Diastolic heart function--pathophysiology, characterization, and therapeutic approaches

Microtubule destabilization with colchicine increases the work output of myocardial slices

Cardiac microtubules have recently been implicated in mechanical dysfunction during heart failure. However, systemic intolerance and non-cardiac effects of microtubule-depolymerizing compounds have made it challenging to determine the effect of microtubules on myocardial performance. Herein, we leverage recent advancements in living myocardial slices to develop a stable working preparation that recapitulates the complexity of diastole by including early and late phases of diastolic filling. To determine the effect of cardiac microtubule depolymerization on diastolic performance, myocardial slices were perfused with oxygenated media to maintain constant isometric twitch forces for more than 90 min. Force-length work loops were collected before and after 90 min of treatment with either DMSO (vehicle) or colchicine (microtubule depolymerizer). A trapezoidal stretch was added prior to the beginning of ventricular systole to mimic late-stage-diastolic filling driven by atrial systole. Force-length work loops were obtained at fixed preload and afterload, and tissue velocity was obtained during diastole as an analog to trans-mitral Doppler. In isometric twitches, microtubule destabilization accelerated force development, relaxation kinetics, and decreased end diastolic stiffness. In work loops, microtubule destabilization increased stroke length, myocardial output, accelerated isometric contraction and relaxation, and increased the amplitude of early filling. Taken together, these results indicate that the microtubule destabilizer colchicine can improve diastolic performance by accelerating isovolumic relaxation and early filling leading to increase in myocardial work output.

Right ventricular diastolic abnormalities in systemic sclerosis. Relation to left ventricular involvement and pulmonary hypertension

OBJECTIVES

To investigate right ventricular diastolic function in systemic sclerosis (SSc) and its relation to clinical features of the disease.

METHODS

Seventy seven unselected SSc patients and 33 healthy subjects were submitted to echocardiography and echo Doppler study to assess left and right systolic as well diastolic function and to estimate maximal arterial systolic pulmonary pressure (PAP). In addition, the patients were investigated to define the SSc subset and the extent of skin and internal organ involvement.

RESULTS

An abnormal right ventricular filling, as expressed by an inverted tricuspidal (Tr) E/A ratio (Tr E/A ratio <1), was detected in 31 of the 77 SSc patients (40%) and in 0 of the 36 controls ( p<0.001 ). All the 31 patients with an inverted Tr E/A ratio were found to have a PAP > 30 mm Hg. Twenty resulted to have an inverted mitral (Mit) E/A ratio (Mit E/A ratio <1), indicating an abnormal left ventricular filling. In multiple regression analysis, Tr E/A ratio resulted to be independently correlated to both PAP (r= -0.35;p<0. 003) and Mit E/A ratio (r=0.39;p<0.001).

CONCLUSIONS

This study points out an impaired right ventricular filling in a significant percentage of SSc patients whatever the subset. This alteration is independently correlated to both PAP and left ventricular filling abnormalities.

End-diastolic pressure-volume relationship in sepsis: relative contributions of compliance and equilibrium chamber volume differ

BACKGROUND

Compliance is a complex parameter to measure both clinically and in the laboratory. Investigations in recent years have interpreted changes in the end-diastolic pressure-volume relationship (EDPVR) as changes in compliance. However, without considering the equilibrium chamber volume (LV volume when transmural pressure = 0), changes in the EDPVR may not reflect changes in left ventricular chamber compliance. In the present study, chamber compliance was differentiated from equilibrium chamber volume to determine their respective contributions to the EDPVR in a clinically relevant animal model of chronic sepsis.

MATERIALS AND METHODS

Rats were made septic by intraperitoneal injection of a cecal slurry (200 mg/kg; 5 ml/kg of 5% dextrose in water). At 1, 3, and 7 days post-sepsis induction, hearts were perfused on an isolated heart apparatus. A latex balloon was placed in the left ventricle to record peak systolic and end-diastolic pressures at various volumes, and the starting volume in the balloon was recorded. Systolic performance was evaluated by calculating the developed pressure (systolic pressure minus end-diastolic pressure) and peak dP/dt at end-diastolic pressures of 5 and 10 mm Hg.

RESULTS

Developed pressure and peak dP/dt were impaired 3 days after sepsis induction and continued to be so through Day 7 of sepsis. The diastolic data were fitted to an exponential equation, the results of which indicated a strong leftward shift in the EDPVR through 7 days of sepsis with a concomitant decrease in equilibrium chamber volume. The LV chamber compliance decreased at 1 day after sepsis induction, as indicated by significant changes in regression coefficients for the curves, transiently returned toward control by Day 3, but decreased again by 7 days of sepsis.

CONCLUSIONS

Our data indicate that early in sepsis, compliance changes contribute to a left-shifting EDPVR, but at later times in the course of the disease, unstressed chamber volume becomes an important determinant of the left shift. The decrease in compliance (suggesting diastolic dysfunction) occurred prior to systolic impairment, which may have valuable prognostic implications for septic patients.

Pharmacological strategies for improving diastolic dysfunction in the setting of chronic pulmonary hypertension

BACKGROUND

Right ventricular (RV) hypertrophy is an adaptive process that occurs in the setting of chronic pulmonary hypertension (CPH) and can lead to alterations in normal RV diastolic properties. This study was designed to investigate the effects of NO and milrinone on RV diastolic dysfunction in the setting of CPH and RV hypertrophy by use of a canine model of monocrotaline pyrrole (MCTP)-induced CPH.

