Autonome Dysfunktion und Betablocker beim Multiorgandysfunktionssyndrom

[Relationship between cardiac output, heart rate and microcirculation in patients with multiorgan dysfunction syndrome]

BACKGROUND

Multiple organ dysfunction syndrome (MODS) is one of the main causes of death in intensive care units. There is evidence that microcirculation in sepsis and coronary shock is regulated separately from hemodynamics. This study investigates the relationship between heart rate (HR), cardiac output (CO) and microcirculation in patients with MODS.

METHODS

This is a partial analysis of the "MODIFY study" (Reducing Elevated Heart Rate in Patients With Multiple Organ Dysfunction Syndrome [MODS] by Ivabradine). During the period 05/2010-09/2011, the microcirculation of 46 patients with septic and coronary MODS was measured using the sidestream dark field technique on the day of inclusion and 96 h later. Patients were randomized into a control and ivabradine treatment group.

RESULTS

Overall, there is a relevant improvement in microcirculation over time small perfused vessels, SPV [%] on day 0, d0:56.5 ± 34.2/d4:73.2 ± 22.1 (p = 0.03); perfused vessel density, PVDsmall [1/mm2] d0:7.5 ± 5.0/d4:9.8 ± 3.4 (p = 0.04); proportion of perfused vessels, PPVsmall [%] d0:51.6 ± 31.6/d4:66.7 ± 21.8 (p = 0.04); microcirculatory flow index, MFI d0:1.7 ± 1.0/d4:2.2 ± 0.7 (p = 0.05). Administration of ivabradine shows no effect. In patients with coronary MODS, there is a relevant correlation between microcirculatory parameters and cardiac output (SPV [%]: r = 0.98, p = 0.004). Patients with coronary MODS show better microcirculation values at high heart rates (> 100 bpm), while patients with septic MODS show an opposite relationship.

CONCLUSION

The results indicate that in critically ill patients, depending on the genesis of the MODS, there are different relationships between HF or CO values, on the one hand, and the parameters of the microcirculation, on the other.

[Heart rate control in shock]

Heart rate is well established in the diagnosis of shock; however, the mechanisms regulating heart rate, systemic resistance and blood pressure remain unclear. The concept of heart rate control in shock-related tachycardia has been known for about 50 years. Elevated heart rates in septic shock have been identified as an indicator of increasingly inefficient hemodynamics, worsening perfusion and organ function as well as of an unfavourable prognosis. Many drugs used for heart rate control also lower blood pressure. The challenge of this therapeutic concept is achieving optimal heart rate control without provoking critical hypotension. Only in recent years has the development of highly cardioselective, short- and ultrashort-acting β‑blockers such as esmolol and landiolol made it possible to prove the feasibility and usefulness of heart rate control in certain types of shock.

Ivabradine: potential clinical applications in critically ill patients

It has been extensively demonstrated that an elevated heart rate is a modifiable, independent risk factor for cardiovascular events. A high heart rate increases myocardial oxygen consumption and reduces diastolic perfusion time. It can also increase ventricular diastolic pressures and induce ventricular arrhythmias. Critical care patients are prone to develop a stress induced cardiac impairment and consequently an increase in sympathetic tone. This in turn increases heart rate. In this setting, however, heart rate lowering might be difficult because the effects of inotropic drugs could be hindered by heart rate reducing drugs like beta-blockers. Ivabradine is a new selective antagonist of funny channels. It lowers heart rate, reducing the diastolic depolarization slope. Moreover, ivabradine is not active on sympathetic pathways, thus avoiding any interference with inotropic amines. We reviewed the literature available regarding heart rate control in critical care patients, focusing our interest on the use of ivabradine to assess the potential benefits of the drug in this particular setting.

Reducing elevated heart rate in patients with multiple organ dysfunction syndrome by the I (f) (funny channel current) inhibitor ivabradine : MODI (f)Y trial

BACKGROUND

Heart rate (HR) is of relevant prognostic value not only in the general population and patients with cardiovascular disease, but also in critically ill patients with multiple organ dysfunction syndrome (MODS). An elevated HR in MODS patients is associated with a worse prognosis. Beta-blocker (BB) administration has been shown to reduce mortality in MODS. In most cases, negative inotropic effects prevent administration of BBs in MODS patients. In this trial we investigate, whether the "funny current" (I (f)) channel inhibitor ivabradine is able and apt to reduce pathologically elevated HR in MODS patients. We hypothesize that critically ill patients could derive particular benefit from the specific HR-lowering agent ivabradine.

METHODS

MODI (f)Y is a prospective, single centre, open label, randomized, controlled two arms, phase II-trial to evaluate the potential of ivabradine to reduce an elevated HR in MODS patients. The primary end point is the proportion of patients with a reduction of HR by at least 10 beats per minute (bpm) within 4 days. This trial will randomize 70 patients (men and women, aged ≥18 years) with newly diagnosed MODS, with an elevated HR (sinus rhythm with HR ≥90 bpm) and contraindications to BB therapy. Treatment period will last for 4 days. All patients will be followed for 6 months.

RESULTS

The first patient was randomized on May 21, 2010.

CONCLUSIONS

The MODI (f)Y trial is the first application of ivabradine as a pure heart rate reducing agent in MODS patients.