Background: Only few data evaluating the prognostic impact of blood-derived potassium levels (K) on arrhythmic endpoints in patients with implantable cardioverter-defibrillators (ICD) is available. Therefore, this study evaluates the prognostic impact of potassium levels on recurrences of ventricular tachyarrhythmias in consecutive ICD recipients.
Methods: A large retrospective registry was used including all consecutive patients presenting with ventricular tachyarrhythmias on admission from 2002 to 2016 at one institution. Patients were divided into three subgroups: hypokalemia (i.e., K < 3.3 mmol/L), normokalemia (i.e., K 3.3 - 4.5 mmol/L), and hyperkalemia (i.e., K > 4.5 mmol/L). Kaplan-Meier and Cox regression analyses were applied for the evaluation of the primary endpoint of first recurrences of ventricular tachyarrhythmias at one year. Secondary endpoints comprised of first appropriate ICD therapy, first cardiac rehospitalization, and all-cause mortality at one year.
Results: Five hundred and thirty ICD recipients with a median potassium level of 4.23 mmol/L were included (67%: normokalemia, 27%: hyperkalemia, and 6%: hypokalemia). Whereas hyperkalemia was not associated with increasing risk of recurrent ventricular tachyarrhythmias, hypokalemia was associated with decreasing freedom from recurrent ventricular tachyarrhythmias (HR = 2.135; 95% CI 1.158 - 3.937; p = 0.015), even after mul-tivariable adjustment (HR = 2.577; 95% CI 1.236 - 5.372; p = 0.012). Higher risk of recurrences was especially attributed to higher rates of electrical storm in the presence of hypokalemia (15% vs. 3 - 4%). Negative impact of hypokalemia was mainly attributed to secondary preventive ICD (HR = 2.637; 95% CI 1.325 - 5.248; p = 0.006). Moreover, hypokalemia was associated with increasing risk of appropriate ICD therapies (HR = 1.920; 95% CI 0.912 - 4.042; statistical trend: p = 0.086), which was still demonstrated after multivariable adjustment. In contrast, risk of first cardiac rehospitalization and all-cause mortality were not affected by potassium levels.
Conclusions: In consecutive ICD recipients with ventricular tachyarrhythmias at index, hypokalemia - but not hyperkalemia - was associated with increasing risk of recurrent ventricular tachyarrhythmias and appropriate ICD therapies.