METHODS AND RESULTS

Sixteen mongrel dogs (22 to 24 kg) were used. Animals underwent percutaneous pulmonary artery (PA) catheterization to measure pulmonary hemodynamics before and 8 weeks after injection of 3 mg/kg MCTP (n=8) or placebo (control, n=8). Eight weeks after injection, all hearts were instrumented with a PA flow probe, sonomicrometric dimension transducers, and micromanometers. Data were collected at baseline and after both NO and milrinone administration. Diastolic properties were quantified by use of the end-diastolic pressure-volume relationship and the time constant of ventricular isovolumic relaxation. Eight weeks after injection, significant increases in the PA pressure and pulmonary vascular resistance were observed in MCTP dogs. Significant worsening of RV diastolic function occurred in association with significant increases in the ratio of RV dry weight to LV+septal dry weight. NO and milrinone administration both led to significant improvements in RV diastolic properties.

CONCLUSIONS

In the setting of MCTP-induced CPH, significant worsening of RV diastolic function was observed in association with significant increases in the ratio of RV dry weight to LV+septal dry weight, suggesting that these changes are partially due to RV hypertrophy. The significant improvement in RV diastolic properties after both NO and milrinone administration suggests that these agents may be effective forms of pharmacological therapy for improving RV diastolic dysfunction in the setting of CPH.

Diastolic indexes during dobutamine stress echocardiography in patients early after myocardial infarction

The aim of this study was to determine whether Doppler parameters assessed during dobutamine stress echocardiography in the early phase after myocardial infarction could discriminate patients with residual ischemia from those without. Thirty-six patients after a recent myocardial infarction with and without residual ischemia underwent dobutamine stress echocardiography, adenosine sestamibi scintigraphy, and coronary angiography within 2 weeks after the acute event. The only diastolic Doppler parameter discriminating the two groups was the isovolumic relaxation time (IVRT) measured at the peak of the dobutamine infusion. It became shorter in both groups but significantly more in patients without than in those with residual ischemia despite a larger increase in heart rate in the latter group. IVRT at rest was 78 +/- 18 msec and decreased with high-dose dobutamine to 54 +/- 11 msec in the control group and to 69 +/- 16 msec in the ischemic group (p < 0.01). In addition, the rate-corrected IVRT (IVRTc) was calculated: IVRTc = IVRT/sqrtRR. The value of IVRTc = 80 at peak dobutamine infusion is able to discriminate patients with residual ischemia from those without with a sensitivity of 80% and a specificity of 70%.

Highland mountain hiking and coronary artery disease: exercise tolerance and effects on left ventricular function

Physical exercise has become a well-established concept in the secondary prevention of coronary artery disease. We investigated the exercise requirements of extensive highland mountain hiking (8.7 km, 470 m to 1220 m over sea level, average incline 8.5%, mean walking velocity < 3 km x h-1) in 11 regularly exercising male patients with history of MI and stable coronary artery disease (CAD; mean age +/- SD:61.0 +/- 3.9 yr) and 9 age-matched male healthy controls (CO; mean age +/- SD:61.2 +/- 5.0 yr). All subjects underwent continuous ECG monitoring; arterial blood pressure and blood lactate concentrations were measured several times during mountain hiking. Before and after exercise, cardiac dimensions and functions were assessed by two-dimensional echocardiography and Doppler echocardiography. The mean exercise levels for heart rate and blood lactate were compared with the corresponding data of a multistage upright cycle ergometry. Clinical manifestations of coronary insufficiency, left ventricular myocardial dysfunction, or cardiac arrhythmias > Lown IIIb were not observed in any case. No significant differences in left atrial and left ventricular dimensions and no changes in systolic left ventricular function compared with the preexercise values were found after the mountain hike tour. Doppler echocardiography demonstrated significant changes in diastolic left ventricular function in CAD, but not in CO. The peak exercise intensity during mountain hiking was equivalent to a workload of 100-125 W (1.25-1.5 W x kg-1 body weight) in a multistage upright cycle ergometry. Extensive highland mountain hiking may be a low risk alternative within the outpatient rehabilitation program for secondary prevention of CAD for MI patients with a cycle ergometric exercise tolerance > 1.5 W x kg-1 body weight.

Cardiac mechanical energy and effects on the arterial tree

Blood flow pulsatility is the result of the heart's activity as a pump unable to develop steady flow, and its interaction with the arterial tree. Thus, the heart is a cyclic energy generator whose adequate function requires the two phases of this cycle to be normal. Diastolic properties determine the degree of filling of the ventricles and the strength of the following systole. Systole, in turn, must generate enough energy to overcome forces opposing ejection. These can be divided into internal (the mechanical characteristics of the ventricle itself) and external loads (the characteristics of the arterial tree). As a result, hydraulic energy is imparted to blood (external ventricular work) that manifests itself as blood pressure and flow. Given the cyclic nature of cardiac activity, the external ventricular work has steady and pulsatile components. The steady component is energy lost during steady flow because of vascular resistance, and the pulsatile work is that lost in arterial pulsations and mainly depends on the aortic impedance. Thus, the characteristics of the arterial tree will determine the relative contribution of these two components to blood flow and the efficency of the heart. In addition, the arterial tree modifies the different waves (pressure and flow) traveling in the circulation. These modifications have important consequences for cardiac function. The ventricle and the arterial tree constitute a coupled biological system, and its overall performance is a function of the behavior of each unit at any given moment.