Abnormalities in atrial pressures

Elevations in RA pressure are often a clue to cardiovascular pathology. Increased mean RA pressure is seen in valvular heart disease, constrictive pericarditis, restrictive cardiomyopathy, cardiac tamponade, fluid overload (e.g., renal failure), pulmonary hypertension, left to right shunts, pulmonary embolus, RV infarction, LV systolic or diastolic failure, and congenital heart disease. It is important to note that mean RA pressures may appear normal in patients with heart disease who are dehydrated.

The A wave is accentuated in patients with noncompliant ventricles and therefore can be increased in patients with ventricular ischemia, infarction, or hypertrophy from pressure or volume overload. A prominent RA A wave can occur in tricuspid regurgitation, pulmonic regurgitation, or stenosis as well as pulmonary embolus or cor pulmonale from any cause (Figure 5.2a and Tables 5.1 and 5.2). Intermittent cannon A waves can be seen in complete heart block or ventricular tachycardia as the atria are contracting intermittently against a closed AV valve (Figure 5.2b). In patients with atrial flutter or atrial tachycardia, A waves may be present at an accelerated rate. Small A waves are rare in RA tracings but common in LA tracings (Figure 5.2c).

Abnormalities in the X descent are seen with severe tricuspid regurgitation (TR) or mitral regurgitation (MR) when the X descent and C wave can be interrupted by a prominent V wave.

The V wave reflects atrial pressures during ventricular systole and thus can be useful as a clue to the presence of AV valve regurgitation. In the RA a prominent V wave can be seen in patients with tricuspid regurgitation and the RA pressure tracing can take on a ventricularized character when TR is severe (Figure 5.3) [3]. Ventricularization of the RA pressure tracing is the most specific finding, but is found in a minority of patients with severe TR (see Chapter 13). In a study of 60 patients who had right ventriculography, Lingamneni et al. found that ventricularization of the right atrial pressure contour was present in only 40% of patients with severe TR [4]. Cha et al., in their study of 59 patients with severe TR diagnosed on right ventriculography and/or at the time of surgery, found that a ventricularization pattern was present in 31%, and that prominent V waves (not further defined in the paper) and steep Y descents were present in an additional 37% of the patients [5]. In contrast, Pitts et al. reported that neither prominent right atrial V waves nor elevated mean right atrial pressures reliably predicted the presence of moderate or severe tricuspid regurgitation (as determined by echocardiography), but that the absence of right atrial V waves and elevated mean right atrial pressures were relatively specific for excluding significant tricuspid regurgitation [6]. For the purposes of their study, a “prominent” right‐sided V wave was defined as (1) V wave >15 mm Hg, (2) a difference between V wave and mean RA pressure >5 mm Hg, or (3) a ratio of V wave to mean RA pressure >1.5.

Commonly, however, the left‐sided V wave receives the most attention and that is what we will focus on in this section (examples are shown in Figure 5.4). The PA systolic pressure waveform and left atrial V wave are generated at the same time (assuming that the ventricles contract at the same time), however the V wave in the PCWP tracing will be seen later because of the delay in transmission of left atrial pressure to the catheter tip. Moore et al., in their study of 13 patients with large V waves, found that the onset of the V wave was approximately 110 milliseconds after the onset of the pulmonary arterial upstroke [7].

The V wave in the PCWP (or LA) tracing is dependent on the pressure–volume relationship of the left atrium and left atrial compliance as well as the volume of blood entering the atrium. A large V wave indicates a rapid rise in LA pressure during ventricular systole and can occur in setting of a noncompliant left atrium and normal flow (e.g., atrial ischemia) or a normally compliant left atrium with large flow (e.g., acute mitral regurgitation). Conversely, if the left atrium has a large capacitance then a prominent V wave may be absent even in the presence of severe mitral regurgitation.

