The effect of premature ventricular contraction on left ventricular relaxation, chamber stiffness, and filling in humans

Diagnostic Role of Incidental Premature Contractions During Doppler Echocardiography

Cardiac sonographers often perceive premature beats as a limiting factor during echocardiography because they alter filling and contractility, and loops recorded during or after a premature contraction are often discarded. Here we present 2 cases in which the incidental occurrence of premature beats on Doppler echocardiography contributed to the diagnosis. (Level of Difficulty: Intermediate.)

The quest for load-independent left ventricular chamber properties: Exploring the normalized pressure phase plane

The pressure phase plane (PPP), defined by dP(t)/dt versus P(t) coordinates has revealed novel physiologic relationships not readily obtainable from conventional, time domain analysis of left ventricular pressure (LVP). We extend the methodology by introducing the normalized pressure phase plane (nPPP), defined by 0 ≤ P ≤ 1 and -1 ≤ dP/dt ≤ +1. Normalization eliminates load-dependent effects facilitating comparison of conserved features of nPPP loops. Hence, insight into load-invariant systolic and diastolic chamber properties and their coupling to load can be obtained. To demonstrate utility, high-fidelity P(t) data from 14 subjects (4234 beats) was analyzed. PNR, the nPPP (dimensionless) pressure, where -dP/dtpeak occurs, was 0.61 and had limited variance (7%). The relative load independence of PNR was corroborated by comparison of PPP and nPPP features of normal sinus rhythm (NSR) and (ejecting and nonejecting) premature ventricular contraction (PVC) beats. PVCs had lower P(t)max and lower peak negative and positive dP(t)/dt values versus NSR beats. In the nPPP, +dP/dtpeak occurred at higher (dimensionless) P in PVC beats than in regular beats (0.44 in NSR vs. 0.48 in PVC). However, PNR for PVC versus NSR remained unaltered (PNR = 0.64; P > 0.05). Possible mechanistic explanation includes a (near) load-independent (constant) ratio of maximum cross-bridge uncoupling rate to instantaneous wall stress. Hence, nPPP analysis reveals LV properties obscured by load and by conventional temporal P(t) and dP(t)/dt analysis. nPPP identifies chamber properties deserving molecular and cellular physiologic explanation.

N-terminal prohormone brain natriuretic peptide-proBNP levels in ventricular arrhythmias in children

BACKGROUND

Ventricular arrhythmias are the most common consequences of structural and functional heart diseases, but cases with no evident pathology are also observed. A parameter indicating asymptomatic circulatory failure could support decisions related to possible treatment of ventricular arrhythmias.

HYPOTHESIS

The study objective was the evaluation of N-terminal prohormone brain natriuretic peptide (NT-proBNP) levels in children with ventricular arrhythmias and an attempt to determine if this parameter may be used for diagnosis and prognosis of ventricular arrhythmias.

MATERIAL AND METHODS

The study population was comprised of 36 children age 5 to 17.5 years old with idiopathic ventricular arrhythmias (Group B) graded mild or potentially malignant; 29 patients with mild ventricular arrhythmias were included into Group B1; and 7 patients with potentially malignant cases into Group B2. In all the patients, NT-proBNP assays were performed.

RESULTS

The NT-proBNP levels in Groups B, B1, B2 and the control group (Group K) were as follows: 41.5 +/- 15.1 pg/mL, 35.5 +/- 18.5 pg/mL, 66.3 +/- 24.9 pg/mL and 31.5 +/- 15.1 pg/mL, respectively. Between the groups with and without arrhythmias (Group B vs Group K), no statistically significant differences in NT-proBNP levels were found. However, markedly higher NT-proBNP levels were shown in the children with potentially malignant arrhythmias (Group B2) compared to the patients with mild arrhythmias (B1) and the control group (Group K).

CONCLUSIONS

The level of NT-proBNP increases with the severity of ventricular arrhythmia. NT-proBNP assays can be helpful for diagnosing and grading the severity of ventricular arrhythmias.

Transmitral flow velocity-contour variation after premature ventricular contractions: a novel test of the load-independent index of diastolic filling

The new echocardiography-based, load-independent index of diastolic filling (LIIDF) M was assessed using load-/shape-varying E-waves after premature ventricular contractions (PVCs). Twenty-six PVCs in 15 subjects from a preexisting simultaneous echocardiography-catheterization database were selected. Perturbed load-state beats, defined as the first two post-PVC E-waves, and steady-state E-waves, were subjected to conventional and model-based analysis. M, a dimensionless index, defined by the slope of the peak driving-force vs. peak (filling-opposing) resistive-force regression, was determined from steady-state E-waves alone, and from load-perturbed E-waves combined with a matched number of subsequent beats. Despite high degrees of E-wave shape variation, M derived from load-varying, perturbed beats and M derived from steady-state beats alone were indistinguishable. Because the peak driving-force vs. peak resistive-force relation determining M remains highly linear in the extended E-wave shape and load variation regime observed, we conclude that M is a robust LIIDF.

