Sinus node recovery time assessment revisited: role of pharmacologic blockade of the autonomic nervous system

Accelerated QT adaptation following atropine-induced heart rate increase in LQT1 patients versus healthy controls: A sign of disturbed hysteresis

Hysteresis, a ubiquitous regulatory phenomenon, is a salient feature of the adaptation of ventricular repolarization duration to heart rate (HR) change. We therefore compared the QT interval adaptation to rapid HR increase in patients with the long QT syndrome type 1 (LQT1) versus healthy controls because LQT1 is caused by loss-of-function mutations affecting the repolarizing potassium channel current IKs , presumably an important player in QT hysteresis. The study was performed in an outpatient hospital setting. HR was increased in LQT1 patients and controls by administering an intravenous bolus of atropine (0.04 mg/kg body weight) for 30 s. RR and QT intervals were recorded by continuous Frank vectorcardiography. Atropine induced transient expected side effects but no adverse arrhythmias. There was no difference in HR response (RR intervals) to atropine between the groups. Although atropine-induced ΔQT was 48% greater in 18 LQT1 patients than in 28 controls (p < 0.001), QT adaptation was on average 25% faster in LQT1 patients (measured as the time constant τ for the mono-exponential function and the time for 90% of ΔQT; p < 0.01); however, there was some overlap between the groups, possibly a beta-blocker effect. The shorter QT adaptation time to atropine-induced HR increase in LQT1 patients on the group level corroborates the importance of IKs in QT adaptation hysteresis in humans and shows that LQT1 patients have a disturbed ultra-rapid cardiac memory. On the individual level, the QT adaptation time possibly reflects the effect-size of the loss-of-function mutation, but its clinical implications need to be shown.

Recommendations for the use of electrophysiological study: Update 2018

The field of cardiac electrophysiology has greatly developed during the past decades. Consequently, the use of electrophysiological studies (EPSs) in clinical practice has also significantly augmented, with a progressively increasing number of certified electrophysiology centers and specialists. Since Zipes et al published the Guidelines for Clinical Intracardiac Electrophysiology and Catheter Ablation Procedures in 1995, no official document summarizing current EPS indications has been published. The current paper focuses on summarizing all relevant data of the role of EPS in patients with different types of cardiac pathologies and provides up-to-date recommendations on this topic. For this purpose, the PubMed database was screened for relevant articles in English up to December 2018 and ESC and ACC/AHA Clinical Practice Guidelines, and EHRA/HRS/APHRS position statements related to the current topic were analyzed. Current recommendations for the use of EPS in clinical practice are discussed and presented in 17 distinct cardiac pathologies. A short rationale, evidence, and indications are provided for each cardiac disease/group of diseases. In conclusion, because of its capability to establish a diagnosis in patients with a variety of cardiac pathologies, the EPS remains a useful tool in the evaluation of patients with cardiac arrhythmias and conduction disorders and is capable of establishing indications for cardiac device implantation and guide catheter ablation procedures.

Power spectral and Poincaré plot characteristics in sinus node dysfunction

A salient feature of the normal sinus node activity is its prominent beat-to-beat variability, which shows self-similarity on different time scales (fractal dynamics). However, in patients with sinus node dysfunction, short-term time sinus cycles show exaggerated variability, the characteristics of which have not been analyzed. Therefore, Poincaré plots and power spectral analysis were applied to short-term variations of sinus cycles in 30 patients with and 30 patients without sinus node disease. Three patterns of behavior were observed in sick sinus patients: type 1, completely normal (n = 3); type 2, randomlike pattern in the Poincaré plots with "white noise" power spectra (n = 9); and type 3, a transitional pattern, characterized by remnants of normal behavior mixed with scattered points (n = 18). In control subjects, only type 1 (n = 27) and type 3 (n = 3) patterns were observed, P < 0.0001. The power spectral changes in sinus node dysfunction are thus characterized by a loss of the inverse power law relationship, which both has implications for heart rate variability analysis and might offer a new diagnostic approach.

Disorders of Sinus Function

Sinus node dysfunction is a common entity with significant clinical implications. Establishing a diagnosis may, on occasion, tax the skills of the clinician. Many causes have been cited, but no single factor appears to be established. Immunologic abnormalities may play a part in the etiologic process. Clinical invasive electrophysiology studies may be used to establish a diagnosis. In general, medical therapy must be integrated. Controversy exists regarding the best method of permanent pacing. Treatment may need to be individualized to the type of arrhythmia noted. Long-term prognosis is a large factor in choice of therapy, related to the underlying disease. Prevention of atrial fibrillation may occur with dual-chamber pacing; however, anticoagulation appears essential in this patient subgroup. The 5-year mortality rate in these patients is high and does not appear to be significantly improved with artificial pacing. Mortality is prominently influenced by the coexistence of cardiovascular and valvular heart disease. Patients who die do not differ substantially from survivors with regard to type of sinus dysfunction, occurrence of tachyarrhythmia, or distal conduction abnormalities. The survival rate in patients with sick sinus syndrome and congestive heart failure is significantly lower, and the incidence of embolic events remains high in patients with permanent pacing and the sick sinus syndrome. Thus, it has been proposed that all patients exhibiting the bradycardia-tachycardia syndrome be fully anticoagulated. The incidence of atrial fibrillation is significantly lower in patients with atrial demand pacing (22.3% versus 3.9%) than in patients with ventricular pacing and is accompanied by a decreased incidence of systemic embolization (13% versus 1.6%). Reports comparing survival with use of dual-chamber pacing versus ventricular pacing are encouraging in patients with congestive heart failure. At present, the natural history of the disease is unknown; furthermore, clinical risk factors for the development of symptoms have not been defined, and no electrophysiologic measure of sinus node function has been demonstrated to have reliable predictive value. Therefore, common practice has been to withhold pacemaker therapy in the asymptomatic patient.