Right ventricular systolic pressure elevated at 30 40 mmhg

RV Pressure

RV pressure is recorded at the maximal systolic pressure, minimal early diastolic pressure, and end-diastolic pressure (Fig. 2). Normal RV systolic pressure is 20–30 mmHg and normal diastolic pressure is 3–7 mmHg (Table 2). The RV waveform has a rapid upstroke and downstroke during systole. Ventricular diastole consists of three phases: early rapid filling, slow filling, and atrial systole. The end-diastolic pressure is measured as the pressure after atrial contraction and immediately before the onset of ventricular contraction. RV pressure can be elevated in PH, pulmonary embolism, and pulmonic stenosis.

Right Ventricular Pressure Overload Models

RV pressure overload is achieved by constricting the pulmonary artery. This leads to an increased workload on the right ventricle as pressure has to be higher to achieve the same blood flow. In small animals, RV pressure overload is less frequently performed than LV, which is potentially due to two main reasons: (1) RV hypertrophy and failure have a much lower prevalence in humans than LV HF and (2) surgery for pulmonary artery banding is much more demanding in small animals. The pulmonary artery is much more fragile than the aorta and the right ventricle is not able to withstand stress during manipulation of pulmonary artery. The technique has been described for mice [73] but has also been used in rats [93] and at different ages [94].

Right Ventricular Pressure Overload

Although RV pressure overload alone may occur because of PS or PH, pure RV pressure overload is uncommon in adult hearts because RV hypertension is usually associated with TR and RV dilation. Initially, RV pressure overload reduces the normal motion and curvature of the IVS toward the RV and causes the appearance of abnormal IVS flattening throughout the cardiac cycle. As RV pressure overload progresses to more severe RVH, the center of mass of the heart shifts toward the RV. This causes a characteristic paradoxical septal motion of the IVS bowing toward the LV that is most pronounced at end-systole when RV systolic afterload is at its peak (i.e., the time when RV pressure is the highest; Fig. 7.3). When comparing the paradoxical septal motions of RV pressure overload versus RV volume overload, the key point to remember is that the most pronounced IVS bowing toward the LV occurs at end-systole with RV pressure overload and at end-diastole with RV volume overload.

Tricuspid annular plane systolic excursion (TAPSE) is another method to assess global RV systolic function. TAPSE refers to the long-axis, apex-to-base lateral tricuspid annulus systolic excursion. Because of the relatively fixed septal attachment of the tricuspid annulus, its displacement is asymmetric, and TAPSE appears more as a hinge-like motion. Normal TAPSE is 17 mm or greater toward the cardiac apex, and reductions in TAPSE values are suggestive of RV systolic dysfunction.

Right heart catheterization remains the gold standard in assessment of hemodynamics in patients with PH as well as a confirmatory method for diagnosis. RHC is performed in patients who have suspected PH after the initial screening. This procedure focuses on measuring PA pressure, PVR, and the effects of vasodilator therapy on the pulmonary circulation. The underlying principle for vasodilator testing as a diagnostic step is identifying patients who are responders to vasodilator therapy because these patients are more likely to benefit from treatments with medications such as oral calcium channel blockers. Inhaled NO is most commonly used in acute vasodilator testing, but intravenous (IV) epoprostenol and IV adenosine are acceptable alternatives. A positive result of vasodilator testing is defined as a decrease in mPAP of at least 10 mm Hg to an absolute mPAP of less than 40 mm Hg without decreasing the CO.

Pressure Loading

The right ventricular pressure is most commonly elevated because of an unobstructed ventricular component of the atrioventricular septal defect. Right ventricular hypertension, however, can also reflect increased left atrial pressure and pulmonary hypertension. This can be produced, for example, by an associated partition within the left atrium, or by left-sided malalignment of the atrial relative to the ventricular septum, with an associated obstructive interatrial communication. Such right ventricular hypertension is also seen in some patients with isolated atrial shunting, when there is a large left-to-right shunt and increased flow of blood to the lungs. Included amongst these patients will be those with stenosis of or regurgitation across the left atrioventricular valve. An alternative cause for pulmonary hypertension in this setting is the presence of an obligatory shunt from left ventricle to right atrium. This also produces, effectively, a large left-to-right shunt.

