An overview of the connections between adenosine and the heart rate is hardly short of clinical comparisons and diagnostic associations. The connections are vast even when sparing all of the interactions of the tedious biochemical details. In the clinical realm alone, adenosine is as varied in its effect on heart rate as it is in its uses to diagnose heart problems. Adenosine is a fascinating compound in its cardiac affects. It can speed the heart rate up, and it can also slow it down. It also can bring the cadence back when a steady rhythm fails.
Anti-arrhythmics
Compounds that exert an effect on cardiac muscle contractions are called anti-arrhythmics. Typically, these drugs are grouped into five categories according to how they effect cardiac contraction. The higher the class, the less that is known about its underlying mechanism of effect. Adenosine is a class 5 anti-arrhythmic, meaning the nitty-gritty microbiology is not comfortably understood. The nomenclature is helpful if you are a biochemist, but a patient is not concerned with the "way" that adenosine works on the heart, but rather that it "does" work on the heart --- that is much easier to observe. Health-care providers are accustomed to referring to anti-arrhythmics according to their class, which understandably appears odd to patients --- most other pharmaceuticals are not presented in this way.
Direct Diagnostic Connection
Individuals who suffer from cardiac arrhythmia may gain some relief from prescribed drugs that treat their symptoms, but to gain to the most therapeutic results, physicians need to pinpoint the anatomical origins within the heart that give rise to the arrhythmia. With millions of cardiac cells constituting a single heart, and it taking only a handful to create disruption, finding the culprit is sometimes a difficult task. An injection of adenosine, however, has the direct effect of drastically slowing a fast arrhythmia known as AV nodal re-entry tachycardia, or AVNRT -- a big word that basically identifies the location of an arrhythmia, providing the physician recourse to treat and sometimes cure the cause of the arrhythmia, rather than having to combat and manage the symptoms.
Indirect Diagnostic Connection
During a cardiac stress tests, patients typically exercise on a treadmill or a stationary bike. As their heart rate increases, the vessels providing blood flow to the heart itself begin to dilate and bring into view areas where these vessels may present with a potential blockage, which could give rise to a heart attack. As important as the stress test is, medical conditions may prohibit certain patients from performing the exertion needed to complete the test. But adenosine can dilate these vessels as well, so the effects of an exercising heart rate are indirectly produced by an adenosine stress test without taxing the heart.
Side Effect Connection
The connection between adenosine and heart rate is apparent not only in diagnostics but also in side effects. Many of adenosine's side effects mimic the effects associated with changes in the heart's rate. Some side effects of adenosine include brief sensation of lightheadedness, chest pressure, facial flushing and shortness of breath. Like the diagnostic effects, side effects of adenosine may directly or indirectly influence heart rate. Nonetheless, adenosine is always administered under physician supervision, and its effect are short-lived, while its potential findings may help save a life.
References
- "Journal of Clinical Science"; Effects of Adenosine on Heart Rate Variability in Humans; Rongen G.A., et al.; June 1996
- Cleveland Clinic: Nuclear Adenosine Stress Test
- Harvard Medical School: Atlas of Myocardial Perfusion SPECT: Adenosine
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