Experimental model of inappropriate sinus tachycardia: initiation and ablation

Three-dimensional functional anatomy of the human sinoatrial node for epicardial and endocardial mapping and ablation

The sinoatrial node (SAN) is the primary pacemaker of the human heart. It is a single, elongated, 3-dimensional (3D) intramural fibrotic structure located at the junction of the superior vena cava intercaval region bordering the crista terminalis (CT). SAN activation originates in the intranodal pacemakers and is conducted to the atria through 1 or more discrete sinoatrial conduction pathways. The complexity of the 3D SAN pacemaker structure and intramural conduction are underappreciated during clinical multielectrode mapping and ablation procedures of SAN and atrial arrhythmias. In fact, defining and targeting SAN is extremely challenging because, even during sinus rhythm, surface-only multielectrode mapping may not define the leading pacemaker sites in intramural SAN but instead misinterpret them as epicardial or endocardial exit sites through sinoatrial conduction pathways. These SAN exit sites may be distributed up to 50 mm along the CT beyond the ∼20-mm-long anatomic SAN structure. Moreover, because SAN reentrant tachycardia beats may exit through the same sinoatrial conduction pathway as during sinus rhythm, many SAN arrhythmias are underdiagnosed. Misinterpretation of arrhythmia sources and/or mechanisms (eg, enhanced automaticity, intranodal vs CT reentry) limits diagnosis and success of catheter ablation treatments for poorly understood SAN arrhythmias. The aim of this review is to provide a state-of-the-art overview of the 3D structure and function of the human SAN complex, mechanisms of SAN arrhythmias and available approaches for electrophysiological mapping, 3D structural imaging, pharmacologic interventions, and ablation to improve diagnosis and mechanistic treatment of SAN and atrial arrhythmias.

Targeted Treatment of Inappropriate Sinoatrial Node Tachycardia Based on Electrophysiological and Structural Mechanisms

The purpose of this review is to determine the causal mechanisms and treatment of inappropriate sinoatrial tachycardia (IST), defined as a non-physiological elevation in resting heart rate. IST is defined as a resting daytime sinus rate >100 beats/minute and an average 24-hour heart rate >90 beats/minute. Potential causal mechanisms include sympathetic receptor hypersensitivity, blunted parasympathetic tone, or enhanced intrinsic automaticity within the sinoatrial node (SAN) pacemaker-conduction complex. These anomalies may coexist in the same patient. Recent ex-vivo near-infrared transmural optical imaging of the SAN in human and animal hearts provides important insights into the functional and molecular features of this complex structure. In particular, it reveals the existence of preferential sinoatrial conduction pathways that ensure robust SAN activation with electrical conduction. The mechanism of IST is debated because even high-resolution electroanatomical mapping approaches cannot reveal intramural conduction in the 3-dimensional SAN complex. It may be secondary to enhanced automaticity, intranodal re-entry, or sinoatrial conduction pathway re-entry. Different pharmacological approaches can target these mechanisms. Long-acting β blockers in IST can act on both primarily increased automaticity and dysregulated autonomic system. Ivabradine targets sources of increased SAN automaticity. Conventional or hybrid ablation may target all the described abnormalities. This review provides a state-of-the-art overview of putative IST mechanisms. In conclusion, based on current knowledge, pharmacological and ablation approaches for IST, including the novel hybrid SAN sparing ablation, are discussed.

Stellate ganglion block and cardiac sympathetic denervation in patients with inappropriate sinus tachycardia

Background

Inappropriate sinus tachycardia (IST) remains a clinical challenge because patients often are highly symptomatic and not responsive to medical therapy.

Objective

To study the safety and efficacy of stellate ganglion (SG) block and cardiac sympathetic denervation (CSD) in patients with IST.

Methods

Twelve consecutive patients who had drug‐refractory IST (10 women) were studied. According to a prospectively initiated protocol, five patients underwent an electrophysiologic study before and after SG block (electrophysiology study group). The subsequent seven patients had ambulatory Holter monitoring before and after SG block (ambulatory group). All patients underwent SG block on the right side first, and then on the left side. Selected patients who had heart rate reduction ≥15 beats per minute (bpm) were recommended to consider CSD.

