Effects of mild hyperkalemia on conduction velocity and effective refractory period in various parts of the dog heart in situ

Heart rate during sinus rhythm is modulated through the autonomic nervous system, which generates short-term oscillations. The high-frequency components in these oscillations are associated with respiration, causing sinus arrhythmia, mediated by the parasympathetic nervous system. In this study, we evaluated whether slow, controlled respiration causes cyclic fluctuations in the frequency of the fibrillating atria. Eight patients (four women; median age 63 yr, range 53-68 yr) with chronic atrial fibrillation (AF) and third-degree atrioventricular block treated by permanent pacemaker were studied. ECG was recorded during baseline rest, during 0.125-Hz frequency controlled respiration, and finally during controlled respiration after full vagal blockade. We calculated fibrillatory frequency using frequency analysis of the fibrillatory ECG for overlapping 2.5-s segments; spectral analysis of the resulting frequency trend was performed to determine the spectrum of variations of fibrillatory frequency. Normalized spectral power at respiration frequency increased significantly during controlled respiration from 1.4 (0.76 -2.0) (median and range) at baseline to 2.7 (1.2-5.8) (P ϭ 0.01). After vagal blockade, the power at respiration frequency decreased to 1.2 (0.23-2.8) (P ϭ 0.01). Controlled respiration causes cyclic fluctuations in the AF frequency in patients with long-duration AF. This phenomenon seems to be related to parasympathetic modulations of the AF refractory period. atrial fibrillation; autonomic nervous system; spectrum analysis; noninvasive CYCLIC FLUCTUATIONS IN HEART rate during sinus rhythm vary in response to a range of physiological regulatory systems. These fluctuations have been utilized to study autonomic regulation of human cardiovascular physiology (2, 12, 28). The origin of variations in the sinus interval is not fully explained but appears to be predominantly determined by interactions between the autonomic nervous system, hormonal efferent systems, and cardiac pacemaker cells (12,28). Analysis of heart rate variability by spectral methods (frequency domain analysis) is widely used to study autonomic tone and variations thereof. For example, fluctuations in the so-called high-frequency (HF) band (0.15-0.4 Hz) correspond to normal respiratory frequencies and are thought to reflect parasympathetic tone (26). These fluctuations have been shown to be abolished by parasympathetic withdrawal (1, 2, 28).Although variations in beat-to-beat intervals (i.e., RR intervals) are usually examined in frequency domain analysis studies, it is assumed that during sinus rhythm the variability of heart rate is determined by changes in autonomic input to the sinoatrial node [i.e., it is assumed that variations in the atrioventricular (AV) interval do not significantly influence total heart rate variation]. Studies on heart rate variability in settings outside of sinus rhythm are sparse, but a few studies on atrial tachycardia (15) and atrial fibrillation (AF) (34, 35) have been performed. These studies utilized ana...

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“…Experimental studies are limited, but those available have not shown an effect of acetylcholine on conduction velocity (20,31).…”

Section: Comparison Of Dynamic Changes In the Electrophysiological Prmentioning

confidence: 99%

Rapid fluctuations in atrial fibrillatory electrophysiology detected during controlled respiration

Holmqvist¹,

Stridh²,

Waktare³

et al. 2005

American Journal of Physiology-Heart and Circulatory Physiology

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Effects of hypokalemia on the various parts of the conduction system of the dog heart in situ

Chah¹,

Braly²,

Bouzouita³

et al. 1982

Naunyn-Schmiedeberg's Arch. Pharmacol.

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The effects of hypokalemia were studied on the various parts of the conduction system by means of His bundle potential recording in the heart of vagotomized dogs. Plasma potassium concentration was lowered by extracorporeal dialysis, precautions being taken against the simultaneous impairment of other parameters, especially humoral. In order to make sure that the changes in atrioventricular conduction observed were due to hypokalemia, a control series of experiments was carried out, under strictly identical conditions except that the dialysis fluid was not devoid of potassium. The following alterations were observed during the lowering of potassium concentration from 3.2 to 1.6 mmol/l: atrioventricular node conduction time (AH interval) increased steadily up to 250% of control values; conduction time in atrial contractile tissue (SA interval) and His Purkinje system (HV interval) exhibited variations much later and much smaller; conduction time in ventricular contractile tissue was not significantly affected; effective refractory period (ERP) of atrial muscle, initially the longest in ERPs of conduction system in vagotomized animals, was shortened by about 20%. The mechanism of all these alterations is discussed.

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Potentiation by hypokalemia of the effects of acetylcholine on the canine heart in situ

Bertrix¹,

Bouzouita²,

Lang³

et al. 1984

Naunyn-Schmiedeberg's Arch. Pharmacol.

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In the heart in situ of vagotomized dogs, atrioventricular conduction was studied by the His bundle potential recording, sinus rate continuously registered and the effective refractory period (ERP) of the atrial muscle measured by the extrastimulus method. The modifications induced by the acute lowering of plasma potassium concentration from 3.5 to 2.0 mmol/l obtained by hemodialysis appeared to be similar to those due to parasympathetic stimulation and the effects of hypokalemia and acetylcholine (ACh) on the atrioventricular (A-V) and sinoatrial nodes as well as on the atrial contractile tissue gave rise to potentiation. Intraaortically injected near coronary ostia in a dose lower than liminal dose, ACh enhanced to a large extent all the phenomena elicited by hypokalemia, since the variations respectively observed under the influence of hypokalemia alone and the combination of hypokalemia and ACh were as follows: lengthening of conduction time in the A-V node by 100 and 180%, reduction of sinus rate by 10 and 20%, shortening of the atrial ERP by 20 and 40%.

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Effects of mild hyperkalemia on conduction velocity and effective refractory period in various parts of the dog heart in situ

Cited by 4 publications

References 24 publications

Rapid fluctuations in atrial fibrillatory electrophysiology detected during controlled respiration

Rapid fluctuations in atrial fibrillatory electrophysiology detected during controlled respiration

Effects of hypokalemia on the various parts of the conduction system of the dog heart in situ

Potentiation by hypokalemia of the effects of acetylcholine on the canine heart in situ

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