Systems, methods, and interfaces are described herein for noninvasively determining an optimal coronary sinus branch to cannulate for a medical electrical lead. One exemplary method involves applying an electrode apparatus having a plurality of electrodes to a torso of a patient. One of a right ventricular (RV) lead is introduced to a right ventricle or a right atrial (RA) lead is introduced to a right atrium. Noninvasively ultrasonic energy is introduced to a target tissue selected from a set of target tissues. In response to delivering ultrasonic energy to the cardiac tissue, a processing unit receives a torso-surface potential signal from each of a plurality of electrodes distributed on a torso of a patient for the target tissue. Signals are sensed from one of the RA lead and the RV lead in response to delivering ultrasonic energy. For at least a subset of the plurality of electrodes, calculating, with the processing unit, a torso-surface activation time based on the signal sensed from the electrode. Determining whether the tissue site or the another tissue site provides optimal cardiac resynchronization.