Effect of beta blockade on heart rate variability during vessel occlusion at the time of coronary angioplasty

Multiple Factor Analysis of the Autonomous Nervous System during PTCA

This study describes the Autonomic Nervous System (ANS) response before, during and after a percutaneous transluminal coronary angioplasty (PTCA). The study population consisted of 37 patients undergoing PTCA from Staff-3 Database. Classical Heart rate variability (HRV) parameters: RR mean, SD, rMSSD, LF, HF, LF/HF and LF/(HF+LF) were extracted and a multiple factorial analysis (MFA) was carried out. Preliminary results show that sympathetic activity increases during and after PTCA, and global HRV decreases during PTCA and increases after PTCA. These findings suggest that MFA provides a powerful tool allowing assessment of ANS's response during PTCA.

Temporal changes and prognostic significance of measures of heart rate dynamics after acute myocardial infarction in the beta-blocking era

Previous studies have shown that indexes describing heart rate (HR) dynamics may predict subsequent deaths of patients after an acute myocardial infarction (AMI). Because beta-blocking (BB) drugs affect both mortality and HR dynamics, the prognostic power of measurements of HR dynamics may have changed in the current era of BB therapy. This study assessed the temporal changes and prognostic significance of time-domain, spectral, and fractal indexes of HR variability along with HR turbulence after an AMI among patients with optimized BB medication. SD of NN intervals, spectral indexes, the short-term fractal scaling exponent (alpha(1)), power-law slope (beta), and turbulence onset and slope were measured in 600 patients at 5 to 7 days after AMI and in 416 patients at 12 months after AMI. In the multivariate analysis, after adjusting for clinical variables, only reduced fractal HR indexes, alpha1 and beta (p <0.01 for both), turbulence onset, and slope (p <0.05 for both), measured at the convalescent phase after AMI, predicted subsequent cardiac death. All time-domain and spectral HR variability indexes and turbulence onset increased significantly during the 12-month period after AMI (p <0.001 for all), whereas the fractal indexes and turbulence slope remained unchanged. Late after AMI, reduced beta (p <0.05) and turbulence slope (p <0.01) were the only independent predictors of cardiac mortality. Traditional time-domain and spectral measurements of HR variability and turbulence onset improved significantly after AMI, whereas the fractal HR dynamics and turbulence slope remained stable. Fractal HR variability and HR turbulence retain their prognostic power in the BB era, when measured either at the convalescent or late phase after AMI.

Wavelet analysis of instantaneous heart rate: a study of autonomic control during thrombolysis

Myocardial infarction (MI) is known to elicit activation of the autonomic nervous system. Reperfusion, induced by thrombolysis, is thus expected to bring about a shift in the balance between the sympathetic and vagal systems, according to the infarct location. In this study, we explored the correlation between reperfusion and the spectral components of heart rate (HR) variability (HRV), which are associated with autonomic cardiac control. We analyzed the HR of patients during thrombolysis: nine anterior wall MI (AW-MI) and eight inferoposterior wall MI (IW-MI). Reperfusion was determined from changes in ST levels and reported pain. Reocclusion was detected in four patients. HRV was analyzed using a modified continuous wavelet transform, which provided time-dependent versions of the typically used low-frequency (LF) and high-frequency (HF) peaks and of their ratio, LF/HF. Marked alterations in at least one of the HRV parameters was found in all 18 reperfusion events. Patterns of HRV, compatible with a shift toward relative sympathetic enhancement, were found in all of the nine reperfusion events in IW-MI patients and in three AW-MI patients. Patterns of HRV compatible with relative vagal enhancement were found in six AW-MI patients (P < 0.001). Significant changes in HRV parameters were also found after reocclusion. Time-dependent spectral analysis of HRV using the wavelet transform was found to be valuable for explaining the patterns of cardiac rate control during reperfusion. In addition, examination of the entire record revealed epochs of markedly diminished HRV in two patients, which we attribute to vagal saturation.

