Comparative effects of volume loading on pulmonary venous flow in dogs with normal heart and with myocardial ischemia

Non-Invasive Management of Peripheral Arterial Disease

BACKGROUND

Peripheral arterial disease (PAD) is common and symptoms can be debilitating and lethal. Risk management, exercise, radiological and surgical intervention are all valuable therapies, but morbidity and mortality rates from this disease are increasing. Circulatory enhancement can be achieved using simple medical electronic devices, with claims of minimal adverse side effects. The evidence for these is variable, prompting a review of the available literature.

METHODS

Embase and Medline were interrogated for full text articles in humans and written in English. Any external medical devices used in the management of peripheral arterial disease were included if they had objective outcome data.

RESULTS

Thirty-one papers met inclusion criteria, but protocols were heterogenous. The medical devices reported were intermittent pneumatic compression (IPC), electronic nerve (NMES) or muscle stimulators (EMS), and galvanic electrical dressings. In patients with intermittent claudication, IPC devices increase popliteal artery velocity (49-70 %) and flow (49-84 %). Gastrocnemius EMS increased superficial femoral artery flow by 140 %. Over 4.5-6 months IPC increased intermittent claudication distance (ICD) (97-150 %) and absolute walking distance (AWD) (84-112 %), with an associated increase in quality of life. NMES of the calf increased ICD and AWD by 82 % and 61-150 % at 4 weeks, and 26 % and 34 % at 8 weeks. In patients with critical limb ischaemia IPC reduced rest pain in 40-100 % and was associated with ulcer healing rates of 26 %. IPC had an early limb salvage rate of 58-83 % at 1-3 months, and 58-94 % at 1.5-3.5 years. No studies have reported the use of EMS or NMES in the management of CLI.

CONCLUSION

There is evidence to support the use of IPC in the management of claudication and CLI. There is a building body of literature to support the use of electrical stimulators in PAD, but this is low level to date. Devices may be of special benefit to those with limited exercise capacity, and in non-reconstructable critical limb ischaemia. Galvanic stimulation is not recommended.

Correlation between left ventricular end-diastolic pressure and peak left atrial wall strain during left ventricular systole

OBJECTIVE

Left atrial (LA) reservoir function is determined by integration of LA relaxation and left ventricular (LV) systolic function, and LV diastolic dysfunction increases LA volume at end systole. This study investigates the effect of LV end-diastolic pressure on LA wall tension during LV systole.

METHODS

A total of 101 stable patients with sinus rhythm undergoing cardiac catheterization were studied. LA wall extension during LV systole was evaluated as LA wall strain in the longitudinal direction obtained using two-dimensional ultrasound speckle tracking imaging. LV end-diastolic pressure and LV end-systolic and end-diastolic volumes were obtained in cardiac catheterization, and LV ejection fraction was determined.

RESULTS

Peak LA wall strain during LV systole had a significant inverse correlation with LV end-diastolic pressure (r = - 0.76, P < .0001). This correlation was also significant in patients with preserved LV systolic function (LV ejection fraction > or =50%) (r = - 0.64, P < .0001). In patients with peak LA wall strain during LV systole of less than 30%, 89% had elevated LV end-diastolic pressure (> or =16 mm Hg).

CONCLUSION

Elevated LV end-diastolic pressure is associated with a decrease of peak LA wall strain in the longitudinal direction during LV systole. In patients with peak LA wall strain during LV systole of less than 30%, the majority had elevated LV end-diastolic pressure, while most patients with peak LA wall strain during LV systole 45% or higher had normal LV end-diastolic pressures. In patients whose LV ejection fraction is 50% or more, when peak LA wall strain during LV systole is between 30% and 44%, it is not possible to predict LV end-diastolic pressure from peak LA wall strain measures.

Relationships between velocities of pulmonary venous flow and plasma concentrations of atrial natriuretic peptide in healthy dogs

OBJECTIVE

To investigate the relationship between velocities of pulmonary venous flow (PVF) and plasma concentrations of atrial natriuretic peptide (ANP) in healthy dogs.

ANIMALS

7 healthy Beagles.

PROCEDURES

Dogs were anesthetized, intubated, and positioned in left lateral recumbency. Lactated Ringer's solution was infused (200 mL/kg/h) for 60 minutes via a cephalic vein. Transmitral flow and PVF velocities were measured echocardiographically by use of the apical 4-chamber view. Pulmonary capillary wedge pressure (PCWP) and ANP concentrations were determined.

RESULTS

IV infusion significantly increased heart rate and PCWP. Similarly, the ANP concentration significantly increased from baseline (before infusion of lactated Ringer's solution) values. Transmitral flow velocities were significantly increased, although the ratio of velocity of the flow during early ventricular diastole (E wave) to velocity of the atrial flow (A wave; E:A ratio) was unchanged. Regarding the PVF velocities, forward flow during ventricular systole (S wave) and retrograde flow during atrial contraction were significantly increased, whereas velocity of the forward flow during ventricular diastole (D wave) was unchanged. Ratio of the velocity of the S wave to velocity of the D wave was increased significantly, and this ratio was significantly correlated with PCWP or ANP concentration. However, the E:A ratio was not correlated with PCWP or ANP concentration.

