Differences in Electrical Delay Between the Mid-septum and Apex with the Right Ventricular Lead: Novel Implications for Pacemaker Sensing.

Ventricular sensing relies on the analysis of a local intracardiac electrogram in reference to the QRS on the surface electrocardiogram. If both signals do not coincide in time, there is a delay in sensing intrinsic ventricular activity. We evaluated possible differences in the electrical delay between the mid-septum and apex as determined by the right ventricular (RV) lead position using a pacing system analyzer (PSA) during conventional pacemaker implantation. Patients without significant heart disease and intrinsic atrioventricular conduction underwent their first Medtronic (Minneapolis, MN, USA) or Abbott (Chicago, IL, USA) dual-chamber pacemaker implantation with the RV lead first positioned at the apex and then subsequently at the mid-septum. Real-time ventricular sensing data were obtained through PSA to determine the electrical delay Q-VS value as the time difference between the QRS and the released RV-sensed event marker "VS." Among 212 patients, 139 had narrow QRS and 73 had complete right bundle branch block (RBBB). Overall, both narrow QRS and RBBB patients exhibited shorter Q-VS lengths at the mid-septum compared to the apex (50.4 ± 24.2 ms and 66.7 ± 32.3 ms vs. 63.9 ± 27.6 ms and 71.7 ± 32.2 ms; P < .0001 and P < .001, respectively). The Q-VS in patients with Abbott devices was significantly shorter compared to that in patients with Medtronic devices at both the mid-septum and the apex in both patient groups (P < .0001). In conclusion, RV lead positioning at the mid-septum is associated with a shorter electrical delay compared to positioning at the apex in both narrow QRS and RBBB patients.

Mechanisms of Atrial Fibrillation: How Our Knowledge Affects Clinical Practice.

Atrial fibrillation (AF) is a very common arrhythmia that mainly affects older individuals. The mechanism of atrial fibrillation is complex and is related to the pathogenesis of trigger activation and the perpetuation of arrhythmia. The pulmonary veins in the left atrium arei confirm that onfirm the most common triggers due to their distinct anatomical and electrophysiological properties. As a result, their electrical isolation by ablation is the cornerstone of invasive AF treatment. Multiple factors and comorbidities affect the atrial tissue and lead to myocardial stretch. Several neurohormonal and structural changes occur, leading to inflammation and oxidative stress and, consequently, a fibrotic substrate created by myofibroblasts, which encourages AF perpetuation. Several mechanisms are implemented into daily clinical practice in both interventions in and the medical treatment of atrial fibrillation.

Paradoxical pacing spikes during a wide complex tachycardia in biventricular defibrillator. What is the mechanism? Is it undersensing due to troubleshooting?

We present the case of a 68-year-old man with a cardiac resynchronization therapy-defibrillator Medtronic device implanted 3 years ago, admitted to our hospital due to a wide complex tachycardia with unexpected pacing spikes inside QRS complexes. Although that could be easily attributed to ventricular undersensing, more complicated mechanisms are involved, including the origin of the tachycardia, the parameters of the device, and the position of the device and the leads.