Stiffness and relaxation components of the exponential and logistic time constants may be used to derive a load-independent index of isovolumic pressure decay

In current practice, empirical parameters such as the monoexponential time constant tau or the logistic model time constant tauL are used to quantitate isovolumic relaxation. Previous work indicates that tau and tauL are load dependent. A load-independent index of isovolumic pressure decline (LIIIVPD) does not exist. In this study, we derive and validate a LIIIVPD. Recently, we have derived and validated a kinematic model of isovolumic pressure decay (IVPD), where IVPD is accurately predicted by the solution to an equation of motion parameterized by stiffness (Ek), relaxation (tauc), and pressure asymptote (Pinfinity) parameters. In this study, we use this kinematic model to predict, derive, and validate the load-independent index MLIIIVPD. We predict that the plot of lumped recoil effects [Ek.(P*max-Pinfinity)] versus resistance effects [tauc.(dP/dtmin)], defined by a set of load-varying IVPD contours, where P*max is maximum pressure and dP/dtmin is the minimum first derivative of pressure, yields a linear relation with a constant (i.e., load independent) slope MLIIIVPD. To validate the load independence, we analyzed an average of 107 IVPD contours in 25 subjects (2,669 beats total) undergoing diagnostic catheterization. For the group as a whole, we found the Ek.(P*max-Pinfinity) versus tauc.(dP/dtmin) relation to be highly linear, with the average slope MLIIIVPD=1.107+/-0.044 and the average r2=0.993+/-0.006. For all subjects, MLIIIVPD was found to be linearly correlated to the subject averaged tau (r2=0.65), tauL(r2=0.50), and dP/dtmin (r2=0.63), as well as to ejection fraction (r2=0.52). We conclude that MLIIIVPD is a LIIIVPD because it is load independent and correlates with conventional IVPD parameters. Further validation of MLIIIVPD in selected pathophysiological settings is warranted.

The influence of premature ventricular contractions on left ventricular function in asymptomatic children without structural heart disease: an echocardiographic evaluation

BACKGROUND

Isolated monomorphic premature ventricular contractions (PVCs) are not uncommon in the pediatric population. The degree of cardiac dysfunction caused by PVCs in children without structural heart disease is unknown.

PURPOSE

To investigate the influence of PVCs on echocardiographic left ventricular (LV) systolic function in children without structural heart disease.

METHODS

Forty asymptomatic children with isolated monomorphic PVCs without structural heart disease were selected. The median age was 6 years, range of 3-12 years. The following subgroups were compared: frequent vs. infrequent PVCs (> or < or = 10/min); short vs. long coupling interval (RR'/RR ratio < or = or > 0.6); and short vs. long QT interval (QT < or = or > 400 ms). Using echocardiography the left ventricular ejection fraction (LVEF in percentage) and cardiac index (CI in L/min/m2) were measured for both normal sinus beats (SB-LVEF and CI), PVCs (PVC-LVEF and CI) and the average LVEF and CI were calculated. All values were expressed as means +/- SD.

RESULTS

In all children LV dimensions and the SB-LVEF and CI were within normal limits. The PVC-LVEF (48 +/- 5) and PVC-CI (1.57 +/- 0.19) were significantly decreased and the average CI was 2.41 +/- 0.29. In 27 pts with > 10 PVCs/min the average LVEF and CI decreased to 53 +/- 5 and 2.08 +/- 0.24 respectively. In 16 pts with PVCs and a short coupling interval (RR'/RR < or = 0.6) the PVC-LVEF and PVC-CI was 43 +/- 0.03 and 1.50 +/- 0.14, which was significantly lower than in 24 pts with a long coupling interval (58 +/- 4, 1.88 +/- 0.11). In 11 pts with a prolonged QT interval (> 400 ms) the PVC-LVEF and PVC-CI was significantly lower than in the 29 children with a shorter QT interval, 41 +/- 5 vs. 55 +/- 4 and 1.46 +/- 0.13 vs. 1.86 +/- 0.15 respectively (all p < 0.01).

CONCLUSION

In asymptomatic children with isolated monomorphic PVCs the average ejection fraction and cardiac output is markedly reduced if PVCs are frequent (> 10/min), have a short coupling interval or a prolonged QT interval.

Postextrasystolic left ventricular isovolumic pressure decay is not monoexponential

OBJECTIVE

The relationship between the left ventricular (LV) relaxation time constant and early diastolic filling is not fully defined. This study provides additional evidence that LV isovolumic pressure fall in the normal intact heart in response to certain interventions is not adequately described by a model of monoexponential decay and that its relationship to filling is complex.