In the left atrium or pulmonary capillary wedge pressure tracing, a prominent V wave suggests mitral regurgitation, but is neither sensitive nor specific. Some investigators have advocated using a grading system where a V wave that is twice the mean wedge pressure is suggestive of severe MR and a V wave maximum of three times mean wedge pressure is diagnostic of severe MR, but this has not been widely validated (Table 5.3). Although not typical, a prominent V wave can occasionally be observed in patients with mitral stenosis if the LA is relatively noncompliant, with limited ability to accept expanded filling volumes.

In patients with severe MR and a large V wave, mean PCWP can overestimate LV end‐diastolic pressure. In a study by Haskell and French [8], mean PCWP pressure overestimated LVEDP by approximately 30% (in this study, a large V wave was defined as being greater than the A wave by more than 10 mm Hg). A better estimate of LVEDP was obtained by using the trough of the X descent.

The Y descent or decay in the V wave occurs during the opening of the AV valve and represents rapid emptying of the atria into the ventricle (which results in a drop in pressure). It is a marker of passive ventricular filling and thus anything that prevents or enhances early diastolic filling affects the character of the Y descent. Conditions with high ventricular pressures during early diastole tend to be associated with blunted Y descents (e.g., tamponade or mitral stenosis). Y descents are usually blunted in cardiac tamponade but can become more prominent during inspiration; the Y descent becomes more apparent following pericardiocentesis. Conditions with low ventricular pressures during early diastole and prominent passive filling of the ventricle (e.g., constrictive pericarditis) tend to have large Y descents. Various examples of Y descents are shown: mitral stenosis can cause an attenuation or flattening of the terminal Y descent (Figure 5.5); venous pressures are elevated and Y descents are prominent in constrictive pericarditis (Figure 5.6); both X and Y descents are blunted in a case of right ventricular infarction (Figure 5.7); and Y descents are blunted, especially during expiration, in a case of cardiac tamponade (Figure 5.8). The Y descent can vary with the position of the patient in the rare instance of large atrial myxoma.

Physical exam

Physical examination of jugular venous pulse (JVP) provides valuable information to clinicians, as the JVP is a manometer of pressure in the right atrium. To determine JVP, sit the patient at 45° and turn his or her head slightly away from you. Use the internal jugular vein (not external jugular vein) medial to the clavicular head of sternocleidomastoid and measure JVP in centimeters above the sternal notch (vertical not diagonal distance). The venous pulse can usually be analyzed more readily using the right internal jugular vein, as the right innominate and jugular veins extend in an almost straight line from the superior vena cava. Sir Thomas Lewis in 1930 proposed a simple bedside method for measuring central venous pressure. He found that the catheter‐measured CVP was equal to 5 cm plus the vertical distance of the JVP from the sternal angle and that this measurement was independent of the individual’s position (e.g., supine, semiupright, or upright). Remember that CVP in cm of blood must be divided by 1.34 to get pressure in mm Hg. Also note that the distance between the sternal angle and the midportion of the RA, which Lewis estimated at 5 cm, varies considerably between individuals and is affected by age and anterior–posterior diameter of the chest [9].

JVP can be used to assess right heart filling pressures and the waveform can provide information suggestive of specific diagnoses. Raised JVP with normal waveform is suggestive of right heart failure and/or fluid overload. The lack of pulsations in a patient with elevated JVP would be suggestive of SVC obstruction. Various abnormalities of the A wave, V wave, X descent, or Y descent suggest diseases outlined in Tables 5.2 and 5.3. An increase in JVP with inspiration (Kussmaul’s sign) is suggestive of constrictive pericarditis.

Important points

• The atrial waveform is composed of the positive atrial (A) and ventricular (V) waves and the X and Y descents.
  
• The A wave is prominent with abnormalities of RV and LV compliance (e.g., hypertrophy, ischemia).
  
• The V wave is accentuated in cases of atrioventricular valve regurgitation (RA V wave in TR, LA V wave in MR).
  
• The X and Y descents are diminished or absent in pericardial tamponade.
  
• The X and Y descents are accentuated in constriction and restrictive myocardial disease.