Effect of Acute Changes in Heart Rate on Doppler Pulmonary Artery Acceleration Time in a Porcine Model: Results

Table 1 summarizes the data for Doppler PA peak flow velocity, acceleration time, ejection time, AT/ET ratio, and PA pressure in seven pigs at atrially paced heart rates of 100 and 140 beats per minute. Mean PA pressure (14 ±5 mm Hg) remained constant over the entire range of paced heart rates. As shown in Table 1 and Figure 2, both PA acceleration time and PA ejection time were decreased at the higher heart rate (p<0.01). The PA acceleration time decreased from a mean (± SD) of 110 ± 12 to 83 ± 11 ms in going from a paced heart rate of 100 to 140 beats/min. The PA ejection time decreased from 315 ±23 to 237 ±21 ms over this range of heart rates. In contrast, the PA peak flow velocity and the AT/ET ratio did not change significantly over this range of heart rates. The AT/ET ratio was .35 ± .02 at a heart rate of 100 and 0.36 ± .03 at a heart rate of 140 beats/min. Figure 2 displays PA flow velocity recordings from an experimental pig obtained at heart rates of 100 (upper panel) and 140 (lower panel) beats/min. PA pressure remained the same at both heart rates in this and the other pigs. Although both PA acceleration time and PA ejection time were less at the higher heart rate, the AT/ET ratio remained unchanged.

Discussion
Several Doppler methods have been outlined for evaluating pulmonary artery pressure. The modified Bernoulli equation has been used to estimate PA systolic pressure from the peak velocity of the tricuspid regurgitation jet.* This equation has also been used to estimate PA diastolic pressure from the peak flow velocity in the pulmonic regurgitation jet. The iso-volumic relaxation time has been used in conjunction with a heart rate nomogram published by Burstin to estimate PA systolic pressure. Each of these methods has strengths and limitations. For example, the tricuspid regurgitation and pulmonic regurgitation jets cannot always be recorded in the clinical situation. Further, the isovolumic relaxation time is affected by factors other than heart rate and PA pressure—eg, the right atrial pressure—and may give erroneous estimates of PA pressure with high right atrial pressures. starlix 60 mg

Doppler measurement of acceleration time in the pulmonary artery or right ventricular outflow tract has been noted to be useful in estimating the PA pressure by several authors.’ We have noted that in patients with PA acceleration time <120 ms, mean PA pressure (in mm Hg) is inversely related to the pulmonary artery acceleration time (r= —0.87) by the following equation:
PA mean pressure = 90 — 0.62 x PA AT
Table 1—PA Doppler 6* Pressure Data

Measurement HR= 100 HR =140 p Value
PFV cm/s 69 ±15 62 ±18 N.S.
AT, ms 110 ± 12 83 ±11 <0.01
ET, ms 315 ±23 237 ±21 <0.01
AT/ET .35 ±.02 .36± .03 NS
PA pressure, mean, mm Hg 14 ±5 14 ±5 NS

 

Figure 2. Pulmonary artery flow velocity tracings recorded at heart rates of 100 beats/min (upper panel) and 140 beats/min (lower panel) in an experimental pig. Values for acceleration time (AT), ejection time (ET), and the ratio AT/ET are displayed below each beat. Although PA acceleration time and PA ejection time were decreased at higher heart rate, AT/ET ratio remained unchanged.

Figure 2. Pulmonary artery flow velocity tracings recorded at heart rates of 100 beats/min (upper panel) and 140 beats/min (lower panel) in an experimental pig. Values for acceleration time (AT), ejection time (ET), and the ratio AT/ET are displayed below each beat. Although PA acceleration time and PA ejection time were decreased at higher heart rate, AT/ET ratio remained unchanged.


Category: Pulmonary Artery

Tags: heart rate, porcine model, pulmonary artery