The 60/60 sign in echocardiography refers to the coexistence of a truncated right ventricular outflow tract acceleration time (AT <60 ms) with a pulmonary arterial systolic pressure (PASP) of less than 60 mmHg (but more than 30 mmHg). In the presence of right ventricular failure, it is consistent with an acute elevation in afterload, commonly due to an acute pulmonary embolism.
Pathology
The right ventricle (RV) generates a stroke volume which equals that of the left ventricle; it does so at lower pressures, relatively diminutive chamber dimensions, and far thinner walls (<3 mm) 4. This compliance also renders the right ventricle exquisitely sensitive to sudden elevations in afterload; facing elevated pressures, the right ventricle will dilate, lacking the capacity to generate an appropriate increase in pressure.
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Chronic elevations in right ventricular afterload, however, allow a series of compensatory geometrical changes to occur; chamber dilation and increased wall thickness allow initial preservation of RV stroke volume, albeit at markedly elevated pressures 4.
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Right ventricular dilation and contractile dysfunction occur in both acute (for example in pulmonary embolism) and chronic cor pulmonale, but only the latter typically demonstrates systolic pressures markedly above normal ranges, commonly in excess of 60 mmHg. The inability to generate such pressures, therefore, may be thought to be more suggestive of acute cor pulmonale.
Radiographic features
Echocardiography
The relevant structures of interest are the right ventricular outflow tract (RVOT) and tricuspid valve; the apical 4 chamber view or parasternal RV inflow views are preferred for the latter, while the former is best assessed with a basal parasternal short axis view.
- the RVOT is best assessed with pulsed wave Doppler (PWD)
- normal acceleration time (AT) is >90 ms
- an AT <60 ms is markedly abnormal
- thought to be a reflection of increased mean pulmonary arterial pressure (mPAP) 2
- in the absence of pulmonic stenosis, pulmonary arterial systolic pressure (PASP) is equal to RV systolic pressure (RVSP) which is derived from the following:
- the pressure gradient across the tricuspid valve (TV)
- a tricuspid regurgitant (TR) jet is first sought using color flow Doppler (CFD) across the TV and right atrium
- the maximum TR jet velocity (Vmax) is quantified with continuous wave Doppler (CWD)
- the simplified Bernoulli equation then allows derivation of the trans-tricuspid pressure gradient
- right atrial pressure (RAP), which is commonly estimated by observing the diameter and respiratory variation of the inferior vena cava (IVC)
- the pressure gradient across the tricuspid valve (TV)
- if calculated PASP is <60 mmHg and >30 mmHg with an AT <60 ms the 60/60 sign is considered to be present
- up to 94% specific for acute cor pulmonale due to an acute pulmonary embolism
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