cascading two notch filters designed using iirnotch

Hello, I want to develop a 50 Hz notch filter for ECG denoising. While using iirnotch I'm getting around 20 dB attenuation and a very narrow bandwidth. Now I want to increase the attenuation more. So I found that if I filter the signal with the same coefficients, the attenuation is more. Instead of filtering twice with the same coefficients, is there a way to cascade the filter with itself?

S1=xlsread('D:\mtech\Work\For analysis\Nila.csv');
X=S1(:,2);
f0=50;fs=1334;
wo = f0/(fs/2);  bw = wo/25;
[b,a] = iirnotch(wo,bw);
% fvtool(b,a);
out=filtfilt(b,a,X);