Correlation of intracardiac pressures and electrical atrial potentials with morphology and function of overloaded atria assessed by echocardiography

Summary

Background:
In pts with chronic complete heart block or single chamber pacing and preserved sinus depolarization, left and right atria (LA, RA) may suffer from increased intraatrial pressure resulting from atrioventricular dyssynchrony (AVDys), dilate and lose their contractile function.

Purpose:
To find out whether any correlation exists between the echocardiographicaly measured LA, RA morphological and functional parameters on one hand and the intracardiac RA pressures and electrical potentials on the other hand in patients with chronic AVDys.

Methods:
In 26 pts (77 ±10 yrs., 16 males), where a chronic AVDys was the most important patophysiological mechanism of atrial overloading, the intraatrial pressures (atrial, right ventricular, pulmonary arterial and wedge pressure /PWP/) and electrical potentials (upper, middle, lower part of RA and RA appendage) were correlated with atrial diameters, volumes, ejection fraction and filling parameters.

Results:
There was a moderate inverse correlation between the LA ejection fraction and PWP: r = - 0,489, p = 0,025 at a level of significance 0.05), but no relationship between PWP and LA size/volumes. No correlation between RA potentials or intracardiac pressures and RA morphologic or functional features were documented.

Conclusions:
In this study, an inverse correlation between the capillary wedge pressure and left atrial ejection fraction in pts with chronic atrioventricular dyssynchrony was documented.

Key words:
intracardiac pressure – electric intracardiac potential – atrium – morphology – function – echocardiography

Introduction

The morphology and function of cardiac atria may be affected by a number of factors. Increased pre- or afterload as well as disturbed ventricular function may, after some time, induce certain haemodynamic changes reflected in the morphology and function of the left atrium (1-6). Atrioventricular (AV) dissociation in complete atrioventricular block (AVB) is a model of a haemodynamically very adverse condition, with the atrium working most of the time against strong resistance, which may lead to an increase in intraatrial pressure, and to atrial dilatation with a tendency to arrhythmias as a common manifestation of electrical instability of the atrium (7, 8). (In reverse atrioventricular synchronization in those patients dependent on ventricular pacing and having ventriculoatrial conduction the situation may be even worse.) The experience of our implantation centre shows that difficulties may occur in inserting the electrode to the chronically overloaded and dilated atrium, as the atrial electrical potential is often not sufficient for reliable sensing. Complications due to improper sensing may be seen even after implantation (9). However, not enough findings exist proving the characteristics of atrial electrical potentials to be related to atrial morphology and function.

Therefore, it has been the aim of this study to find out whether any relation exists between the intracardially measured pressure and atrial dilatation in patients with implanted physiological/sequential stimulation for AVB or for reverse synchronization; and to find out whether right atrial dilatation may in these patients be related to lower right atrial electrical potential measured at the time of surgery.

Patients:

The study group (see Tab. 1) consisted of 26 patients indicated for implantation of permanent physiological/sequential pacing who were meeting the following inclusion criteria: a) chronic AV dissociation at complete AV block, or b) permanent single ventricular (VVI) pacing with complete AV dissociation or reverse synchronization, c) informed consent of the patient with the protocol of the study, including not only the indicated procedure (implantation of the pacemaker /PM/ but also right heart catheterization, d) good quality image on echocardiography. Presence of significant valve defect or significant systolic LV dysfunction (ejection fraction /LVEF/ lower than 35%) was the exclusion criterion. Thirteen of the patients had hypertension and 11 ischemic heart disease in their histories. One patient had had pulmonary embolization, in 7 haemodynamically insignificant degenerative changes of the left heart valves were seen.

Of the 26 patients, primoimplantation for 3^rd degree-AVB was indicated in 12 (46 %), (of whom 2 had a 2^nd to3^rd degree block). Of them, 7 patients had the AVB lasting longer than 4 months, while in 5 the duration of the block was unclear, but their symptoms were also suggestive of a chronic block. The remaining 14 patients (54 %) underwent, for various indications, VVI implantation at preserved sinus atrial depolarization, resulting in AV dissociation or reverse synchronization. At the moment of inclusion in the study, the average time of pacing equalled 7.4 years (4 – 15 years).

