My pharmacology professor glossed over the mechanism that causes edema besides briefly discussing after/preload. If Calcium channel blockers and beta blockers both are negative ionotropes then why isn't heart failure some form of adverse effect in both drug classes?
It has to do with different mechanism of action of both substances. Both calcium channel blockers and beta blockers are used to lower blood pressure, but the ways, how the hypotensive effect is achieved, are different.
As a first approximation, the arterial blood pressure PA evolves with
PA = PV + R * dV/dt,
where PV is central venous pressure, R is total peripheral resistance and dV/dt is cardiac output.
Calcium channel blockers have vasodilatory action, i.e. they lower R. Beta-blockers act mainly on the heart so that they decrease dV/dt. Both mechanisms lower blood pressure, but the ways are different.
Different are also their side effects. Beta-blockers may lead to bradycardia (and other problems), and calcium channel blockers increase the hydrostatic pressure in the precapillary circulation, thereby permitting fluid shifts into the interstitial compartment. Beta-blockers have even a slight vasoconstrictor effect.
This is the reason why patients on calcium channel blockers are more prone to oedema than persons on beta-blockers.
Makani H, Bangalore S, Romero J, Htyte N, Berrios RS, Makwana H, Messerli FH. Peripheral edema associated with calcium channel blockers: incidence and withdrawal rate--a meta-analysis of randomized trials. J Hypertens. 2011 Jul;29(7):1270-80. doi 10.1097/HJH.0b013e3283472643. PMID 21558959.