A raised pulmonary arterial pressure, therefore, is a feature of patients having atrioventricular septal defects with large ventricular components. In those with shunting exclusively at atrial or ventriculo-atrial levels, it is caused by high pulmonary blood flow, or obstruction to pulmonary venous return. Elevated flow to the lungs, and increased right ventricular pressures, are instrumental in the development of obstructive pulmonary vascular disease. This develops earlier than is usually the case for those having an isolated ventricular septal defect. It is now accepted that this tendency is further accentuated in the presence of Down’s syndrome because of the susceptibility of such patients to obstruction of the upper airways and associated alveolar hypoventilation. This tendency to more rapid progression of pulmonary vascular disease is one of the reasons underscoring the trend to earlier surgical intervention for those patients with a common atrioventricular valvar orifice. Most centres would now elect to operate on such patients within the first 6 months of life.

Etiology and Tricuspid Valve Morphology

TR secondary to right ventricular (RV) pressure and/or volume overload is more common than that associated with a primary anatomic lesion of the TV. Secondary TR, usually referred to as functional TR, is characterized by intrinsically normal TV leaflets but abnormal coaptation, often as a result of a combination of RV remodeling and tricuspid annular dilation (Fig. 20.1). Measures of RV sphericity (apical four-chamber RV systolic area/RV long-axis dimension)2 and eccentric dilation3 have been associated with ventricular displacement of the TV coaptation margins, producing leaflet tethering (or tenting) with incomplete systolic coaptation. As measured from the apical four-chamber view (Fig. 20.2), both the tethering distance2 from the TV annular plane and tethering area3 enclosed by the displaced leaflets and the annular plane independently correlate with the severity of functional TR. With the development of functional TR, the TV annulus dilates, becomes more circular, and loses its normal saddle-shaped configuration.4 With progressive TV annular enlargement, readily assessed by the 2-D distance between insertion of the anterior and septal leaflets in the apical four-chamber view, worsening functional TR also is noted.3 With significant TV leaflet tethering, however, functional TR can be observed without significant TV annular dilation.2

In one study of patients with moderately severe to severe TR identified by echocardiography, 86% were found to have functional TR compared with 14% with a primary abnormality of the TV leaflets.5 Pulmonary hypertension, either primary or secondary, is the most common cause of functional TR. Moderate to severe TR has been observed in 60% of patients with severe symptomatic primary pulmonary hypertension.6 Secondary pulmonary hypertension as a result of chronic lung disease, left ventricular failure, or left-sided valvular disease (most commonly mitral), when accompanied by significant functional TR, has a more ominous prognosis.5,7,8-10 Systolic pulmonary artery pressures >55 mm Hg are likely to cause some degree of TR with structurally normal TV leaflets, whereas TR occurring with systolic pulmonary artery pressures <40 mm Hg usually indicates a primary abnormality of the TV apparatus11; however, TR related to RV infarction and atrial septal defects (ASDs) are exceptions.

Functional TR may also occur in pure RV volume-overloaded states without pulmonary hypertension, such as with ASDs with a large left-to-right shunt. Intrinsic myocardial disease with RV infarction with postinfarct remodeling and RV dysplasia are also associated with functional TR, usually in the presence of considerable diastolic RV pressure overload.

TR resulting from a primary abnormality of the TV, also referred to as organic TR (Fig. 20.3), is far less common than functional TR.5,12 Conditions affecting the left-sided valves, such as degenerative myxomatous disease, infective endocarditis and, rarely, rheumatic disease, may also involve the TV.11,12

Ebstein's anomaly, the most common congenital cause of TR, is associated with a morphologic spectrum of variably dysplastic and tethered TV leaflets displaced toward the RV apex.13 TR may occur many years after mediastinal radiation therapy, although it is less frequently observed than left-sided, radiation-induced valvular regurgitation.14 Traumatic TR caused by disruption of the TV support apparatus has been associated with many forms of chest trauma and may elude diagnosis for years after the acute event.15

Pacemaker and cardioverter-defibrillator leads can cause severe TR by multiple mechanisms, including TV leaflet perforation, lead entanglement within the TV support apparatus, lead adhesion to a TV leaflet, or lead impingement preventing normal TV leaflet closure.16

Uncommon systemic diseases such as hypereosinophilic syndrome and carcinoid may affect the TV,11 resulting in severe TR. In carcinoid syndrome, the TV leaflets are characteristically thickened, retracted, and immobile in a semiopen position with obvious incomplete central coaptation.17 Similar, but somewhat less dramatic, changes have been reported in patients with drug-induced TV disease associated with anorectic agents18 and ergot alkaloids such as ergotamine19 and pergolide.20

