Pacing therapy for atrioventricular dromotropathy: a combined computational-experimental-clinical study

AIMS

Investigate haemodynamic effects, and their mechanisms, of restoring atrioventricular (AV)-coupling using pacemaker therapy in normal and failing hearts in a combined computational-experimental-clinical study.

METHODS AND RESULTS

Computer simulations were performed in the CircAdapt model of the normal and failing human heart and circulation. Experiments were performed in a porcine model of AV dromotropathy. In a proof-of-principle clinical study, left ventricular (LV) pressure and volume were measured in 22 heart failure (HF) patients (LV ejection fraction <35%) with prolonged PR interval (>230 ms) and narrow or non-left bundle branch block QRS complex. Computer simulations and animal studies in normal hearts showed that restoring of AV-coupling with unchanged ventricular activation sequence significantly increased LV filling, mean arterial pressure, and cardiac output by 10-15%. In computer simulations of failing hearts and in HF patients, reducing PR interval by biventricular (BiV) pacing (patients: from 300 ± 61 to 137 ± 30 ms) resulted in significant increases in LV stroke volume and stroke work (patients: 34 ± 40% and 26 ± 31%, respectively). However, worsening of ventricular dyssynchrony by using right ventricular (RV) pacing abrogated the benefit of restoring AV-coupling. In model simulations, animals and patients, the increase of LV filling and associated improvement of LV pump function coincided with both larger mitral inflow (E- and A-wave area) and reduction of diastolic mitral regurgitation.

CONCLUSION

Restoration of AV-coupling by BiV pacing in normal and failing hearts with prolonged AV conduction leads to considerable haemodynamic improvement. These results indicate that BiV or physiological pacing, but not RV pacing, may improve cardiac function in patients with HF and prolonged PR interval.

Prevalence of first-degree atrioventricular block and the associated risk factors: a cross-sectional study in rural Northeast China

Background

First-degree atrioventricular block (AVB) has traditionally been regarded as a benign condition but recent studies have challenged this conception. Prevalence of 1–2% have been reported in developed countries in Asia. However, no epidemiologic studies have established the prevalence of first-degree AVB in developing countries. The aim of the study was to investigate the prevalence of first-degree AVB in rural northeast China and identify the associated risk factors.

Methods

This cross-sectional study was undertaken from September 2017 to May 2018 in rural areas of Liaoning Province. It involved 10,926 participants aged ≥40 years (85.3% of those who were eligible). First-degree AVB was confirmed by at least two independent cardiologists. Risk factors were evaluated using stepwise logistic regression.

Results

The prevalence of first-degree AVB was 3.4% (95% confidence interval [CI]: 3.0–3.8%). Males had a higher prevalence than females (5.1% vs. 2.2%, p < 0.001). The regression model involving all participants showed that age (odds ratio [OR]: 1.32; p <0.001), male sex (OR: 1.72; p = 0.001), height (OR: 1.25; p = 0.008), systolic blood pressure (SBP) (OR: 1.15; p = 0.003), triglycerides (TG) (OR: 1.10; p < 0.001), high-density lipoprotein cholesterol (HDL-C) (OR: 0.73; p < 0.001), heart rate (OR: 0.78; p < 0.001), and exercising regularly (OR: 0.73; p = 0.030) were independent risk factors.

Conclusions

First-degree AVB is highly prevalent in rural areas of northeast China. The associated independent risk factors include being male, older, and taller, higher SBP and TG, lower HDL-C and heart rate, and lack of exercise.

Occurrence of significant long PR intervals in patients implanted for sinus node dysfunction and monitored with SafeR™: The PRECISE study

BACKGROUND

Long PR intervals may increase cardiovascular complications, including atrial fibrillation. In pacemakers, the SafeR™ mode monitors PR intervals, switching from AAI to DDD when criteria for atrioventricular block are met.

AIMS

The PRECISE study evaluated the incidence and predictors of long PR intervals and their association with incident atrial fibrillation after 1 year in patients implanted for sinus node dysfunction and free from significant conduction disorders at baseline.

METHODS

This French, prospective, multicentre, observational trial enrolled patients implanted with a REPLY™ dual-chamber pacemaker. Pacemaker memory recorded long PR intervals (defined as first-degree atrioventricular block mode switches occurring after six consecutive PR/AR intervals≥350/450ms) and atrial fibrillation incidence (fallback mode switch>1minute/day). Predictors were identified from baseline variables (age, sex, AR and PR intervals, atrial rhythm disorder and medication) using logistic regression.

RESULTS

Of 291 patients with sinus node dysfunction enrolled, 214 were free from significant conduction disorders at baseline (mean age 79±8 years; 44% men; PR/AR intervals<350/450ms). After 1 year, long PR intervals had occurred in 116 patients (54%) and atrial fibrillation in 63 patients (30%). Amiodarone was the only independent predictor of long PR interval occurrence (odds ratio 2.50, 95% confidence interval 1.20-5.21; P=0.014). There was a strong trend towards an association between long PR interval and atrial fibrillation incidence (odds ratio 1.86, 95% confidence interval 0.97-3.61; P=0.051).

CONCLUSIONS

Half of the patients with pure sinus node dysfunction developed long PR intervals in the year following pacemaker implantation. Amiodarone was the only independent predictor of long PR intervals. There was a strong trend towards an association between long PR intervals and incident atrial fibrillation.

Symptomatic first-degree atrioventricular block in a young woman after taking a fat burner supplement

A 22-year-old woman collapsed at home and was brought to the accident and emergency department. History revealed that she was fit and taken T5 capsule the night before the collapse. There was no history of similar collapses or seizure. Examination revealed blood pressure (BP) of 104/69 mmHg and a heart rate (HR) of 70 bpm. Chest, cardiovascular, and neurology examination were unremarkable. However, on standing, her HR increased to 120 bpm, and her BP dropped to 62/40 mmHg. Blood Na, K, Ca, Mg, phosphate, creatinine, complete blood count, T4 cortisol, and thyroid-stimulating hormone (TSH) were normal. The electrocardiogram (ECG) on the ambulance revealed sinus rhythm with normal morphology but a significant first-degree atrioventricular block with a PR interval of 280-300 ms. The patient was treated for orthostatic hypotension with intravenous fluids. Her symptoms gradually improved. The repeat ECG taken 24 h after admission showed reduced PR interval to 230ms. The patient was followed up in the clinic after 1 week with normal ECG with a PR interval of 200 ms and a normal echocardiogram. The findings are discussed.