HOT CRT-The Effective Combination of Conventional Cardiac Resynchronization and His Bundle Pacing.

Background and Objectives: Cardiac Resynchronization Therapy (CRT) has, besides its benefits, various limitations. For instance, atrial fibrillation (AF) has a huge impact on the therapy efficacy. It usually reduces the overall BiV pacing percentage and leads, inevitably, to lack of fusion beats. In many patients with heart failure that could benefit from resynchronization, the QRS morphology is often IVCD and atypical, or non-LBBB, which further diminishes the CRT response. In those cases, we established His pacing combined with LV pacing as a feasible option to reduce the impact of AF on the CRT response and regain partially physiological ventricular activation to improve the electromechanical sequence. Materials and Methods: We implanted two patients with AF, HF, EF < 35%, NYHA II-III and QRS > 150 ms with CRT-D systems modified to HOT-CRT and observed their clinical, ECG and echocardiographic improvements over a follow-up period of three months. Results: In both patients we observed improvements of the initial parameters. We were able to shorten the QRS duration to approx. 120 ms, improve NYHA functional class, increase the EF by approximately 12% and distinctly reduce mitral regurgitation. Conclusion: Since the conventional CRT reaches its limits within this specific patient group, we need to consider alternative pacing sites and the effective combination of them. Our results and respectively other studies that are also mentioned in the current guidelines, support the feasibility of HOT-CRT in the above mentioned patient group.

Concepts of Cardiac Dyssynchrony and Dynamic Approach.

Cardiac conduction involves electrical activity from one myocyte to another, creating coordinated contractions in each. Disruptions in the conducting system, such as left bundle branch block (LBBB), can result in premature activation of specific regions of the heart, leading to heart failure and increased morbidity and mortality. Structural alterations in T-tubules and the sarcoplasmic reticulum can lead to dyssynchrony, a condition that can be treated by cardiac resynchronization therapy (CRT), which stands as a cornerstone in this pathology. The heterogeneity in patient responses underscored the necessity of improving the diagnostic approach. Vectocardiography, ultra-high-frequency ECG, 3D echocardiography, and electrocardiographic imaging seem to offer advanced precision in identifying optimal candidates for CRT in addition to the classic diagnostic methods. The advent of His bundle pacing and left bundle branch pacing further refined the approach in the treatment of dyssynchrony, offering more physiological pacing modalities that promise enhanced outcomes by maintaining or restoring the natural sequence of ventricular activation. HOT-CRT emerges as a pivotal innovation combining the benefits of CRT with the precision of His bundle or left bundle branch area pacing to optimize cardiac function in a subset of patients where traditional CRT might fall short.

The clinical utility of direct His-bundle pacing in patients with heart failure and permanent atrial fibrillation.

In patients with significantly impaired left ventricle function permanent atrial fibrillation (AF) often coexists with symptoms of heart failure. Based on various studies, it is assumed that in patients with heart failure in functional class III and IV AF occurs in 40-50% of patients. AF adversely affects cardiac hemodynamics, and its harmfulness increases particularly in the failing heart. The lack of mechanical function of the left atrium, the usually fast ventricular rate and the irregular sequence of ventricular contraction constitute the spectrum of harmful effects of this arrhythmia. Therefore, the only way to address the underlying problem of AF, which is irregular ventricular rhythm, is to pace the ventricles and to slow or block the AV conduction. Classic, right ventricular pacing is contraindicated in this population as it promotes the abovementioned disorders by initiating additional dyssynchrony of left ventricular contraction with reduction of its contractility and aggravation of AF-related mitral regurgitation. The possibility of direct His bundle pacing (DHBP) significantly extended the clinical armamentarium of cardiac pacing. The restoration of the physiological electrical activation could significantly contribute to echocardiographic and clinical improvement. With time and the development of dedicated tools for direct His bundle pacing the success rate of implantations became more than 90% and the acceptable pacing thresholds under 2.0 V (1 ms) could be achieved in most patients. This contributed to the broader clinical application of DHBP in different patient' groups with various pacing indications. The authors of the paper discuss different electrocardiographic and clinical indications for DHBP.

His-Optimized and Left Bundle Branch-Optimized Cardiac Resynchronization Therapy: In Control of Fusion Pacing.

Fusion pacing, which exploits conduction via the intrinsic His-Purkinje system, forms the basis of recent cardiac resynchronization therapy (CRT) optimization algorithms. However, settings need to be constantly adjusted to accommodate for changes in AV conduction, and the algorithms are not always available (eg, depending on the device, in case of AV block or with atrial fibrillation). His-optimized cardiac resynchronization therapy (HOT-CRT), and left-bundle branch optimized cardiac resynchronization therapy (LOT-CRT) which combines conduction system pacing with ventricular fusion pacing, provide constant fusion with ventricular activation (irrespective of intrinsic AV conduction). These modalities provide promising treatment strategies for patients with heart failure, especially in those with chronic atrial fibrillation who require CRT (in whom the atrial port is usually plugged and can be used to connect the conduction system pacing lead).