METHODS AND RESULTS

To gain further insight into the relationship between LV relaxation and early rapid filling we measured LV isovolumic relaxation rate, peak early filling velocity (E), LV volumes, and transmitral pressures at baseline and in the first postextrasystolic beat after a short-coupled extrasystole in 9 anesthetized dogs. Postextrasystolic isovolumic relaxation rate was slowed as measured by 3 commonly used time constants, while E was increased 32%. LV contractility and peak pressure were also increased, while LV end-systolic volume was decreased. LV minimum pressure was deceased, while the early diastolic transmitral pressure gradient was increased. Although all relaxation time constants measured over the entire isovolumic relaxation phase indicated slowed relaxation, direct measurement of isovolumic relaxation time indicated no change in relaxation rate. Calculation of the time constants and direct measurement of isovolumic relaxation time during early isovolumic pressure decay indicated slowed postextrasystolic pressure decay rate compared with baseline, while calculation of time constants and direct measurement of isovolumic relaxation time during late isovolumic relaxation indicated augmented postextrasystolic pressure decay rate versus baseline.

CONCLUSIONS

This non-exponential behavior of LV isovolumic pressure decay in postextrasystolic beats after short-coupled extrasystoles provides further evidence that the relationship that exists between ventricular relaxation and early filling is not simple. The results are interpreted in terms of current theoretical formulations that attribute control of myocardial relaxation to the interaction between inactivation-dependent and load-dependent mechanisms.

The role of Doppler echocardiography in the assessment of left ventricular diastolic function

The role of Doppler echocardiography of transmitral filling velocities in the assessment of diastolic function in man has not been adequately defined. It is now appreciated that multiple interacting factors such as loading conditions influence the transmitral velocity profile independent of intrinsic left ventricular diastolic function. Extrapolating the status of diastolic function from the transmitral velocity profile is complicated by these factors. The load dependence of ventricular filling has tempered the initial enthusiasm for the clinical application of the Doppler technique. In the present review, studies examining invasive parameters of diastolic function and Doppler indices of diastolic filling are discussed to gain greater insight and understanding of the role of Doppler echocardiography in the noninvasive assessment of diastolic function. These studies have demonstrated a relatively consistent influence of left ventricular relaxation, chamber stiffness, and left atrial pressure on the transmitral velocity filling profile. Impairment of relaxation impedes early filling and may result in a compensatory increase in atrial contribution to filling. An independent decrease in left atrial pressure from altered loading conditions may also reduce filling in early diastole. Increased left ventricular chamber stiffness (i.e., noncompliant left ventricle) impairs atrial contribution to filling and may enhance early filling. Theoretically, reduced left atrial contractility may decrease atrial contribution to filling. Pulmonic vein flow demonstrating increased retrograde flow during atrial systole helps to exclude impaired left atrial contractility. An increased left atrial pressure from altered loading conditions may also augment early filling. Therefore, an invasive or clinical assessment of left atrial pressure as being increased, decreased, or normal greatly aids in the interpretation of the transmitral filling velocity profile when inferences on the status of diastolic function are being made. Diastolic dysfunction is likely when a given pattern of filling cannot be explained on the basis of left atrial pressure. In situations where reasonable estimates on the status of left atrial pressure cannot be done, striking alterations in the transmitral velocity filling profile may be useful.

Dependence of Doppler echocardiographic transmitral early peak velocity on left ventricular systolic function in coronary artery disease

The influence of systolic function on pulsed Doppler echocardiographic transmitral flow velocity patterns was assessed before and after postextrasystolic (PES) potentiation in 12 normal subjects (control group) and in 25 patients with previous healed myocardial infarction (MI) group. Simultaneous high-fidelity left ventricular pressure measurements were performed in all patients. A programmed single-coupled right ventricular extrasystole was induced during echocardiographic and subsequent cineangiocardiographic recordings. Adequate angiograms for volumetric analysis in both baseline and PES beats were obtained in 23 patients (7 in the control group and 16 in the MI group). PES potentiation of contraction was more pronounced in the MI group than in the control group. PES changes in ejection fraction, stroke volume and end-systolic volume were significantly greater in the MI group than in the control group (11 vs 5%, p less than 0.005; 15 vs 5 ml/m2, p less than 0.005; and -13 vs -4 ml/m2, p less than 0.01, respectively). In contrast, PES potentiation prolonged the time constants of left ventricular pressure decline derived from exponential curve fits with a zero (Tw) and non-zero (Tb) asymptote pressure in the MI group to the same extent as in the control group (4 vs 5 ms, difference not significant [NS], and 9 vs 11 ms, NS, respectively). In the PES beat, peak E velocity remained unaltered (48 vs 49 cm/s, NS) in the control group, whereas it increased significantly (p less than 0.0001) from 47 to 51 cm/s in the MI group.(ABSTRACT TRUNCATED AT 250 WORDS)