Functional assessment of the dynamic profile of tricuspid annular motion.

BACKGROUND: Maximal systolic tricuspid annulus (TA) descent by M-mode (MM) is a well described and accepted standard reference of right ventricular (RV) systolic function; however, the contribution of each individual TA contour during the cardiac cycle has not been well characterized. Therefore, the aim of this study was to define each peak and nadir component of the constantly moving annulus.
MATERIAL AND METHODS: Standard echocardiographic data was collected from 35 patients over a wide range of both normal and abnormal RV systolic function. Time to onset and total duration of each recognizable component of the TA tissue Doppler imaging (TDI) signal was measured and correlated to each individual change in contour of the TA, obtained by MM, during the cardiac cycle.
RESULTS: In this heterogeneous patient population, careful measurement of each recognizable component of the TA TDI signal corresponded to conformational changes in the TA contour. Furthermore, these TA TDI intervals were imprinted into the TA MM tracing and precisely identified specific systolic as well as diastolic events, regardless of RV systolic function or pulmonary hypertension severity.
CONCLUSIONS: Careful observation of the constant dynamic motion of the TA, aided by high temporal resolution MM, allows better understanding of each individual component of annular motion. It appears that each peak and nadir component not only is useful in characterizing RV systole and diastole, but also would be invaluable to assess the functional relationship that exists between the right atria and ventricle; particularly, when annular motion directly reflects the contribution of both cardiac chambers.

INTRODUCTION

Knowledge of the role of the right ventricle (RV) in health and disease historically has lagged behind the obviously important left ventricle with the RV traditionally being considered a mere bystander. However, numerous clinical reports have now identified RV dysfunction with adverse clinical outcomes prompting better recognition of RV dysfunction.[123456789]

The use of objective measures such as M-mode (MM) and tissue Doppler imaging (TDI) interrogation of the tricuspid annulus (TA) has been proven both simple and reproducible to improve our echocardiographic interpretation of RV systolic function.[1011121314151617181920] However, in contrast to TDI, which provides information in terms of RV systole and diastole;[171819] MM interpretation of TA motion has simply been used to describe the maximal longitudinal descent as a marker of RV systolic function.[1011121314151617181920]

Since the TA is in constant motion throughout the cardiac cycle, it is important to characterize the specific contribution of RV function to each peak and nadir component of the annulus noted in MM tracings. The dynamic motion of the TA embedded in an MM image will provide additional physiologic information when interpreting an echocardiogram with regards to overall RV performance.

Even though a correlation between motion assessed by MM and velocity measurements by TDI might appear simplistic findings, mostly deducible from fundamental cardiac physiology, this type of side-by-side analysis has never been investigated and might prove useful in defining the specific contribution of TA motion seen by MM, in both systole and diastole.

To that extent, we designed a pilot study in which both MM and TDI interrogations of the TA were used in the same individual to accurately delineate the individual contribution of each component of TA motion throughout the cardiac cycle. We then carefully measured time intervals that characterize the occurrence of systole and diastole, as seen in the corresponding TA TDI signal, and found the specific imprint correlate in the corresponding TA MM image. Since our group has extensively studied the effects of chronic pulmonary hypertension (cPH) on RV performance;[17181920212223] we then investigated how each individual TA motion component was altered in cPH patients.

MATERIAL AND METHODS

We queried our echocardiographic database and identified 35 consecutive patients who had adequate acoustic windows with visualization of the RV, including well visualized TA with clear MM images and TDI signals for proper analysis. All patients were in normal sinus rhythm at the time of the study, had no premature atrial or ventricular beats, or paced rhythm. In addition, all patients had normal left ventricular systolic function, with no left ventricular wall motion abnormalities and no history of previous cardiac surgery.

The protocol was reviewed and approved by the Institutional Review Board of the University of Pittsburgh Medical Center.

Standard measurements of RV end-systolic and end-diastolic areas to calculate RV fractional area change[212223] as well as left ventricular volumes and ejection fraction were measured from the apical four- and two-chamber views using biplane Simpson's rule according to American Society of Echocardiography standards.[12]

Tricuspid annular TDI patterns were obtained by placing a 5 mm sample volume positioned at the lateral corner between the TA and the RV lateral wall using the apical four chamber view, as described for MM,[17182122] utilizing tissue velocity imaging at a frame rate of 60-100 frames per second.[1920] A typical TDI signal consists of an initial positive signal representing isovolumic contraction that is then followed by another positive signal corresponding to TA systolic velocity. The diastolic component of the TA signal is composed of three negative deflections, the first one represents isovolumic relaxation, followed by early phase of diastolic myocardial velocity (Ea) and the last negative deflection is representative of the late phase of diastolic myocardial velocity (Aa) after atrial contraction. All velocities were recorded for at least three consecutive cardiac cycles during end-expiration. Once all TA systolic and diastolic signals were identified [Figure 1a], we then measured time to onset of these signals as depicted in Figure 1b.

Figure 1

(a) Representative tissue Doppler image of the tricuspid annulus showing proper identification of all signals including isovolumic contraction (IVC) and systolic signals as well as the isovolumic relaxation (IVR), early and late diastolic signals. (b) Same tissue Doppler image showing how each individual time interval was measured from the onset of the QRS denoted by the solid vertical white line. White arrows head shows the time to onset to the isovolumic contraction signal; thin solid white arrow represents time to onset of the systolic signal, while the thick solid white arrow measures the time to termination of the tricuspid annular systolic signal. The thin dotted arrow denotes time to onset of diastole while the thick dashed white arrow defines time to termination of diastole

To determine the specific motion and timing of all components of the TA, in the apical four-chamber view, we oriented the MM cursor to the junction of the tricuspid valve plane with the RV free wall aligning the motion of the annulus along the MM cursor. From this view, overall TA excursion is recorded from the lowest point seen after atrial ascent until maximal descent is recorded during ventricular systole.

