Left Ventricular Pacing to Avoid Cardiac Enlargement Study

In this prospective, we will randomly assign 98 patients who need permanent pacemaker due to complete atrioventricular block or sick sinus syndrome to receive left ventricular pacing (49 patients) or right ventricular apical pacing (49 patients). Patients will be paced with temporary pacemaker lead, and only those with paced QRS duration ≥185 ms will be enrolled. The primary endpoint is left ventricular ejection fraction measured by modified Simpson method at 12 months. The secondary end points include left ventricular systolic end-systolic and diastolic volume, LV strain, NYHA functional class, exercise performance (using treadmill test), quality of life (using SF-36v2), NT-proBNP at 12 months.