First-degree atrioventricular block may not be that benign after all

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I n this issue of the Journal, Uhm et al. [1] report a study from Korea, which indicates that first-degree atrioventricular block (AVB) is associated with an increased risk of advanced AVB, atrial fibrillation and left ventricular dysfunction in patients with hypertension. First-degree AVB is a result of conduction delay occurring in the right atrium, AV node, His bundle or Purkinje network. Potential underlying mechanisms suggested by the authors include atherosclerosis of the coronary arteries, atrial fibrosis, dilated cardiomyopathy, infiltrative cardiomyopathies, left ventricular dysfunction, neuromuscular disease and insufficient blood pressure control causing left ventricular hypertrophy. Therefore, first-degree AVB may be a marker of underlying heart disease, rather than being an independent predictor of left ventricular dysfunction. The current study by Uhm et al. [1] retrospectively examined 3816 hypertensive middle-aged participants with sinus rhythm on baseline ECG and no cardiac implantable electronic devices, baseline left ventricular dysfunction, ventricular preexcitation or advanced AVB. The 544 (14.3%) participants with first-degree AVB were older, used more nondihydropyridine calcium channel blockers, had more left ventricular hypertrophy and longer QRS duration at baseline. In Cox multivariate analyses, baseline firstdegree AVB was associated with subsequent development of atrial fibrillation, left ventricular dysfunction and advanced AVB. In earlier studies, first-degree AVB was not associated with higher morbidity and mortality and has previously been considered a benign finding of no adverse prognostic significance [2,3]. More recently, a growing body of literature has emerged that first-degree AVB might be an ominous sign compared with patients with normal AV conduction [4,5]. In the Heart and Soul Study, including 938 patients with stable coronary artery disease, first-degree