Autonomic blockade and sick sinus syndrome. New concept in the interpretation of electrophysiological and Holter data

Use of machine learning and Poincaré density grid in the diagnosis of sinus node dysfunction caused by sinoatrial conduction block in dogs

BACKGROUND

Sinus node dysfunction because of abnormal impulse generation or sinoatrial conduction block causes bradycardia that can be difficult to differentiate from high parasympathetic/low sympathetic modulation (HP/LSM).

HYPOTHESIS

Beat-to-beat relationships of sinus node dysfunction are quantifiably distinguishable by Poincaré plots, machine learning, and 3-dimensional density grid analysis. Moreover, computer modeling establishes sinoatrial conduction block as a mechanism.

ANIMALS

Three groups of dogs were studied with a diagnosis of: (1) balanced autonomic modulation (n = 26), (2) HP/LSM (n = 26), and (3) sinus node dysfunction (n = 21).

METHODS

Heart rate parameters and Poincaré plot data were determined [median (25%-75%)]. Recordings were randomly assigned to training or testing. Supervised machine learning of the training data was evaluated with the testing data. The computer model included impulse rate, exit block probability, and HP/LSM.

RESULTS

Confusion matrices illustrated the effectiveness in diagnosing by both machine learning and Poincaré density grid. Sinus pauses >2 s differentiated (P < .0001) HP/LSM (2340; 583-3947 s) from sinus node dysfunction (8503; 7078-10 050 s), but average heart rate did not. The shortest linear intervals were longer with sinus node dysfunction (315; 278-323 ms) vs HP/LSM (260; 251-292 ms; P = .008), but the longest linear intervals were shorter with sinus node dysfunction (620; 565-698 ms) vs HP/LSM (843; 799-888 ms; P < .0001).

CONCLUSIONS

Number and duration of pauses, not heart rate, differentiated sinus node dysfunction from HP/LSM. Machine learning and Poincaré density grid can accurately identify sinus node dysfunction. Computer modeling supports sinoatrial conduction block as a mechanism of sinus node dysfunction.

Heart rate dynamics during and after exercise in postoperative congenital heart disease patients. Their relation to cardiac autonomic nervous activity and intrinsic sinus node dysfunction

BACKGROUND

Abnormal exercise-related heart rate (HR) dynamics, that is, blunted exercise HR response, lower peak HR, and delayed HR recovery after exercise, are associated with high morbidity and mortality in adults with acquired and congenital heart disease (CHD). However, the precise mechanisms underlying the abnormal HR dynamics remain unclear.

OBJECTIVES

The purpose of this study is to evaluate the precise contribution of cardiac autonomic nervous activity (CANA) and sinus node function on exercise-related HR dynamics in postoperative patients with CHD.

METHODS

We analyzed our previous data in 53 postoperative patients with CHD who had undergone pharmacologic evaluation, including intrinsic HR, and compared the results with HR dynamics.

RESULTS

Intrinsic HR (84% +/- 11%) was lower than the expected value and independently correlated with resting HR (P < .05). Univariate analysis demonstrated that all CANA indices significantly correlated with most HR dynamic parameters. On multivariate analysis, basal parasympathetic nervous activity significantly influenced all HR dynamics (P < .05-.0001), except for peak HR, whereas postsynaptic beta sensitivity of the sinus node significantly influenced all HR dynamics (P < .05-.001), except for early HR recovery. Resting plasma norepinephrine significantly correlated with all HR dynamics (P < .05-.001), except for resting HR.

CONCLUSIONS

Lower resting and peak HRs are independently associated with intrinsic sinus node dysfunction and abnormal sympathetic CANA, respectively. A blunted HR increase and delayed early HR recovery are independently associated with impaired sympathetic and parasympathetic CANAs with the greater influence on a blunted exercise HR increase.

Nonpharmacologic validation of the intrinsic heart rate in cardiac transplant recipients

BACKGROUND

The maximum sinus rate during exertion in humans is inversely related to age. However, the sinus rate at rest is quite variable. The intrinsic heart (IHR) following pharmacologic blockade of autonomic tone with propranolol and atropine has been proposed as a test of sinus node function and is related to age by the linear regression equation: IHR = 118.1 - (0.57 x age). Whether this relationship exists for transplanted hearts for which the donor sinus node is denervated has not been determined.

METHODS

The relationship between the resting heart rate and the age of the donor heart was examined in 103 patients 1 year following orthotopic cardiac transplantation in the absence of rejection or intercurrent illness. Patients receiving beta-blockers, calcium blockers, antiarrhythmic drugs, digitalis, theophylline, or with biopsy evidence of rejection or abnormal coronary arteriograms were excluded from analysis.

RESULTS

The recipient age, left ventricular ejection fraction, pulmonary capillary pressure, cardiac index, donor heart ischemic time and cardiopulmonary bypass time did not correlate with the rate of the resting donor sinus node. The resting heart rate was inversely related to age of the donor heart by the linear regression equation: HR = 112.0 - (046 x age).

CONCLUSION

The resting rate of the denervated sinus node is related to donor age with a regression equation that is similar, though slightly slower, than that predicted after pharmacologic autonomic blockade.

Heart rate variability. Is it influenced by disturbed sinoatrial node function?

Analysis of heart rate variability (HRV) is commonly used to assess the influences of the autonomic nervous system on the heart; however, its relation to the sinoatrial node function has not been clearly defined. In this study, the authors performed HRV investigations in 150 patients (51 women and 99 men; mean age, 49 years; range, 17-80 years) in whom clinical observation and electrophysiologic transesophageal studies proved sinoatrial node dysfunction (SAND) and in 50 healthy control subjects (19 women and 31 men; mean age, 37 years; range, 15-60 years). All examined subjects underwent transesophageal left atrial overdrive pacing for the evaluation of sinus node recovery. The HRV analysis was based on 1-minute esophageal electrocardiographic recordings. Two time-domain HRV variables were measured: variability range ([VR]) the difference between the longest and the shortest sinus cycle length, divided by basic sinus cycle length) and beat-to-beat variability ([DSCL]--the maximum difference between any two consecutive sinus cycle lengths) during a 1-minute recording. Because of the known effects of age and basic sinus cycle, statistically adjusted means of VR and DSCL were compared. In patients suffering from SAND, DSCL was significantly higher than in the control subjects (198 +/- 206 vs 98 +/- 89 ms, respectively), as was VR (30.3 +/- 23.3% vs 20.9 +/- 121.1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological testing of sinus node function: diagnostic and prognostic application-including updated information from sinus node electrograms

Sinus node function, including automaticity, conduction, and refractoriness, can be studied in the human electrophysiology laboratory. This review details the current methods used for such studies and discusses their clinical value. Of special emphasis in this article is the role of sinus node electrography in the clinical laboratory. Included also is an update of the data relating the duration of sinus node depolarization as measure on sinus node electrograms to other parameters that assess sinus node function as well as data supporting the direct relationship between the duration of the sinus node depolarization as the severity of sinus node dysfunction.