Results

The mean (SD) baseline heart rate (HR) was 106 (21) bpm. The HR significantly decreased to 93 (20) bpm (P = .02) at 10 minutes after right SG block and remained significantly slower at 97(19) bpm at 60 minutes. Left SG block reduced HR from 99 (21) to 87(16) bpm (P = .02) at 60 minutes. SG block had no significant effect on blood pressure or HR response to isoproterenol or exercise (all P > .05). Five patients underwent right (n = 4) or bilateral (n = 1) CSD. The clinical outcomes were heterogeneous: one patient had complete and two had partial symptomatic relief, and two did not have improvement.

Conclusion

SG blockade modestly reduces resting HR but has no significant effect on HR during exercise. Permanent CSD may have a modest role in alleviating symptoms in selected patients with IST.

Radiofrequency catheter ablation for inappropriate sinus tachycardia in a patient with systemic lupus erythematosus: a case report

Background

Systemic lupus erythematosus (SLE) is known to cause inappropriate sinus tachycardia (IST). However, there is limited evidence available with regard to the treatment of IST in this setting. In this article, we report a case of drug refractory IST in a patient with SLE treated with radiofrequency catheter ablation (RFCA) using a non-contact mapping system.

Case summary

A 33-year-old woman had been diagnosed with SLE in 2001. She presented with complaints of persistent palpitations for 1 month and persistent sinus tachycardia. She underwent RFCA using a non-contact mapping system for drug refractory IST. The voltage and activation maps did not show obvious differences in the earliest activation site at heart rates (HRs) 90–150 b.p.m. In contrast, the areas of breakout sites were clearly distinguished between those from the normal P-wave zones at HR <140 b.p.m. and those from higher rate sites at HR >140 b.p.m. Radiofrequency catheter ablation was performed in those areas as the target for ablation. Thereafter, the symptoms steadily disappeared and the maximum HR—using 24-h Holter monitoring—decreased from 156 to 120 b.p.m.

Discussion

Radiofrequency catheter ablation using a non-contact mapping system was applied to the treatment of drug refractory IST in a patient with SLE. Of note, IST in such patients may be left untreated. This approach may be considered as a first-line therapy option for drug refractory IST in patients with SLE.

Cardiac automaticity: basic concepts and clinical observations

PURPOSE

The purpose of this report was to review the basic mechanisms underlying cardiac automaticity. Second, we describe our clinical observations related to the anatomical and functional characteristics of sinus automaticity.

METHODS

We first reviewed the main discoveries regarding the mechanisms responsible for cardiac automaticity. We then analyzed our clinical experience regarding the location of sinus automaticity in two unique populations: those with inappropriate sinus tachycardia and those with a dominant pacemaker located outside the crista terminalis region.

RESULTS

We studied 26 patients with inappropriate sinus tachycardia (age 34 ± 8 years; 21 females). Non-contact endocardial mapping (Ensite 3000, Endocardial Solutions) was performed in 19 patients and high-density contact mapping (Carto-3, Biosense Webster with PentaRay catheter) in 7 patients. The site of earliest atrial activation shifted after each RF application within and outside the crista terminalis region, indicating a wide distribution of atrial pacemaker sites. We also analyzed 11 patients with dominant pacemakers located outside the crista terminalis (age 27 ± 7 years; five females). In all patients, the rhythm was the dominant pacemaker both at rest and during exercise and located in the right atrial appendage in 6 patients, in the left atrial appendage in 4 patients, and in the mitral annulus in 1 patient. Following ablation, earliest atrial activation shifted to the region of the crista terminalis at a slower rate.

CONCLUSIONS

Membrane and sub-membrane mechanisms interact to generate cardiac automaticity. The present observations in patients with inappropriate sinus tachycardia and dominant pacemakers are consistent with a wide distribution of pacemaker sites within and outside the boundaries of the crista terminalis.

Innappropriate Sinus Tachycardia After Superior Vena Cava Isolation In Addition To Pulmonary Veins Isolatin Of Paroxysmal Atrial Fibrillation Cryoballoon Ablation

We report a case of persistent inappropriate sinus tachycardia (IST) after pulmonary vein and superior vena cava (SVC) isolation with cryoballoon ablation for paroxysmal atrial fibrillation (PAF). After the cryoballoon ablation (CBA) procedure, the patient presented with sinus tachycardia of 105 beats/minute. The patient was successfully treated with metoprolol and ivabradine therapy.

