Although numerous digital video formats, with various pixel aspect ratios, can be converted to the the NTSC standard adopted by the FCC, "NTSC" is an analog signal format (EIA RS-170A), and therefore, it is not defined in terms of pixels.

The RS-170A specifications define an analog waveform in terms of frequency, timing, phase relationships and amplitudes. Not a pixel hiding in that haystack anywhere.

So, if someone says that NTSC is H-pixels by V-pixels, what they mean is the specific digital-to-analog converter they are using requires the digital input be in that format to be able to output a proper analog NTSC signal.

Hence my answer above - it depends on the converter.