Right Ventricular Pressure Overload

To produce a model of right ventricular pressure overload in mice, the pulmonary artery was constricted.88 The animals were anesthetized and ventilated as described for aortic constriction. After opening the chest in the third intercostal space, a suture was tied around the pulmonary artery against a 25-gauge needle for a moderate degree of stenosis and against a 26-gauge needle for severe stenosis. Two weeks after pulmonary banding an increase in the weight of the right ventricle and myocyte cross-sectional area were found. To determine whether these animals develop right ventricular dysfunction, quantitative digital contrast microangiography was used for assessment of right ventricular function. Severe chronic pressure overload was shown to induce a reduction in ejection fraction and an increased end-diastolic volume, indicating right ventricular dysfunction. Thus, this mouse model mimics several features of right ventricular hypertrophy and failure similar to those found in human patients.

Pulmonary Arterial Balloon Angioplasty

Indications for angioplasty when the right ventricular pressures are normal or only mildly elevated are controversial. In infants and children, however, significantly diminished perfusion to one lung in spite of a normal right ventricular pressure is an accepted indication for intervention. More aggression may be needed in patients requiring staged palliation culminating in Fontan circulation in order to have good sized pulmonary arteries despite small gradients. Overall, accepted indications for balloon angioplasty include right ventricular hypertension, right ventricular dysfunction, perfusion mismatch, with less than one-quarter of flow directed to one lung, pulmonary hypertension in the unaffected lung, or presence of severe pulmonary regurgitation.103

The basic principles of balloon angioplasty are applied. After haemodynamic stabilisation, a stiff wire position is achieved in a good distal vessel of the lung. Angiography is performed and the size and length of stenosis are measured. The Multitrack catheter is useful for multiple haemodynamic measurements and performing angiography. The diameter of the balloon is determined by the diameter of a normal vessel adjacent to the stenosis. A higher ratio of balloon-to-stenosis diameter increases the chance of success, but also the risk of dissection, rupture, or aneurysmal formation. The success rate in one series was higher when the diameter of the balloon was more than 3 times the diameter of the stenosis, with a significantly greater diameter achieved after the procedure.104 Outcome is assessed by an increase in the diameter by more than half, a reduction of the ratio of right ventricular to systemic arterial pressures, or by assessment of distribution of perfusion to the lungs.

Complications are more frequent after dilation of tight stenoses requiring oversized balloons and high pressures of inflation. Stenoses were impossible to dilate in half the patients on one series, with recurrent stenoses occurring in up to one-third.105 The Valvuloplasty and Angioplasty registry documents an incidence of complications on one-eighth of patients, including rupture of vessels and death. Success has been achieved in two-thirds of patients unresponsive to conventional angioplasty by using high-pressure balloons.34 Trauma can also be produced to the pulmonary arteries, usually with the tear occurring distal to the area of the stenosis.106 Pulmonary hypertension was found to be a significant risk factor for such trauma.

Cutting balloons, as produced by Boston Scientific (Fig. 17-23), and used successfully in resistant coronary and peripheral arterial lesions, are now being used for resistant stenotic lesions in the pulmonary arteries that are un-dilatable even at high pressures. The balloon has three or four microtome blades, attached along the length of the balloon, that protrude on inflation to create controlled cuts on the walls of the stenosed vessels. On deflation, the balloon folds over the blades. Early results in lesions resistant to conventional balloon angioplasty have been encouraging.107,108 Overall, cutting balloons improve the gain in luminal diameter, albeit with a slight increased risk of vascular trauma.

Analysis

•

Rate of rise in RV pressure (dP/dT)

The rate of rise in RV pressure is well correlated with systolic function and can be measured using the rate of rise in velocity of the TR jet.

The TR jet is interrogated using CW Doppler and the time interval between velocities of 1 and 2 m/s is measured (in contrast to the 1–3 m/s time interval used with LV dP/dT assessment from the MR jet).

The pressure differential can be calculated by converting the measured velocities into pressures using the simplified Bernoulli equation.

dP=pressure gradient at 2 m/s−pressuregradient at 1 m /s=4(v2m/s)2−4(v1m/s)2

dT=time interval in seconds

Normal dP/dT values are greater than 1000 mm Hg/s.

CO

As with the LV, SV (in mL or cm3) of the RV can be calculated by measuring flow through a known CSA.

Although SV can be theoretically measured anywhere, the most common site for measurement is the relatively cylindrical RVOT.

CSA (in cm2) can be measured utilizing RVOT diameter obtained in the ME RV inflow-outflow or the UE aortic arch SAX views, assuming that the CSA is circular.

