Atrioventricular block delay

November 1996 A NREMT/Health Technician at TOCDF has alleged to have been harassed by plant supervisors for suggesting suspected organophosphate poisoning of TOCDF workers based on the technician having observed increased numbers of bradycardias (slow heart rates) and atrioventricular blocks (delays or block in cardiac electrical conduction) amongst these TOCDF workers. 

Conduction delays, such as first-degree atrioventricular block... 

Atrioventricular block. There are many types of AV block, such as a first-degree block in which atrial impulses are delayed in the AV conduction to the ventricle. This is shown on the ECG as a prolongation of the PR interval. Digitalis toxicity or excessive K+ levels can be causative. 

Fig. 10.12 (A) Same patient as Fig. 10.11. Pulmonary capillary wedge pressure shows large cannon waves. Scale 0-40mmHg. (B) Same patient after testing with a temporary dual chamber pacemaker with a physiologic AV delay. Note the normal pulmonary capillary wedge pressure. The patient was markedly improved after the implantation of a dual chamber pacemaker with AV delay optimization. (Barold SS. Acquired Atrioventricular Block. In Kusumoto F, Goldschlager N (Eds), Cardiac Pacing for the Clinician, Philadelphia, PA Lippincott, Williams Wilkins, 2001 with permission).

The main toxins of the yew species are the alkaloids taxine A and taxine B, which are present in all parts of the shrub except the fleshy part of the berry. These compounds are capable of causing symptoms similar to digitalis poisoning including hypotension, bradycardia, and depressed myocardial contractility and conduction delay. The mechanism appears to involve a block of the distal part of the conduction tissue of the heart, which can result in fatal arrhythmias. Atrioventricular conduction is particularly susceptible to yew alkaloids. 

Auricchio A, Stellbrink C, Block M, et al. Effect of pacing chamber and atrioventricular delay on acute systolic function of paced patients with congestive heart failure. Circulation 1999 99 2993-3001. 

A dual chamber pacemaker (with one lead In the atrium and another in the ventricle) provides versatile programming functions and can sense and pace In both the atrium and ventricle. This type of pacemaker mimics the normal cardiac cycle and maintains atrioventricular (AV) synchrony. It may be used for patients with chronic or intermittent AV block and for those who need atrial pacing or have delayed AV conduction or an increased risk of heart block. 

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