Mechanism of prolongation of pre-ejection period in the hypertrophied left ventricle with normal systolic function in unanesthetized hypertensive dogs

The effect of telmisartan on the ventricular systolic function in dogs with experimental supraventricular tachyarrhythmia

Maintaining a good ventricular systolic function is important in the long-term therapy of dogs with supraventricular tachyarrhythmia (SVTA). The objective of this study was to evaluate the inhibitory effect of telmisartan on myocardial injury and the resulting ventricular systolic dysfunction in a canine model of SVTA. A total of 14 dogs were randomly assigned to a Telmisartan (oral telmisartan, 1.0 mg/kg daily, n=7) or a Control (no drug administration, n=7) group; the duration of rapid atrial pacing (RAP) was 3 weeks for both groups. The cardiac troponin I (cTnI) concentration in the Control group was significantly increased after 3 weeks compared to that before RAP initiation (baseline), but no significant difference was observed in the Telmisartan group. Moreover, the cTnI concentration at 3 weeks was significantly lower in the Telmisartan group than in the Control group. The left ventricular fractional shortening was significantly decreased at 3 weeks compared to that at baseline in both groups. However, fractional shortening at 3 weeks was significantly higher in the Telmisartan group than in the Control group. The cardiac output values in the Control group were significantly decreased at 3 weeks compared with those at baseline, but no significant difference was observed in the Telmisartan group. This study demonstrates that telmisartan inhibits the reduction in ventricular systolic function and prevents myocardial injury in a canine model of SVTA. Therefore, telmisartan is suggested as a novel treatment for canine SVTA.

Wave Intensity Analysis Can Identify Eccentric Cardiac Hypertrophy in Hypertensive Patients With Varied Left Ventricular Configurations

OBJECTIVES

The primary aim of this study was to determine whether wave intensity can discriminate cases of eccentric hypertrophy in patients with essential hypertension who have varied left ventricular configurations.

METHODS

A total of 155 hypertensive patients with different ventricular configurations (27 normal configuration, 42 concentric remodeling, 62 concentric hypertrophy, and 24 eccentric hypertrophy) were recruited. We performed a noninvasive wave intensity analysis of the common carotid artery and conventional echocardiography. Blood pressure and flow velocity were measured in the right carotid artery of all patients.

RESULTS

The left ventricular ejection fraction (LVEF) in the eccentric hypertrophy group was significantly lower than the values in the other groups (P < .05). The R-W1 interval/W1-W2 interval ratio (where W1 indicates the first positive peak and W2 the second positive peak) in the eccentric hypertrophy group was much higher than the values in the other groups (P < .05). However, there were no significant differences in W1, W2, and negative area among these groups. Pearson correlation analysis showed that R-W1/W1-W2, R-W1, and W1-W2were correlated with the LVEF, whereas there was no correlation between W1, W2, negative area, and the reflection coefficient with the LVEF.

CONCLUSIONS

We propose that by using the R-W1/W1-W2 ratio, wave intensity analysis can identify hypertensive patients with eccentric hypertrophy without the need for echocardiography.

Pre-ejection period to estimate cardiac preload dependency in mechanically ventilated pigs submitted to severe hemorrhagic shock

BACKGROUND

Respiratory change in pre-ejection period (ΔPEP) has been described as a potential parameter for monitoring cardiac preload dependency in critically ill patients. This study was designed to describe the relationship between ΔPEP and pulse pressure variation (PPV) in pigs submitted to severe hemorrhagic shock.

METHODS

In 17 paralyzed, anesthetized mechanically ventilated pigs, electrocardiography, arterial pressure, and cardiac output derived from pulmonary artery catheter were recorded. Hemorrhagic shock was induced by removal of blood volume followed by restoration. PEP was defined as the time interval between the beginning of the Q wave on the electrocardiogram and the upstroke of the invasive radial arterial pressure curve.

RESULTS

At baseline, ΔPEP and PPVs were both <12% with PPV significantly correlated with ΔPEP (r = 0.96, p < 0.001). Volume loss induced by hemorrhage significantly increased PPV and ΔPEP values (p < 0.05). During severe hemorrhage, PPV correlated well with ΔPEP (r = 0.88, p < 0.001) with PPV values significantly higher than ΔPEP (p < 0.05). However, the reproducibility of ΔPEP measurements was significantly better than PPV during this step (p < 0.05). Retransfusion significantly decreased PPV and ΔPEP (p < 0.05) with PPV significantly correlated to ΔPEP (r = 0.94, p < 0.001).

CONCLUSION

Available correlations between PPV and ΔPEP at each time of the study were observed, meaning that ΔPEP is a reliable parameter to estimate and track the changes in cardiac preload dependency. Moreover, during the severe hemorrhagic shock period, ΔPEP measurements were more reproducible than PPV values.

