For patients with cardiogenic shock that is refractory to the preceding treatments, several options remain open. Electrical cardiac pacing may help restore heart rate and should be considered for patients with shock and a heart rate below 40 beats/min. At the level of the heart cell, CCBs delay both systolic calcium transients and diastolic calcium reuptake. The heart cell cannot be forced into normal rhythmicity and electrical depolarization. In fact, ventricular stroke volume tends to be maximized at a heart rate of 45 to 50 beats/min. Electrical pacing faster than this rate actually may reduce stroke volume. As a result, electrical pacing at too rapid a rate may not improve cardiac output.
4-Aminopyridine (4-AP) is a potassium channel blocking agent that is now available for the treatment of multiple sclerosis. Based on several animal studies of verapamil toxicity, (4-AP) can be considered for a patient who is dying despite all efforts. 2324 4-Aminopyridine should be infused in doses of 10 to 50 pg/kg/h.
Venovenous hemodialysis or venovenous charcoal hemoperfusion can lower the plasma concentration of verapamil and diltiazem. However, these procedures should be considered with caution. Both require insertion of a large-bore dialysis catheter, and both require heparin anticoagulation. Hemodialysis—and to a lesser extent hemoperfusion—can worsen cardiovascular instability in a patient already suffering hypodynamic shock. First, to achieve adequate drug removal, relatively high rates of blood flow across the artificial kidney may be required. Second, hemodialysis can remove plasma catecholamines. Third, approximately 10 percent of patients develop an idiosyncratic hypotensive response to the polysulphone membrane used in most hemodialysis and hemoperfusion circuits. Thus, when the pump is started, the patient's blood pressure may drop. Also, with large ingestions, a mass of drug usually is present in the patient's intestine for at least 12 h, which allows ongoing drug absorption. For these reasons, continuous hemoperfusion is advised over episodic dialysis.
Intraaortic balloon counterpulsation also has been reported to improve shock from verapamil poisoning. 2526 Extracorporeal cardiopulmonary bypass also may provide a bridge to survival, especially if used in conjunction with hemodialysis or hemoperfusion.
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