Catheter ablation for atrial fibrillation in a subset of patients with concomitant hypertension

AIM: To study patients with atrial fibrillation and hypertension who had successful catheter ablation for changes in blood pressure 1 year later.

METHODS: A retrospective study was performed on patients who had catheter ablation for atrial fibrillation (AF) and hypertension (HTN) which included local autonomic ganglionated plexi denervation and pulmonary veins isolation. Of the records of 119 patients, follow-up data was found in order to determine the presence of sinus rhythm and data on systolic (SBP) and diastolic blood pressure at 2 wk, 3 mo, 6 mo and 1 year after the ablation procedure. Transthoracic echocardiograms were taken at the time of the catheter procedure to determine left atrial dimensions (LADs) and left ventricular size.

RESULTS: There was no significant difference in the pre-ablation mean blood pressures between the two groups (P = 0.08). After 1 year 33 of the 60 with AF and HTN were in sinus rhythm, of whom 12 had normal LADs, ≤ 4 cm Group 1, and 21 had enlarged left atria (LADs > 4 cm, Group 2). For Group 1, at 1 year of follow up, there was a significant difference in the SBP (119.2 ± 13 mmHg) compared to pre-ablation (142.6 ± 13.7 mmHg, P = 0.001). For Group 2, there was no significant difference in the SBP, pre-ablation (130.3 ± 17.5 mmHg) and at 1 year of follow up (130.4 ± 13.4 mmHg, P = 0.75). All patients were on similar anti-hypertensive medications. There was a trend for a greater left ventricular size in Group 2 compared to Group 1.

CONCLUSION: We suggest that Group 1 had HTN due to sympathetic hyperactivity, neurogenic HTN; whereas HTN in Group 2 was based on arterial vasoconstriction.

Usefulness of non-contact mapping for radiofrequency catheter ablation of inappropriate sinus tachycardia: new procedural strategy and long-term clinical outcome

OBJECTIVES

The present study evaluated the clinical benefits of a new therapeutic method of radiofrequency catheter ablation (RFCA) using an EnSite system for inappropriate sinus tachycardia (IST).

MATERIALS AND METHODS

Six patients with debilitating IST underwent RFCA using EnSite. Using the beta-adrenergic blocker and agonist, the heart rate was controlled between 70 to 150 bpm before and after the RFCA. The areas of the breakout sites (BOSs) were clearly distinguished between those from the normal P-wave zones during rates of less than 100 bpm and those from more upper rate sites during rates of more than 100 bpm using the EnSite system, in accordance with the appearance of tall P-waves (tall P-wave zone) in the IST patients. This was selected as the target for ablation.

RESULTS

After the RFCA, the BOSs observed during heart rates of more than 100 bpm moved completely from the tall P-wave zone to the normal P-wave zone in the IST patients. The total number of heart beats and average heart beat on the 24-h Holter monitoring decreased statistically from that before the RFCA to that after, and no adverse heart rate responses was observed after the RFCA. Before the RFCA, the brain natriuretic peptide was elevated, New York Heart Association functional class was worse, and there was an impaired exercise tolerance observed with exercise electrocardiogram testing. The RFCA for the IST significantly improved those parameters.

CONCLUSION

This new therapeutic method for IST using EnSite is effective and produces clinical benefits.

Right diaphragmatic paralysis following endocardial cryothermal ablation of inappropriate sinus tachycardia

Inappropriate sinus tachycardia (IST) is a rare disorder amenable to catheter ablation when refractory to medical therapy. Radiofrequency (RF) catheter modification/ablation of the sinus node (SN) is the usual approach, although it can be complicated by right phrenic nerve paralysis. We describe a patient with IST, who had symptomatic recurrences despite previous acutely successful RF SN modifications, including the use of electroanatomical mapping/navigation system. We decided to try transvenous cryothermal modification of the SN. We used 2 min applications at -85 degrees C at sites of the earliest atrial activation guided by activation mapping during isoprenaline infusion. Every application was preceded by high output stimulation to reveal phrenic nerve proximity. During the last application, heart rate slowly and persistently fell below 85 bpm despite isoprenaline infusion, but right diaphragmatic paralysis developed. At 6 months follow-up, the patient was asymptomatic and the diaphragmatic paralysis had partially resolved. This is the first report, we believe, of successful SN modification for IST by endocardial cryoablation, although this case also demonstrates the considerable risk of right phrenic nerve paralysis even with this ablation energy.