Electrocardiographic changes related to parasympathetic tone during right coronary angioplasty

The role of basal parasympathetic tone in reducing the heart rate and causing electrocardiographic (ECG) changes during right coronary angioplasty was evaluated in 19 patients with angina pectoris. To measure parasympathetic tone, time and frequency domain parameters of heart rate variability were assessed using 24 h of ambulatory ECG data recorded before angioplasty. There was an age-dependent reduction in heart rate. However, no parameters of heart rate variability were responsible for the changes in heart rate. In contrast, the degree of ST segment elevation during angioplasty correlated significantly with the high-frequency component of heart rate variability. Therefore, the increased parasympathetic tone, as assessed by spectral analysis, may augment the early ST segment elevation induced by right coronary occlusion.

Time-varying spectral analysis of heart rate and left ventricular pressure variability during balloon coronary occlusion in humans: a sympathoexicitatory response to myocardial ischemia

OBJECTIVES

We assessed time-varying spectral components of heart rate and left ventricular (LV) pressure variability during coronary angioplasty to elucidate dynamic autonomic responses to transient myocardial ischemia.

BACKGROUND

Sympathoexcitatory reflexes elicited by acute coronary occlusion are rarely addressed in the clinical settings because of a lack of technique to monitor transient changes in sympathetic activation.

METHODS

RR interval and LV pressure and volume were serially recorded in 14 patients with effort angina during balloon coronary angioplasty. Wavelet analysis was applied for determination of nonstationary spectral components of RR interval and LV peak pressure variability.

RESULTS

The wavelet analysis revealed that coronary occlusion provoked low-frequency (LF) fluctuations of RR interval (seven patients) and LV peak pressure (six patients) at 0.06 +/- 0.01 Hz, but not in the remaining patients. Following the balloon inflation, the LF component of RR interval began to increase after the onset of myocardial ischemia, peaked at about 80 s, and then declined in the late phase of inflation. Consequently, the ratio of low to high frequency component rose to be significantly greater in the LF augmentation group than in the no LF augmentation group in the middle phase of coronary occlusion. The patients with no LF augmentation had little evidence of myocardial ischemia as reflected by changes in ST segment and LV systolic function during coronary occlusion.

CONCLUSIONS

The wavelet analysis of RR interval and LV pressure variability clearly showed a dynamic profile of spectral components in response to transient coronary artery occlusion. The resultant regional myocardial ischemia elicited a profound sympathoexcitatory response followed by a gradual suppression. This method provides a useful tool to gain a new insight into the nonstationary autonomic influence on the cardiovascular system.

Autonomic mechanisms and sudden death after abrupt coronary occlusion

In spite of recent advances in secondary prevention, sudden cardiac death has remained a major public health problem as the majority of fatalities occur in subjects without a history of severe heart disease. Abrupt rupture of a vulnerable plaque resulting in thrombotic occlusion of a coronary artery is a common cause of sudden death in this population. Coronary occlusion does not, however, invariably lead to sudden death but may cause acute myocardial infarction or exacerbation of chest pain. Extensive studies in experimental animals and increasing clinical evidence indicate that autonomic nervous activity has a significant role in modifying the clinical outcome. Sympathetic hyperactivity favours the genesis of life-threatening ventricular tachyarrhythmias while vagal activation exerts an antifibrillatory effect. Strong afferent stimuli from the ischaemic myocardium impair arterial baroreflex and may lead to dangerous haemodynamic instability. Studies with a human angioplasty model have shown that there is wide interindividual variation in the type and severity of autonomic reactions during the early phase of abrupt coronary occlusion, a critical period for out-of-hospital cardiac arrest. The site of the occlusion is not a significant determinant of the reactions, whereas the severity of a coronary stenosis, adaptation or ischaemic preconditioning, beta-blockade and gender seem to affect the autonomic reactions and occurrence of complex ventricular arrhythmias. Clinical and angiographic factors are, however, poor predictors of autonomic reactions in an individual patient. Recent studies have documented a hereditary component for autonomic function, and genetic factors may also modify the clinical manifestations of acute coronary occlusion.