CSARVOT=3.14 (dRVOT/2)2 or CSAPA=3.14 (dPA/2)2

Flow through the RVOT is measured using PW Doppler, obtaining a sample velocity over time. The distance traveled by blood in a single beat is measured in centimeters and known as the VTI (Figure 6-48).

SV (cm3)=CSA (cm2)× VTI (cm)

Right-sided CO can be calculated by multiplying the SV by the HR:

CO (L/min)=[SV (mL)×HR (beats/min)]/1000

Right-sided CI can be calculated by factoring in the patient's BSA (in m2). A normal CI is greater than 2 L/min/m2.

Calculation of right-sided CO may be particularly beneficial when intracardiac shunts are present and pulmonary flow is greater than systemic flow (Qp/Qs > 1).

Right ventricular systolic pressure (RVSP)

The pressure gradient between the RV and the RA is first calculated using the simplified Bernoulli equation and the maximum velocity of the TR jet (see Figure 6-45).

ΔPRV−RA=4(TR jet) 2

The RSVP can be calculated if right atrial (RA) pressure is known.

RVSP=ΔPRV−RA+Ra pressure  (CVP)

In absence of PS or RVOT obstruction, RVSP and PA systolic pressure are equivalent.

Hepatic venous flow may be used to assess global RV function

Impaired RV systolic function can result in blunting of systolic inflow and augmentation of diastolic inflow, but this must be differentiated from elevated RA pressures for other reasons.

Severe TR results in reversal of systolic hepatic venous flow, and this may be seen with severe RV systolic dysfunction (Figure 6-49).

Key Points

Pitfalls

The RV is particularly load dependent, and wide variation in CO and dP/dT can be seen with differences in afterload.

dP/dT and RVSP can be calculated only if there is TR.

Measurements of velocities will be underestimated if the angle of Doppler interrogation is not parallel to motion/flow, giving falsely low estimations of ventricular function.

Inaccurate 2D measurements of RVOT diameter will grossly impair the ability to calculate an accurate right-sided CO, particularly because this measurement is squared in the equation.

Step 4: Determine the Size of the Shunt

•

In the absence of increased right ventricular pressure, the severity of left-to-right shunting is proportional to the size of the defect.

In an unrestricted defect, equalization of ventricular pressure will occur over time, reflecting the development of pulmonary hypertension.

The greater the size of the lesion and the lower the pulmonary resistance, the larger the left-to-right shunt.

Key Points

Align the defect so that the VSD jet is parallel to the cursor to obtain a peak velocity via pulsed or continuous wave (CW) Doppler.

Right ventricular pressure can be estimated from the modified Bernoulli equation using the peak velocity across a VSD based on blood pressure as an estimate of systemic pressure.

4 × (peak velocity across the VSD)2 = pressure difference between the LV and RV.

Blood pressure—4 × (peak velocity across the VSD)2 = estimated right ventricular pressure.

With equal ventricular pressure, the size of the shunt is determined by arterial and systemic vascular resistance.

Use angulation of the plane of sound or alternative imaging rather than using theta (θ) to change your angle of interrogation. Using theta (θ) will provide an inaccurate measurement by altering the Bernoulli equation.

Right Atrial Compression, Inversion, or Collapse

Right atrial pressures are lower than RV pressures throughout most of the cardiac cycle. Because intrapericardial pressure is evenly distributed over the heart, one would surmise that right atrial compression would occur before RV compression as pericardial pressure is raised. This is borne out in imaging studies in which the right atrium and ventricle are continuously imaged during pericardiocentesis.44 Subsequently, right atrial inversion, which tends to begin in late ventricular diastole (just before or at the p wave if sinus rhythm is present) but persists into early ventricular systole, is an extremely sensitive sign of cardiac tamponade59 (Fig. 30-12). However, it is less specific than RV diastolic collapse (see Table 30-3). The depth of right atrial collapse bears an imprecise relationship to the intrapericardial pressure or hemodynamic effect of the fluid.50,60 Conversely, the right atrial inversion time index (determined by counting the total number of frames showing atrial inversion divided by the total number of frames in the cycle), has been reported to have a high sensitivity and specificity for the presence of clinical cardiac tamponade60 (see Table 30-3). It should be noted that respiration, and although less well studied, the same factors that interfere with RV diastolic collapse may diminish right atrial collapse. Ventricular pacing has also been reported to affect the accuracy of this sign.60