P wave morphology during spontaneous and paced pulmonary vein activity: differences between patients with atrial fibrillation and normal controls

Irritant Inhalation Evokes P Wave Morphological Changes in Spontaneously Hypertensive Rats via Reflex Modulation of the Autonomic Nervous System

Irritant inhalation is associated with increased incidence of atrial fibrillation (AF) and stroke. Irritant inhalation acutely regulates cardiac function via autonomic reflexes. Increases in parasympathetic and sympathetic reflexes may increase atrial susceptibility to ectopic activity and the initiation of arrhythmia such as AF. Both age and hypertension are risk factors for AF. We have shown that irritant-evoked pulmonary–cardiac reflexes are remodeled in spontaneously hypertensive (SH) rats to include a sympathetic component in addition to the parasympathetic reflex observed in normotensive Wistar-Kyoto (WKY) rats. Here, we analyzed P wave morphology in 15-week old WKY and SH rats during inhalation of the transient receptor potential ankyrin 1 agonist allyl isothiocyanate (AITC). P Wave morphology was normal during vehicle inhalation but was variably modulated by AITC. AITC increased RR intervals (RRi), PR intervals, and the P Wave duration. In SH rats only, AITC inhalation increased the occurrence of negative P waves. The incidence of AITC-evoked negative P waves in SH rats was dependent on RRi, increasing during bradycardic and tachycardic cardiac cycles. Inhibition of both parasympathetic (using atropine) and sympathetic (using atenolol) components of the pulmonary–cardiac reflex decreased the incidence of negative P waves. Lastly, the probability of evoking a negative P Wave was increased by the occurrence of preceding negative P waves. We conclude that the remodeled irritant-evoked pulmonary–cardiac reflex in SH rats provides a substrate for altered P Wave morphologies. These are likely ectopic atrial beats that could provide a trigger for AF initiation in structurally remodeled atria.

Atrial fibrillation: a historical perspective

Atrial fibrillation (AF) undoubtedly has become one of the most well studied arrhythmias today in terms of pathophysiology and diagnostic and therapeutic (interventional) electrophysiology. Although it lends itself to an apparently easy diagnosis on a surface ECG, myriad electromechanical mechanisms underlie its origin. An era of technology has been reached that makes AF not only "treatable" but also potentially "curable." This article aims at walking through the historical corridors and maze that have led to the present-day understanding of this most common yet complex arrhythmia.

Vein of Marshall Activity During Sustained Atrial Fibrillation

BACKGROUND

The human vein of Marshall (VOM) activation patterns during sustained (persistent or permanent) atrial fibrillation (AF) have not been studied in detail.

METHODS

VOM was cannulated via coronary sinus in six patients (67.3 +/- 7.5 years old) having either persistent (N = 4) or permanent (N = 2) AF presenting for radiofrequency catheter ablation.

RESULTS

At sinus rhythm in patients with persistent AF, there were frequent ectopic beats from the VOM as well as from left and right pulmonary veins (PVs). The ectopic activity originating from the VOM was highly fragmented. The P wave morphology associated with VOM ectopy was isoelectric in leads I and aVL, positive in leads II, III, aVF, and V2-V5, which is similar to the P wave morphology associated with left PV ectopic beats. During AF the activation cycle length at VOM was 140 +/- 31 msec, which was significantly shorter than that in other atrial sites (P < 0.05). Similarly, the dominant frequency at VOM (9.71 Hz +/- 1.52 Hz) was significantly higher than that at other atrial sites (P < 0.0001). In one patient, VOM ablation was associated with AF termination during radiofrequency energy application.

CONCLUSIONS

Ectopic activity with complex local electrogram originating from VOM is commonly seen in patients with sustained AF. The P wave morphology associated with the ectopic beats from VOM and from the left PVs was similar. The rate of activation at VOM is significantly faster than other atrial and PV sites during AF. These findings show that rapid activation is present in the VOM during sustained AF in human patients.

QRS subtraction and the ECG analysis of atrial ectopics

The recognition of the ubiquitous role of short coupled ectopics in the initiation of paroxysmal atrial fibrillation has renewed interest in their localization with the ultimate aim of facilitating their neutralization by catheter ablation. The P-waves resulting from such ectopics are partly or completely concealed by the QRST of the preceding beat and therefore their morphology has been underutilized for localization purposes. Subtraction has been the most commonly used technique for QRST suppression and though an averaged template offers a higher signal-to-noise ratio, the immediately preceding QRST provides the best match between template and target and allows simple, nearly real-time, and accurate subtraction without distorting the underlying P-wave. Algorithms derived from clinical tachycardias as well as pacemapping have permitted a rational analysis and accurate prediction (81%) of the correct pulmonary vein of origin. Other nonpulmonary sources may also be similarly localized, particularly with the help of a catalogue of pacemaps from various sites. Incessant arrhythmia and frequent aberrancy limit the effectiveness of QRST suppression by subtraction. Further improvements in the localizing resolution of the P-wave may depend upon knowledge of the relationship between recording electrodes and the underlying atria.