by echocardiography in stable patients with uncomplicated acute myocardial infarction over a 95-minute period; and (2) the hemodynamic variables are stable in uncomplicated myocardial infarction over a 95-minute period.