Methods:

Patients indicated for pacemaker implantation for chronic AV block or for upgrade of single chamber ventricular pacing to a sequential pacing underwent echocardiographic examination prior to PM implantation (at AV dissociation or reverse synchronization). Then a right catheterization was performed through the sheath inserted into the subclavian vein to measure right heart intracardiac pressures and electrical potentials. Then, through the same subclavian puncture, the surgeon went on using the routine procedure of implanting physiological (DDD or VDD) stimulation to patients with AVB, or by adding an atrial electrode and upgrading the original VVI PM for a dual chamber system (DDD). Correlations were then determined of the pressures and electrical potentials with the values measured echocardiographically.

Echocardiographic examination:

was carried out with the patient resting on the bed. The recordings were stored to be analyzed later off-line. The average value was then calculated of repeatedly measured parameters of 6 to 12 cardiac cycles, with the patient’s respiratory variability being considered as negligible. Table 2 shows a summary of the followed parameters (dimensions, atrial volumes, and the haemodynamic parameters of left ventricular filling – E- wave /passive/ and A wave /active/ component, and atrial ejection fraction.) In parasternal long axis image the “tracing echo – leading echo” method was used to measure LA1 dimension. When determining the long axis in four-chamber projection (parameters LA11Lo and RA11Lo), the dimensions were measured from the last echo of the closed AV valve to the leading echo of the posterior (in fact anatomically proximal) atrial walls. To determine the transversal axis (LA11RL and RA11RL), the distance between the clearly defined inner echoes of the lateral wall and the septum in the middle of the atria was taken into account.

Simpson´s method was used to calculate the atrial ejection fraction (active ejection) from the atrial volume at the end of P- wave and the minimum volume during the atrial systole. The largest ejection fraction from the atrio-ventricular interference cycle, i.e. the cycle with the best conditions for atrial contraction (a physiologically delayed QRS complex following the P- wave) was considered as the standard value. In this way it is relatively easy to evaluate atrial contractility unaffected by dyssynchrony. Time velocity integrals (TVI) were processed using manual tracing of Doppler spectral curves along the external aspect of the envelope. The minute index value was then derived as an adequate multiple of the sum of all time-velocity integrals (TVI) processed within 8 to 10 s at the given orifice. All parameters in a given patient were always measured by the same operator. The average intraindividual variability of atrial parameters at B mode was 4%, while at Doppler measurement it was 2%.

Right heart cathetrization:

was also performed in AV dyssynchrony through the subclavian approach using the Swan-Ganz catheter 7F. Mingograf Elema (Siemens) and SMU 611 (Hellige) were used to register the pressure curves. The reference level “0” was set at two thirds of the distance of the sternoclavicular joint from the base. The stabilized average values of mean pressures (central venous, ventricular, pulmonary arterial and pulmonary capillary wedged pressures) were recorded.

Electrophysiological examination: Steerable quadripolar catheter (Mansfeld Polaris 7F) was used for the procedure. Under sciascopic multi-plane control it was introduced into the right atrium, reaching the stabile contact with the right atrial wall. The stabilized values obtained at bipolar registration of the atrial wall potentials were considered as decisive. As the potentials may differ in individual atrial portions, they were registered at the upper, middle and the lower parts of the atrium and within atrial appendage.

Discussion:

A well documented atrial overload exists e.g. in a significant mitral stenosis. An attempt has been made by us to prove a relation between a functional disorder – AV dyssynchrony and atrial overload. However, our initial hypothesis that we would be able to prove a relationship between the morphological and functional parameters of the overloaded atria, i.e. that the more dilated atria would have lower electrical potential and higher pressures, could not have been proved. The main cause of atrial dilatation and dysfunction in our sample of patients was supposed to be an atrioventricular dyssynchrony. However, the possible presence of some other factors and their effects increasing atrial overload could not be eliminated. This was not considered as a significant obstacle in our study. Age or diastolic dysfunction may deteriorate atrial pressures: effects of such factors have been known for quite some time (10-13). Our sample is relatively age homogeneous, consisting of elderly patients, so that the possible affection by age should not vary too much. As mentioned above, some of the patients are hypertensive, which may lead to worsened conditions of ventricular filling (6;14;15), contributing thus to left atrial dilatation. Should, however, diastolic dysfunction mean a distortion – it would rather influence the results in favour of our hypothesis, which did not happen. On the other hand, the obtained correlations are due to processing a relatively small number of patients, so that some of the statistical results may be distorted by that. This is the toll paid to the exclusion of patients with valvular defects (aortal degenerative stenosis) and other incorrigible causes of atrial overload. They were not included in our study though it is just them who most often qualify for cardiostimulation.

