Monthly Archive February 2019

Atrial fibrillation treatment by frequency control strategy

The choice of treatment depends on whether the goal is to control the frequency of ventricular contractions while maintaining atrial fibrillation (AF) or maintaining sinus rhythm. These two strategies are called “rate control” and “rhythm control” (rhythm control), respectively. In general, frequency control is easier than rhythm control.

Atrial fibrillation (AF) results in a loss of mechanical atrial systole before ventricular contraction and often inadequately high heart rate. This leads to a decrease in cardiac output. Therefore, one would expect that the patient’s condition would be better while maintaining normal sinus rhythm than while maintaining persistent or paroxysmal AF.

Nevertheless, several large studies have revealed that in terms of mortality, hospitalization rate and quality of life, the rhythm control strategy is no better than the strategy aimed at controlling heart rate. Patients who participated in these studies were predominantly elderly, and many of them suffered from cardiovascular disease.

Therefore, the results obtained cannot be applied without fail to all patients with atrial fibrillation (AF). For example, young people with paroxysmal idiopathic AF often have more pronounced symptoms, and maintaining sinus rhythm in them is more appropriate.

Although studies have shown that treatment strategies aimed at maintaining sinus rhythm are not better than the “frequency control” strategy, it is important to note that a stable preservation of the normal heart rhythm was not achieved in many patients from the “rhythm control” group. Therefore, it is highly likely that maintaining a normal rhythm still leads to a therapeutic outcome.

This assumption is confirmed by the results of both long-standing and recent studies that indicate that maintaining sinus rhythm improves the quality of life and tolerance to physical exertion. If a safe and relatively cheap way to maintain sinus rhythm is found, the “frequency control” strategy can, of course, be abandoned.

Some patients with atrial fibrillation (AF), despite effective heart rate control, experience very uncomfortable symptoms and feel much better with normal sinus rhythm. Others, including those who did not experience symptoms prior to treatment, feel quite well when pursuing a “frequency control” strategy. Thus, the treatment must be selected individually.

Often the strategy of “rhythm control” ends in failure, which makes it necessary to use the strategy of “frequency control”. However, in patients with severe clinical symptoms, an “aggressive” approach to maintaining sinus rhythm is justified.

Thrombin inhibitors for atrial fibrillation (AF)

It was shown that dabigatran in a dose of 150 mg 2 times a day is more effective in preventing ischemic stroke than warfarin, and in a dose of 110 mg 2 times a day is not inferior to warfarin in effectiveness. Unlike warfarin, therapeutic levels of the drug are observed already 2 h after administration, and the state of stable equilibrium plasma concentration is reached within 2 days. Dabigatran is excreted primarily by the kidneys and is therefore contraindicated for severely impaired renal function or continued massive bleeding.

The dose of the drug should be reduced to 110 mg 2 times a day if the patient is over 80 years old or if the patient is receiving verapamil or when a high risk of bleeding is assumed. In moderate renal insufficiency, the drug is recommended to be administered at a dose of 75 mg 2 times a day.

In the UK, according to the latest changes in recommendations, it is allowed to use new oral anticoagulants (such as dabigatran) after talking with the patient about the advantages and disadvantages of these drugs compared to warfarin. However, these recommendations do not apply to women aged 65-74 without other cardiovascular risk factors that have up to 2 points inclusive on the CHA2DS2VASc scale.

The main adverse effects are relatively rare dyspeptic disorders, diarrhea. Simultaneous systematic use of ketoconazole, cyclosporine, itraconazole or tacrolimus is contraindicated. It was also reported on the interaction of the drug with dronedarone and amiodarone.

Reception of dabigatran should be suspended 2 days before the planned operation, and if the clearance of the drug is reduced due to renal failure, 3-4 days. There is no specific antidote. If the patient switches from warfarin to dabigatran, the reception of the latter should be started with an MHO of less than 2.0.

Warfarin for Atrial Fibrillation

Warfarin, an antagonist of vitamin K, is well known in clinical practice, but it has significant drawbacks. To regulate the dose of the drug in order to maintain an internationally normalized ratio (MHO) at the therapeutic level (between 2.0 and 3.0), regular blood tests are required. In a significant proportion of patients, maintenance of anticoagulation at a therapeutic level cannot be achieved.

Many drugs affect the metabolism of warfarin and can lead to excessive anticoagulation (these include antibiotics, anticonvulsants, some statins, amiodarone, tamoxifen, and alcohol). The risk of bleeding may increase while taking aspirin. In connection with these shortcomings of the drug, doctors are often reluctant to prescribe warfarin, and patients in some cases refuse to take it.

Before surgery, it may be necessary to stop taking warfarin, which was prescribed to prevent systemic thromboembolic complications in patients with AF. In such cases, it is customary to prescribe heparin as a temporary bridge, but the use of heparin often creates the problem of bleeding and the formation of postoperative hematomas. In fact, the need for such a “heparin bridge” rarely arises: you can stop taking warfarin 3 days before the operation and resume 3 days after it.

More modern drugs. Recently, thrombin and factor Xa inhibitors have become available, which are prescribed in fixed dosages and therefore do not require regular blood tests to monitor their effectiveness. It has been shown that they are at least as effective as warfarin, and their use is associated with less or at least a similar risk of bleeding (especially intracranial hemorrhage), in addition, they interact to a lesser extent with other drugs. Nevertheless, although the results of clinical studies are promising, the experience of using these tools in clinical practice is still small.