Abstract
In this closed-chest preparation in 10 anesthetized pigs, we determined
the effects of left ventricular (LV) contractility changes on the
echocardiographic contrast intensity variation of a second-generation
contrast agent within the LV cavity. The peak positive rate of change
in LV pressure (dP/dt(max)), as an index of the isovolumetric phase,
was gradually reduced by administration of halothane and propranolol,
and the velocity of circumferential fiber shortening (Vcfs) was referenced
as an index for the LV ejection phase. Contrast intensity-time curves
of the LV cavity were obtained after transpulmonary transmission
of the contrast agent. An off-line densitometric method was performed
to determine peak maximum and minimum intensities (I(max), I(min))
and their difference (I(amp)). Compared with baseline values, at
reductions in dP/dt(max) of 50% and 75%, the contrast intensity parameters
I(max), I(min), and I(amp) were decreased by 23% +/- 6% and 44% +/-
5%, 24% +/- 5% and 44% +/- 3%, and 31% +/- 6% and 45% +/- 3%, respectively
(P <.05). Significant correlations were observed between I(amp) and
dp/dt(max) (r = 0.82, P <.003, n = 30) and their changes (r = 0.59,
P <.03, n = 20), but correlations between contrast indexes and Vcfs
were only moderate. The sensitivity of I(amp) to indicate changes
in dP/dt(max) and Vcfs was 0.95 and 0.83, respectively. The cyclic
variation of LV intracavitary contrast intensity reflects the isovolumetric
contraction phase better than the ejection phase. The results suggest
that measurements of cyclic intensity changes may contribute to the
assessment of myocardial contractility changes. Underlying biophysical
mechanisms and load dependency of this phenomenon require further
investigation.
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