To the Editor: In a recent issue of Circulation, Zaman et al1 report a model for the preoperative risk stratification of patients at risk for developing atrial fibrillation (AF) after isolated coronary artery bypass grafting (CABG). They studied 326 patients prospectively and demonstrated that prolonged signal-averaged P-wave duration (SAPD), advanced age, and male sex identified patients at a ...

Concrete is one of civilization’s most durable building materials. The ancient Romans used concrete 2,000 years ago to make structures that still stand today. People now use the material’s modern versionaggregates such as sand or gravel held together by a cement and water pastemore than all other construction materials combined. The world produced 4.3 billion metric tons of cement in 2014, an...