What is bradycardia and how to detect it with Microlife's PAD Technology?

Bradycardia is the medical term for low heart frequency. The heart frequency must be kept within certain limits in order to contribute to a physiological blood pressure and organ blood supply.

A. Definition & Limits
There are several medical definitions of bradycardia. Most definitions of bradycardia refer to frequencies lower than 60 [bpm], some medical guidelines however refer to a limit of 55 [bpm].... 50 [bpm].

The variety of definitions arise from the fact that possible clinical bradycardia symptoms are very much dependent on specific patient collectives.

B. Causes
Generally most bradycardias may have three underlying reasons:

1. Pathologic cardiac frequency setting
A low heart frequency might be due to various cardiovascular disorders, they are either of
- cardiac origin (e.g. sick sinus syndrome, cardiac blockages) or of
- extra - cardiac origin (e.g. vegetative nerve system).

2. Medication
A broad variety of drugs may cause bradycardia. Some of these medications are particularly applied in hypertension therapy (e.g. receptor blocker).

3. Adaptation to training
High levels of endurance training may lead to a significantly increased stroke volume (e.g. cyclists), which is often associated with a cardiac bradycardia. This has to be judged as a physiological adaptation caused by the training.

C. PAD bradycardia detection
The PAD technology detects bradycardia. All acquired and qualified pulse periods in the course of an oscillometric measurement are analyzed by means of a high sophisticated detection and classification S/W module.

This in built procedure automatically checks, whether the ingoing pulses are statistically equal or lower than the so called bradycardia separation pulse frequency PFBDS. The separation pulse frequency is defined as follows:

PFBDS / [bpm]=49 [bpm].

The bradycardia separation frequency of 49 [bpm] is intentionally lower than e.g. 55 [bpm].

That's out of the following reasons:

1. High specificity of PAD pulse bradycardia detection
The microlife PAD represents a technology with an exceptional HIGH SPECIFICITY regarding the detection of pulse arrhythmia. This is integrated in order to greatly minimize false positive arrhythmia results. The high specificity of the method results in the need of a slightly stricter bradycardia limit setting.

With the chosen limit of about 50 [bpm] an exceptional specificity is achieved. That means, that the great majority of all users who obtain a bradycardia PAD indication at a given time, will suffer from a relevant bradycardia at the time of the measurement.

2. Medication induced bradycardia
Some hypertension treatment schemes (like receptor antagonists) and a broad variety of other medications may lower the heart frequency as a main or side effect. In many patients heart frequencies between 60 [bpm] and 50 [bpm] are well accepted without any adverse symptoms. However if the heart frequency starts dropping under 50 [bpm] an indication should be given, which is the case with PAD.

3. Training - induced bradycardia
Sportsmen and - women may develop some training - induced bradycardia. They normally do not need and want any irritating arrhythmia indication in the region between about 50 [bpm] and 60 [bpm]. Nevertheless, frequencies lower than about 50 [bpm] should be indicated, as they may represent a pathological frequency drop.

Forschungsinstitut für klinische Medizintechnik
Silberhälden 6
D - 71732 Tamm GermanyTamm, July 13th, 2005