When, for practical reasons, the measurements are not made simultaneously, other limitations may result. Echocardiography was performed in some patients on the day prior to implantation (i.e. catheterization). Since the dyssynchrony was present throughout the period between echo and catheterization, as it had been for years before, sudden changes in haemodynamics are not likely to occur within the 24 hours between echo and catheterization. Although some changes may appear within several minutes after AV synchronization (16), substantial changes in cardiovascular parameters develop only later. It was the pre-synchronization measurements that we decided to take as basis for determining correlations. Given the small size of the sample, non-simultaneous measurements, and not very high pressure values found at catheterization, it is not surprising that unsystematic, weak or no correlations of echocardiographic parameters with the pressures and potentials were documented.

As for intracardiac pressures, the correlation, though rather weak, of LA systolic function with PWP documented in our study seems logical. It is possible that the lower ejection fraction is related to the depression of the atrial systolic function. However, a corresponding decrease in atrial wave integral or a relation to atrial volumes could not have been proved. On the other hand, in another study carried out by us in the same sample, echocardiographic examination was performed also immediately after AV synchronization; though the main pathophysiological mechanism of overload had been removed already by sequential pacing, also here it resulted in the inverse correlation of pressure with LA EF: r = -0.567, p = 0.014, the level of significance 0.05 (unpublished results). This supports our hypothesis of atrial exhaustion (remodelling). Literary data suggest that invasively measured pressures be closely related rather to the LA pre-ejection period and the ejection time of the left atrium (3;4;6), but we lacked such registration tools to allow us to measure precisely these intervals. Apart from the well established standard methods of calculating heart pressure gradients in stenoses or regurgitation, the evaluation of LA diastolic function and the prediction of filling pressures are rather difficult. The velocities and integrals of E and A waves are affected by many factors (age, heart frequency, intravascular volume and filling pressures, presence of regurgitations, etc.). Analysis is usually complicated by the difficulty to separate the effects of one factor from those of others, and by the fact that the development of such parameters is often not linear (17;18). Nowadays, the parameters of the pulmonary venous flow and tissue Doppler measurement of annular velocities are most often used to demonstrate left atrial haemodynamics and to predict the filling pressure. Transoesophageal echocardiography (19) is more reliable to obtain pulmonary venous flow values, as the pulmonary venous flow pattern correlates with left atrial pressures, or left atrial filling pressure, respectively (20-22). The functional indicators of atrial appendage are also in a very good correlation with invasively measured pressures (2324). The integration of tissue Doppler parameters (TDI) has meant advancement in the diagnosis of left ventricular systolic and diastolic dysfunctions, though atrial systolic function may also be demonstrated by mitral annulus velocity during atrial contraction (wave Am). Besides, atrial muscle strain can also be examined (25;26). However, in the beginning of our study, transoesophageal echocardiography/TDI technique was not available in our institution. The mean intracardiac pressure values as obtained in our sample were not too high, but the high age of the population must be taken into account. The elderly have generally a lower perception of thirst and may be relatively hypovolemic. Moreover, the surgical intervention was preceded by a 12-hour fasting. Despite that, the measurements were systematic and the data obtained under standard conditions in the whole sample, so that the determined correlations should not be influenced.

