No actual numbers here, but according to the American Heart Association (AHA), patients who receive immediate aggressive bystander CPR after cardiac arrest due to lightning strike actually have a decent chance even without external defibrillation.
This was a surprise to me, as I was always taught that a return of spontaneous circulation (ROSC) after sudden cardiac arrest was unlikely, and that the whole reason for performing CPR was to keep the brain and heart viable until the defibrillator arrived...
This is from the AHA website under "Emergency Cardiovascular Care" (notes in italics and bolded text are mine):
The National Weather Service estimates that an average of 70 deaths and 630 injuries occur due to lightning strikes in the United States
each year. Lightning strike injuries can vary widely, even among
groups of people struck at the same time. Symptoms are mild in some
victims, whereas fatal injuries occur in others.
The primary cause of death in victims of lightning strike is cardiac
arrest, which may be associated with primary VF (ventricular fibrillation) or asystole (absence of detectable electrical activity).
Lightning acts as an instantaneous, massive direct-current shock,
simultaneously depolarizing the entire myocardium. In many
cases intrinsic cardiac automaticity may spontaneously restore
organized cardiac activity and a perfusing rhythm. However,
concomitant respiratory arrest due to thoracic muscle spasm and
suppression of the respiratory center may continue after ROSC (return of spontaneous circulation). Unless
ventilation is supported, a secondary hypoxic (asphyxial) cardiac
arrest will develop.
Lightning also can have myriad effects on the cardiovascular system,
producing extensive catecholamine release or autonomic stimulation.
The victim may develop hypertension, tachycardia, nonspecific ECG
changes (including prolongation of the QT interval and transient
T-wave inversion), and myocardial necrosis with release of creatinine
Lightning can produce a wide spectrum of peripheral and central
neurological injuries. The current can produce brain hemorrhages,
edema, and small-vessel and neuronal injury. Hypoxic encephalopathy
can result from cardiac arrest.
Victims are most likely to die of lightning injury if they experience
immediate respiratory or cardiac arrest and no treatment is provided.
Patients who do not suffer respiratory or cardiac arrest, and those
who respond to immediate treatment, have an excellent chance of
recovery. Therefore, when multiple victims are struck simultaneously
by lightning, rescuers should give the highest priority to patients in
respiratory or cardiac arrest.
For victims in cardiac arrest, treatment should be early, aggressive,
and persistent. Victims with respiratory arrest may require only
ventilation and oxygenation to avoid secondary hypoxic cardiac arrest.
Resuscitation attempts may have high success rates and efforts may be
effective even when the interval before the resuscitation attempt is