A week after the initial TA TDI time intervals were obtained, tricuspid annular plane systolic excursion (TAPSE) MM measurements were performed to determine if the individual peak and nadir components in the TAPSE MM would match the previously recorded TA TDI measurements. These TAPSE measurements were performed without knowledge of the previously recorded TA TDI readings and the patient's identity was decoded to avoid bias in the measurements.

Finally, continuous-wave Doppler was utilized to record the tricuspid regurgitation jet from multiple windows, and the pulmonary artery systolic pressure was derived using the modified Bernoulli equation and an estimate of mean right atrial pressure using the diameter and collapse index of the inferior vena cava and the hepatic venous flow pattern.[2425]

All echocardiographic parameters were calculated off-line using the commercially available tool section of the Acuson Syngo system (WS 3000 Diagnostic Workstation, Siemens, California.). Two cardiac sonographers collected all echocardiographic images and the same echocardiographer analyzed all the data. Measurements of each variable were collected from three consecutive beats and the mean of each variable with its standard deviation was used for comparison analysis using the 2-tailed Student's t-test for paired and unpaired data, respectively. A P value <0.05 was considered statistically significant for all analyses.

RESULTS

Characterization of each individual peak and nadir motion component of the TA during systole and diastole was studied in all 35 patients and the echocardiographic variables of the study group are shown in Table 1.

Table 1

Standard echocardiographic and Doppler measurements

Timing of each TA systolic and diastolic flow component using TDI is shown in Table 2.

Table 2

Tricuspid annular tissue Doppler imaging time intervals

As described in the Methods Section, each specific systolic and diastolic event denoted by the TA TDI signal was superimposed on the corresponding TAPSE MM tracing of the same patient and each peak and nadir TAPSE component on the MM tracing was identified as seen in Figures 2a and b. Finally, each MM TAPSE intervals were carefully measured and listed on Table 3.

Figure 2

(a) Representative M-mode (MM) tracing of the TA showing time to onset of systolic events, intervals were taken from measurements obtained from the TA tissue Doppler imaging signal.(b) Representative MM tracing of the TA showing time to termination of diastolic events; intervals were taken from measurements obtained from the TA tissue Doppler imaging signal

Table 3

Tricuspid annular M-mode time intervals

Representative TA TDI images with its corresponding TAPSE MM tracing and the respective time intervals they represent are shown [Figures 3a and b].

Figure 3

(a) Representative tricuspid annular tissue Doppler image with its corresponding MM tracing and the respective time intervals they represent from a patient from Group I. (b) Representative tricuspid annular tissue Doppler image with its corresponding MM tracing and the respective time intervals they represent from a patient from Group II

DISCUSSION

The results of this study describe for the first time the characteristic dynamic profile of a TAPSE MM tracing. Specifically, it describes each peak and nadir component in relation to RV systolic and diastolic events as the TA moves throughout the cardiac cycle.

From a mechanistic point of view, it is well known that RV wall motion is complex.[2627] First, during systole, there is longitudinal shortening of the RV inflow along the base to the apex axis with radial motion of the RV free wall towards the common septum. Second, there is circumferential motion that gives a rotation or a squeeze of the ventricle.[28] Therefore, MM with its well-known temporal resolution,[2930] allows accurate interrogation of the full TA excursion along its longitudinal axis throughout the cardiac cycle. It is important to point out that in addition to knowledge of maximal TA plane systolic excursion, known to correlate with RV fractional area change;[1011121314151617181920212223] a more detailed notion of the full extent of TA motion is needed to understand RV performance and atrio-ventricular interactions.

We acknowledge some limitations. First is the small number of patients included in our study. However, this was a proof of concept approach that allowed proper identification of the systolic and diastolic components of TA annular motion. Second, it is important to point out that TA TDI and MM images were not obtained simultaneously and respiration, loading conditions and heart rate can be variable and might change the occurrence of events. However, all signals were obtained at the end of expiration and there was no significant difference in heart rate between the TDI and MM counterparts. Finally, no assumptions can be made on how abnormal left ventricular systolic function or the presence of any arrhythmia would affect the interpretation of these signals and their intervals.

In summary, it should not be surprising to identify that the value of TA MM assessment goes well beyond its already well recognized utility in assessing maximal systolic excursion.[1011121314151617181920] Even though the 3-D TA motion was not studied; the results of this analysis demonstrated an accurate imprint, although imperfect as, of systolic as well as diastolic events on TA MM tracings. Careful identification of these events can be made as seen in Figure 4. Even though it can be argued that these findings would be expected and likely deducible from the fundamentals of cardiac physiology; this side-by-side analysis was simply intended to enhance the potential role of TA MM beyond its current role in assessing longitudinal RV function. These results seem to imply that evaluation of a still-frame TA MM tracing not only is useful in identifying RV systole; however, also diastole. Further studies are now needed to use TAPSE MM tracings to prospectively study atrio-ventricular relationships as well as ventricular interdependence and dyssynchrony.

Figure 4

Representative tricuspid annular MM tracing encompassing a detailed description of all peaks and nadirs. Traditional maximal longitudinal systolic excursion or tricuspid annular plane systolic excursion is seen by the dotted vertical line at the onset of the electrical QRS and denoted by the dotted arrow. Isovolumic contraction signal is demarcated by the two solid white vertical lines. Ventricular systole occurs from the second white vertical solid line and the broken line with dots line, while diastole is encompassed by the same broken line with dots and the last hashed line. Late diastole is denoted by dashed and two dots line and the hashed line. Atrial contraction occurs within the latter after onset of the electrical P wave on the electrogram and is seen by the solid white arrow