As for the right heart parameters, a comparison of the level of pulmonary hypertension as measured by heart catheterization with Doppler measurements has not been made. On echocardiography, pulmonary hypertension may be quantified if there is a small regurgitation jet on the tricuspid valve (maximum jet velocity indicates the pressure gradient between the right ventricle and the right atrium, which, added to an estimated right atrial pressure, equals the right ventricular pressure value). In our sample, just insignificant regurgitations were often found on the tricuspid valve at baseline. With respect to different filling in individual cycles in AV dyssynchrony, the values were not constant. Moreover, after synchronization, the jets – caused most often by asynchronic closure of AV valve leaflets - often disappear. Therefore, they were of no use for pulmonary hypertension evaluation. Besides, the pressures measured in this way correlate with direct manometry only on condition of absolutely simultaneous measurements, which, under our conditions, could not have been ensured. For several reasons, indirect pulmonary hypertension parameters (right ventricular size, character of the flow in right ventricle outflow tract) were not considered by us as reliable at predicting pressure values, and were thus not evaluated.

Literary data on correlations of intracardiac ECG signal and echocardiographic parameters are virtually non-existent. Papers have been published dealing with surface electrocardiogram showing surface electrocardiogram not to be sensitive enough to predict right atrial enlargement, with P size at V2 lead being the most sensitive (27). Somewhat better is the left atrial enlargement prediction from the presence of negative P wave at V1 lead (28) and other ECG parameters, but, generally, it is not very reliable (29). This tendency of predominance of left atrial enlargement would rather correspond to higher voltage of dilated atria at an early stage. It is logical that atrial size is related to P wave duration, or interatrial conduction time (30-32). Recently, most studies deal with more delicate relationships between electrocardiogram and functional haemodynamic parameters. E.g., left atrial pre-ejection period (LAPEP) is in a significant correlation with P wave duration and PR time interval (33). Though no correlation was found of LAPEP with wedged pressure, a significant correlation was seen of mean PWP or left ventricular end diastolic pressure (LVEDP) with left atrial ejection time (LAET): r = -0.72 and -0.75, resp. (3;34). On the other hand, Okamoto et al. did not prove correlation of LAET or LAPEP with left atrial dimensions (35). In our study, these parameters were not followed up, because e.g. to measure LAPEP we would have needed a higher quality registration device than the one we had at our disposal. When correlating atrial potentials with atrial dimensions, the results obtained have not proved our original hypothesis that dilated atria would lose their potential. It cannot be excluded that some dilated atria may have eccentric hypertrophy and thus, in that stage, their potential may not be lower.

When evaluating the results obtained in our sample, it might be interesting to compare them with those of healthy population of the same age. Tables are available for healthy middle age population, giving their normal sizes or volumes, or their ratio (27;36), but not specifically for the elderly, where the situation is complicated by higher morbidity. Nevertheless, it is evident from our study that though the dispersion of our patients´ volumes is rather high, the values are mostly higher than in normal individuals in middle age category.

Abbreviations:

• AVB: atrioventricular block
• DDD: dual chamber pacing
• LA₁: left atrium in parasternal long axis
• LA₁₁Lo: LA₁₁RL: long axis and rigt-to-left axis of left atrium in apical view
• LAEDV, LAESV: enddiastolic/endsystolic left atrial volume
• LAEF_max: biggest LA ejection fraction in AV dyssynchrony
• LVd: left ventricle diastolic diameter
• LVs: left ventricle systolic diameter
• LVEDV, LVESV: left ventricle enddiastolic/endsystolic volume
• LVEF: left ventricle ejection fraction
• PWd: left ventricle posterior wall diameter in diastoly
• RA₁₁Lo, RA₁₁RL, RAEDV, RAESV, RAEF: corresponding right atrial parameters
• Sd: left ventricle septal diameter in diastoly
• TVI: time-velocity integral
• TVI-A, TVI-E, V_max A: Složky průtoku na mitrálních chlopni, přičemž E = pasivní a A = aktivní vyprázdnění levé síně
• TVIA_max, V_maxA_max: time velocity integral and peak velocity of the biggest A wave
• VDD: atrioventricular sequential stimulation with ventricular single chamber pacing
• VVI: ventricular single chamber pacing
• ∑E/min, ∑A/min: sum of E, resp. A wave time velocity integrals/min.