DOPPLER HAEMODYNAMIC EFFECTS OF DOBUTAMINE DURING STRESS ECHOCARDIOGRAPHY
A. Hamilton*, A. Russell, J. Ardill, S. Ettorre.
B. Repatriation General Hospital, Daw Park, South Australia.
Dobutamine traditionally is used as an inotropic agent in patients with left ventricular dysfunction. Its haemodynamic effects in this setting are well known. Its effects in a population without left ventricular failure is less well known.
In this study we examined the haemodynamic responses to dobutamine and atropine infusion in patients undergoing routine dobutamine stress echocardiography (DSE), with Doppler ultrasound.
In sixty-nine consecutive patients (35 males and 34 females, age was 69.9±9.9 years) dobutamine was infused at 5, 10, 20, 30, 40, 50 mcg/kg/min in 3 minute stages. Atropine was given if HR response was inadequate after 40 mcg/kg/min. Dobutamine was discontinued if an endpoint was reached i.e. ischaemia, hypotension or target HR, etc. 2D images, left ventricular outflow tract (LVOT) velocity time integral (VTI or stoke distance), HR and cuff blood pressure were obtained at each stage. From these data we calculated, MAP, minute distance (LVOT VTI x HR), cardiac work index (CWI) = (LVOT VTI x HR x MAP) and peripheral resistance index (PRI=MAP/LVOT VTI x HR). Wall motion was assessed from the 2D images. If a new wall motion abnormality was detected the study was considered positive. Stages within each case were ranked from peak dose to rest. Statistical analysis was performed using ANOVA. Results are expressed as mean ± SD from baseline to peak.
There were 52 negative and 17 positive studies. HR increased from 71±14 to 120±19 bpm p<.001, mean CWI from 1598±496 to 2285±863 m.mmHg/min p<.001, minute distance from 16.5±4.2 to 28.2±9.2 m/min p<.001, MAP decreased from 96.7±13.9 to 81.0±15.5 mmHg p<.001 and PRI from 6.2±1.8 to 3.1±1.1mmHg/m/min p<.001. In patients with ischaemia CWI increased by only 18% vs 60% p<.001 in those patients with a negative test. Negative tests showed a gradual increase in CWI to peak whereas positive tests showed an initial increase but became different at the third last stage.
Dobutamine in this clinical setting is a chronotropic vasodilator. Changes in peripheral resistance, heart rate, MAP occurred independently of ischaemia. Cardiac work initially rose then fell in patients who had a positive test.
Doppler haemodynamic indices may provide a more sensitive index of myocardial ischaemia in DSE.
