Remove the shells from the shrimp and reserve. Transfer the shrimp to a bowl and add the baking soda and salt. Toss to coat and set aside.
Heat the olive oil in a large, deep skillet until shimmering. Add the reserved shells and saute for 10 minutes over a low flame. Remove the shells from the skillet and discard.
Add the shrimp to the skillet and saute until just pink. Transfer the shrimp to a plate and set aside.
Add more oil to the pan if needed and add the shallots and a pinch of salt. Sweat the shallots for 5 minutes or until just translucent. Add the garlic and saute until fragrant, about 2 minutes more. Add the anchovy paste and chili flakes and saute until the paste melts.
Pour in the canned tomatoes. Roughly break them apart using the end of a spoon. Stir in the vodka and a healthy pinch of salt. Bring the mixture to a boil and toss in the oregano. Reduce to a simmer and let cook for 10 minutes.
While the sauce is simmering, place a large pot of water over high heat and bring to a boil. Liberally salt the water and add the rigatoni. Cook the rigatoni according to a package's directions. Drain the pasta and rinse. Set aside until ready to use.
Once the 10 minutes have passed, remove the oregano bundle and discard it. Transfer the sauce to a food processor and blitz until smooth. Return the sauce to the skillet and place over a low flame. Add the cream and crab meat and stir to combine. Add the shrimp back in and stir until heated through.
Stir the pasta into sauce until well coated. Divide the pasta amongst 4-6 pasta bowls and garnish with shredded Grana Padano cheese and fresh oregano leaves. Serve immediately with a glass of bubbly.