CONCLUSIONS AND CLINICAL RELEVANCE

PVF velocities were strongly correlated with PCWP and plasma ANP concentration in clinically normal dogs. Therefore, PVF velocities may serve as a sensitive indicator and provide additional information for monitoring acute preloading conditions and estimating atrial filling abnormalities in dogs.

Assessing diastolic function with Doppler echocardiography using a novel index: ratio of the transmitral early diastolic velocity to pulmonary diastolic velocity

We developed a novel index to assess left ventricular (LV) relaxation as the ratio of transmitral early diastolic velocity to pulmonary diastolic velocity (E/D ratio). Mixed breed dogs (n=7) were anesthetized and their respiration was controlled. A 3.5-Fr micromanometer-tipped catheter was placed into the left ventricle. Dobutamine (5.0 or 10 microg/kg/min) or esmolol (100 or 500 microg/kg/min) was administered via the cephalic vein. The transmitral flow (TMF) and pulmonary venous flow (PVF) were recorded using transthoracic echocardiography from the apical long-axis view. The heart rate, systolic LV pressure, +dP/dt, and -dP/dt were significantly elevated by dobutamine, but significantly reduced by esmolol. Dobutamine significantly decreased tau, whereas esmolol significantly increased tau. The TMF-derived E and PVF-derived D wave velocities increased significantly with dobutamine, but decreased significantly with esmolol. A significant correlation was detected between the E and D wave velocities (r=0.92). Consequently, the E/D ratio was decreased significantly with dobutamine, and increased significantly with esmolol. Furthermore, the E/D ratio was significantly correlated with -dP/dt (r= -0.64) and tau (r=0.84). Our results suggest that the E/D ratio reflects LV relaxation, and may potentially provide further information on LV relaxation.

Comparison between invasive hemodynamic measurements and noninvasive assessment of left ventricular diastolic function by use of Doppler echocardiography in healthy anesthetized cats

OBJECTIVE

To compare Doppler echocardiographic variables of left ventricular (LV) function with those obtained invasively via cardiac catheterization under a range of hemodynamic conditions.

ANIMALS

7 healthy anesthetized cats (1 to 3 years of age).

PROCEDURE

Cats were anesthetized and instrumented to measure the time constant of isovolumic relaxation (tau [tau]), LV end-diastolic pressure (LVEDP), peak negative and positive rate of change of LV pressure, arterial blood pressure, and cardiac output. Echocardiographic variables of diastolic function (isovolumic relaxation time [IVRT], early LV flow propagation velocity [Vp], transmitral and pulmonary venous flow velocity indices, and LV tissue Doppler imaging indices) were measured simultaneously over a range of hemodynamic states induced by treatments with esmolol, dobutamine, cilobradine, and volume loading. Correlation between invasive and noninvasive measures of LV filling was determined by univariate and multivariate regression analyses.

RESULTS

Significant correlations were found between tau and IVRT, peak Vp, peak late transmitral flow velocity, and peak systolic pulmonary venous flow velocity. A significant correlation was found between LVEDP and early diastolic transmitral flow velocity (peak E) and the ratio of peak E to peak Vp, but not between LVEDP and peak Vp.

CONCLUSIONS AND CLINICAL RELEVANCE

IVRT and Vp can be used as noninvasive indices of LV relaxation; Vp was independent of preload and heart rate in this study. The E:Vp ratio may be useful as an indicator of LV filling pressure.

Effects of age, body weight, and heart rate on transmitral and pulmonary venous flow in clinically normal dogs

OBJECTIVE

To determine the influence of age, body weight (BW), heart rate (HR), sex, and left ventricular shortening fraction (LVSF) on transmitral and pulmonary venous flow in clinically normal dogs.

ANIMALS

92 client-owned dogs 3 months to 19 years old.

PROCEDURE

Transthoracic Doppler echocardiography recordings of transmitral flow and pulmonary venous flow were obtained in conscious unsedated dogs. Influence of age, BW, HR, sex, and LVSF on diastolic variables was assessed, using statistical methods such as ANOVA on ranks and univariate and multivariate forward stepwise linear regression analyses.

RESULTS

Age significantly influenced isovolumic relaxation time (IVRT, r = 0.56), ratio between peak velocity of the early diastolic mitral flow wave-to-peak velocity of late diastolic mitral flow wave (E:A; r = -0.44), deceleration time of early diastolic mitral flow (DTE; r = 0.26), and peak velocity of atrial reversal pulmonary venous flow wave (AR-wave; r = 0.37). Significant changes of mitral inflow and pulmonary venous flow variables were evident only in dogs > 6 and > 10 years old, respectively. Body weight significantly influenced DTE (r = 0.63), late diastolic flow duration (r = 0.60), and AR duration (r = 0.47), whereas HR significantly affected DTE (r = -0.34), IVRT (r = -0.33), and peak velocity of AR (r = 0.24). Sex or LVSF (range 22 to 48%) did not influence any echocardiographic variables.

CONCLUSIONS AND CLINICAL RELEVANCE

Age, BW, and HR are important factors that affect filling of the left atrium and left ventricle in clinically normal dogs.