Effects of enfonidipine hydrochloride in dogs with experimental supraventricular tachyarrhythmia

It is required not to increase the ventricular rate and to preserve the ventricular systolic function in treating supraventricular tachyarrhythmia (SVTA). The objective of this study is to investigate whether or not Efonidipine hydrochloride (EH), a T and L dual type Ca(2+) channel blocker, suppresses the increasing ventricular rate without reducing the ventricular systolic function using canine SVTA models by rapid atrial pacing (RAP) method. Clinically healthy fourteen beagles were used. The 14 dogs were randomly assigned to the EH-administered group (EH group, n=7) and non-EH-administered group (control group, n=7). The EH group was orally-administered EH at 5 mg/kg SID during RAP. On the other hand, the control group was applied RAP without oral administration of EH. Duration of RAP was for 3 weeks for both groups. The ventricular rate for the EH group was significantly lower than that for the control group. The left ventricular- fractional shortening for the control group declined significantly compared to baseline. Those for the EH group did not show any changes over time and were significantly higher than the control group. The ratio between pre-ejection period and ejection for the EH group were significantly lower than those of the control group. In conclusion, the study demonstrated that EH suppresses the increasing ventricular rate without reducing the ventricular systolic function in canine SVTA model. Therefore, EH is expected to become a new treatment for canine SVTA.

Spectrum of M-mode echocardiographic abnormalities in 75 cats with systemic hypertension

A retrospective study was performed in 75 hypertensive cats to determine the spectrum and frequency of M-mode echocardiographic abnormalities. Results indicated that 21.3% of the cats had M-mode measurements within normal reference ranges. For cats with echocardiographic abnormalities, changes were variable. Thirty-nine percent of hypertensive cats had hypertrophy of the interventricular septum in diastole, and 41.3% had hypertrophy of the left ventricular (LV) posterior wall in diastole. One cat in five had a dilated left atrium, while fractional shortening and LV internal dimension in diastole were normal in 82.7% and 86.7% of the cats, respectively. The marked variability of echocardiographic findings in hypertensive cats made echocardiography an unreliable screening test for hypertension.

The influence of cardiac preload and positive end-expiratory pressure on the pre-ejection period

The pre-ejection period (PEP) has recently been described as a potential parameter for monitoring cardiac preload. This study further investigated the influence of changes in intravascular volume status and the application of positive end-expiratory pressure (PEEP) on the pre-ejection period. In ten pigs, ECG, arterial pressure and stroke volume derived from an aortic flowprobe were registered. Global end-diastolic volume (GEDV) was measured by transcardiopulmonary thermodilution. Total blood volume (TBV) and intrathoracic blood volume (ITBV) were measured by the dye-dilution technique. Measurements were performed during normovolaemic conditions, after volume loading with haemodilution blood (20 ml kg(-1)) and following haemorrhage (30 ml kg(-1)) without PEEP and with PEEP (15 cm H(2)O) applied. Volume loading increased GEDV, ITBV, TBV and SV, whereas PEP remained constant. However, the changes were not significant (P > 0.05). Subsequent haemorrhage significantly decreased GEDV (from 436 to 308 ml), ITBV (from 729 to 452 ml), TBV (from 2,131 to 1,488 ml) (all P-values <0.05), and SV (from 20.7 ml to 14.3 ml, P < 0.001). However, PEP did not change significantly (from 73 to 82 ms, P > 0.05). No correlation between the changes in PEP and changes in any other variable was observed. It is concluded that PEP is not sensitive to the changes in intravascular volume status.

The respiratory change in preejection period: a new method to predict fluid responsiveness

The accuracy and clinical utility of preload indexes as bedside indicators of fluid responsiveness in patients after cardiac surgery is controversial. This study evaluates whether respiratory changes (Delta) in the preejection period (PEP; DeltaPEP) predict fluid responsiveness in mechanically ventilated patients. Sixteen postcoronary artery bypass surgery patients, deeply sedated under mechanical ventilation, were enrolled. PEP was defined as the time interval between the beginning of the Q wave on the electrocardiogram and the upstroke of the radial arterial pressure. DeltaPEP (%) was defined as the difference between expiratory and inspiratory PEP measured over one respiratory cycle. We also measured cardiac output, stroke volume index, right atrial pressure, pulmonary arterial occlusion pressure, respiratory change in pulse pressure, systolic pressure variation, and the Deltadown component of SPV. Data were measured without positive end-expiratory pressure (PEEP) and after application of a PEEP of 10 cmH2O (PEEP10). When PEEP10 induced a decrease of >15% in mean arterial pressure value, then measurements were re-performed before and after volume expansion. Volume loading was done in eight patients. Right atrial pressure and pulmonary arterial occlusion pressure before volume expansion did not correlate with the change in stroke volume index after the fluid challenge. Systolic pressure variation, DeltaPEP, Deltadown, and change in pulse pressure before volume expansion correlated with stroke volume index change after fluid challenge (r2 = 0.52, 0.57, 0.68, and 0.83, respectively). In deeply sedated, mechanically ventilated patients after cardiac surgery, DeltaPEP, a new method, can be used to predict fluid responsiveness and hemodynamic response to PEEP10.