Biomedical subjects

W Heddle

Publications and source records attributed to W Heddle.

4 recordsLinked to original sources

PubMed1993

Effects on cardiac performance of atrioventricular node catheter ablation using radiofrequency current for drug-refractory atrial arrhythmias.

Patients with atrial fibrillation or atrial flutter (AF) are candidates for radiofrequency (RF) catheter ablation of the atrioventricular (AV) node with the aim being to control heart rate. As patients with AF can have markedly impaired ventricular function, information concerning the hemodynamic effects of AV node ablation using RF current would be valuable. Fourteen consecutive patients (mean age 65 +/- 3 years) with drug-resistant AF underwent AV node catheter ablation with RF current and had permanent pacemaker implantation. The mean left ventricular ejection fraction (EF) by two-dimensional echocardiography immediately before ablation was 42 +/- 3% (range 14%-54%) and their mean exercise time was 4.4 +/- 0.4 minutes. Complete AV block was achieved in all 14 patients with 6 +/- 2 RF applications (range 1-18). There was no evidence of any acute cardiodepressant effect associated with delivery of RF current, and EF 3 days after ablation was 44 +/- 4%. By 6 weeks after ablation, the left ventricular EF was significantly improved compared to baseline (47 +/- 4% postablation vs 42 +/- 3% preablation; P < 0.05), and this modest increase in EF was accompanied by an improvement in exercise time (5.4 +/- 0.4 min). In conclusion, delivery of RF current for AV node catheter ablation in patients with AF and reduced ventricular function is not associated with any acute cardiodepressant effect. On the contrary, improved control of rapid heart rate following successful AV node ablation is associated with a modest and progressive improvement in cardiac performance.

Aged↗

PubMed1985

Comparison of exponential and hyperbolic models of conduction through the atrioventricular node.

Conduction through the atrioventricular node (AVN) is assessed during electrophysiology study by relating the output to the input generated by an atrial extrastimulus. This extrastimulus scans electrical diastole of the heart to enable output to be plotted against input. Using this technique, we compared two mathematical models of the AVN, a rectangular hyperbola and a decaying exponential, respectively. The models were compared in 40 curves from 32 patients with only one AVN transmission pathway. Standard errors of the estimate were usually (25/40 trials) less with the exponential model, suggesting this the preferred algorithm for further development.

Adolescent↗

PubMed1985

Examination of an exponential model of conduction through the human atrioventricular node.

The atrioventricular node (AVN) has been modeled by relating output (A2H2 or H1H2) to input (A1A2) where A and H are atrial and His bundle electrograms during fixed rate atrial pacing (A1A1) or with an extrastimulus (A2). (Formula: see text) This study examined this model in 61 nonselected patients, specifically for AVN (in)stability and the possibility of multiple pathways. After programmed atrial stimulation at two basic cycle lengths of 600 ms and 462 ms, A1H1, A2H2 and H1H2 were digitized and plotted as a function of A1A2. Seven of 104 trials were rejected as SD. A1H1 was greater than 15 ms, suggesting AVN instability. Another 26 and 34 plots, respectively, of A2H2 and H1H2 were rejected because of inadequate data. In the remainder, goodness of fit of the single exponentials was tested statistically in three ways: R2, the runs test, and the Kendall rank coefficient test. Results were compared with an electrophysiologist who examined plots for one or more pathways (either discontinuous curves or slope change in a continuous curve). Single exponentials were successfully fitted (by runs test) in 44/71 and 34/63 of A2H2 and H1H2 plots, respectively, usually in accordance with the cardiologist. Discordance between computations and the cardiologist could be attributed to data scatter and lack of a sufficiently rigid stimulation protocol. The identification of bifurcation points in the presence of multiple pathways, particularly when manifest as a change in slope (approximately 6% of trials) rather than discontinuity of plots (approximately 20% of trials) remains an outstanding problem.

Adolescent↗

PubMed1979

Sick sinus syndrome and AV node re-entry.

A 69-year-old man presented with recurrent palpitations since childhood. Electrophysiology studies performed on two separate occasions revealed the combination of sick sinus syndrome and AV node re-entrant tachycardia. The case is reported because it illustrates marked temporal variability in the electrophysiological properties of the dual AV node pathways, and also deleterious effects of verapamil on sinoatrial node function.

Aged↗